Abstract:Soil pollution, in particular, soil heavy metal pollution is a severe problem in China, which has now come to the extent of threatening food security of the nation, for heavy metals accumulate in edible parts of the crops produced in some severely contaminated areas. However the currently used standard for soil environmental quality does not fit the demands of the soil environmental management today, which manifested in the index system is that the number of indices covering heavy metals pollution is limited. So far the standard of China has only eight heavy metals covered, much fewer than that of the USA, Canada, the Netherland etc., which has led to inefficient management of some soil pollution problems popped up recently with the development of economy in China. Therefore, the objective of this study is to find the gaps between China and those developed countries and regions in the establishment of soil standard for heavy metals, and to provide some proposal for the revision of China’s soil environment quality standard in the future. A worldwide investigation has been conducted on the soil environmental standard of those developed counties and regions, such as USA, Candia, the Netherland, Germany, Australia, Japan, Taiwan (China) and so on. The item counts, kinds and species of the heavy metals involved in these soil standards were mainly concerned of. Meanwhile, in depth study and systematic analysis was conducted of indices of heavy metals in the standards for soil environment of some developed countries and regions for comparisons with ours. Similarity and difference were both found based on the comparison. The similarity is that the high toxic elements such as Cd, Hg and As are contained in the soil standards of most countries and regions. The differences are mainly in relation to the speciation of the elements. The hexavalent chromium and organic mercury are contained in the soil standard of some developed countries and regions due to their high toxicities. However, standards of chromium and mercury are simply provided based on the total content in China’s Soil Environmental Quality Standard. Another difference is the usage of extractable speciation in addition to the total content of heavy metals in the standard of some developed countries such as Germany, Switzerland and Japan while not in the standard of China. This could be owing to the large diversity of soil types in China and be difficult to find a common extracting agent for all the soil types. Meanwhile, China has its own characteristics in soil heavy metal pollution, which includes beryllium, antimony, thallium and vanadium pollution as a result of high geochemical background in the calcareous rock soil or some mining areas that mainly located in the south China. These heavy metals pollution have threatened to human health of local residents. On such a basis, suggestions are put forth for revising the current standard of the country, including amendment of the criteria for valences and forms of highly toxic heavy metals, like hexavalent chromium and organic mercury; setting up of criteria for newly emerged heavy metal pollutants, like beryllium, antimony, thallium, vanadium, etc.; and exploration for establishment of a bioavailability-based index system for extractable forms of heavy metals, by taking into account soils or rocks in calcareous regions with high heavy metals background values, so as to provide some scientific basis for management of soil heavy metal pollution risks in China.

Abstract:Lack of effective monitoring techniques has become a bottleneck in the study on scaling problem in soil science and hydrology. In recent years, some geophysical methods, of which Electrical Resistivity Tomography (ERT) is representative, were introduced into the researches on soil hydrological processes in vadose zones, which provides a new strong tool for solving the scaling problem. Coupled with the petrophysical relationships between soil electrical resistivity and other soil properties, ERT can be used to realize multi-scaled non-destructive continuous monitoring of soil properties or states. In this paper, a review is presented of the basic steps and characteristics of ERT, and its applications to the studies on soil hydrological processes. At the same time, in-depth discussion was conducted of problems in and potentials of the application of the ERT technology to the studies on soil hydrological process in vadose zones.

Abstract:Soil organic matter (SOM) is a key index in estimating soil fertility and soil C sequestration. Consequently, the study on temporal and spatial variability of SOM is of great significance to assessing regional soil C sequestration potential and realizing sustainable utilization of soil resources. For this research, Jiangsu Province, East China was selected as a subject for case study and comparative study was done of the data of the Second National Soil Survey and the data collected in 2006, using the geostatistic and GIS technologies, to explore temporal and spatial variability of SOM in the surface soil layer (0 ~ 20cm) of the province during the period (1980 - 2006), and its driving forces, as well. Results show that the mean SOM content increased from 16.55 ± 8.50 g kg-1 in 1980 to 18.31 ± 8.32 g kg-1 in 2006, and its coefficient of variation decreased from 51.36% to 45.44%. The variograms of SOM of the years both fitted the exponential model, with nugget coefficient rising from 51.85% to 56.52%, suggesting that the effect of stochastic variability of SOM content intensified and spatial autocorrelation weakened. The codomain decreased from 71.55 km to 37.83 km, indicating decreasing spatial autocorrelation distance. A general trend was observed that soils high in initial SOM content decreased in the content and vice versa, and the increment reduced in margin from north to south of the province. The application of large volumes of chemical fertilizers improved crop production, and increased soil biomass from crop leftover and roots. The extrapolation of straw incorporation brought large volumes of organic matter into the soil, contributing to accumulation of SOM. Changes in land use brought about changes in SOM. Reclamation of land into paddy fields, upland and forest lands increased SOM content and vice versa.

