• Volume 59,Issue 5,2022 Table of Contents
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    • >Reviews and Comments
    • Research Progresses on Farmland Soil Ecosystem Multifunctionality

      2022, 59(5):1177-1189. DOI: 10.11766/trxb202109290532

      Abstract (1414) HTML (3049) PDF 2.60 M (1972) Comment (0) Favorites

      Abstract:Building healthy soil is a prerequisite for the improvement of cultivated land productivity. It is fundamental for meeting the challenges of food security and environmental protection as well as realizing the agricultural green development and a community of shared future. The core of building healthy soil is to realize the soil ecosystem multifunctionality. In the new era of ecological civilization construction, research on the evaluation and cultivation of soil multifunctionality, and the underlying mechanisms have become hotspots and frontiers of global soil health initiatives. In this paper, we systematically review the concepts of soil functions, soil ecosystem services and soil ecological multifunctionality. The impact of soil biodiversity on soil multifunctionality and the synergies and trade-offs between soil functions are discussed as well. Also, the approaches to evaluating and quantifying soil functions are summarized. Finally, we put forward the pathways of healthy soil cultivation based on the integrated regulation of soil multifunctionality beyond the single pursuit of high grain yield. Different strategies to increase soil multifunctionality are proposed: adjusting the way of land use and agricultural structure at the national scale, coordinating resource allocations at a regional scale, constructing agricultural infrastructure and landscape pattern at the landscape scale, and optimizing the field soil management practices to improve soil health and multifunctionality at the field scale. It is necessary to explore the maintenance mechanism of soil multifunctionality at different temporal and spatial scales, and to combine modern technologies with relevant policies and implementation plans for functional soil management, emphasizing the multi-dimensional role of soil multifunctionality in sustainable environmental policy and management. It will provide important support for the coordinated development of mountain, water, forest, farmland, lake and grass life community, and the implementation of the national strategy of carbon peak and carbon neutrality.

    • A Review of Responses of Soil Nitrous Oxide Emissions to Nitrogen Input in Forest Ecosystems

      2022, 59(5):1190-1203. DOI: 10.11766/trxb202105150258

      Abstract (697) HTML (2020) PDF 1.83 M (1236) Comment (0) Favorites

      Abstract:Rising nitrous oxide(N2O)concentrations in the atmosphere have exacerbated global warming. Forest soil plays a vital role in regulating atmospheric N2O concentration. The effect of nitrogen(N)input on the N2O fluxes of forest soil has attracted much attention. However, the response mechanism of forest soil N2O emissions to N input, especially the regulatory effects of plants and microorganisms on N2O flux, has not been systematically studied. Therefore, this article reviews how N input affects forest soil N2O emissions through forest vegetation(root N absorption, litter decomposition, and formation of arbuscular mycorrhizal)and soil microorganisms(microbial biomass and community composition). The results show that the competitive N uptake of plants can reduce the promotion of N input on N2O emissions. Importantly, the magnitude of its effect may mainly depend on the state of the soil "N saturation". Plant litter mainly affects N2O emissions of forest soil under the background of N input through nutrient return and the release of secondary metabolites during the decomposition process. The former has a promoting effect and the latter has an inhibitory effect. The arbuscular mycorrhiza mainly regulates forest soil N2O fluxes by absorbing available N and water, promoting the formation of aggregates, and changing the N2O-related functional gene community. Nitrogen input leads to soil acidification or nutrient limitation, which can reduce microbial biomass and/or influence the composition of microbial communities, and then affects N2O emissions. Nitrogen input also affects different production pathways of N2O, which is regulated by soil moisture, the concentration of N2O substrates, and the abundance of functional genes associated with soil N2O emissions(AOB、 AOA、nirK、nirS and nosZ). In the future model predictions, plant N absorption, litter decomposition, mycorrhiza and N2O production pathways can be fully incorporated into the model to improve the accuracy of model predictions, and provide a scientific basis for formulating forest management policies and greenhouse gas abatement measures under the background of global change.

    • The Application of Phosphate Oxygen Isotopes in Soil Phosphorus Cycling

      2022, 59(5):1204-1214. DOI: 10.11766/trxb202104210205

      Abstract (624) HTML (3186) PDF 638.06 K (1303) Comment (0) Favorites

      Abstract:Phosphorus(P)is an important element in the soil ecosystem. Researching P cycling in soil is of great significance to improve the utilization efficiency of P fertilizer and reduce the ecological environmental risk of P. Using stable isotopes tracer technology to trace P cycling is limited due to its one stable isotope. In the environment, most P exists as phosphate with a stable P-O bond. In the natural ecosystem, without the participation of microorganisms, oxygen isotopic fractionation is slow and negligible. The phosphate oxygen isotopes technique is an effective method for tracing the biogeochemical behavior of P in the environment. This paper systematically reviews the current research and future development of phosphate oxygen isotopes technology. Firstly, the application principle of phosphate oxygen isotopes is introduced. Secondly, the methods for sample extraction, purification and measurement of oxygen isotopic composition of inorganic P and organic P are systematically described. Modified Hedley sequential extraction is most used in classing the inorganic P form. The organic P is purified by combining size exclusion chromatography and ultraviolet digestion. Thirdly, the characteristics of oxygen isotopic composition and Spatio-temporal distributions of inorganic P and organic P are also described. In general, highly active phosphorus has a higher oxygen isotopic composition which could also fluctuate over time. According to existing reports, there is no spatial variability in soil phosphate oxygen isotopic composition. Fourthly, the application prospect of phosphate oxygen isotopes technique in soil P cycling is discussed from two aspects: ( )The ⅰ microbial utilization of soil P can be evaluated according to the balance of phosphate oxygen isotopes composition.(ii)Tracing the soil P cycling basis on the characteristics of oxygen isotopic composition of different P sources and forms. Then, this paper analyses the influencing factors of soil phosphate oxygen isotopic composition. The most important factor is the source of P. Importantly, the exogenous P entering the soil could break the original balance of P cycling, and directly affects the P content and the characteristics of oxygen isotopes. Environmental conditions, including temperature, moisture, pH, oxygen isotopic composition of water also have great impacts on soil phosphate oxygen isotopes. Oxygen isotopic fractionation is mainly driven by organisms, so organisms play an important role in soil P cycling which can be affected by both microbial community and plant diversity. In addition, the processing of samples treatments influence the reliability of the results. Finally, the future research directions of this technology are proposed in three parts: ( )Establishing standard methods of pret ⅰ reatment for phosphate oxygen isotopes; (ii)Strengthening the study of organic P oxygen isotopes; (iii)Combining multiple methods to reveal the mechanism of soil P cycling. This paper hopes to provide a new perspective and scientific guidance for the development and application of phosphate oxygen isotopes technique in the field of soil science and environmental science.

    • Research Progress on the Environmental Behavior of Heavy Metals in Soil Tracing by Stable Isotopes

      2022, 59(5):1215-1227. DOI: 10.11766/trxb202101180694

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      Abstract:With the revolutionary breakthrough of high-precision mass spectrometry represented by multiple-collector inductively coupled plasma mass spectrometry(MC-ICP-MS), the research on stable isotopes has been developed by leaps and bounds. Heavy metal stable isotopes have become an effective tool to trace the circulation of heavy metals in soils, showing great application potential in identifying pollution sources, analyzing key processes, and tracking environmental behaviors. Based on the basic concept of isotopes, this paper systematically introduces the applications in using heavy metal stable isotopes to trace the source and fate of heavy metals in the soil environment, the transport and transformation of heavy metals in soil-plant system, and the environmental behaviors of metal nanoparticles. Processes influencing heavy metal stable isotope fractionation, such as redox, precipitation, dissolution, adsorption and desorption, complexation reaction, and biological action, are further summarized. Finally, the research outlook for the applications of tracing heavy metal environmental behavior by heavy metal stable isotopes is proposed, which plays a significantly important role in the prevention, control, and remediation of metal contamination in soil.

