[Spatial Distribution and Risk Assessment of Heavy Metals in Sediments of the Ruxi Tributary of the Three Gorges Reservoir]

Sediment column and soil samples collected from 12 sampling sites in four regions of the Ruxi River, a typical tributary of the Three Gorges Reservoir, were analyzed for eight selected heavy metals including Cr, Ni, Cu, Mn, Zn, Cd, Pb, and Hg to evaluate their spatial and vertical distribution, source, and biological toxic effects. The results showed that the average concentrations of heavy metals were (79.60±11.87), (41.340±4.999), (32.69±8.70), (823.34±125.76), (122.11±22.82), (0.393±0.140), and (29.122±6.811) mg·kg^-1 for Cr, Ni, Cu, Mn, Zn, Cd, and Pb, respectively, and (74.84±39.50) μg·kg^-1 for Hg, all of which exceeded the sediment background values of the Yangtze River. A spatial trend of decreasing metal concentrations was observed from the reach influenced by the human activities of Ruxi town to the backwater zone and then to the natural river reach. Moreover, in the backwater zone, the heavy metals in sediments and soil along the river were significantly lower than those in sediments, indicating that the sediments and soil were not one primary source for these metals in backwater zone sediment. From the vertical distribution of sediment, in addition to Pb, the highest level of metals was observed at 8 cm in the reach influenced by human activities, and their concentrations decreased with sediment depth in the backwater zone and natural river beach. Significant correlation was found between all the heavy metals (P<0.01, except Ni), indicating a potential homology of these metals in the Ruxi River. Evaluation results of the geoaccumulation index reveal that there exists light to partial moderate Cd and Zn pollution in the Ruxi River. The evaluation of biotoxicity effects showed that Ni was likely to have toxic effects on organisms with a probability of 10% to 75%, and Cd, Zn, Hg, Cu, Pb, and Cr are likely to have biotoxic effects at<10% probability. The combined effect values of multiple metals indicated that the risk of adverse effects was between low and lower medium in the sediments of the Ruxi River.

[Response of Soil CO2 Emissions to Straw-returning in Citrus/Mushroom Intercropping Systems]

Based on the pattern of citrus tree/stropharia mushrooms intercropping, returning-straw was used as the raw material for the stropharia mushrooms, and an in-situ experiment was conducted to monitor soil CO₂ emissions under different dosage of straw application during the stropharia growth period. Soil CO₂ emissions and the influencing factors were analyzed under different treatments of cultivated (HSM, ASM, and DSM) and uncultivated stropharia mushrooms (HS, AS, and DS). The mushroom yield and soil carbon emission efficiency (CEE) were used to provide a theoretical basis for improving the use of land under citrus orchards. The results showed that:① Straw return increased the cumulative CO₂ emissions compared with the control system (conventional planting, CK) and cumulative CO₂ emissions increased with the dosage of straw application. Cumulative CO₂ emissions from soil treated with cultivated stropharia mushrooms were higher than those from soil treated with uncultivated stropharia mushrooms, in the order of DSM (52.09 t·hm^-2) > ASM (41.10 t·hm^-2) > HSM (33.20 t·hm^-2) > DS (27.15 t·hm^-2) > AS (25.34 t·hm^-2) > HS (18.94 t·hm^-2) > CK (12.16 t·hm^-2). Cumulative CO₂ emissions under the DSM treatment significantly increased by 328.37% compared with CK. ② For the treatment of cultivated stropharia mushrooms, peak soil CO₂ emissions occurred during the period of mycelium growth. The highest cumulative CO₂ emissions during this period were obtained under the DSM treatment and accounted for 43.27% of the total cumulative emissions. This was followed by ASM and HSM which accounted for 42.63% and 40.57% of emissions, respectively. ③ Cultivated stropharia mushrooms reduced the temperature sensitivity coefficient (Q₁₀). The soil temperature (5 cm depth) had a significant effect on the soil CO₂ emission rate (P<0.01) but soil moisture did not (P>0.05). Soil temperature explained 27% to 71% of the variation in soil CO₂ emissions rates, and the two-factor fitting of soil temperature and soil moisture explained 36% to 82% of the variation. ④ For the treatment of cultivated stropharia mushrooms, the ranked yield of each treatment was DSM (49.7 t·hm^-2) > ASM (47.0 t·hm^-2) > HSM (23.3 t·hm^-2), and ASM had the highest soil CEE (1.14). Therefore, under the system of citrus tree/stropharia mushroom intercropping, straw return can increase soil CO₂ emissions, with the highest emissions being obtained when a double dosage of straw was applied. However, the optimal amount of straw still needs to be determined in combination with changes in soil nutrients and crop yields.