Abstract:A total of 191 soil samples were collected from Wensu, Hetian and Baicheng counties for analysis of original reflectances, which were then subjected to continuum removal and first derivative of continuum removal for analysis of hyperspectral absorption characteristics and sensitive bands of salts. On such a basis, a number of hyperspectral inversion models for quantification of soil salt contents (S_t) were established. Results show that there was no obvious relationship between soil reflectance and S_t in 400~2 400 nm bands, and an apparent negative relationship between the data of continuum removal and S_t in 640~700 nm bands and a positive one in 710~780 nm bands. Prediction accuracies of the inversion models were improved significantly after the original reflectances underwent continuum removal. The inversion models established on spectral indices and spectral absorption features were inferior in stability and prediction accuracy to the PLSR models based on spectral reflectance in 400~2 400 nm bands or sensitive bands after continuum removed (CR) and first derivative of continuum removal (FDCR). Among all the models, the inversion models between S_t and FDCR were higher in determination coefficient and lower in root mean square error than the inversion models between S_t and CR. But the former was lower than the latter in prediction accuracy. Among all the inversion models, only the ones based on full spectrum and 640~700 nm continuum removal were higher than 2.5 in RPD, reaching 2.62 and 2.52, respectively and moreover, little difference was found between the two in all the other evaluation indices. The PLSR inversion model based on the continuum-removal data of the 640~700 nm bands is the most effective one in predicting St of paddy soils in Southern Xinjiang Uygur Autonomous Region of China.

Abstract:The formation of an albic horizon in stagnic anthrosol has a special significance to genesis and development of the soil. To explore causes of the formation, four profiles of stagnic anthrosols with an albic horizon (E-A1, E-A2, E-A3 and E-A4) and and one (Ref), the same in parent material but without the horizon, as reference, in the Taihu Lake region were sampled for analysis of morphological characteristics, soil mechanical composition , clay mineral composition, contents of iron oxides, and geochemical characteristics of macro- and trace-elements. Of the five soil profiles, soil particle size compositions were dominated with silt, which accounted for 60%~75% and did not vary much between soil layers in the profile, with variation coefficient being < 10%. Contents of macro and trace elements did not vary much either, with CVs being less than 10%. All these indicated albic horizons developed from parent materials similar to those the overlying and the underlying layers did from. However, in Profile E-A1, the albic horizon was quite high in silt content (75.04%) and in CV of medium-fine silt (38.05%) and medium-fine silt/coarse silt (61.85%) as well, which indicates that the profile is not uniform in parent material. All these demonstrate that the variations of soil properties in Profiles E-A2, E-A3, E-A4 and Ref were caused by soil formation, while that in Profile E-A1 was also affected by the environment of sedimentation, besides soil formation. The albic horizons in Profiles E-A2, E-A3 and E-A4 are higher than their overlying and the underlying horizons in contents of smectite, illite, silt, coarse silt, SiO₂, CaO and Zr, but lower in contents of hydromica, chlorite, free iron, Al₂O₃, Rb, Li, Ba and REE. Profile Ref was quite similar to Profile E-A2, E-A3, E-A4 in all characteristics except that the albic process appeared only in the plow layer, which is not fit to be defined as albic horizon. In Profile E-A1, some soil properties were not spatially homogeneous, for instance, silt content is not the highest in the albic horizon, but increased with depth in the soil profile, which suggests that the formation of an albic horizon in stagnic anthrosols in the Taihu Lake region is a result of the subjection of loessial lagoon sediments to periodical alternation of flooding and draining mechanical washing and leaching of active iron during anthrostagnic process (Profiles E-A2, E-A3 and E-A4), or a result of the subjection of parent material to mechanical washing caused by rise and fall of the water surface in the lake during its sedimentation process and then to leaching of active iron during repeated anthrostagnic processes (Profile E-A1).

Abstract:Gradients and lengths of the slopes in the Lianshui River Basin, Xingguo County, Jiangxi Province were extracted using DEMs different in resolution, i.e. 10m, 25m, 50m and 100m, and analyzed for difference in accuracy difference between the DEMs in calculating the combined gradient and length, using the GIS digital terrain analysis method and the mathematical analysis method. Results show that 1) significant differences exist between slope gradients obtained by DEMs different in resolution, indicating that the gradient decreases with declining resolution and that the lower the accuracy, the greater the generalized effect on terrain information; and that the mean slope gradient obtained by DEM 100m in resolution is only 45.04% of that by DEM 10m in resolution;. 2) the slopes in the valley vary in length mainly in the range of 0~80m and their lengths elongate with declining resolution; and 3) the mean LS factor values obtained by the DEMs regardless of resolution vary in the range from 6.10 to 7.10; the combination of slope gradient and slope length factors reduces the effects of single slope gradient or single slope length factor; and as the topographic fluctuation increases in extent, the dominating role in LS factor shifts from slope gradient to slope length.

