Abstract:In an agricultural ecosystem, soil organic matter (SOM) is an index key to estimating soil C sequestration, soil fertility and quality, etc. Estimation of these soil properties at an acceptable level of accuracy is very important. In this research, a square area (116^°45′32″~117^°2′14″E，34^°31′12″~34^°45′6″N), about 580 km2, was chosen as an example in the northwest of the Xu-Huai alluvial plain (Xuzhou and Huaiyin). A total of 168 soil samples were collected according to nested scenario’s, for analysis of SOM content and soil texture. And furthermore, spatial variability of SOM in the surface layer of this region was analyzed using the geostatistics and GIS method, and its dominating factors, too, by means of variance analysis and regression analysis. Descriptive statistics of the results shows that the SOM content of the region varying in the range of 21.80 ± 7.43 g kg^-1 with a variation coefficient being 34.08%, both belonging to a moderate level. Geostatistical analysis suggests that the study area was very strong in spatial autocorrelation and structural factors played a dominating role in spatial variability of SOM, which was significant in anisotropy. The variation at 45^° in direction was the most severe. SOM in the area was distributed in a band, decreasing from northeast to southwest. Variance analysis and stepwise regression analysis indicates that mechanical composition of the soil was the dominating factor, which alone could explain 64.9% of the SOM spatial variability of the region, and land use, parent material and soil type followed in role. The four factors together could explain 74.6% of the variability of SOM in the study area.

Abstract:The information about spatial distribution of soil attributes over a large area is the basic one required for land surface process modeling. Spatial interpolation based on sampling sites in the field is an important way to acquire such information. The existing spatial interpolation methods usually call for sound representativeness of all the sampling sites for the whole study area in soil attribute spatial distribution. However, limited by budget and/or field accessibility for sampling, in most cases, the sampling sites chosen can hardly reflect comprehensively the spatial distribution of soil attributes of the study area. A soil attribute soil map worked out with the existing interpolation methods based on such sampling is often low in precision and the poor representativeness of the sampling makes it hard to measure the uncertainty it brings about in prediction. In order to make reasonable use of such samples and measure prediction uncertainty effectively, this paper presents a new method that uses the individual representativeness of each sample to predict soil attribute of unvisited locations and to quantify prediction uncertainty. Based on the assumption that the more similar the environment conditions of two sites, the more similar the soil attributes of the two, it is held that every sampling site can be used to represent an area similar to the site in environment, and the representativeness can be measured by similarity degree of the two. By analyzing environmental similarity, uncertainty in prediction can be measured, and with environmental similarity as weight, soil attribute values of the area a sampling site represents can be worked out. This method was once used to predict soil organic matter (SOM) content in the surface soil layer of the Yili District, Xinjiang Uyghur Autonomous Region for validation. As demonstrated, the method is an effective approach to using a sampling site that is poor in global representativeness to predict soil attribute spatial distribution of the area it represents, and the uncertainty of the prediction is positively related to the predicated residual, which can be used effectively to indicate credibility of the prediction.

Abstract:Using the environmental information gathered and results of the numerical classification obtained by fuzzy c-means algorithm, regression models of soil taxonomic distance-environmental covariates were developed after spatial autocorrelation of taxonomic distance, to predict the taxonomic distances between soils at any spatial positions and the central profiles established in the study area. Based on the above prediction, a digital soil map with grid resolution of 25 m was produced after defuzzification and fragment-incorporation. It was clearly shown in the digital soil map that Typic Endorusti-ustic Cambosols was soil type with the biggest distribution percentage, covering about 36% of the total study area, while Parasalic Siltigi-ustic Cambosols, the soil type with the second biggest coverage, occupying around 24% of the land surface. By analysis on spatial variability of both determinable trend and undeterminable residual involved in soil taxonomic distance, the influences of soil-forming environment and stochastic factors on soil spatial variation were discussed. It was concluded that, compared to predictive map originated from a stochastic model, the digital map produced by the employment of soil taxonomic distance-environmental covariate regression model displayed a similar pattern of spatial soil distribution. However, much more information contained and reasonable delineation borders in the digital map was indicative of its capacity to demonstrate continuity and transition of soil distribution, and to explain spatial soil variation induced by micro-environmental factors and human activities.