[Influence of Spatial Pattern of Paddy Field on the Losses of Nitrogen and Phosphorus in Three Gorges Reservoir Area]

This paper used three plots of paddy field in Wangjiagou small catchment in Fuling District, Chongqing Municipality as a case study. Wangjiagou, located in Three Gorges Reservoir Area, provided a good case in terms of its closeness of surface runoff. The samples of individual rainfall of twelve times and process of two typical individual rainfalls on three plots of sloping paddy field were collected from 2014 to 2015. These samples were used to analyze the influence of spatial pattern of sloping paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The samples of daily runoff in subcatchments in 2010 and 2015 were used to analyze the influence of spatial pattern change of subcatchments' paddy field on the concentration of nitrogen and phosphorus in the surface runoff. The results indicated that the removal rates of TN, NO₃^--N and TP of paddy field at the valley bottom were higher than those in the mid-slopes. The removal rate of TP would be higher if plot size of paddy field at the bottom got bigger. During individual rainfall event, the losses concentration of TN, NO₃^--N and TP in the paddy fields was significantly different among three different spatial patterns during the previous period of heavy rain event, but it became different during the next period of moderate rain event. The two subcatchments' spatial pattern change of paddy field had weakened the intercepting purification ability of nitrogen and phosphorus losses of paddy field in 2015, compared with that in 2010. TN's losses concentration increased significantly during the periods of light and moderate rain event and base flow. TP's losses concentration fluctuated during the event from moderate rain to heavy rain. Hence, increasing the area of paddy field of catchment and optimizing its spatial pattern reasonably were found as effective measures to control agricultural non-point source pollution in the Three Gorges Reservoir Region.

[Distribution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Estuary of the Tributaries in the Three Gorges Reservoir, SW China]

To investigate the pollution status of sediments at the junction of the Three Gorges Reservoir area, sediment samples were collected over four seasons from the junction of the estuary located at a tributary of the Ruxi River and the Yangtze River. The content of eight heavy metals (HMs), including Cr, Zn, Mn, Ni, Cu, As, Cd, and Pb, in sediments was determined by ICP-MS. The results showed the average levels of investigated HMs (in mg·kg^-1) were Cr (45.24), Zn (46.46), Mn (406.14), Ni (20.885), Cu (12.49), As (7.02), Cd (0.253), and Pb (11.042). The distribution analysis indicated that the levels of HMs at the river mouth were higher than that of the tributaries of the middle reaches and the two sections nearby. The seasonal distribution shows that the heavy metal content in the spring sediment is higher than in summer, autumn and winter. In addition, the correlation analysis indicated that the eight HMs possessed similar homologous characteristics and had common exogenous inputs. The assessment of the Geo Accumulation Index showed slight Cd pollution in the estuary of Ruxi River, and the Potential Ecological Risk index showed that Cd presented moderate ecological risks. The toxic effect of benthonic organisms was possibly correlated to Ni contamination at the intersection of the tributary and main stream, which was supported by the evidence from the sediment quality criteria. In conclusion, the rating of ecological risk at the mouth of the Ruxi River tributary is slight.