Abstract:Taking cropland soil in the Mollisol region of Northeast China as object, an indoor experiment was carried out to have the soil subjected to simulated freezing-thawing alternation for investigation of effects of the alternation on macro-pores in the soil profile using CT (Computerized tomography) thorough quantifying and analyzing variation of the number, average area, Feret diameter and roundness of macro-pores with soil depth (0~40 cm，40~80 cm，120~160 cm). Results show that the alternation did not change the characterization of macro pores in 0~40 cm but significantly reduced the average area and Feret diameter of pores in 40~80 cm by 46.72% and 17.32%, respectively (p<0.05). Pores, 1~2 mm and ≥5 mm in diameter were found most vulnerable to the alternation, decreasing by 9.58% and 42.19% (p<0.05), respectively. The findings confirmed the possible effect of argillic horizon stagnating water, and susceptibility of the pore structure in argillic horizon to the alternation, thus demonstrating that seasonal freezing-thawing alternation is the major cause of surface soil erosion and gully erosion of the Mollisol region through weakening erosion resistance of its argillic horizon and enhancing the effect of the argillic horizon stagnating water.

Abstract:To explore effects of collapse fissures caused by coal mining on soil water holding capacity of slope lands after rainfalls, post-rainfall dynamics of soil water in different soil layers on either side of a collaspse fissure in slope lands different in aspect was studied. Results show that on slope lands rains bring some water mainly into the 0~20 cm soil layer, but the water in the soil layer is quickly lost after the rain; after rainfall, the soil on the shady slope is higher in moisture content and soil moisture contents in the soil layers of 0~10, 10~20 and 20~40 cm differ sharply(p<0.05). Eight days after rainfall, soil moisture contents around the fissures vary greatly, especially along the edge of the upper part of a fissure, and the difference in soil moisture content between the soil of the fissure and that far from the fissure is significant (p<0.05). On sunny slopes soil moisture loss after rainfall is high and the mean soil moisture loss around the fissures may reach as high as 3.31%. It is quite obvious that the appearance of fissures to a certain extent breaks the slope rain water holding pattern and aggravates soil moisture loss in some parts of a slope, which should not be neglected in the process of revegetation and construction.

Abstract:Viruses usually exist simultaneously with various dissolved organic matter, inorganic colloids, and microbial cells in wastewater, while little has been done on effects of microbial cells and their exudates on fate of viruses in the environment. In this study, bacterial cells were harvested and their exuded extracellular polymeric substances (EPS) were extracted from the media that had been used to cultivate three typical strains of bacteria. The aim is to (1) compare red soils in virus adsorption capacity; (2) investigate effect of the presence of the bacteria on virus adsorption onto the red soils; and (3) evaluate relative contributions of the bacterial cells and their exuded EPS to the effect. Results show that among the four kinds of sterilized red soils, Argiargiudic Ferrosols and Allitiargiudic Ferrosols was the highest in virus adsorption capacity, Rhodiudic Ferralosols followed, and Ferriudic Cambosols lagged behind, being the lowest. The presence of bacterial cells did not have much effect on the adsorption, and in a certain kind of red soil it displayed a promotive trend. However, the presence of EPS alone or of cells and EPS simultaneously significantly reduced virus adsorption capacities of all the four studied soils, by 36% or 30%, respectively, which indicates that the effect of the presence of bacteria reducing virus adsorption by the soils is attributed mainly to the EPS bacteria exude. The findings demonstrate that it is essential to take into account the presence of bacteria and its effect in assessing virus adsorption capacity of a certain medium. Otherwise, it is very likely to have it overestimated.

Abstract:To easily and accurately characterize electrochemical properties of large particles, a homemade streaming potential device was used to measure streaming potential of Fe hydroxide-coated quartz for calculation of its ζ potential. Results show that this device is capable of determining streaming potential (ΔE) accurately regardless of hydraulic differential (ΔP). Between the two exists an excellent linear relationship, which guarantees the accuracy of streaming potential coefficient (C) obtained through fitting ΔE with ΔP. Hence, the ζ potential of Fe hydroxide-coated quartz figured out from C is good enough to characterize the surface electrochemical characteristics of the Fe hydroxide-coated quartz very well. In the same electrolyte solution, absolute value of the ζ potential of Fe hydroxide-coated quartz decreases with the increase in coating degree. When ionic strength is low, the electric double layer on Fe hydroxide-coated quartz is quite thick, occupying a large proportion of a capillary pore, thus making it necessary to take into account the effect of surface electric conduction in measuring ζ potential of coated particles based on streaming potential. The electric double layer on Fe hydroxide-coated quartz is compressed with increasing ionic strength of the electrolyte solution, thus causing the absolute value of ζ potential to decline. The isoelectric point of Fe hydroxide-coated quartz measured with the streaming potential method was 4.6. When the electrolyte solution pH went above the isoelectric point, ζ potential of Fe hydroxide-coated quartz was negative and turned more negative with rising pH. However, when the solution pH fell below the isoelectric point, the ζ potential turned positive and increased with declining pH. A significantly positive relationship between the ζ potential of quartz worked out from streaming potential and the ζ potential of quartz colloids measured with the electrophoresis method was observed, suggesting that the streaming potential method for measuring ζ potential of particles was reliable.