    • >Research Articles
    • Impact of Long-term Land-Use Patterns on Chemical Composition of Soil Organic Matter in Mollisol Profile

      2022, 59(5):1228-1237. DOI: 10.11766/trxb202106010286

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      Abstract:【Objective】The objective of this study was to assess the effect of land-use changes on the composition and stability of soil organic matter (SOM). 【Method】Based on a 29 years long-term experiment in typical Mollisol region, we investigated the contents of labile fractions of SOM in depths of 0~10、10~20、20~40、40~60、60~80 and 80~100 cm. Furthermore, Fourier transform infra-red and solid-state 13C nuclear magnetic resonance spectroscopies were applied to estimate the differences in functional C groups of SOM under different land uses. The land-use types included cultivated land (CL), restored grassland (GL)and artificial spruce forest land (FL). 【Result】The contents of soil labile organic C fractions (i.e. microbial biomass C, dissolved organic C, light fraction organic C and readily oxidizable organic C)were higher in GL and FL than in CL at all soil depths, and followed the order of GL> FL >CL. With the increase of soil depth, the aliphatic C, OCH3 and O-alkyl C groups of SOM gradually decreased, while the aromatic C and carboxyl C gradually increased. This indicated that the stability of SOM increased with soil depth. The proportion of OCH3 and O-alkyl C groups from plant residues were highest in the GL across all depth, followed by FL, and lowest in the CL. The SOM of CL had higher proportion of aromatic C and carboxyl C groups than that of GL and FL. This resulted a higher humification degree of SOM in CL. 【Conclusion】Our results suggest that land use changes modify the chemical composition of SOM both in the topsoil and subsoil. Vegetation restoration could increase labile components of SOM. In contrast, long-term cultivation prompted the accumulation of recalcitrant fractions in SOM.

    • Succession of Microbial Community in Typical Black Soil under Different Land Use Pattern

      2022, 59(5):1238-1247. DOI: 10.11766/trxb202103040128

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      Abstract:【Objective】To explore the succession of soil microbial community structure and its environmental driving mechanism under different land use pattern, soil samples were collected from plots in a long-term(32 years)field experiment station in the black soil region of Northeast China.【Method】 The long-term field experiment was started on different land usage in the National Field Research Station of Agro-Ecosystem of Chinese Academy of Sciences in 1985. The experiment was designed with three treatments and three replicates, i.e. bareland(vegetation removed), cropland(crop rotation without fertilizer), and grassland(natural meadow vegetation). Soil samples were collected for analysis from the 0~20 cm soil layer in October 2017. Soil microbe was determined by the Illumina high-throughput sequencing technology on MiSeq platform. 【Result】The soil organic matter was 52.07 g·kg-1, 54.83 g·kg-1 and 61.54 g·kg-1 in the treatments of bareland, cropland and grassland, respectively. Compared to the bareland, the soil organic matter increased by 8.0% and 27.5% in the cropland and grassland, respectively. The available nitrogen, phosphorus and potassium also increased significantly in cropland and grassland. At the same time, the total abundance of microbe increased from 2.25×107 copies·g-1 dry soil to 8.08×107 copies·g-1 dry soil and 1.69×108 copies·g-1 dry soil in the three treatments, respectively. The abundance of microbe increased by 2.58 times and 6.51 times in cropland and grassland, respectively. At the phylum level, dominant microbe were Proteobacteria, Actinobacteria, and Acidobacteria, whose relative abundances were more than 19% and with no significant differences in the three treatments(P > 0.05). The 54 of 228 microbial genera detected showed significant differences(P < 0.05)among the three treatments, and most of them showed relatively low abundance. The genera of Gemmatimonas, Rhodoplanses, Arenimonas showed significant differences and higher abundance in the three treatments. The redundancy analysis showed that soil properties were the main environmental driving force for the differentiation of microbial community structure, including cation exchange capacity, total nitrogen, organic matter, available nitrogen, available phosphorus and available potassium. Network analysis showed that Granulicella had the strongest association with soil properties and other microbial genera, suggesting that this genus can be used as an indicator to assess changes in the black soil. 【Conclusion】 The vegetation cover was an key factor for the succession of soil microbial communities. Research should thoroughly explore the functions and agricultural environmental significance of microbe under in-situ conditions in black soil in the future, to provide theoretical references for maintaining the virtuous cycle of nutrient and developing sustainable agricultural ecological management models.

    • Transport of Straw-derived Carbon in Black Soil and Cinnamon Soil and Its Response to Nitrogen Fertilization

      2022, 59(5):1248-1257. DOI: 10.11766/trxb202105210059

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      Abstract:【Objective】 A laboratory incubation was conducted to study the transport characteristics of soil native carbon(Cs)and straw-derived carbon(Cstr)after adding wheat straw and nitrogen fertilizer in black soil and cinnamon soil. 【Method】 There are four treatments: Control(soil only, no straw or nitrogen added), N(soil with nitrogen fertilization, 170 kg·hm-2), R(soil with straw addition, 8 580 kg·hm-2), RN(soil with nitrogen fertilizer 170 kg·hm-2 and straw addition 8 580 kg·hm-2). The wheat straw used was isotope 13C labeled. Soil samples were collected and fractionated into three different soil organic carbon fractions(light fraction-LF, occluded particulate organic carbon-OPOC, heavy fraction-HF)at 0, 180, 300 days. 【Result】 The results showed that the soil incubation was a carbon loss process of soil carbon mineralization. Nitrogen fertilization showed an inhibitory effect on carbon mineralization in both soils, and the effect in cinnamon soil was more significant in straw-added treatments compared to no straw-added treatments. The percentages of Cs loss in the two soils were ranked as HF>OPOC>LF. Straw application increased the percentage of Cs loss in HF from 2.83% to 5.53%(P<0.05)in black soil and decreased the percentage of Cs loss in OPOC from 1.86% to 0.82%(P<0.01)in cinnamon soil. Importantly, the Cstr in LF was gradually transferred to OPOC and HF, and the transfer became slower after 180 days. By the end of incubation(300 days), the total residual rate of Cstr in cinnamon soil showed no significant difference compared to that in black soil. The residual rate of Cstr in LF was 4.98%-8.52% in cinnamon soil and was significantly higher than that in black soil(1.71%-2.47%). Compared to R treatment, RN treatment almost doubled the residual rate ofCstr in LF of cinnamon soil.【Conclusion】The HF was the main source of Cs loss. Nitrogen fertilization inhibited carbon mineralization in the two soils. Straw addition exhibited a positive priming effect on the carbon mineralization of HF in black soil and an inhibitory effect on the mineralization of OPOC in cinnamon soil. The degradation degree of LF-Cstr in cinnamon soil was lower than that in black soil and could be limited by nitrogen application.