[Comparison of Relationship Between Conduction and Algal Bloom in Pengxi River and Modao River in Three Gorges Reservoir]

Pengxi River is the largest tributary in the northern bank of Yangtze River in the Three Gorges Reservoir (TGR) region, and serious algal bloom has been reported since 2003 when the TGR dam started impounding water. On the other hand, Modao River, a tributary in TGR locating in the same county with Pengxi River, was rarely reported with algal bloom in the same time period. In this study, water samples were collected on the same day in both rivers in spring and summer, the most likely blooming seasons in TGR, to compare the water quality parameters and Chlorophyll-a(Chl-a) concentration dynamics in order to understand the mechanism of algal bloom in TGR. The results showed that the maximum value of Chl-a in Pengxi river reached 60.5 μg·L^-1 in spring, and was only 7.8 μg·L^-1 in summer, while in Modao river the Chl-a content was 2.92 μg·L^-1 in spring and 7.48 μg·L^-1in summer. Both rivers stratified during samplings, but having layers of thermocline and hypolimnion with the lack of epilimnion, and most of Chl-a content was located in thermocline. Also in both rivers, TN and TP exceeded the international threshold for eutrophication, with the average TN and TP values of 2.305 mg·L^-1 and 0.053 mg·L^-1in Pengxi River in spring, and 1.673 mg·L^-1 and 0.097 mg·L^-1 in summer, respectively, while in Modao River the values were 1.875 mg·L^-1 and 0.075 mg·L^-1 in spring, and 1.79 mg·L^-1 and 0.054 mg·L^-1 in summer respectively. Nutrients concentrations showed no significant correlation with Chl-a. On the other hand, conductivity value and trend were totally different between the two rivers:in Modao River in spring, the conductivity in upstream was only 75% of that in the main stream of the Yangtze River, and the backwater from the main stream reached to the middle in Modao river, where the highest Chl-a among all the river sampling sites was detected; summer conductivity distribution was similar with that in spring. Different from Modao River, the conductivity in upstream of Pengxi River in spring was 150% of that in the main stream of Yangtze, the backwater from the main stream reached area between sampling sites of PX04 and PX05 (upper than the middle reach); its upstream had significantly high content of Chl-a and conductivity, and these two factors were significantly positively correlated. The study showed that other than N and P, other ions in the Pengxi River played an important role in bursting "bloom", and need to be considered regarding bloom control.

[Effect of Nano Zeolites on pH, CEC in Soil and Cd Fractions in Plant and Soil at Different Cadmium Levels]

Soil incubation experiment and pot experiment were carried out to investigate the influence of nano zeolite (NZ) and ordinary zeolite (OZ) on the soil pH, cation exchange capacity, concentration of soil Cd, soil Cd fraction and Cd uptake by Chinese cabbage when exposed to different Cd pollution levels(1, 5, 10 and 15 mg·kg^-1). The results of soil incubation experiment showed that the nano zeolite and ordinary zeolite dose(5, 10 and 20 g·kg^-1) increased the soil pH and cation exchange capacity, and decreased the concentration of soil exchangeable Cd, while increased the concentration of Cd in carbonate, Fe-Mn oxide, organic matter and residual fraction. The lowest EX-Cd was observed in the high nano zeolite (20 g·kg^-1) treatment. The soil pH and cation exchange capacity was extremely negatively correlated with the concentration of soil exchangeable Cd(P<0.01),and extremely positively correlated with the concentration of soil Fe-Mn oxide Cd(P<0.01). The results of pot experiment showed that the FDC of exchangeable Cd in soil decreased by 6.4%-63.2%, and the FDC of water-extractable and ethnol-extractable Cd in Chinese cabbage decreased by 2.1%-56% and 11.8%-100% with zeolite application, respectively. Moreover, the reduction effect of nano zeolite on Cd concentration in soil and plant was better than that of ordinary zeolite. The FDC of Cd fraction in shoot of Chinese cabbage showed correlation with the FDC of carbonate Cd and organic matter Cd in soil(P<0.05) when exposed to 1 mg·kg^-1 Cd pollution. Moreover, correlation was also found in the FDC of organic matter Cd and residual Cd in soil(P<0.05) under 5 mg·kg^-1 Cd pollution.