Abstract:With the aim of exploring and conserving soil resources, and promoting soil science, China conducted the second nation-wide soil survey in 1979, and has made substantial achievements out of the survey. To make better use of the results and also to keep abreast of the development in science and technology, constructing a soil database became an urgent task. After ten years of joint efforts, a soil database for Zhejiang Province was completed, encompassing 1:50 000 digitized soil maps for all the counties of the Province and consisting of three sections, i.e. spatial data, attribute data and meta data. The use of the techniques of automatic and semi-automatic soil boundary recognition developed through independent R

Abstract:In this study, effects of clean wind and sandy wind on wind erosion of gravelly farmland were simulated in a wind tunnel. Results show that wind erosion rate in virgin gravelly lands (0.37 g m^-2 min ^-1) is only 1/4 and 1/5 of that in cropland and wasteland, respectively. Wind erosion rate increased exponentially with wind speed, and the increasing rate is lower in virgin gravelly land than in cropland and wasteland. Once the virgin gravelly land is ploughed, its wind erosion rate is close to those in cropland and wasteland under normal wind speed, being 1.67 g m^-2 min ^-1, 1.75 g m^-2 min ^-1 and 1.83 g m^-2 min ^-1, respectively, whereas it is much lower than those in cropland and wasteland under a gale, reaching 3.61 g m^-2 min ^-1, 58.83 g m^-2 min ^-1and 13.92 g m^-2 min ^-1, respectively. Wind bearing sands from gravelly land leads to a significant increase in wind erosion rate in cropland and ploughed gravelly land, but light sand deposition in virgin gravelly land, however, wind bearing soil from crop land leads to remarkable soil deposition in virgin gravelly land, ploughed gravelly land and wasteland, but strong erosion in cropland. The wind erosion (deposition) under wind bearing sands shows a relationship of quadratic curve function with wind velocity. Gravelly land is obviously much higher than cropland in aerodynamic roughness length, being 0.023 cm and 0.002 cm, respectively, and the difference widens with wind speed. Wind profiles over gravelly land and cropland varying with wind speed can be described with an exponential function. Apparently, after being mulched with gravels, cropland and wasteland can greatly increase their wind erosion resistance and dust withholding capacity.

Abstract:In order to systematically investigate variation of splash detachment under soybean cover and to establish a simple practical model, with which to evaluate effects of soybean crop on splash detachment, rainfalls, 40mm h^-1 and 80mm h^-1 in intensity, were simulated indoors for measuring thoughfall intensities and splash detachment rates under soybean canopy at different growth stages, analyzing relationships of splash detachment rate and throughfall intensity with LAI, and exploring spatial distribution of splash detachment rates under soybean canopy. Results show that compared to bare soil, the field with soybean was 62.85% and 60.74% lower in average splash detachment rate of the whole growth period under rainfall, 40 mm h^-1 and 80 mm h^-1, in intensity, respectively. The average splash detachment rate under soybean canopy displayed a significant trend of rising with LAI and rainfall intensity. The splash detachment rates at various monitoring points were significantly affected by the throughfall intensities at the corresponding positions, especially under the rainfall, mm h^-1 in intensity, increasing with throughfall intensity. The spatial distribution of splash detachment rates corresponded to a certain extent with the distribution of throughfall under soybean canopy. In another word, in places where throughfall under canopy concentrated, splash detachment would increase to a certain extent, thus leading to uneven distribution of splash detachment rates under canopy. Therefore, throughfall is the major source of energy triggering splash detachment and affecting its distribution. The splash detachment model proposed in this study could provide some theoretical support for soil erosion control and effective use of irrigation water on slope lands.

