Abstract:【Objective】The special environment of coastal saline-alkali land restricts the transformation and utilization of soil nitrogen. Microorganisms in saline-alkali paddy environment mediate ammonia oxidation in rice rhizosphere in a key process of soil nitrogen cycling. However, due to research blindness and outdated technology, the effect of seawater rice rhizosphere effect on the microbial community structure of ammonia oxidation in coastal saline-alkali soil is rarely reported. 【Method】In this study, the saline tolerant rice species ‘Haidao 86’ was used as the experimental material for the pot experiment. The pot experiment was conducted with low (2 g·kg-1) and high (6 g·kg-1) salt concentrations. Soil physicochemical properties and microbial biomass were measured and analyzed, and high-throughput sequencing of ammonia-oxidizing microorganisms was conducted to analyze the effects of different treatments of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) community structure in the rice rhizosphere.【Result】Results showed that after 70 days of rice growth, pH of rhizosphere soil decreased by 0.82 and 0.70, soil organic matter (SOM) content decreased by 6.41 g·kg-1and 4.46 g·kg-1, humus (HU) content increased by 5.76 g·kg-1 and 4.45 g·kg-1, total nitrogen (TN) content decreased by 0.46 g·kg-1 and 0.37 g·kg-1 for low and high salt concentrations, respectively. Rice rhizosphere effect significantly increased soil microbial biomass carbon, microbial biomass nitrogen and microbial respiration intensity, reaching peak values on the 55th day of planting with 850.0 mg·kg-1, 72.2 mg·kg-1 and 231.9 mg·kg-1·d-1 for high salinity treatment and 546.1 mg·kg-1, 53.7 mg·kg-1 and 171.2 mg·kg-1·d-1 for low salinity treatment, respectively. The rhizosphere effect had no noticeable influence on the Chao1 index, Shannon index and Simpson index of AOA. At the genus level, the dominant bacteria of AOA were norank_c_environmental_samples_p_Crenarchaeota, unclassified_k_norank_d_Archaea, and Nitrososphaera. The rhizosphere effect of seawater rice significantly affected the richness, diversity and abundance of AOB in coastal saline-alkali soil. It can significantly increase the abundance of environmental_samples_f_Nitrosomonadaceae and Nitrosospira. Also, correlation analysis between the AOB community and soil environment showed that environmental_samples_f_Nitrosomonadaceae and Nitrosospira had a significant positive correlation with HU and a significant negative correlation with pH. 【Conclusion】The results of this study indicate that planting tolerant rice species can improve nutrient cycling in coastal saline-alkali land, and the rhizosphere effect of saline-alkali tolerant rice mainly affects the community structure of AOB in acidic soil.

Abstract:[Objective] The utilization efficiency of phosphorus fertilizer is generally low in agro-ecosystems as phosphorus is readily co-precipitated with iron and manganese oxyhydroxides, iron aluminides, or directly adsorbed to the soil minerals, particularly in the red soil ecosystem. Thus, understanding the subsequent effects of phosphorus retained in the soil on soil ecological function and crop nutrient supply is of significance to guide the management of phosphorus fertilization.[Method] Based on a long-term fertilization experiment in red upland soil, this study investigated the effect of the conventional fertilization (CK) and short-term phosphorus fertilizer input (at rates of 0, 50, 100, 150 and 1 000 kg·hm–2, P2O5) on soil nutrients, soil nitrogen cycle process and crop yields after 27 years. We evaluated the relationship between these factors and the residual effect of phosphorus using the multivariate statistical analysis method.[Result] Short-term P fertilizer addition at a high rate (1 000 kg·hm–2, P1000) had no significant effects on soil total carbon (TC), total nitrogen (TN) and microbial biomass (MBC) compared to the conventional fertilization treatment (CK). Also, it significantly increased soil pH, nitrogen mineralization rate (Nmin), soil nitrogenase activity (SNA), and potential nitrification rate (PNR) (P < 0.05), while it significantly decreased the net N2O emission potential (NN2O) (P < 0.05). Compared with the low phosphorus dosage treatments (50, 100, 150 kg·hm–2), P1000 significantly increased soil available phosphorus (AP), Nmin, SNA, PNR and potential N2O production rate (PN2O) by 33.3%-76.4%, 88.2%-388.1%, 111.4%-4 826.3%, 22.6%-152.4% and 13.8%-78.9%, respectively (P < 0.05), but significantly decreased the net N2O emission potential by 64.6%-78.9% (P< 0.05). These results suggest that the application of a high dosage of phosphorus fertilizer has a strong residual effect on soil microbial activity and nitrogen processes even after 27 years. Spearman correlation analysis and redundancy analysis showed that AP and pH were the most important factors affecting soil microbial activities. Maize yield in the recent three years showed no significant difference among all treatments but was significantly positively correlated with TP, AP and pH. In comparison to low phosphorus treatments, P1000 treatments showed a promotion effect of 3%-23% on maize yield based on the historical yield data during 1991—2019.[Conclusion] Our results reveal that the short-term application of a large amount of phosphorus fertilizer has significant positive effects on maintaining soil fertility, microbial activity, soil nitrogen cycle function activity and crop yield even after 27 years, owing to the promotion of soil pH and slow release of available phosphorus.