[Effect of Nano Zeolite on Growth, Activity of Antioxidant Enzyme, and Chemical Fractions and Concentration of Cd in Chinese Cabbage]

Pot experiment was carried out to investigate the influence of nano zeolite (NZ) and ordinary zeolite (OZ) on the growth, activities of antioxidant enzyme, Cd fraction and Cd concentration in two varieties of Chinese cabbage. The results showed that the activities of SOD, CAT and POD in the shoot and root of two varieties increased, and the dry weight of shoot and the total dry weight of Chinese cabbage increased by 4.5%-96.5% and 3.4%-88.4%, respectively. The application of zeolite effectively reduced the Cd concentration of shoot and root in the two varieties of Chinese cabbage, and the reduction range increased with the increase of the application amount of zeolite. Under the low Cd condition (1mg·kg^-1 Cd), the Cd concentration of edible parts (shoots) in SD4 variety and XJC3 variety decreased by 1.0%-75.0% and 19.5%-68.9% (except the Cd₁+OZ₅/OZ₁₀ processing), respectively. Under the high Cd condition (5 mg·kg^-1 Cd), the Cd concentration of the edible parts (shoots) in SD4 variety and XJC3 variety decreased by 7.2%-53.2%(except Cd₅+OZ₁₀ processing) and 0.7%-63.0%, respectively. The Cd concentrations of the edible parts (shoots) in tow varieties of Chinese cabbage in the nano zeolite treatments decreased by 10.5%-65.7% compared with the ordinary zeolite treatments. In Cd contaminated soils (1 mg·kg^-1 and 5 mg·kg^-1 Cd),) the total extraction amount of Cd in the edible parts (shoots) of SD4 variety reduced by 12.4%-68.8% and 13.2%-55.6% (except of Cd₅+OZ₅ processing), and the total extraction amount of Cd in the edible parts (shoots) of XJC3 variety reduced by 9.4%-71.5% and 3.1%-38.7% (except of Cd₁+OZ₅ processing), respectively. The application amount of nano zeolite (NZ) and ordinary zeolite (OZ) was more, the reduction range of the total extraction amount of Cd in the edible parts (shoots) of two varieties of Chinese cabbage was greater.

[Effect of Nano Zeolite on Chemical Fractions of Cd in Soil and Uptake by Chinese Cabbage at Different Soil pH and Cadmium Levels]

Incubation experiments were carried out to investigate the influence of different nano zeolite(NZ) and ordinary zeolite(OZ) levels(0, 5, 10 and 20 g·kg^-1) on the fraction distribution coefficient (FDC) of Cd and soil CEC at different soil pH (4, 5, 6, 7 and 8) when exposed to different cadmium(Cd) levels(1, 5, 10 and 15 mg·kg^-1), and pot experiment were carried out to investigate the effects of nano zeolite(NZ) and ordinary zeolite(OZ) on the growth, Cd concentration and Cd accumulation of Chinese cabbage. The results showed that nano zeolite and ordinary zeolite decreased the concentration and FDC of exchangeable Cd (EX-F), and increased the concentration and FDC of carbonate(CAB-F), Fe-Mn oxide(FMO-F), organic matter (OM-F) and residual fraction(RES-F) in incubation experiments. At the end of incubation, the FDC of soil exchangeable Cd decreased from 72.0%-88.0% to 2.4%-10.7%. The decreasing effect of zeolite on the concentration and FDC of exchangeable Cd (EX-F) increased with the increase of zeolite, and the decreasing effect of nano zeolite (NZ) was better than that of ordinary zeolite (OZ). During the culture of 28 d, the concentration of different Cd fractions in soil was in order of EX-F>RES-F>FMO-F>CAB-F>OM-F under different pH conditions. Exchangeable fraction Cd was the dominant fraction of Cd in soil during the whole incubation. Soil CEC had significant negative correlation with soil exchangeable Cd (EX-F) (P<0.01), and significant positive correlation with the concentrations of Fe-Mn oxide(FMO-F) and organic matter (OM-F) in soil(P<0.01). Nano zeolite and ordinary zeolite effectively increased soil CEC, and soil CEC increased with the increase of the pH value of soil in the zeolite treatments. Significant negative correlation was found in soil pH with soil exchangeable Cd (EX-F)(P<0.01). The dry weight of plant tissues in Chinese cabbage increased by 14.3%-131.4% in the presence of nano zeolite(NZ) and ordinary zeolite(OZ), and Cd concentration of shoot and root decreased by 1.0%-75.0% and 3.8%-53.2%, respectively. Higher concentration and accumulation of Cd were observed in XJC3 variety than those in SD 4 variety. Compared with ordinary zeolite (OZ), nano zeolite (NZ) was better in increasing the biomass of Chinese cabbage as well as decreasing accumulation of Cd in Chinese cabbage.