    • Distribution Characteristics of Microbial Gene Abundance in Key Processes of Soil Nitrogen Cycling in Black Soil Zone

      2022, 59(5):1258-1269. DOI: 10.11766/trxb202110220381

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      Abstract:【Objective】Surveys of spatial distribution patterns of microbial community diversity and composition and the factors driving such patterns is indispensable to understand the biological diversity and maintain mechanism. Recently, the researches on soil microbial distribution patterns and their driving force going very rapidly, many research pointed out that microbial communities were geographically distributed and the hypothesis of the microbial random distribution pattern has been ruled out. Although the spatial distribution characteristics of the functional genes basing on the individual nitrogen cycling community have been investigated, the coupling analysis of microbial distribution patterns involved in the nitrogen cycling on the entire process especially on spatial scale is relatively rare. In this study, authors investigated the correlation analysis on the abundance characteristics of functional genes in the key processes of soil nitrogen cycle including nitrogen fixation, ammonia oxidation and denitrification, to reveal the similarities and differences of microbial abundance in different nitrogen cycling processes in the black soil zone of Northeast China, and to clarify which soil factors is important regulating the distribution of community numbers. 【Method】In this study, 26 soil samples were collected with different soil carbon contents basing on the database of China Black Soil Ecology. The soil sampling regions was across the black soil zone in northeast China from Changtu(42°50'N, 124°07'E)in Liaoning Province to Nenjiang(49°07'N, 125°13'E)in Heilongjiang Province(intervals of 25 to 741 km). Soil edaphic factors, including soil pH, total carbon(TC), total nitrogen(TN), total phosphorus(TP), available phosphorus(AP), available potassium(AK), nitrate nitrogen(NO3-N), and ammonium nitrogen(NH4+-N), were measured by standard soil testing procedures. Quantitative real-time PCR technology was used to determine functional gene abundance involved in the key processes of nitrogen cycle, including nitrogen fixation(nifH), ammonia oxidation with ammonia-oxidizing archaea(AOA)amoA and ammonia-oxidizing bacteria(AOB)amoA and denitrification(nirS, nirK and nosZ).【Result】The soil pH ranged from 4.56 to 6.57, and soil TC ranged from 11.77 g·kg-1 to 53.53 g·kg-1. Soil TC content was significantly correlated with latitude(P < 0.001), but was not soil pH(P = 0.985). The abundances of different nitrogen cycling genes are significantly lower in low soil pH(4.5~ 5.0)than other soil sampling sites. The abundance of nifH genes in soybean-planting soils is significantly higher than that of soil samples planted with maize(above 5%~19%)in the adjacent soil sample sites. The abundance of AOA amoA is significantly higher than that of AOB amoA, and the abundance ratio of AOA amoA to AOB amoA ranges from 3.1 to 91.0. The abundance of nitrogen cycling functional genes is positively correlated with soil pH and TC(P < 0.01). The non-metric multidimensional scaling analysis(NMDS)showed that the NMDS1, which mainly represents nitrogen cycling gene composition in black soil zone, was significantly positively correlated with soil pH and TC. The variance partitioning analysis revealed that the distribution of nitrogen cycling genes was mainly dependent on soil pH, TC, latitude, TP and TN, among which contribution of soil pH and TC is the highest, and accounts for 6.69% and 4.38%, respectively. The random forest analysis reconfirmed that soil pH and TC were the main driving factors shaping the spatial distribution patterns in nitrogen cycling microbial gene abundance. 【Conclusion】 This study reveals that in addition to soil pH and TC contents, spatial distance also has an important impacts on the distribution of microorganisms in key processes of soil nitrogen cycling in black soil zone, which provides scientific basis for understanding the biogeochemical cycling process mediated by soil microbe in farmland ecosystems.

    • Soil Erosion Characteristics of Different Soil and Rock Mosaic Slopes Under the Condition of Successive Rainfalls

      2022, 59(5):1270-1278. DOI: 10.11766/trxb202011020606

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      Abstract:【 Objective】The discontinuity of natural rainfall makes the influence of successive rainfalls on soil erosion different from that of single rainfall on slope erosion. Under the condition of not disturbing the slope after rainfall, the soil erosion characteristics of different soil and rock mosaic slopes in karst area under conditions of successive rainfalls were explored.【 Method】 Using the method of artificial rainfall simulation, the soil erosion characteristics of three types of soil and rock mosaic slopes(i.e., FE, rock fully embedded in the soil layer, not exposed to the surface; PE, rock partly embedded in the soil layer, exposed to the surface; RC, rock not embedded in the soil layer, covering the surface)were studied under four rainfall conditions(24 h interval). The test slope was 25°, and the rainfall intensity was 50 mm·h–1. The rainfall lasted for 90 min. 【 Result】 Results showed that(1)with the increase of rainfall events, the surface runoff of FE, PE and RC increased, while the interflow and the underground runoff increased first and then decreased. In the first two rainfall scenarios, the surface runoff of three types of soil rock mosaic slope had no obvious regularity, but in the last two rainfall, the surface runoff was PE > FE > RC; (2)with the increase of rainfall events, the FE, PE and RC surface sediment yield increased. In addition to the first rainfall, the surface sediment yield in the last three rainfalls was PE > FE > RC. Also, the sediment yield of PE surface was 1.04-4.82 times that of the FE and RC surfaces, respectively; (3)with an increase of rainfall events, under the influence of early rainfall, the soil moisture content increased, and the runoff time of surface runoff and interflow in subsequent events was advanced by 5-16 min. 【Conclusion】Under successive rainfalls, the rock embedding in the soil has the effect of increasing the surface runoff and sediment yield. These results provide a scientific basis for further understanding the response of soil and water loss process to climate change on karst rocky desertification slope.

    • An Intelligent Model of Cultivated Land Quality Evaluation Based on Random Forest and Its Application

      2022, 59(5):1279-1292. DOI: 10.11766/trxb202012030670

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      Abstract:【Objective】Constructing a scientific and quantitative quality-assessment model for cultivated land is important for understanding cultivated land quality, and can provide a theoretical basis and technical support for formulating rational and effective management policies and realizing the sustainable use of cultivated land resources. To accurately reflect on the systematic, complex, and differential characteristics of cultivated land quality, this study aimed to explore an intelligent cultivated land quality assessment method that avoids the subjectivity of determining indicator weights while improving assessment accuracy. 【Method】In this study, taking Xiangzhou in Hubei Province of China as the study area, 14 indicators were selected from four dimensions—terrain, soil conditions, socioeconomics, and the ecological environment—to build a comprehensive assessment index system for cultivated land quality. A total of 1, 590 representative cultivated land quality samples in Xiangzhou were selected, of which 1, 110 were used as training samples, 320 as test samples, and 160 as validation samples. Three models of entropy weight(EW), back propagation neural network(BPNN), and random forest(RF)were selected for training, and the assessment results of cultivated land quality were output through simulations to compare the assessment accuracy of the three methods to verify the reliability and superiority of the RF model. In addition, the distribution pattern of cultivated land quality grades in Xiangzhou in 2018 was also analyzed in this study. 【Result】 The results are summarized as follows: (1)The overall quality of cultivated land in Xiangzhou was better, with a larger area of second- and third-grade farmland, accounting for 54.63%, and the grades conformed to a positive distribution trend. From the distribution point of view, the spatial distribution of cultivated land quality in Xiangzhou was unbalanced, influenced by the topography and socioeconomic development level and showing an obvious geographical differentiation pattern, with overall characteristics of high in the north-central area and low in the southern area. The distribution of cultivated land quality grades also varied widely among towns.(2)The RF model for cultivated land quality assessment required fewer parameters and could simulate the complex relationships between indicators more accurately and analyze each indicator’s contribution to cultivated land quality scientifically.(3)In terms of the average quality index of farmland, RF > BPNN > EW. The spatial patterns of the quality index from RF and BPNN were similar, and both were significantly different from EW.(4)Compared to BPNN and EW, RF had a higher data mining ability and training accuracy, and its assessment result was the best. The coefficient of determination(R2)was 0.8145, the mean absolute error(MAE)was 0.009, and the mean squared error(MSE)was 0.012. 【Conclusion】 The findings in this study showed that RF was more suitable for the quality assessment of cultivated land with complex nonlinear characteristics. This study enriches and improves the index system and methodological research of cultivated land quality assessment at the county scale, and provides a theoretical basis for achieving a threefold production pattern of cultivated land quantity, quality, and ecology in Xiangzhou, while also serving as a reference for the evaluation of cultivated land quality in similar regions.