Abstract:To investigate effects of tillage pattern on soil respiration in dry cropping farmlands in purple soil hilly region in Southwest China, an LI6400-XT portable photosynthesis measurement system equipped with a soil respiratory chamber (6400-09) was used in an experiment conducted in the experimental field of the Southwest University in Beibei, Chongqing. Respiration and hydrothermal factors of the soils under the same wheat/corn/soybean triple intercropping system, but different tillage patterns were measured and analyzed during the crop growing period. The tillage patterns or treatments were coded as T (traditional tillage), R (ridge tillage), TS (traditional tillage + straw mulching), RS (ridge tillage straw mulching), TSD (traditional tillage straw mulching decomposing inoculants), and RSD (ridge tillage straw mulching decomposing inoculants) and each had 3 replicates. Results show that soil respiration rate varied significantly with the season and from treatment to treatment as well. The daily mean soil respiration rate under wheat and soybean in the wheat-soybean row was 1.53 μmol m^-2 s^-1 and 4.10 μmol m^-2 s^-1, respectively and varied between treatments, displaying an order of T < R < TS < TSD < RS < RSD. In the blank-corn-black row, the daily mean soil respiration rate of the soil under corn reached 2.56 μmol m^-2 s^-1, ranging between those under wheat and soybean, and varied between treatments, displaying an order of R < T < RS < TS < RSD < TSD. The total soil respiration rate of the field under the intercropping system was 1.54～2.13 g m^-2 and varied between treatments, displaying an order of T < R < RS < TS < TSD < RSD. The experiment also shows that soil temperature and soil moisture content were the two major factors affecting soil respiration, explaining 28.9 %~53.7 % and 13.7 %~42 % of its seasonal variation. Regression analysis of the relationship between soil respiration and soil hydrothermal factors reveals that exponential equation (R_s =0.311e ^0.095T) fits well the relationship between soil respiration and soil temperature at 10 cm in soil depth and the temperature sensitivity index (Q10) of soil respiration was 2.25~2.69. However, the relationship between soil respiration and soil moisture content can be best described with a parabolic function. The threshold of soil moisture soil respiration responds to was 14.94%. In short, the findings may serve as reference to the study on rules of the variation of soil respiration in the farmland ecosystem and mechanisms for controlling its affecting factors, and are of some important significance to global carbon budgeting and assessment of regional carbon sources and pools.

Abstract:Tropospheric ozone (O₃) pollution affects plant growth and indirectly plant potassium (K) uptake. Effects of elevated atmospheric ozone (p O₃) (50% higher than the ambient p O₃) on biomass and K uptake and distribution of five modern cultivars of wheat (Tritcium aestivum L. cv. Yangmai 15 (Y15), Yangmai 16 (Y16), Yannong 19 (YN19), Yangfumai 2 (YF2) and Jiaxing 002 (JX002) ) were investigated in fully open-air field in the Yangtze River delta. Results show that straw and grain responded more than root to elevated pO3. Y16, YN19 and JX002 decreased in yield, while Y15 and YF2 as not affected did not show any change. Under elevated p O₃, YF2 and JX002 decreased significantly in straw biomass, Y16 displayed a rising trend while Y15 and JX002 declining ones, indicating that the effect of elevated pO3 on accumulation and distribution of biomass of wheat varied with wheat cultivar. Simultaneously, YN19, Y15 and JX002 decreased significantly in total plant potassium uptake, while Y16 displayed a declining trend and YF2 a rising one. Elevated p O₃ also affected content and distribution of potassium in the plant and the effect varied with cultivar, too. Y16, YF2, YN19 and Y15 declined in K distribution ratio in root, which suggested that elevated p O₃ promoted potassium transfer from root to shoot, but JX002 increased, which meant elevated p O₃ retarded potassium transfer to shoot. Obviously, mechanism of the response to elevated p O₃ of wheat in absorption and distribution of potassium varied with cultivar. Elevated p O₃ significantly decreased the partial productivity of potassium fertilizer in Y16, YN19 and JX002 by 13.2% ~ 35.7%, but did not have such effect in Y15 and YF2, while it decreased K fertilizer utilization rate of JX002 and increased that of YF2, while it did not affect much that of Y15, Y16 and YN19. Therefore, it is advisable to take into account the factor of variety in evaluating O₃ effects on accumulation and distribution of biomass in wheat and potassium turnover in the plant–soil system.