[Effects of Soil Moisture and Temperature Variations on Organic Carbon Mineralization of Purple Soil in the Hydro-fluctuation Belt of the Three Gorges Reservoir]

Soil sampling in the field and an incubation experiment in the laboratory was conducted to investigate the effects of soil moisture and temperature on soil organic carbon (SOC) mineralization of purple soil in the hydro-fluctuation belt of the Three Gorges Reservoir. Three incubation temperatures (10, 20 and 30℃) and four moisture levels (40% water holding capacity (WHC), 70% WHC, 100% WHC and submerged condition) were used in the experiment. In the entire incubation period (66 d), the SOC cumulative mineralization reached the maximum at 100% WHC, but there was no significant difference between 100% WHC and submerged condition (P>0.05). At 10℃ and 20℃, the SOC cumulative mineralization at 100% WHC and under submerged condition was not significantly different from that at 70% WHC treatment, but significantly higher than that at 40% WHC treatment. While the cumulative mineralization of organic carbon at 100% WHC and under submerged condition was significantly higher than that at 70% WHC and 40% WHC when the temperature was 30℃ (P<0.05). The results indicated that compared with 70% WHC treatment, the higher moisture content (100% WHC and submerged condition) had no negative effects but rather promotion effects on the mineralization of SOC at high temperature (30℃). Under the same soil moisture conditions, the SOC cumulative mineralization of purple soil in the hydro-fluctuation belt increased as temperature increased. Moreover, the analysis of variance showed that SOC cumulative mineralization was significantly affected by temperature and soil moisture, and there was a significant interaction with temperature and soil moisture (P<0.05). Fitting of two-pool first-order model was performed to indicate that temperature and soil moisture influenced the contents of labile SOC fraction and the mineralization rates of recalcitrant SOC fraction, which led to the differences of SOC cumulative mineralization under the different treatments. With the increasing temperature, the temperature sensitivity was significantly decreased in the 40% WHC treatment, but there was no obvious difference when the soil moisture content was not less than 70% WHC.

[Reduction Effect of Reduced Phosphorus Fertilizer and Combining Organic Fertilizers on Phosphorus Loss of Purple Soil Sloping Field]

In order to better understand the effect of reduced phosphorus fertilizer and combining organic fertilizers on phosphorus loss of purple soil sloping field, three rainfall-runoff events were monitored using field runoff observation method in the purple soil sloping field in 2014. There were six treatments in this research, including optimized fertilization (P), optimized fertilization+pig manure application (MP), optimized fertilization+straw return (SP), optimized fertilization which was reduced by 20%+pig manure application (MDP), optimized fertilization which was reduced by 20%+straw return (SDP), without phosphate (P0). The results indicated that the interflow was the main pathway of runoff for purple soil sloping field. The average contents of total phosphorus (TP) and the phosphorus loss load of overland flow were all much higher than those of the interflow. The overland flow was the main pathway of the phosphorus loss load for purple soil sloping field. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of purple soil sloping field. Compared with the treatment P, the average content of total phosphorus on SDP was reduced by 57% and that on MDP was reduced by 48% in the storm rainfall. Combining straw was better than pig manure. The average contents of the phosphorus loss load of typical rainfall changed between 0.01 and 0.26 kg·hm^-2. In different fertilization treatments, the average contents of the phosphorus loss load followed the order of P > MP > SP > MDP > SDP > P0. Reduced phosphorus fertilizer and combining organic fertilizers had a significant reduction effect on phosphorus loss of overland flow, but increased soil phosphorus leaching for purple soil sloping field.