    • Study of Soil Organic Carbon Sequestration Rate and Potential of Farmland Soil in Fujian Province Based on the Large Scale Soil Database

      2022, 59(5):1293-1305. DOI: 10.11766/trxb202012040671

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      Abstract:【Objective】Farmland soil organic carbon pool is one of the most important soil carbon pools and its sequestration and emission have a huge impact on global climate change. It is essential to estimate the soil carbon sequestration rate and potential of farmland soils accurately for managing soil fertility and the ecological environment. Fujian Province is characterized by a large population and small land use and strong spatial heterogeneity of soil. It is of great significance to identify the dynamic evolution trend of soil organic carbon and future carbon sequestration potential of cultivated land in this region for formulating the national strategy of "carbon neutrality" and food security in subtropical regions of China.【Method】This study covered five counties including Minhou, Pucheng, Tongan, Wuping and Yongding, located in different geographical locations in Fujian Province. Soil attributes data based on the data of field measurements at 30, 211 sampling sites in 1980 and 15, 948 sampling sites in 2008, scattered in these five counties were analyzed. The 1980 soil spatial database was digitized during the Second Soil Survey 1: 50 000 soil map and the 2008 soil spatial database was extracted from the annual 1: 50 000 land-use status map. Through ArcGIS software and the Ordinary Kriging method, we related the soil spatial data and soil attributes to obtain a high-precision farmland soil database. Based on the most detailed soil database of 1: 50 000 at the regional scale, we used the biogeochemical process model DNDC(DeNitrification and Decomposition)to simulate the organic carbon changes in these five counties from 1980 to 2009 and to get predicted value from 2010 to 2039. Also, we estimated the soil carbon sequestration rate and potential of farmland soil in the province by the method of scaling up. 【Result】 Results show that the carbon sequestration amount of the cultivated land in Fujian Province from 1980 to 2009 was 7.37 Tg, and the carbon sequestration potential from 2010 to 2039 was 7.04 Tg. The average annual carbon sequestration rate for the two periods was 190 kg·hm-2 and 176 kg·hm-2, respectively. Among them, paddy soil and saline paddy soil showed the highest carbon sequestration rate in soil type and soil subgroup, respectively, and was greater than 175 kg hm-2 in different periods. The carbon sequestration rate of the red soil group and soil subgroup was the lowest, with an average rate between –29~3 kg·hm-2. Generally, the total carbon sequestration of paddy soil was higher than 6.5 Tg in different periods, accounting for more than 92% of the province's total carbon sequestration, which is the key to formulating carbon sequestration and emission reduction measures in the future. 【Conclusion】Results of this study indicate that the cultivated soil in Fujian province showed a weak "carbon sink" effect from 1980 to 2009 and 2010 to 2039. This indicates that the current farmland management measures in this area are conducive for carbon sequestration of cultivated soil and should continue to be promoted. Meanwhile, due to the high variability in soil properties, the soil organic carbon(SOC)change in Fujian province was strongly influenced by soil type, soil subgroup and soil genus. Therefore, in future "carbon sink" policy formulation, it is necessary to formulate corresponding management measures for specific soil types.

    • Micromorphological Evidence on the Pedogenic Characteristics and Reticulated Mechanism of Aggradation Red Earth

      2022, 59(5):1306-1320. DOI: 10.11766/trxb202011240643

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      Abstract:【Objective】The aggradation red earth sediment is widely distributed on terraces in the middle and lower reaches of the Yangtze River, especially in the piedmont of Lushan Mountain in China. Their sequences haves well recorded the weathering history during Quaternary in South China. Therefore, the objectives of this research were to(1)investigate the micromorphological characteristics of aggradation red earth sequence and(2)reveal the paleosol pedogenic environment. 【Method】The research profile was L-HH(29°32 '07.88 "N, 116°04' 19.53"E, H=87 m)at the eastern piedmont of Lushan Mountain. Nine undisturbed samples were collected from the different pedogenic unit and made into thin sections, which were observed by plane polarized(PPL)and crossed polarized light(XPL)using Zeiss Axio Lab. A1 polarizing microscope in the laboratory. A total of 159 bulk samples were collected along with the profile at 5~6cm intervals. Moreover, particle size, chroma, susceptibility and geochemical data of the 159 bulk samples were measured.【Result】L-HH profile can be divided into reticular red soil unit(RRS), reticulated yellowish-brown soil unit(RYB)and yellowish-brown soil unit(YBS)from the bottom up. The soil matrix under Fe-impregnation was mainly composed of clay and colloid, the content of which is up to 50%~70%. The fragments included quartz, plagioclase and muscovite, while the secondary mineral was mostly illite and vermiculite. Also, heavy minerals that were observed included apatite, zircon, rutile and tourmaline. These results suggest in general that the soil units have a moderate-strong degree of chemical weathering. However, there were differences in detail among different units. The voids types of RRS are dominated by large linear channels with good connectivity and smooth wall. Also, the pedological features were mainly composed of coating, ferromanganese nodules, and diffuse concentric rings. Additionally, the illuvial coating developed along the voids wall and formed interbedded layers. Mn-coating was mostly superposed on the Fe-coating, and some pores were filled with the coating. Besides, part of the illuvial Fe-clay coating had a decolorization phenomenon. Thus, the pedogenic environment of RRS was characterized by strong summer monsoon, high soil moisture content, and increased seasonal climate contrast. Furthermore, the voids types of RYB were dominated by vughs, chamber voids and well-connected channels. Fe-Mn features were abundant in the soil matrix. The types of pedological features were rich with Fe masses, ferromanganese nodules and rhizospheric concentric iron-rings scattered in the matrix. The brown-red or grey-black flaky coating was developed repeatedly along the voids wall, and the deposition thickness was increased. Also, the soil moisture decreased, but the alternation between dry and wet was still significant. This, indicated a warm and dry environment. The voids types of YBS were dominated by plane voids, chamber voids, irregular voids, and vughs. Also, the voids’ wall was rough and the channel connection was poor. The pedological features mainly included diffused coating. A thin Fe-illuvial coating was found on some voids wall. During this period, the temperature and moisture conditions became worse. The climate was dry and cool, and the winter monsoon was strengthened. Also, changes of environmental proxies along the profile strongly supported the results of soil micromorphology. From the bottom up, the soil moisture content decreased continuously, and the climate tended to be dry and cool. The micromorphological characteristics support the view that the reticulation process was controlled by iron differentiation. Moreover, the micromorphological characteristics also showed that soil voids and plant roots accelerated the process of reticulation. 【Conclusion】The findings in this study demonstrate that there is a significant correspondence between soil micromorphological characteristics and environmental proxies in the L-HH profile. This is an important indicator for interpreting the pedogenic environment of red earth, monsoon evolution signal. and the reticulated mechanism.