Abstract:Based on observed meteorological data, such as daily mean wind speed, daily mean air temperature, daily mean air humidity, daily mean water vapor pressure, daily mean total radiation, daily mean land surface temperature, daily mean rainfall, and daily mean evaporation, and daily mean soil moisture at 10 cm, 20 cm and 30 cm in depth, statistical relationships were established between meteorological variables and soil moisture using the Support Vector Machine (SVM) technique, and on such a basis, models for simulation and prediction of soil moisture were built up. It was found that responses of soil moisture to meteorological variables somewhat lagged behind, and were affected by soil depth. The model for prediction of soil moisture taking into account the lag correlation was more accurate than the one that did not count the lag correlation. Besides, using the meteorological variables, the model was more accurate in simulating and predicting the soil moisture at 10 cm in depth than in doing the soil moisture at 20 cm or 30 cm in depth. By taking into account the close relationships between the soils at 10 cm and 20 cm and between the soils at 20 cm and 30 cm in soil moisture, it is advisable to use the support vector machine technique in simulating and predicting soil moisture at 20 cm or 30 cm on the basis of the soil moisture at 10 cm or 20 cm. The findings indicate that the model for simulation of soil moisture is very high in accuracy.

Abstract:Mobile colloid may play an important role in the transport of contaminants in soils and ground water, especially for strongly adsorbed heavy metals. Effect of colloid SiO₂ on transport of Cd in saturated soil was studied in an indoor soil column and effluent experiment. Results of the experiment were simulated numerically with the CDE (convection-dispersion equation). It was found that the colloid inhibited mobility of Cd, making it spend longer time getting through the column and lower in concentration in the effluent and that Cd adsorption was mainly controlled by dynamic reaction. The OSM (one site nonequilibrium model) coupled with the Freundlich isothermal adsorption could better simulate Cd transport in the loamy sand soil. The Cd adsorption feature parameter β obtained through simulation was quite small which indicates that the adsorption surface of the soil was rather nonuniform. SiO₂ colloid penetrated the column pretty quickly. Its transport in the soil could well be described with the CDE coupled with kinetic attachment-detachment reaction. As affected by colloid, the CDE could successfully simulate transport of Cd in the soil with SiO₂ in presence. Meanwhile the parameter sensitivity analysis indicated that the smaller the k_amc and the k_aic , the larger the k_dmc and thek_dicand the more convenient the transport of Cd.

Abstract:Mulch on soil surface can reduce soil evaporation, which is of important significance to soil water conservation. Based on the principle of sensible heat balance, effect of gravel mulch on evaporation from the near-surface soil layer was explored. Using the heat pulse technology, measurement and calculation was done of soil evaporation rate, sensible heat flux, difference in sensible heat flux between the upper and lower layers, the latent heat of vaporization, and change in sensible heat storage. Results show that the sensible heat flux and the difference in sensible heat flux between the upper layer and lower layer was lower in soil under gravel mulch than in bare soil. As compared with the latter, the former did not show much change in sensible heat storage in the near-surface soil layer, so of the 3～9mm, 15～21mm and 27～33mm soil layer, p value of the t test was 0.439, 0.100 and 0.096, respectively, all > 0.05; the sensible heat flux was decreasing with the p value of the t test of the soils at 3mm, 15mm and 27mm, being 0, 0 and 0.005, respectively, all < 0.05; the difference between the upper and lower parts of a soil layer in sensible heat flux was narrowing with the p value of the t test of the 3～9mm and 15～21mm soil layers, being both 0<0.05 and of the 27~33mm soil layer, being 0.059>0.05; the latent heat of vaporization was increasing with the p value of the t test of the 3～9mm, 15～21mm and 27～33mm soil layers, all being 0<0.05; as the energy used for soil evaporation was decreasing, soil evaporation rate was also declining with the p value of the t test of the 3～9mm and 15～21mm soil layers being both 0<0.05 and of the 27～33mm soil layer being 0.100>0.05. The soil evaporation rate changed in the same way as the soil sensible heat flux did. Compared with bare soil, the gravel-mulched soil would have delayed peaks of soil evaporation rate and difference between the upper and lower parts of the soil layer in sensible heat flux. In the 3～9mm and 15～21mm soil layers, the peaks would appear 2 days later than that in the bare soil. Therefore, mulching of gravel on the land surface may affect soil evaporation, which is mainly embodied in reduction of soil evaporation rate and delay of the appearance of its peak.