Abstract:To investigate effects of the interactions between river water and groundwater on soil environment along river banks, thirty-one soil samples were collected from 6 soil profiles, different in distance from the river, located along the Shima River in Dongguan City in China of and analyzed for heavy metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) by ICP-AES, and luminescent bacterium(Vibrio fischeri, LUMIStox 300) inhibition rate of soil extracted with deionized water. Results show that the concentration of Cd, Cu, Ni, and Zn was 2.8～11.2mg kg^-1, 9.7～298mg kg^-1, 11.4～69.7mg kg^-1 and 40.4～465mg kg^-1, respectively. Cd reached 6.06 in geo-accumulation (Igeo), and the level of extremely severe pollution. In terms of Igeo, the heavy metals followed the sequence of Cd > Zn > Cu > Ni > Cr > Mn >As > Pb > Fe. Differences between the soils in concentrations of the heavy metals were related to their soil organic matter (SOM) content and fraction of micro particles (< 63 μm, CSP). Cr, Cu, Ni, Zn and Mn concentration was significantly and positively related (p<0.05 or p<0.01) to SOM content and Cr and Ni concentration was to the fraction of micro particles. In terms of toxic unit (∑TU, mean of the whole profile), the six soil profiles followed an order of S3 > S2 > Sb > S1 > S4 > Sa. Profile S3 was the highest in ∑TU (5.51), belonging to the moderate toxic level. And the luminescent bacterium inhibition rates of their soil extracts varied in the range from 2.45% to 16.5%, indicating that the heavy metal pollutions in these soils could be sorted into the category of low or non toxicity. Bio-toxicity test could be used to better represent and characterize the eco-toxicity of polluted soils as some speciation of heavy metals in soil may be not bio-available.

Abstract:To raise the comprehensive benefits (including ecological, economic and social benefits) of phytoremediation of heavy metal contaminated soils for smooth development of the work, a case study was conducted of Guixi, using a coupled model to analyze spatial differentiation of benefits of the phytoremediation and to screen out proper types of plants for use in phytoremediation. Results show that comprehensive benefits of the phytoremediation varied from region to region Comprehensive benefits was the lowest in Shuiquan, being only 0.173 6, the highest, in Sumen, reaching as high as 0.835 4; and approximate in Jiuniugang and Pangyuan, both being lower than 0.4, and falling into the category of low benefit region. Among the types of vegetation used in phytoremediation, mixed plantation of arbor trees and shrubs was the best and mono-planting was the poorest in overall benefit. It is, therefore, recommended that the high-efficiency planting pattern in Sumen, i.e. mixed plantation of Photinia fraseri and Koelreuteria paniculata, be promoted.

Abstract:In order to study the effects of applying combined amendment (prepared by mixing limestone and sepiolite at a mass ratio of 2:1, LS) on remediation results in heavy metal contaminated paddy soils, a field experiment was conducted in a paddy soil near a mining area in southern Hunan, China. The experiment results indicated that applying 0～1.8 kg m^-2 of LS significantly increased soil pH and CEC, and decreased exchangeable contents of soil Pb, Cd, Cu and Zn. With increasing in applying amount of LS, the remediation results became more notable. The reduction of exchangeable Pb, Cd, Cu and Zn was an outcome of rising soil pH, CEC and soil colloid adsorption capacity due to addition of limestone and sepiolite. Meanwhile, applying LS resulted obviously in reducing contents of Pb, Cd and Cu in brown rice of the three tested rice varieties (Hanghuazhan, Fengyou 9, and II You 93 in Chinese system), and the maximum reduction of Pb, Cd and Cu contents in brown rice were 55.8%, 66.9%, and 37.4%, respectively. However, applying LS had no significant effects on Zn contents in brown rice. As a result of applying 1.8 kg m^-2 of LS to the paddy soil, the Cd content in brown rice of Fengyou 9 could be decreased to 0.195 mg kg^-1, lower than the limits stipulated in the National Standard GB 2762-2012, Maximum Content of Contaminants in Food (0.20 mg kg^-1). The reduction of Pb, Cd and Cu accumulation in brown rice was due to LS reduced exchangeable contents of soil heavy metals, and there were significantly positive linear correlations between the exchangeable contents of Pb, Cd, Cu in soil and contents of Pb, Cd, Cu in brown rice in natural logarithm.