[Variation Characteristics of Inorganic Phosphorus in Purple Soil Profile Under Different Conservation Tillage Treatments]

In this study the effects of tillage methods (rice-winter paddy field conventional farming, CF; rice-winter paddy field combing ridge with no-tillage, RNT1; rice-wheat or rape combing ridge with no-tillage, RNT2; rice-wheat or rape conventional paddy-upland rotation tillage, CR) on purple soil profile of different forms of inorganic phosphorus distribution characteristics were investigated in a long-term experimental site established in 1990, Chongqing City, China. The results showed that compared to the status before the experiment, the total phosphorus, available phosphorus and various morphologies of inorganic phosphorus all increased to a certain degree in the soils with different long-term tillage treatments,and the contents of different forms of inorganic phosphorus in soil size ranked as RNT2> CF> CR> RNT1. Except that the contents of Fe-P in the lower layer were higher than those in the upper layer, contents of Ca₂-P, Ca₈-P, Al-P, Ca₁₀-P and O-P in the arable layers were all higher than those in the lower layers. The effects of farming practices on the availability of various phosphorus forms were significant. They were in the order of CR> RNT> CF. Long-term conventional paddy-upland rotation tillage was more advantageous to crops in the absorption of phosphorus. It was shown by relevant analysis that the contribution of various groups of inorganic phosphorus to purple soil was in the order of Ca₂-P(0.9369)> Al-P(0.9158)> Ca₈-P(0.9012)> Fe-P(0.8287)> Ca₁₀-P(0.8059)> O-P(0.7472).

[Characterization of phosphorus forms in different organic materials]

The existing forms of phosphorus in seven organic waste materials including biogas residues of swine manure (ZZ), biogas residues of cattle manure (NZ), compost of cattle manure and corn straw (NJD), compost of sewage sludge (WD) and compost of rural daily garbage (NSLD) were characterized according to phosphorus fractionation procedures developed by DOU et al. The result showed that there was a great difference in the total phosphorus (TP) and the total phosphorus of various forms (P(t)) among different organic materials. ZZ had the highest content of TP with the value of 23.59 g x kg(-1); while NZ had the lowest TP content with the value of 3.61 g x kg(-1). The contents and proportions of phosphorus fractions in ZZ, NZ, NJD and WD followed the order of HCl-P > Residues-P > NaHCO3-P > NaOH-P > H2O-P, while followed the order of HC1-P > Residues-P > H2O-P > NaHCO3-P > NaOH-P in the three NSLDs. The proportion of HCl-P in the total fractionated phosphorus (P(tt)) in seven organic materials ranged from 47.75% to 84.96%, which indicated that most of P in organic materials existed in the forms that were easier to be extracted by strong extracting agents like HCl, which was difficult to be absorbed by plants. The inorganic phosphorus accounted for 79.72% -94.76% of the total phosphorus in the organic materials. Of all the phosphorus forms, the NaHCO3-P had the highest inorganic phosphorus fractions, but the inorganic phosphorus was mainly distributed in HCl-P. The organic phosphorus was mainly distributed in HCl-P and Residues-P. In addition, the higher proportions of inorganic phosphorus in NJD than those of NZ demonstrated that the composting process was benefit for the mineralization of organic phosphorus in organic materials and thus improving its availability.

[Effects of variable temperature on organic carbon mineralization in typical limestone soils]

Soil sampling in the field and incubation experiment in the laboratory were conducted to investigate the responses of soil organic carbon (SOC) mineralization to variable temperature regimes in the topsoil of limestone soils from forest land and dry land. Two incubated limestone soils were sampled from the 0-10 cm layers of typical forest land and dry land respectively, which were distributed in Tianlong Mountain area of Puding county, Guizhou province. The soils were incubated for 56 d under two different temperature regimes including variable temperature (range: 15-25 degrees C, interval: 12 h) and constant temperature (20 degrees C), and the cumulative temperature was the same in the two temperature treatments. In the entire incubation period (56 d), the SOC cumulative mineralization (63.32 mg x kg(-1)) in the limestone soil from dry land (SH) under the variable temperature was lower than that (63.96 mg x kg(-1)) at constant 20 degrees C, and there was no significant difference in the SOC cumulative mineralization between the variable and constant temperature treatments (P < 0.05). While the cumulative mineralization (169.46 mg x kg(-1)) of organic carbon in the limestone soil from forest land (SL) under the variable temperature was significantly lower than that (209.52 mg x kg(-1)) at constant 20 degrees C. The results indicated that the responses of SOC mineralization to the variable temperature were obviously different between SL and SH soils. The SOC content and composition were significantly different between SL and SH soils affected by vegetation and land use type, which suggested that SOC content and composition were important factors causing the different responses of SOC mineralization to variable temperature between SL and SH soils. In addition, the dissolved organic carbon (DOC) content of two limestone soils were highly (P < 0.01) positively correlated with daily mineralization of soil organic carbon in both temperature treatments, which implied that controlling DOC production was an important way for the temperature influence of SOC mineralization. During the incubation period, SOC mineralization was independent of microbial biomass carbon (MBC) content in both temperature treatments. Combined with mineralization kinetic data, the results showed that, compared to constant temperature 20 degrees C, variable temperature mainly influenced SOC mineralization by changing microbial community activity rather than by changing microbial quantity.