Abstract:In order to study effects of freezing-thawing on characteristics and fractal dimensions of soil microaggregates, samples of brown soil, typical of Northeast China, were collected and subjected to an indoor artificial freezing and thawing test for analysis and determination of composition, mean weight soil surface area (MWSSA), mean weight diameter (MWD) and fractal dimension (D) of soil microaggregates as affected by frequency of freezing and thawing and water content. Results show that changes in these characteristics of soil microaggregates after the treatment varied from fraction to fraction of particle-size. The effect of water content on content of soil microaggregates was significant or extremely significant in all fractions, except the fraction of 0.005～0.001 mm, and so was the effect of the frequency of freezing and thawing. WMSSA first decreased and then increased with increasing freezing-thawing frequency and soil water content. WMD first increased and then decreased with increasing freezing-thawing frequency, but went the other way round with increasing soil water content. And D first decreased and then increased with increasing freezing-thawing frequency, and fluctuated with increasing soil water content. It was found that the treatment first enhanced and then undermined the stability of soil microaggregates and a proper soil water content could improve the stability.

Abstract:Aggregation/Dispersion behavior of soil colloids is closely related to numerous environmental factors and regulated by surface charges of the colloids. Dynamics of the aggregation of variable charge colloids in yellow earths different in pH was studied with the dynamic light scattering technique. Results show that stability of the aggregation of soil colloids was strongly dependent upon pH. The aggregation of colloids induced by HNO₃ or KOH, different in concentration would exhibit the characteristics of fast diffusion limited cluster aggregation (DLCA) or slow reaction limited cluster aggregation (RLCA). In the former, the aggregation induced by HNO₃ was faster in average velocity and in variation than that by KOH, which suggests that the aggregation induced by neutralization of surface charge was faster than that by compression of double electron layers. The use of the pH corresponding to the turning point where average aggregation velocity changes pH in DLCA to estimate zero point of charge (ZPC) provides a new method for measuring ZPC in experiment.

Abstract:Powder X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques were used to investigate variations of the structures of hexagonal birnessites as related to average oxidation states of manganese therein (Mn AOS). As the synthesized series of hexagonal birnessites from HB1 to HB6 decrease from 3.92 to 3.67 in Mn AOS, but increase from 2.838 Å to 2.848 Å in unit cell parameter b. The series also decrease from 12.0 nm to 7.0 nm in the coherent scattering domains (CSD) in the a -b layer plane, forming a stack of 10.6~13.4 layers of manganese oxide octahedron along axis c. With the decrease in Mn AOS, the content of octahedral voids declines from 18% to 8%. Mn AOS and vacancy content have a very significant positive linear relationship, and they both show negatively linear relationships with unit cell parameter b. Linear fitting of X-ray absorption near edge structure spectroscopy (XANES) shows that Mn in these samples is dominated by Mn⁴⁺ and the proportion of Mn^2+/3+ increases with the decreasing content of octahedral voids. Fitting analysis of Mn K -edge extended X-ray absorption fine structure spectroscopy (EXAFS) with a full multiple scattering model demonstrates that the samples, though different in Mn AOS, are similar in crystal structure and Mn local coordination environment. With the decrease in content of octahedral voids and particle size, apparent Mn site occupancy ( f _occ ) decrease from 0.74 for HB1 to 0.66 for HB6, and with the decrease in Mn AOS, the average bond-length of Mn-Mn(O) shells increase.

Abstract:Dissimilatory iron reduction is an important microbial process of the degradation of organic matter in anaerobic environment. It not only affects translocation of some inorganic pollutants, like Cr and U, but also is closely related to emission of greenhouse gases, such as CH₄, N₂O, H₂S, etc. Samples of cinnamon soils, collected from upland farmlands at 7 different locations, were prepared into slurry and then put under anaerobic incubation, to study characteristics of the anaerobic reduction of iron oxide in these soils. Results show that dissimilatory reduction of iron oxide occurred in the cinnamon soils under submergence, with reducing potential ranging from 4.47 to 5.95 mg g^-1 and a reduction rate constant between 0.15 and 0.27 d^-1. In the soils, a portion of crystalline iron oxide was reduced during the process and the mean reduction rate of free iron reached 41.95%. After 40 days of incubation, 99.26% of the NO₃^- and 88.82% of the SO₄^2- in the soils were reduced. And the rate constant, V_max and T_max of the iron reduction was positively related to soil organic carbon content, and the reducing potential negatively related to soil SO₄^2- content.