Abstract:Field experiments were conducted with 11 sites laid out in Yongshou, Shaanxi Province and 7 in Luoyang, Henan Province, and 5 soil samples for each site were collected in 20 cm increment to 100 cm depth, for analysis of initial nitrate N contents. In Yongshou, each experimental site had 7 treatments, i.e. control (without N fertilization), two kinds of nitrate N fertilizers (NN), two kinds of ammonium N fertilizers (AN), and two combinations of nitrate N + ammonium N (NN AN) in a ratio of 2:1, while in Luoyang, each experiment site had only 6 treatments with only one kind of nitrate N fertilizer. In N all treatments, the N application rate was 150 kg hm^-2 as basal fertilizer. The experiments were carried out to explore wheat responses to ammonium N fertilizers and nitrate N fertilizers and their relationships with nitrate N accumulation in different soil layers. Results show that the difference in yield increase between the two kinds of N fertilizers with the same N form was significantly smaller than that between N fertilizers different in N form. Comparison between the fertilizers different in N form in average of yield, yield increment (kg hm^-2) and yield increase rate (%), Treatments NN were the highest in yield and yield increment, followed by Treatments NN AN and Treatments AN in the end. In the experiments, yield increment and yield increase rate declined significantly with the increase in nitrate N accumulation in soil profile. The lower the nitrate N accumulation, the higher the crop response in yield and the more significant the effect of nitrate N fertilizer. It is, therefore, clear to see that nitrate N accumulation in soil profile is the major factor determining crop response to N fertilizer and effect of N fertilizers different in N form. Only in soils low in nitrate N accumulation, can N fertilizer be brought into full play, and can nitrate N show its significant superiority.

Abstract:In order to evaluate impact of planting Eucalyptus on soil fertility and eco-environment in the red soil region of China, soil samples were collected from Eucalyptus and Pinus massoniana plantations and natural broadleaf forests in Luzhai County, Guangxi (China) for analysis and comparison of biological properties and structures of bacterial communities in the soils under different forests, using PCR-DGGE and dilution plate method. Results show that the number of culturable microorganism, such as bacteria, fungi and actinomycetes in the Euclyptus forest soil was lower than in the natural broadleaf forest, but not much different from that in the Pinus massoniana forest soil. Pinus massoniana is an indigenous tree species of Guangxi. In addition，in terms of activities of soil enzymes that are involved in C, N and P recycling (β–Glucosidase, phosphatase and protease) the Eucalyptus plantation was inferior to the other two, and in terms of biomass C and N that characterizes soil fertility, it was inferior to the natural broadleaf forest, but did not have much regular difference from the Pinus massonianaplantation. Meanwhile, in terms of bacterial diversity index, richness and evenness, the Eucalyptus plantation was inferior to the natural broadleaf forest, but not much different from the Pinus massoniana plantation. All the findings indicate thatEucalyptusplantation, even though not so good as natural broadleaf forest, is more or less the same as Pinus massoniana in their impacts on soil fertility and ecological quality in degraded red soil regions in China.

Abstract:Watermelon is susceptible to wilt disease under continuous monocropping management. Watermelon/aerobic rice intercropping can alleviate watermelon wilt disease in continuous management soil. However, the mechanism is not very clear. A pot experiment was carried out to investigate effects of watermelon/aerobic rice intercropping on composition and contents of watermelon root exudates, such as phenolic acids amino acids and organic acids. Results show that watermelon wilt disease was alleviatedunder watermelon/aerobic rice intercropping condition. Compared with control, the treatment of inoculation with FON (Fusarium oxysporum f. sp. niveum）significantly increased the content of phenolic acids in the root exudates, especially coumaric acids, while the treatment of watermelon/aerobic rice intercropping reduced the exudation of most phenolic acids. Even in pots inoculated with FON, watermelon/aerobic rice intercropping significantly reduced the content of phenolic acids in the root exudates. Compared with control, FON inoculation increased the content of amino acids in watermelon root exudates, but did not in pots under watermelon/aerobic rice intercropping condition. And FON inoculation also increased significantly the volume of organic acids in watermelon root exudates, whereas watermelon/aerobic rice intercropping reduced the exudation of most of the organic acids and even in pots inoculated with FON. In conclusion, watermelon/ aerobic rice intercropping may alleviate watermelon wilt disease, which is held to be related to the variation of the composition and volume of the exudates from watermelon roots.

Abstract:A hydroponic experiment was carried out to compare Se-enriching rice ‘Xiushui 48’ with Se ordinary rice ‘Bing 9652’ in Se absorption and Se transport, in expectation of revealing physiological mechanisms of the difference between the two rice cultivars in selenium accumulation in grains. Results show that the two cultivars did not differ much in Km of Se absorption by roots, but Xiushui 48 was 1.57 times as high as Bing 9652 in Vmax. The absorption of Se symplast by roots of the two rice plants was dependent on carrier. Selenium absorption time dynamics tests demonstrate that selenium concentration and content in stems of Xiushui 48 was higher than that of Bing 9652 in all the treatments and all the time, and selenium concentration in the xylem sap of Xiushui 48 was about twice as high as that of Bing 9652. The same in transpiration rate, Xiushui 48 was significantly higher than Bing 9652 in Se content in shoot, which indicates that the two cultivars varies sharply in capacity of transport Se to shoots, that Xiushui 48 can transport Se from roots to shoots more easily, and that efficient transport system is the key to high Se content in shoots of Se enriching rice. Se enriching rice is highly capable of transporting selenium to shoots, partly because of the strong Se carrying capacity of its root xylem.