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°50N, 124°07E)in Liaoning Province to Nenjiang(49°07N, 125°13E)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.

Abstract:【Objective】Nitrification in soil is a highly sensitive process to pH. Responses of nitrification rates and the community structures of nitrifying microorganisms to different N sources in an alkaline purple soil were studied to elucidate the microbiological mechanisms for nitrification. 【Method】Three different N sources and the blank control were used in the 4-week incubation study. Net nitrification rate was calculated by the differences of nitrate concentrations at day 0 and 28. The amoAgene abundances for ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were measured by quantitative PCR before and after the incubation. The relative abundance of nitrite oxidizing bacteria (NOB) was analyzed by binning the sequences of the 16S rRNA gene and the amoAgene into operational taxonomic unit (OTUs) at 97% similarity level. The changes of community structures for AOA, AOB and NOB were studied by high-throughput sequencing method before and after the incubation.【Result】In the 4-week incubation study, compared with blank control (CK), soil nitrification rate was stimulated by application of all three kind of nitrogen sources: ((NH4) 2SO4, NH4Cl and CO(NH2)2). The net nitrification rate for blank control (CK) was 0.86 mg N kg-1 d -1. The highest net nitrification rate was observed for CO(NH2)2treatment (N 3.88 mg kg-1 d -1), which was more than 4-times higher than CK. The addition of NH4Cl and (NH4) 2SO4, showed similar stimulation on nitrification to CO(NH2)2application. The net nitrification for NH4Cl and (NH4) 2SO4were N 3.34 and 3.88 mg kg-1 d-1, respectively. But, NH4Cl also reduced the accumulation of nitrate and inhibited the reduction of ammonium when compared with (NH4) 2SO4, and CO(NH2)2. Along with the accumulation of nitrate, the copies of amoA gene in ammonia oxidizing bacteria (AOB) increased significantly during the first two weeks of incubation (p<0.05). The copy numbers of bacterial amoA genes increased from 0.88×107 g-1soil and 0.85×107 g-1 soil at day-0 to 3.38×107 g-1 soil and 3.55×107 g-1 soil at the day 14 of the incubation, then decreased to 1.46×107 g-1soil and 1.69×107 g-1 soil at the day-28, for (NH4) 2SO4, and CO(NH2)2 treatments respectively. The copy numbers of bacterialamoAgenes were significantly lower in NH4Cl treatment than (NH4) 2SO4, and CO(NH2)2addition at the day 14 (p<0.05). On the other hand, the copies of amoAfor AOA did not change significantly during incubation (p>0.05). Results indicated that nitrification in alkaline purple soil was mainly driven by AOB, but not AOA. Pyrosequencing of the 16S rRNA genes was performed at the whole microbial community level for different treatments and control before and after incubation. Approximately more than 30 000 high-quality 16S rRNA reads were obtained, and targeted reads from putative AOA, AOB and NOB sequences were selected for subsequent analysis. The high-throughput sequencing results further showed that the dominant nitrifying microorganisms were mainly related to Nitrospira, Nitrososmonas and Nitrosospira in the alkaline purple soil. The dominant AOB were classified into Nitrosospira Cluster 3, and the dominant AOA were affiliated with Group 1.1b. Furthermore, the relative abundance of NOB was much higher than that of AOB and AOA, which may imply the presence of Comammox in the studied alkaline purple soil.【Conclusion】Results showed that the nitrification in alkaline purple soil was stimulated by the addition of (NH4) 2SO4, NH4Cl and CO(NH2)2. But NH4Cl also showed a inhibition effect on nitrification when compared with NH4)2SO4, and CO(NH2)2 application. The nitrification process in alkaline purple soil was mainly driven by AOB, but not AOA. The evidences from the high-throughput sequencing results further indicated that the dominant population of ammonia oxidizing bacteria was classified into Nitrosospira Cluster 3 in the alkaline purple soil, and AOA was mainly the Group 1.1b. For NOB, Nitrospira was the dominated species.

Abstract:A summary is presented of progresses that have been achieved since the 1930s in the research on soil nitrogen(N)in China,covering 1)nature of soil N and soil N fertility,2)N in organic manure,3)the fate and yield-increasing effect of chemical fertilizer-N app lied to agricultural fields,4)impacts on the environment of the losses of chemical fertilizer-N applied to agricultural fields,and 5)N balance in the agricultural ecosystem.It is obvious that the research benefits much from the progresses made in other relevant disciplines. And it is,therefore,stated with emphasis that the guiding ideology of the researchin China must give high attention to harmonization and in tegration of high-yield and environment protection.