Abstract:A new method was designed for direct determination of ¹⁵N abundance of NH₄⁺, NO₃^- and NO₂^- in soils with mass spectrometry. The principle of this method was based on analysis and quantification of ¹⁵N abundance of the N₂O produced from NH₄⁺,NO₃^-and NO₂^- through transformation reactions catalyzed with their respective specific chemical reagents separately. The measured values of ¹⁵N abundance of the N₂O tally well with their respective reference values in NH₄⁺, NO₃^- and NO₂^-. The method was characterized by quickness, simpleness and freedom from contamination of atmospheric nitrogen. Especially this method has a very low detection limit, and 5～20 μg N in the sample is adequate for detection. Therefore, it will be of a great help to study on mineralization, nitrification and denitrification of nitrogen in soils.

Abstract:An experiment using the ¹⁵N -labeling method was carried out to investigate effects of application of ammonium nitrate (NH₄NO₃, N 300mg kg^-1) and nitrite(Na NO₂, N 1mg kg^-) on generation of N₂O and NO in mid- subtropical forest soils, different in water regime (60% and 90% of WHC), in Southeast China. Results show that in soils 60% of WHC in soil water content, generation of N₂O and NO was significantly inhibited by high nitrogen input (p <0.01 ) ; while in soils 90 % WHC in soil water content, a similar phenomenon was observed with the generation of N₂Owithin the first 9 hours of incubation, but afterwards the trend turned reversely; When NO₂^- added the inhibitions of high nitrogen input were lifted for all unsterilized soils, addition of NO₂^- immediately offset the inhibitive effect of high soil N content and triggered off generation of a large amount of N₂O and NO, forming a sharp contrast to CK (p <0.01 ). Such a phenomenon did not last long (for 21 h only) in soils 60% of WHC; but it did quite a long time (over 2 weeks) in soils 90% of WHC, which suggests that high water availability and exogenous NO₂^- played an important role in offsetting the inhibitive effect of high soil N content. In this experiment, N₂O was generated mainly in denitrification process of the soil, and what is more, the addition of unlabeled NO₂^-led to rapid increase of hybrid N₂O (¹⁴N¹⁵NO) molecules within the first 21 hours of the experiment, demonstrating that denitrification in the forest soil may probably proceed mainly through codenitrification by fungi, which may explain over 80% of the denitrification. Spearman rank correlation analysis indicates that there is a significantly positive correlation between the NO and N₂Oproduction rates (p <0.05 ) in non-sterilized soils, and the lower the soil water content, the higher the correlation between the two. After addition of NO₂^-, sterilized soil produced more NO than unsterilized soil, but almost no N₂O, which indicates that in acid soils chemical denitrification contributes more to NO than to N₂O.

Abstract:The culture method of undisturbed soil cores - acetylene inhibitor was used in order to study effects of fertilization on N₂O emission fluxes and denitrification rates during summer corn growing season in purple soil in the hilly area of the central Sichuan Basin. Results show that during the season, N loss through N₂O emission and denitrification was significantly higher in purple soil with fertilization than without fertilization. Significant differences were observed between different fertilization treatments. The N₂O emission flux in Treatment OM (pig manure), OMNPK (pig manure with NPK fertilizer), N (pure N fertilizer), NPK (fertilizer NPK), and RSDNPK (crop residues returned with NPK fertilizer) was 3.01, 2.86, 2.51, 2.19 and 1.88 kg hm^-2, respectively, accounting for 1.63%, 1.53%, 1.30%, 1.09% and 0.88%, respectively, of the total fertilizer nitrogen applied to the crop. The N loss through denitrification in those treatments were 6.74, 6.11, 5.23, 4.69 and 4.12 kg hm^-2, respectively, accounting for 3.97%, 3.55%, 2.97%, 2.61% and 2.23%, respectively of the fertilizer N applied during the season. The N loss through N₂O emission and denitrification in Treatment CK (no fertilization) was 0.56 and 0.78 kg hm^-2, respectively, only. Fertilization was obviously the main driving force of peak emergence of soil N₂O emission and denitrification in the early growth stage of corn (2 weeks) in purple soil. Inorganic N (ammonium and nitrate) content was the limiting factor of soil N₂O emission, nitrification and denitrification. Soil moisture driven by rainfall was an important influencing factor. The ratio of N losses through N₂O emission and denitrification ranged from 0.45 to 0.72. Soil N loss was significantly higher through denitrification than through N₂O emissions, which implies that the soil denitrification was the main pathway of fertilizer N loss during the maize growing season in the hilly area of purple soils.