[Effects of ryegrass and arbuscular mycorrhiza on activities of antioxidant enzymes, accumulation and chemical forms of cadmium in different varieties of tomato]

Pot experiments were carried out to investigate the effects of ryegrass and arbuscular mycorrhiza on the plant growth, malondialdehyde (MDA), antioxidant enzyme activities of leaf and root, accumulation and chemical forms of cadmium (Cd) in tow varieties of tomato when exposed to Cd (20 mg x kg(-1)). The results showed that dry weights of fruit and plant, and contents of malondialdehyde (MDA) and antioxidant enzyme activities of leaf and root, and concentrations and accumulations of Cd significantly differed between two varieties of tomato. Dry weights of fruit, roots, stem, leaf and plant were increased by single or combined remediation of ryegrass and arbuscular mycorrhiza, while MDA contents and antioxidant enzyme activities of leaf and root reduced. The total extractable Cd, F(E), F(W), F(NaCl), F(HAc), F(HCl), and F(R) in fruit of two varieties of tomato reduced by 19.4% - 52.4%, 31.0% - 75.2%, 19.7% - 59.1%, 3.1% - 48.2%, 20.0% - 65.0%, 40.7% - 100.0% and 15.2% - 50.0%, respectively. Cadmium accumulations in tomato were in the order of leaf > stem > fruit > root. Cadmium concentrations in leaf, stem, root and fruit of both varieties decreased by single or combined remediation of ryegrass and arbuscular mycorrhiza, and Cd accumulations of stem and plant of two varieties also reduced. Cd accumulations in fruit of two varieties decreased by 42.9% and 43.7% in the combined remediation treatments, respectively. Tolerance and resistance of 'LUO BEI QI' on Cd was more than 'De Fu mm-8', and Cd concentrations and Cd accumulations in fruit and plant were in the order of 'LUO BEI QI' < 'De Fu mm-8' in the presence or absence of single or combined remediation of ryegrass and arbuscular mycorrhiza.

[Prediction of total nitrogen and total phosphorus concentrations in purple soil using hyperspectral data]

Hyper-spectral remote sensing is one of the effective means for prediction of soil nutrients. Taking Wangjiagou small watershed of Three Gorges Reservoir Area as researching zone, based on the soil physicochemical properties, reflective spectrum analysis and measurement, were built predictive models for total phosphorous and total phosphorus concentrations in purple soil. Meanwhile, 33 soil samples from paddy soil were used to validate the prediction models for soil nutrients in purple soil. Results show that the total correlation coefficients between their predicted values and measured values of total nitrogen and total phosphorus concentration in purple soil are 0.672 and 0.498, respectively. Correlation coefficients obtained from predictive model of purple soil nutrients validated by paddy soil samples are 0.550 and 0.124. Therefore, it is reasonable to use hyper-spectrum method to prediction total nitrogen concentration. But prediction accuracy for total phosphorus concentration in purple soil is relatively poor. The prediction model of soil nutrients in purple soil is not suitable for paddy soil.