    • Research on the Characteristics of Preferential Flow Movement Along Varied Hillslopes Covered with Different Vegetation in the Three Gorges Reservoir Area

      2022, 59(5):1321-1335. DOI: 10.11766/trxb202102230616

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      Abstract:【Objective】Studying the effects of topographic position, vegetation cover, and soil property on the characteristics of preferential flow in mountainous areas can enrich research content of hillslope hydrology, and further reveal the mechanism of forestland in soil and water conservation.【Method】Dye tracing experiments using Brilliant blue solution combined with photographed images analysis were carried out in the Dalaoling forestland of the Three Gorges area to explore the transport features of preferential flow along with soil vertical profile and lateral section. Six hillslope sites were selected to conduct dye tracing experiments, including the upslope and downslope covered by evergreen forest(EG), secondary deciduous forest mixed with shrubs(SDFS), and deforested pasture(DP), respectively. Several parameters were analyzed to demonstrate stained feathers along with vertical profile or lateral hillslope, including stained area ratio(SAR), stained path number(SPN), distribution of different preferential flow paths width and lateral flow length along the slope.【Result】Results indicated that: (1)Larger stained area ratio and more stained path number were observed in upper soil horizon than deeper soil horizon. Compared among different vegetation covers, the largest SAR was observed in SDFS, followed by DP and EG, which were 44.2%, 36.1%, and 35.3% at 0-60 cm depth, respectively. While average SPN in SDFS, EG, and DP was 43, 19, 15 at 0-60 cm depth, respectively. For different topographic positions, larger SAR was identified in upslope sites(41.5%)than in downslope sites(35.6%), while upslope sites had less SPN(23)than downslope sites(28)at 0-60 cm depth. Deeper percolated depth was identified at SDFS sites than that of other sites, which showed abundant stained paths even at 60-110 cm depth, while few paths were found at this horizon for EG and DP sites.(2)The stained areas at six sites were dominated by preferential flow paths with 1-10 cm width and >10 cm width, which account for 82.8% of the total stained area. Homogeneous matrix flow and heterogeneous matrix fingering flow were mainly distributed at 0-30 cm depth, while other preferential flow patterns were mainly observed at deeper soil horizons.(3)Compared with EG and SDFS sites, more lateral flow appeared at DP sites showing stained patches extended 50 cm distance along the downslope direction, while only 10-20 cm distance extending was observed at other sites. 【Conclusion】Vegetation types and topographic position affected water infiltration processes through controlling soil properties and affecting water flow paths. Forestland sites had a better ecohydrological function in water conservation than deforested land, as the vertical flow process at DP was inhibited by the plowing hardpan. These led to more lateral flow at the shallow horizon and had more risks triggering a surface runoff. The practices of deep ploughing and reforestation can enrich root channels and benefit soil and water conservation.

    • Root Water Source of Pinus sylvestris L. var. Mongholica Litv. and Influencing Factors in the Southeastern Part of Mu Us Sandy Land, China

      2022, 59(5):1336-1348. DOI: 10.11766/trxb202011060608

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      Abstract:Water shortage is the main limiting factor for vegetation restoration and desertification control in the arid region of northwestern China. 【Objective】Investigation of the root water source and influencing factors of typical plants used for desertification control can provide a basis for scientific sand control and efficient water use in the region.【Method】Pinus sylvestris L. var. mongholica Litv. (P. sylvestris) is an evergreen coniferous tree of the Pinus genus. It is widely used in wind sheltering and sand fixation in the north of China because of its strong root system and ecological adaptability. In this study, the hydrogen and oxygen isotope composition (δ2H and δ18O) of plant xylem water and its potential water sources (precipitation, soil water and groundwater) were measured monthly from June to November 2018 in an artificial P. sylvestris forest (18~20 a). The experiment was carried out in the Gechougou watershed in the southeastern part of Mu Us Sandy Land. The dynamic changes and controls of root water sources were studied by the multiple linear mixed models. 【Result】Our results showed that the range of δ2H was –69.95‰~ –49.25 ‰, –144.81‰~ –6.60‰, –83.62‰~ –48.57 ‰ and –65.63‰~ –53.65 ‰ for xylem water, precipitation, soil water and groundwater, respectively. Also, the range of δ18O was –8.77‰~–8.21‰, –18.86‰~–2.07‰, –9.45‰~–6.54‰ and –9.97‰~–8.26‰, respectively, during the period monitored (June–November). The weighted mean values of δ2H and δ18O in soil water were between the precipitation and groundwater due to the influence of precipitation infiltration and groundwater recharge. Rainfall amount, soil water content and groundwater level in the rainy season (July–September) were 24.80~90.10 mm, 3.36%~8.40% and 5~15 cm higher than that in the dry season (June, October, November). Iso-source model predicted that P. sylvestris mainly used the nearly saturated layer water (>90 cm) (15.40%) and groundwater (70.10%) in June. However, from July to September, the root used water source mainly came from the active and stable soil layer (<80 cm) (61.03%) with the increase in rainfall. Compared with the rainy season (July–September), the contribution of the nearly saturated layer (>70 cm) and groundwater to the root water source increased by 5.82%~28.00% and 20.64%~23.30% in October and November when precipitation decreased. During the detection periods, the average ratio of absorption and utilization by P. sylvestris root from the active layer, stable layer, nearly saturated layer and groundwater were 21.48%, 31.13%, 16.42% and 30.98%, respectively. The dependence on groundwater for P. sylvestris was significantly higher than that of other soil layers, which may be prejudice to survival under extreme drought environments in the future.【Conclusion】 The soil water content was positively correlated with the root water absorption of P. sylvestris. The uplift and decline of groundwater level significantly changed the position of the nearly saturated soil layer, and then affected the absorption and utilization ratio of P. sylvestris from different potential water sources. Therefore, the root water source of artificial P. sylvestris forest was affected by both supply-consumption dynamics of soil water and seasonal fluctuation of groundwater level. This study provides a useful method that identified the absorption and utilization ratio of water by plants from different potential water resources, which will be significant for vegetation restoration in the Mu Us Sandy Land soil-plant ecosystems.

    • The Effect of Sodium Carboxymethyl Cellulose on Water Movement and Soil Hydraulic Parameters of Loamy Sand

      2022, 59(5):1349-1358. DOI: 10.11766/trxb202012070675

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      Abstract:【Objective】Scientific use of sodium carboxymethyl cellulose(CMC)to achieve water conservation and salt control is of great significance for the improvement of coastal sandy saline-alkali soil. It is therefore important to clarify the influence of CMC on the water movement law of coastal soil sand by evaluating the effect of CMC concentration on soil hydraulic parameters.【Method】In this study, a one-dimensional vertical infiltration experiment was carried out to study the effects of different CMC application amounts(0, 0.1, 0.2, 0.4, 0.6 g·kg-1)on the infiltration characteristics, water distribution, and soil hydraulic parameters. 【Result】The results showed that the final cumulative infiltration increased by 4.90%~15.17%, and the infiltration time to reach the preset wetting front depth increased by 61.90%~604.73% with the increase of CMC application. The adsorptivity S in the Philip infiltration model decreased from 0.685 cm·min-0.5 to 0.256 cm·min-0.5 and the parameter KsSf in the Green-Ampt model decreased from 0.633 cm2·min-1 to 0.096 cm2·min-1 with CMC application. The S and the average soil water diffusivity could be described by a quadratic polynomial and exponential function, respectively. Soil water content increased by 0.7%~3.7% because CMC enhanced the soil water holding capacity. Additionally, the retention water content θr, saturated water content θs, and air-entry α reciprocal were positively correlated with the amount of CMC, and inversely proportional to the saturated water conductivity Ks and shape coefficient n. CMC induced a moderate variation to Ks and α, and a minor variation to θr, θs, and n. 【Conclusion】This study can provide a valuable theoretical reference for rational use of CMC for the improvement of coastal saline-alkali soil.