Abstract:Abundances and community structure of archaea, bacteria and fungi in a red soil profile located at Xiangyin County, Hunan province, was investigated with the quantitative real-time PCR (qPCR) and 454 pyrosequencing approaches. Results showed that with increasing soil depth, soil clay increased in content, while organic matter, total nitrogen, and carbon to nitrogen ratio declined. Correspondingly, the numbers of gene copies per gram of dry soil also decreased within the range of10^7.09 ～10^9.30 for archaeal 16S rDNA, 10^8.10 ～10^9.70 for bacterial 16S rDNA, 10^6.54～10^7.95 for fungal 18S rDNA, 10^7.24～10^8.61for archaeal amoAgene, 10^4.76 ～10^6.25 for bacterial amoAgene, 10^5.94～10^7.88for nirK gene, 10^6.81～10^9.21for nirS gene, and 10^7.03～10^9.46 for nosZ gene. Pyrosequencing generated 6 459 archaeal 16S rDNA sequences with an average length of 496 bp, 28 626 bacterial 16S rDNA sequences with an average length of 448 bp, and 4 683 fungal 18S rDNA sequences with an average size of 534 bp. OTU (97% similarity) analysis revealed that the α-diversity was in the order bacteria>fungi>archaea, but there was no significant correlation between microbial α-diversity and soil properties determined. Analysis of the Jaccard dissimilarity indicated that microbial communities in different layers of the same soil profile were closer, compared with the dissimilarity between three surface replicates. Mantel test showed that clay content was the main soil factor explaining the variation of microbial communities. In all the soil samples, archaea was dominated (89%) with Thermoprotei (belonging to Crenarchaeota), of which the distribution was significantly related to soil clay content. The bacterial community consisted mainly of Acidobacteria (33%), Proteobacteria (17%), Chloroflexi (12%), Firmicutes (10%) ， Actinobacteria (7%) and Bacteria incertae sedis (11%) . Acidobacteria and Proteobacteria were found to be more abundant in the surface soils than in other soil layers, while the situations of Chloroflexi and Firmicutes were opposite. All fungal sequences belonged to three phyla, i.e., Ascomycota (87%), Basidiomycota (9%) and Glomeromycota (4%). This work demonstrated the great potential of pyrosequecing technique in revealing microbial diversity and presented background information of microbial communities in the red soil.

Abstract:A pot experiment, designed to have five treatments, was carried out in greenhouse to investigate effects of bio-organic fertilizer(BOF) and BOF plus soil amendments on tobacco bacterial wilt and on microflora in rhizosphere soil. The five treatments were set as follows: T1, the control; T2, the pot soil was applied with common organic fertilizer; T3, the pot soil was applied with the BOF; T4, the pot soil was treated with lime before the application of the BOF; T5, the pot soil was treated with lime and bicarbonate before the application of the BOF. DGGE and plate counting were used to investigate microflora in the rhizosphere soils. Relusults show that T2 not only had no control effect against tobacco bacterial wilt, but also increased the disease index, while the control effects against tobacco bacterial wilt of T3, T4 and T5 varied in the range of 66.7%~87.9%. All the organic fertilizer treatments had some influence on microflora in the rhizosphere, increasing the number of bacteria by 3.5 and 6.1 times and the number of actinomycetes by 3.7 and 3.5 times, but decreasing the number of fungi by 66.2% and 70.1%, respectively in T3 and T4, and increasing the number of bacteria and actinomycetes by 13.6 times and 5.1 times, respectively, but decreasing the number of fungi by 75.0% in T5. The preliminary study found that a combined treatment of the soil with lime and bicarbonate before application of the BOF could control tobacco bacterial wilt effectively by altering composition of the microflora in tobacco rhizosphere, and decreasing the number of pathogens.