Abstract:Based on the grain yields and plant K uptakes of the 122 K fertilizer field experiments conducted on rape as reference, three different extractants (i.e., 1 mol L^-1 neutral NH₄OAc, 1 mol L^-1 boiling HNO₃, 0.2 mol L^-1 NaBPh₄) were used to extract soil K in the experiment soils, and the data were sorted by extractants and by available K and slowly available K. Then correlation analysis was done of the data to define which one was the accurate determination method for soil available K and corresponding indices for soil K abundance and deficiency were established. It was found that the three extractant varied in extraction capacity and displayed an order of NH₄OAc-K > Boiling HNO₃-K > NaBPh₄-K. The soil Ks extracted with NH₄OAc and NaBPh₄ were higher in bio-availability and NaBPh₄ the highest. For winter rape fields in the Yangtze River valley, the index of “Low”, “Medium”, “High” and “Very High” for soil NH₄OAc-K and NaBPh₄-K was <45 mg kg^-1, 45~115 mg kg^-1, 115~190 mg kg^-1 and >190 mg kg^-1; and <125 mg kg^-1, 125~415 mg kg^-1, 415~755 mg kg^-1 and >755 mg kg^-1, respectively. Suumarization of the results showed that the relative yield and relative plant uptake was highly significantly correlated with soil K content extracted with the NaBPh₄ and NH₄OAc method. The soil K critical indices established using the methods and through the field experiments can be used as reference for soil test based fertilizing recommendation for winter rape production in the valley. Moreover, it is essential to pay more attention to rational K fertilization in the region.

Abstract:Based on the long-term stationary field fertilization experiment in Yangliu of Anhui Province, principal component-cluster analysis was done of the data obtained with five types of soil enzymes (urease, acid phosphatase, neutral phosphatase, catalase and invertase) and seven items of soil chemical properties (pH, electric conductivity, organic matter, total nitrogen, alkalytic nitrogen, available phosphorus and readily available potassium) as evaluation indices, to valuate comprehensively effects of long-term fertilization on fertility of the lime concretion black soil at the experimental site. Results show that 2 principal components that could reflect 88.22% of the original information quantity without losing any original variables were extracted from the initial 12 indices. Within the primary group of principal components, ACP, NEP, EC, OM, TN, AN, AP and AK were the major contributors, while among the secondary group of principal components, URE, CAT, INV and pH were the major ones. As biological indicators for comprehensive evaluation of the fertility of Lime concretion black soil, acid phosphatase and neutral phosphatase were better than other three soil enzymes. Hierarchical cluster analysis of the new indices extracted based on scores of the two principal components revealed the effects of different patterns of long-term fertilization displayed an order of HMNPK, MNPK > M > NPK > CK, in other words, mixed application of organic and chemical fertilizer is the best fertilizing model, and followed by application of only organic fertilizer, as no-fertilization and application of solely chemical fertilizer could result in decline of soil fertility.

Abstract:Both abiotic factors and biological factors affect growth of wetland vegetation. Of the former hydrological and soil environmental factors are the major ones and hence the hot spots and focal points of the research on wetland eco-hydrological processes. Investigations were carried out of variation of various soil environment factors in content in shoaly wetlands typical to the Poyang Lake under four different kinds of plant communities, and CCA (Canonical correspondence analysis) ordination was performed of the 20 vegetation sampling plots in the research zone, for analysis of major soil environment factors in the shoaly wetlands and their effects of vegetation distribution. Results show that the soils under four kinds of vegetation communities differed sharply in total nitrogen (TN) content, displaying an order of Carex cinerascen < Artemisia selengens+Cynodon dactylon Phragmites communis Carex cinerascen < Phalaris arundinace Carex cinerascen, and demonstrated a similar trend in variation of total organic carbon (TOC), for these two were significantly positively related. They did not have any significant trend of variation in soil total phosphorus (TP) content. With the increasing distance of the shoaly wetlands from the water body of the lake, content of readily available potassium (AK) in the soils showed an increasing trend, but not great in extent. Soil total nitrogen and soil available phosphorus (AP) was closely related to soil organic carbon and soil available phosphorus was significantly negatively related to soil moisture (SM) content, while content of available phosphorus was significantly related to total nitrogen. To sum up, soil moisture content is the major factor and soil pH and total potassium (TK) content are also important ones among the soil environment factors affecting distribution of vegetation on wetland soils.