    • Influences of Long-term Different N Application Rates on Straw Decomposition and Bacterial Community Structure in a Fluvo-aquic Soil

      2022, 59(5):1359-1368. DOI: 10.11766/trxb202103150145

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      Abstract:【Objective】The problems caused by excessive nitrogen(N) application in agriculture has been of growing concern, but the soil mineral N level and its effect on straw decomposition after long-term N application remain unclear. 【 Method】 We used a fluvo-aquic soil treated for 14 years(2005-2018) with N at the rates of 0(N0), 150(N1), 190(N2), 230(N3) and 270(N4) kg·hm-2·a-1, and conducted a 50-day laboratory incubation experiment with and without straw addition. Soil CO2 emission was determined during the incubation, soil mineral N(nitrate and ammonium nitrogen), dissolved organic carbon(DOC), microbial biomass carbon(MBC) were measure before and after the incubation, and the bacterial community structure was determined using amplicon sequencing of the 16S rRNA genes. 【 Result】 Results show that soil mineral N content and straw decomposition efficiency increased with increasing N application rates and the bacterial community composition was significantly(P<0.05) influenced by N application rates. The network analysis revealed that the co-occurrence pattern among species within the bacterial community during straw decomposition changed with the N application level, and the negative association among bacterial communities was strengthened under a high N application level. At the same time, the dominant position of Proteobacteria was weakened and that of Acidobacteria was enhanced.【 Conclusion】 The soil inorganic nitrogen content increased with the increase of long-term nitrogen application level, resulting in changing in soil bacterial community structure. Thus soil bacterial community structure of different long-term nitrogen application played different roles in the process of straw degradation, which was manifested as the increase of straw degradation with the increase of nitrogen application level. The relationship among soil mineral N content, bacterial community structure and species changed with the difference of long-term N application level. The results of this study provide guidelines for the use of straws to amend soils under N application.

    • Effects of Combined Application of Algae and Bacteria on Paddy Soil Phosphorus Availability and Microbial Community

      2022, 59(5):1369-1377. DOI: 10.11766/trxb202103240159

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      Abstract:【Objective】Phosphorus is a major element essential for biological growth, but its bioavailability and utilization efficiency in soil are low. Microorganisms play important roles in soil phosphorus cycling. In recent decades, phosphate solubilizing bacteria and microalgae have been widely used as biofertilizers, with great effects on soil phosphorus cycling and the composition and activity of microbial communities. Nevertheless, the combined effects of microalgae and bacteria have been given little attention. This study aimed to explore the effects of the combined application of Bacillus megaterium and Chlorella vulgaris on phosphorus availability and the microbial community in paddy soil. 【Method】In this study, a laboratory cultivation experiment was carried out by using Bacillus megaterium, Chlorella vulgaris, and paddy soils from Jurong, Jiangsu, China, with four treatments, including the application of Chlorella vulgaris alone(A), application of Bacillus megaterium alone(B), combined application of Bacillus megaterium and Chlorella vulgaris(A+B)and the control without application of Bacillus megaterium or Chlorella vulgaris(CK). Specifically, we measured soil pH, contents of Olsen-P, total organic carbon(TOC), and total nitrogen(TN). Also, we determined the soil microbial community composition and diversity using 16S and 18S rRNA gene amplification high-throughput sequencing and characterized the metabolic heat release of soil microorganisms using microthermal analysis.【Result】After 30 days of culture, the soil Olsen-P content of combined application of Bacillus megaterium and Chlorella vulgaris(A+B, 15.92 mg·kg-1)was significantly higher than that of the control and Chlorella vulgaris alone(A: 14.46 mg·kg-1, CK: 14.61 mg·kg-1), with an increase of 9.0% compared to the control(14.61 mg·kg-1). The combined application of Bacillus megaterium and Chlorella vulgaris also significantly increased the pH, TN and TOC contents of paddy soil. The relative abundance of Bacillus in the soil of the combined application of Bacillus megaterium and Chlorella vulgaris(1.70%)increased by 27.9% compared to that applied with Bacillus megaterium alone(1.33%), and the relative abundance of Chlorella in Chlorophyta of the combined application of Bacillus megaterium and Chlorella vulgaris(3.14%)increased by 3.18% compared to that applied with Chlorella vulgaris alone(3.04%). Also, the combined application of Bacillus megaterium and Chlorella vulgaris significantly increased the metabolic activity and proliferation rate of soil microorganisms. 【Conclusion】 This study showed that the combined application of Bacillus megaterium and Chlorella vulgaris significantly improved the availability of P in paddy soils and the activity of soil microorganisms. This provides practical information for the development and utilization of algae and bacteria-based compound biofertilizers, and a new perspective for improving the phosphorus availability in paddy soils and for alleviating the accumulation of P and reducing environmental risks.

    • Intercropping with Maize Influences Arbuscular Mycorrhizal Network Formation and Pepper Phytophthora Blight Suppression in Facility Sheds

      2022, 59(5):1378-1385. DOI: 10.11766/trxb202102280112

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      Abstract:【Objective】Arbuscular mycorrhizal(AM)fungi have the potential for biocontrol of soil-borne diseases, e.g., pepper(Capsicum annuum L.)Phytophthora blight. However, the mass production and wide application of AM fungi have not been achieved due to the difficulties associated with in vitro cultivation. Therefore, it would be of great significance if the disease suppression function of soil indigenous AM fungi can be exploited.【Method】In the Pepper Science Park of Shizhu County, Chongqing city, plot experiments in a facility shed were carried out to investigate the effects of intercropping with maize(Zea mays L.)on indigenous AM fungal propagation and pepper Phytophthora blight suppression.【Result】Compared with the control(i.e., mono-cropping of pepper), intercropping with maize significantly increased not only the root mycorrhizal colonization rate of pepper, the rhizosphere AM fungal abundance, and soil phosphatase activity, but also the total nutrient(N, P, and K)acquisition amounts by the two crop species per plot. In contrast, intercropping with maize significantly decreased not only the incidence and severity of pepper Phytophthora blight but also the P acquisition amount and the fruit biomass per pepper plant. Compared to the treatment with the same row distances as control(SRD), the intercropping system which had the same ridge widths as control(SRW)and a relatively higher planting density, induced significantly higher(i)root mycorrhizal colonization rates with both crops, (ii)maize yield per plot, and(iii)total nutrient acquisition amounts by the two crop species per plot. Furthermore, the pepper Phytophthora blight incidence was significantly lower in the intercropping system with SRW than with SRD. 【Conclusion】In facility sheds, intercropping with maize may enhance the suppression of pepper Phytophthora blight by soil indigenous AM fungi via promoting their propagation and thus colonization on pepper roots. Also, the intercropping system with SRW has a relatively higher economic benefit compared to SRD.