Abstract:A pot experiment was carried out using two types of paddy soils (yellow and red paddy soil) different in soil organic matter and pH, and 9 rice cultivars (three hybrid, three indica and three japonica) for exploration of effects of rice cultivars and arsenic (As) pollution on contents of DOC (dissolved organic carbon) and DON (dissolved organic nitrogen) in the soils and interactions among the three factors, rice cultivar, As pollution and soil type. Results show that rice cultivars displayed a significant impact on content of DOC and DON in the soils, and followed a decreasing order of hybrid rice (41.09±0.92 mg kg^-1) > indica rice (38.10 ±1.53 mg kg^-1) > japonica rice (37.74 ±1.37 mg kg^-1) in terms of DOC, and of japonica rice (2.94±0.40 mg kg^-1) > hybrid rice (2.61±0.42 mg kg^-1) > indica rice (1.45±0.17 mg kg^-1) in terms of DON. As pollution decreased DOC and DON contents in the soils, but the effect varied with the rice cultivar. Compared with CK, As pollution decreased DOC by 14.4% and 11.1% and DON by 65.0% and 44.7%, in yellow and red paddy soils, respectively, and the least decline of DOC was in soils cultivated with hybrid rice, while that of DON was in the soils cultivated with indica rice. The average contents of DOC and DON were 22.4% and 45.8% higher, respectively, in the yellow paddy soils than in the red paddy soils without As pollution, which was attributed mainly to the higher organic matter content and pH in the yellow paddy soils. Rice species, As pollution and soil type differed in their effects on soil DOC and DON, and was responsible for 7.7%, 15.5%, and 27.6% of the variation of DOC, while 14.7%, 24.2%, and 2.0% of DON, respectively.

Abstract:Mung bean ( Phaseolus radiatus ) was used as subject in this study exploring responses of root border cells to cadmium toxicity in vitro and in vivo with the methods of pre-suspended culture using agar pour plate and filter paper pad in the later part of the culture. In the experiment mung bean root tips with root border cells unwashed in group A and washed off in group B were treated with different concentrations of Cd²⁺. Results show that Cd²⁺ induced apoptosis and then mucus secretion of the root border cells in vitro. Survival rate of the root border cells in vitro decreased with increasing concentration of Cd²⁺. It was also found that Cd²⁺ induced in vivo generation of root border cells, of which the number increased first and then decreased with the increasing Cd²⁺ concentration. The maximum induction effect was observed when the roots were treated with 50μmolL^-1 Cd²⁺, regardless of whether the root border cells were washed off or not; Cd²⁺ affected survival rate of the root border cells, and in Group A, the survival rate of root border cells decreased gradually with the increasing Cd²⁺ concentration, but in Group B it increased first and decreased later. Compared with the control, the treatments of 25μmolL^-1，200μmolL^-1and 400μmolL^-1 varied significantly (p< 0.05 ), PME activity of root cap increased with increasing Cd²⁺ concentration, and the effect was significant（p<0.05）when the roots were treated with a high concentration of Cd²⁺concentration for 24h. All the above-described findings indicate that mung bean root tips can release more root border cells under Cd²⁺ stress, and the detached root border cells form a layer of mucilage and apoptotic cells to protect the root tips against Cd²⁺ .