Abstract:Chemical analysis, PCR-DGGE and DNA sequencing methods were used to investigate effects of bacterial manure varying in application rate and applied at diffentent time on soil physicochemical properties and microbial community diversity in the rhizosphere of highland barley in Tibet. Results show that application of bacterial manure significantly increased total N, total P, total K, organic matter, alkalytic N, available P and readily available K in the soil, for instance, by 13.32%, 28.42%, 16.20%, 9.81%, 21.36%, 39.35% and 30.48% respectively over that in CK when 750 ml hm^-2 of bacterial manure was applied before sowing; and by 7.25%, 29.35%, 18.04%, 12.86%, 15.90%, 43.27% and 53.99%, respectively, when 2 250 ml hm^-2 of bacterial manure was applied at the jointing stage of the crop. DGGE analysis demonstrates that DGGE atlases of microorganisms in the soils the same in application method, were all quite similar regardless of application rate. Cluster analysis with UPGMA sorted the DGGE atlases into two clusters. Shannon indices suggest that soil microbial diversity in soils applied bacterial manure increased first and decreased gradually afterwards. Application of 750 ml hm^-2 of bacterial manure prior to sowing brought about the highest soil microbial diversity, while application of 2 250 ml hm^-2 at the jointing stage did. Moreover, the former was higher than the latter in nutrient releasing and Shannon index as well. DNA sequencing shows that microbial populations were widely distributed and dominated with bacteria of Actinobacteria class, and a few uncultured strains in the soils applied with bacterial manure, regardless of application rate. Canonical correspondence analysis (CCA) reveals that the distribution of DGGE fingerprints was strongly related to physical and chemical properties of the soil. AN (Alkalytic N), TP and TN were the main environmental factors influencing structure of the microbial community. All the findings demonstrate that application of bacterial manure significantly improves physicochemical properties of the soil and microbial community diversity of the rhizosphere soil of highland barley.

Abstract:To explore effects of configuration of plant community on physical and chemical properties of coastal saline soil, soil samples were collected from fields that had been under plant communities different in configuration for 10 years in polders on east beach of Chongming Island for analysis of physical and chemical properties (soil mechanical composition, bulk density, porosity, field moisture capacity, pH and total salt content). Results show that compared with bare land, shrub-grass land increased in physical clay content by 57.8%, decreased in bulk density by 13.7%, and increased in total porosity and field moisture holding capacity by 18.2% and 17.8% respectively; grass land decreased in bulk density by 27.3%, increased in total porosity and field moisture capacity by 36.8% and 25.2%, respectively, only in the top soil layer (0～10cm), and improved the mechanical composition of the soil in the 0～40cm soil layer, by decreasing its sand content by 65.3% and increasing its physical clay content by 94.6%; And shrub land decreased in bulk density by 16.3% and increased in total porosity and field moisture capacity by 8.8% and 13.0%, respectively, in the 20～40cm soil layer, but did not have much improvement in its soil mechanical composition of the 0～40cm soil layer. The three plant communities showed significant positive effects on pH and total salt content, that is to say, they lowered soil pH to 8.5, making the soils fit for crop growth, and reduced NaCl content down to 2.5 g kg^-1, which falls into the category of slightly salt-affected soil. Correlation analysis of main physical and chemical indexes of the soils revealed that bulk density was in extremely significant negative relationships with total porosity, capillary porosity, and field moisture capacity and in extremely significant positive relationships with soil pH and total salt content. Based on this study, it is held that the configuration of shrub-grass community is more conductive to amelioration of the physical and chemical properties of the saline soil in coastal polders.

Abstract:Peach (Prunuspersica) orchard is a type of land use typical of brown soil in the Yimeng mountains. Soil water repellency (SWR) and soil physicochemical properties, such as soil moisture, soil organic content and soil texture, in the peach orchard brown soil before and after rainfall were analyzed to explore spatial response of SWR of the soil to variation of its physicochemical properties. Soil moisture content and SWR was measured in-situ and a total of 100 topsoil samples were collected, too, in a 1 m×1 m grid pattern for analysis of contents of soil organic matter, sand, silt and clay. On such a basis, classic statistics, geostatistics and spatial correlation analysis were coducted. Results show that the SWR in studied brown soil was strong under the condition of lasting drought and decreased significantly after rainfall, and the SWRs before and after rainfall were both moderate in variability and strong in spatial autocorrelation, showing an exponential pattern in distribution with significant anisotropy. Under the joint function of structural and random variations, especially the structural variation, spatially the SWR was distributed in band following the direction of ploughing and its minimum codomain in vertical direction was 1.4 m. Soil texture was the main factor influencing spatial variability of SWR. SWR was positively related with silt content, but negatively with sand and clay contents in spatial distribution, showing an order of silt > sand > clay in degree of spatial correlation with SWR. SWR was also negatively related with soil moisture in spatial distribution. The negative relationship was quite weak before rainfall and became significant after rainfall.

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