    • Effects of Water-nitrogen Interaction on Greenhouse Gas Emissions in a Paddy Soil

      2022, 59(5):1386-1396. DOI: 10.11766/trxb202011250646

      Abstract (477) HTML (869) PDF 718.52 K (1022) Comment (0) Favorites

      Abstract:【Objective】In order to study the effects of water management-nitrogen fertilizer on greenhouse gas(CH4, N2O and CO2)emission and soil physicochemical properties.【Method】Two irrigation modes including controlled irrigation(C1)and normal irrigation(C2), and three nitrogen application levels(low nitrogen, N1; medium nitrogen, N2 and high nitrogen, N3)were set up under a long-term pilot plot. 【Result】 The results showed that compared with normal irrigation, controlled irrigation significantly reduced the cumulative emissions of CH4 and N2O by 43.12% and 23.53%, respectively. Under normal irrigation, the contents of soil ammonium nitrogen in low nitrogen, medium nitrogen and high nitrogen treatments were 35.26, 38.90 and 35.20 mg·kg-1, respectively, while those under controlled irrigation were 33.08, 34.30 and 42.40 mg·kg-1, respectively. Under the condition of controlled irrigation, CO2 emission was higher than that of conventional irrigation and increased with the increase of nitrogen application level. According to the overall analysis of the Greenhouse Effect, the GWP(global warming potential)of 0.55 t·hm-2 under controlled irrigation was much lower than that of 0.82 t·hm-2, under conventional irrigation, while the GWP of 0.65 t·hm-2 under N2 treatment was much lower than that of 0.74 t·hm-2 under N1 treatment and 0.67 t·hm-2 under N3 treatment. The coupling of water and nitrogen was the main factor affecting N2O emission from the paddy field, and under medium and high concentration of nitrogen application, the contribution of N2O emission from the paddy field to the Greenhouse Effect was greater than that of CH4. 【Conclusion】Therefore, the application of controlled irrigation combined with reduced nitrogen fertilizer can effectively decrease the emissions of greenhouse gases, maintain a high level of soil ammonium nitrogen in paddy soil, which is of great significance for improving soil fertility quality and developing sustainable agriculture.

    • Study on Suitability Zoning of Biochar-based Organic Fertilizer Application in Bijie Tobacco Growing Area

      2022, 59(5):1397-1407. DOI: 10.11766/trxb202011270652

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      Abstract:【Objective】The role of biochar-based organic fertilizers in improving soil fertility and health, in general, has gained a lot of attention in recent times. It is the premise of scientific fertilization to make clear which planting areas are suitable for applying biochar-based organic fertilizer and which areas are not.【Method】Based on 2 059 soil samples in Bijie tobacco planting area of Guizhou Province, this study analyzed the distribution characteristics of soil pH and the spatial changes of soil properties, such as organic matter, available calcium, available magnesium, clay content and cation exchange capacity(CEC). Based on the overall consideration of soil pH and soil acid-base buffer potential, the suitability grade of biochar-based organic fertilizer application in the Bijie tobacco planting area was obtained.【Result】The results showed that the average pH value of all sampling points in Bijie tobacco growing area was 6.5, which was weakly acidic. The average pH values of Dafang County, Qixingguan District and Weining County were only 6.2, 6.3 and 6.3, respectively, while those of Zhijin County, Jinsha County and Qianxi County were more than 7.0. The contents of organic matter, available calcium and magnesium, clay and CEC in tobacco planting soils in different counties were different, which led to the differences of soil acid-base buffer index between different counties. In all counties, the comprehensive index of acid buffer in Dafang and Weining was 0.96, while that in Zhijin was 1.23. Generally, there was a positive correlation between the pH value and the buffering potential of each parent rock soil type. The pH value of sandstone coarse bone soil and yellow soil was lower, and the value of the acid-base buffering potential index was also smaller. Also, the value of carbonate limestone soil with higher pH value was higher than that of other soil types. The suitability grade of biochar-based organic fertilizer calculated by pH value and acid-base buffer composite index showed that except for the purple soil of sand shale, the soil types derived from sandstone and sand shale were the most suitable application grade, and it was very necessary to apply a biochar-based organic fertilizer to improve soil pH value in these soil types. Carbonate and calcareous soils were not suitable for the application, which indicates that biochar-based organic fertilizer is not suitable for the two soil types without changing the current soil pH and acid-base buffer potential. The remaining soil types from other parent rocks belong to the suboptimal grade, and a certain amount of biochar-based organic fertilizer should be applied to these soil types to moderately increase the pH value, to keep the soil pH in a better state.【Conclusion】From the township level, the town numbers of key application, general application, and unsuitable application grades were 82, 144, and 32 respectively. The key application towns of biochar-based organic fertilizer were mainly concentrated in Weining County, Zhijin County, and Hezhang County. The towns with general application grade were more, and most of them were distributed in Dafang County and Qixingguan District. The unsuitable application towns for biochar-based organic fertilizer are mainly concentrated in Qianxi County and Jinsha County. This study fully considered the effects of soil pH value and acid-base buffer potential on the suitability of biochar-based organic fertilizer, and identified the key application, general application and unsuitable application towns in the Bijie tobacco planting area. This study provides a scientific basis for the accurate application of biochar-based organic fertilizer in the Bijie tobacco planting area and also enriches the research connotation of soil management division in the tobacco planting area.

    • The Effect of Controlled Release of Urea Coated with Natural Rubber and Biochemical Inhibitor on Soil Nitrogen Supply and Winter Wheat Growth

      2022, 59(5):1408-1419. DOI: 10.11766/trxb202012010592

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      Abstract:【Objective】The purposes of this research were to(i)reduce or slow down the release and conversion rate of nitrogen, (ii)increase the utilization rate of nitrogen, (iii)increase the yield of wheat, and(iv)reduce environmental pollution.【Method】We applied the coating technology and inhibitor addition technology at the same time to prepare a new type of dual controlled release urea. For preparation, the coating material of the controlled release fertilizer was natural rubber while the inhibitors used were urease inhibitor(NBPT, n-butyl thiophosphoric triamide)and nitrification inhibitor(DMPP, 3, 4-dimethylpyrazole phosphate). According to the different inhibitors added, four kinds of new natural rubber coated urea were prepared: uncoated(CRU1), NBPT coating(CRU2), DMPP coating(CRU3), and(NBPT+DMPP)combined coating(CRU4). The microstructure of natural rubber coated urea was observed by a scanning electron microscope(SEM). The slow-release characteristics of urea nitrogen were determined using a hydrostatic release test. The effects of NBPT and DMPP in controlling nitrogen conversion were determined by soil culture test. Also, we designed field experiments to verify the effects of the four controlled-release urea on soil nitrogen supply and winter wheat growth. 【Result】Natural rubber was used as a membrane material to prepare controlled-release fertilizers, with good film-forming properties, smooth surface and obvious nutrient channels in the profile. When loaded in still water, the controlled release period of natural rubber coated controlled-release fertilizer reached 60 days. Compared with urea(U)treatment, all controlled-release fertilizers significantly reduced the ammonia volatilization rate in the soil and postponed the peak ammonia volatilization days. Also, CRU1, CRU2, CRU3, and CRU4 significantly increased the continuous nitrogen supply capacity of the soil and increased the yield of wheat under 10% nitrogen reduction relative to U treatment. CRU4 was better than adding NBPT and DMPP alone in reducing soil urease activity during the growth period of winter wheat, inhibiting the conversion of soil NH4+-N to NO3-N, and reducing soil ammonia volatilization. Relative to U treatment, winter wheat production of CRU1, CRU2, CRU3, and CRU4 increased by 16.96%, 21.46%, 17.37% and 25.90%, respectively. 【Conclusion】 CRU4 demonstrated the strongest continuous nitrogen supply capacity when applied in soil and the best increase in winter wheat yield. This result indicates that the new controlled-release urea prepared by combining natural rubber and inhibitor-coated urea controlled the dissolution of urea and delayed the urea conversion process. Under the condition of a 10% reduction in nitrogen application rate, the yield of winter wheat can still be significantly increased.