Abstract:A field experiment of foliar application of silicon sol, cerium sol and silicon-cerium composite sol of different concentrations on cabbage in field mildly contaminated with cadmium and lead, was conducted to study effects of the application on yield, quality, antioxidant enzymes (SOD, POD) activities and Cd/Pb absorption, and hence to determine optimum concentration of the silicon sols and cerium sols to be sprayed for relieving toxicity of Cd and Pb. Results show that spraying both silicon and cerium sols could promote growth of cabbage, increase contents of vitamin C and soluble sugar; reduce nitrite content, enhance activities of SOD and POD, the antioxidant enzymes, and decrease contents and accumulation of Cd and Pb in root and shoot. In conclusion, among the treatments of silicon sols and cerium sols different in concentration, the one of 0.50 g kg^-1 (SiO₂) silicon sols and/or 0.20 g kg^-1 (CeO₂) cerium sols was the most significant in effect, but no significant difference was observed between the treatment of spraying one single sol and the treatment of spraying both sols in combination.

Abstract:Abstract For this study, Platycladus orientalis, a major tree species used in afforestation in the Loess Plateau, was chosen. Leaf litters of the current year were gathered from P. orientalis and 8 other tree species that were planned to be planted in mixed forests , and soil from the humus layer (0~20 cm) of a tract of tree-free waste grassland was used as medium, in which litters were to be decomposed. Mixtures of litter from P. orientalis with others were shredded and packed into nylon mesh bags according to a set ratio, separately. Then the bags were buried into the soil contained in pots for incubation under a constant temperature and humidity for 345 days on end. The litters were analyzed for quality and nutrient contents before and after the incubation. Results show that 1) among the nutrients released during decompostion of the leaf litters, K was the most active and easy to get released, while P was generally dull and difficult to get released, and C and N was moderate and often synchronous in releasing, and the recycle period of these nutrients was 1 ~ 2 a; 2）leaf litter of Ulmus pumila in the mixture acted positively, while that of Amorpha fruticosa, Betula platyphylla and Quercus liaotungensis negatively on C release; leaf litter of Populus simonii did positively, while that of B. platyphylla, Q. liaotungensis and A. fruticosa negatively on N release; litters of P. simonii and U. pumila did positively, while litters from all the other trees negatively on P release; and litter of U. pumila did positively, while that of A. fruticosa did negatively on K release; 3) the Principal Component Analysis of comprehensive effects of decomposition of various mixtures of leaf litters on releasing of C, N, P and K revealed that leaf letter of U. Pumila and P. simonii in the mixture was the most significant in promoting nutrient release, and litters from Caragana microphylla and Q. liaotungensis followed, Litter from A. fruticosa, followed by litter from B. platyphylla, H. rhamnoides and R. Pseudoacacia, showed obvious inhibitive effects on nutrient release.

Abstract:On the basis of the site-specific survey and data analyses, we got a viewpoint that the heavy metal contents in the main agricultural regions of China were acceptable and safe, except some specific regions with high risk of heavy metal pollution. Although the heavy metal contents in most farmlands are just “overproof” rather than “polluted”, there is a significant tendency towards the accumulation of heavy metals in farmlands. Meanwhile, based on the summary of publications on soil heavy metals in China such as immobilization and mobilization, plant uptake and barrier, and microbial transformation and utilization of soil heavy metals, some suggestions were proposed on safe utilization of farmlands with high content of heavy metals, establishment of heavy metal thresholds, control and remediation of heavy metal pollution, safely controlling strategies for producing fields, and so on.

Abstract:In recent years, phytoremediation has been highly recommended in remedying heavy metals polluted soils, because of its unique advantages; especially when the application of endophytic bacteria to the phytoremediation provides an effective new approach. During the phytoremediation process, endophytic bacteria alleviate heavy metal toxicity to the plant through its own metal resistance system by making use of their symbiotic relationships with the plant, and promote transport and accumulation of these metals in and growth of the plant under heavy metal stress by solubilizing phosphate, fixing nitrogen and producing phytohormones, siderophores, specific enzymes and antibiotics. This article reviews progresses of the recent researches on mechanisms of endophytic bacteria promoting growth of plants and resistance/phytoaccumulation/translocation of heavy metals by plants, systematically analyzes mechanisms of the bacteria promoting phytoremediation of heavy metals polluted soils and further discusses prospects of the use of endophytic bacteria in phytoremedying heavy metals polluted soil and orientation of the research in future.

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