    • Accumulation of Trace Element and Organic Functional Groups in Different Size Fractions of a Loess Topsoil After Long-term Micronutrient Fertilization

      2022, 59(5):1420-1431. DOI: 10.11766/trxb202012290640

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      Abstract:【Objective】 Trace elements are of vital importance in crop growth. Long-term application of micronutrient fertilizers may affect the distribution of the elements in farmland soil, therefore influencing crop yield and soil organic carbon composition. To explore the accumulations of trace elements in different size fractions of loess soil, we collected topsoils from field plots after 35 years of fertilization with Zn, Mn, and Cu. 【Method】 All the soil samples from the treated plots and control plots(CK)were fractionated into ≥250, 250-125, 125-63, 63-20, and ≤20 μm. The element contents, availability, and soil organic carbon content(SOC)were determined and compared. Also, the types and contents of organic functional groups in different size classes were determined using Fourier Transform Infrared(FTIR)spectrometer. 【Result】 The results show that the content of SOC in the treated plots was at a low level(6-12 g·kg–1)and was not significantly improved after applying Zn, Mn, and Cu fertilizers. Nevertheless, the three trace elements were enriched to different degrees: Zn and Cu fertilizers significantly increased the total contents of Zn and Cu(the degree of enrichment was above 10% and 100% respectively), but no evident Mn enrichment was observed under Mn fertilizer treatment(the degree of Mn was within 10%). The highest concentrations of Zn, Cu, and Mn were observed in the ≤20 μm fractions, but SOC stability in this fraction was the lowest, ranging between 0.30-0.32. This was mainly because of the greater content of the unstable functional group C-O, but lower contents of C=O, C=N, and C=C that were positively correlated with the recalcitrance of SOC. The functional groups(C-O, C=O, C=N)were positively associated with the accumulation of Cu in the soil. Also, the inconsistent relationships of Zn, Mn, and functional groups observed in the loess soil in this study suggest that the governing principals in this study were distinct from previous reports based on SOC-rich soils. 【Conclusion】Findings in this study suggest that long-term application of micronutrient fertilizers did not significantly change the content of organic carbon or organic carbon composition in the topsoil of our study area. Nevertheless, it enhanced the accumulation of Zn, Mn, and Cu in the micro-aggregates to varying degrees. This is affected by the total organic carbon, the content of organic functional groups, and the type and efficiency of elements adsorption together.

    • Analysis of Soil Microbial Community Structure via Integrated Highthroughput Absolute Abundance Quantification (iHAAQ) Method

      2022, 59(5):1432-1446. DOI: 10.11766/trxb202012140588

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      Abstract:【Objective】The high-throughput sequencing technology can easily access the species varieties and the relative abundance of a microbial community. Nevertheless, the relative abundance cannot fully reflect the microbial quantities when using it to evaluate the community. On the other hand, the absolute abundance which is one of the essential parameters for describing a microbial community structure in ecology has been ignored. The absolute abundance can be calculated by integrated high-throughput absolute abundance quantification (iHAAQ) ; which combines high-throughput sequencing and quantitative PCR (qPCR). Both relative and absolute abundances are essential parameters for describing a microbial community structure in ecology. The relative abundance could describe and evaluate the relationship of specific taxa with others in the same sample, while the absolute abundance as a constant parameter is more suitable for describing and evaluating the quantitative variations of specific taxa in a sample or among samples. Thus, this study aimed to provide a comprehensive and in-depth analysis of soil microbial community through the relative and absolute abundances of the archaeal, bacterial, and eukaryotic (fungi) domains of microorganisms (described as three-domain microorganisms) . 【Method】Based on data of soil microbial community in the studies of banana panama disease, the reclaimed sandy agricultural ecosystem and microbial inhibitor, the absolute abundances of archaea, bacteria and fungi in three papers were obtained by iHAAQ. Then the absolute and relative abundances of three-domain microorganisms were further calculated. The α- and β-diversity analyses of archaea, bacteria, fungi and three-domain microorganisms were conducted according to their relative and absolute abundances, respectively.【Result】The results showed that: (1) Compared to archaea and fungi, the bacteria dominated the soil microbial community with higher species varieties and absolute abundance. Meanwhile, the lack of absolute abundance parameters might lead to the misunderstanding of the microbial community. (2) The α-diversity indexes calculated by relative and absolute abundances were the same, while the β diversity indexes were different. (3) In the research of banana panama disease and reclaimed sandy agricultural ecosystem, PCoA results of three-domain microorganisms and bacteria were relatively similar, which indicated that the community structures of three-domain microorganisms were mainly affected by bacteria in these two studies. But no similar results were found in the research of microbial inhibitors.【Conclusion】The iHAAQ method can be applied to the studies that perform high-throughput sequencing and qPCR analyses, simultaneously. It is of great ecological significance to study the three-domain microbial community with the species varieties, relative and absolute abundances obtained by the iHAAQ method, and it should be encouraged for future research.

    • >Research Notes
    • Preliminary Analysis of the Virus Metagenome in a Farmland Black Soil of Northeast China

      2022, 59(5):1447-1456. DOI: 10.11766/trxb202104230215

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      Abstract:【Objective】Viruses exist almost everywhere on Earth. They can infect humans, animals, plants, fungi, and even bacteria, and thus play critical roles in the biogeochemical cycling of elements and energy. Knowledge of the viruses’ community patterns and genomic information is key for proper understanding of their crucial ecological functions. This study aims to quantify the viral community patterns and functions in a farmland black soil of Northeast China and analyze their potential roles in soil ecosystems. 【Method】The metagenome sequences of the viruses were obtained based on metagenomics sequencing technology and were analyzed individually for functional gene analysis, host prediction, and genome assembly of viral Contigs. A bioinformatics software was employed to analyze the diversity patterns of the viruses. 【Result】The results showed that the majority of the viruses in the farmland black soil belonged to Caudovirales(59.38%)and Herpesvirales(2.56%)orders. This consisted of 29 families, with Siphoviridae and Microviridae representing the top two abundant families and accounting for about 44.48% and 20.53%, respectively. Gene annotation analysis revealed that soil viruses may actively contribute to numerous biogeochemical cycling processes, including nitrogen compounds metabolism, catabolism, biosynthesis, methylation, multi-organism metabolism, cellular metabolism, primary metabolism, nucleobase-containing small molecules metabolism, and organic substance metabolism, etc. Additional analysis showed that the virus hosts could be classified into 35 genera that belong to 5 phyla. 【Conclusion】With these quantitative measurements, this study provides necessary information towards advancing the virus gene database of the black soil and its ecological functions.

    • The Responses of Active Cellulose-degrading Bacterial Community to Different Fertilization in Paddy Soils as Revealed by Magnetic Nanoparticle-mediated Isolation Method

      2022, 59(5):1457-1468. DOI: 10.11766/trxb202011270598

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      Abstract:Magnetic nanoparticle-mediated isolation(MMI)method is a promising technology for separating functional microbes from complex microbiota. In this study, we employed the MMI method to recover metabolically active cellulose decomposers from paddy soils with a 28-year history of different fertilization regimes(chemical fertilizers; termed NPK afterwards), organic amendments(OM), and without fertilization(CK)). Our findings suggest that compared to no fertilization, fertilization increased the number and activity of microorganisms, thereby facilitating cellulose degradation. These active cellulose-degrading bacterial phylotypes mainly belong to Bacteroides and Firmicutes at the phylum level, and further to Porphyromonadaceae and Paenibacillaceae at the family level. Also, we found that fertilization increased community stability, partly by decreasing interspecies dependency. Furthermore, OM fertilization increased the numbers of potential ecological function, which makes it more effective than NPK fertilization. These results were consistent with our previous conclusions based on DNA-SIP technology, suggesting that MMI is a powerful approach to recover active cellulose decomposers from a complex microbial community. Above all, these results would deepen our understanding of keystone straw decomposers in paddy soils and their shifts in response to different fertilizations.

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