[Composition and stability of soil aggregates in hedgerow-crop slope land]

Based on a long-term experiment of using hedgerow to control soil and water loss, this paper studied the composition and stability of soil aggregates in a hedgerow-crop slope land. Compared with those under routine contour cropping, the contents of > 0.25 mm soil mechanical-stable and water-stable aggregates under the complex mode hedgerow-crop increased significantly by 13.3%-16.1% and 37.8% -55.6%, respectively. Under the complex mode, the contents of > 0.25 mm soil water-stable aggregates on each slope position increased obviously, and the status of > 0.25 mm soil water-stable aggregates being relatively rich at low slope and poor at top slope was improved. Planting hedgerow could significantly increase the mean mass diameter and geometric mean diameter of soil aggregates, decrease the fractal dimension of soil aggregates and the destruction rate of > 0.25 mm soil aggregates, and thus, increase the stability and erosion-resistance of soil aggregates in slope cropland. No significant effects of slope and hedgerow types were observed on the composition, stability and distribution of soil aggregates.

[Cd uptake in rice cultivars and Cd fractions in soil treated with organic acids and EDTA]

A pot experiment was conducted to examine the yield, quality and cadmium (Cd) uptake in different rice cultivars, and Cd speciation in soil after exposing to Cd (0, 1 and 5 mg x kg(-1)) in the presence of organic acids and ethylenediamine tetraacetic acid (EDTA). The results showed that general increase in the yield for cultivars Xiushui63 and II you527 was observed. Yield of two rice cultivars were in order of organic acids treatment or organic acids + 1/2EDTA treatment > EDTA treatment. The exchangeable, carbonate related and ferric-manganese oxidation related Cd increased; while organic complexation Cd and residules decreased in the presence of organic acids and EDTA. Cadmium concentrations in grain, straw and roots of both cultivars markedly reduced in the presence of organic acids and EDTA. Grain Cd concentration was the lowest for plants treated with EDTA, followed by organic acids + 1/2EDTA, and the highest Cd concentration in grain was found in the treatment with organic acids. Grain Cd concentration decreased by 9.0% to 49.3% and 16.5% to 30.6% at 1 mg x kg(-1) Cd in the presence of organic acids and EDTA, and by 12.7% to 28.5% and 4.3% to 19.1% at 5 mg x kg(-1) Cd. Cadmium concentration and accumulation in plants and total Cd content in soil were higher in Xiushui63 than in that in II you527. Grain Cd concentration decreased, and yield and quality of two rice cultivars increased at the same time in the presence of organic acids + 1/2EDTA.

[Seasonal variation characteristics of phosphorus speciation in the sediment of Changshou Lake]

To further know the seasonal variation characteristics of phosphorus species in lake sediment, the contents of different phosphorus species in the surface sediment sampling from Changshou Lake were determined by using the SMT sequential extraction method in July and November, 2009, and March, 2010. The contents of total phosphorus (TP) basically show an order of the low-water period, high-water period, and normal-water period from high to low, and the maximum appeared in Shoudao (2960.29 mg/kg) while the minimum in Guanjiakou (586.05 mg/kg). The mass fractions of phosphorus associated with hydrous ferric/aluminum oxides (Fe/Al-P) and organic phosphorus (OP) in TP at all sampling sits are in an order of the normal-water period, high-water period, and low-water period from high to low, and the maximum of Fe/Al-P appeared in Lewen (40.01%) while that of OP in the dam mouth (72.44%). The mass fraction of phosphorus bound to calcium salt (Ca-P) in TP is in an order of the low-water period, normal-water period, and high-water period, and the maximum appeared in Baibudang (15.52%). These results suggested that the phosphorus speciation in the sediment of Changshou Lake shows obviously temporal and spatial distribution characteristics, and Fe/Al-P is mainly influenced by pH of the overlying water, while OP is not apparently influenced by dissolved oxygen (DO).

Spatial variability of soil heavy metals in the three gorges area: multivariate and geostatistical analyses

There is a growing concern about environmental contamination in the three gorges area. The objectives of this study were to investigate the spatial variability and the possible influence factors of seven heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) in the center of this area based on multivariate and geostatistical approaches. All analyzed heavy metals were below their background levels, except Cd. The average concentrations of the analyzed elements in topsoil (0-20 cm) were 5.83 mg As kg(-1), 0.21 mg Cd kg(-1), 78.79 mg Cr kg(-1), 21.53 mg Cu kg (-1), 0.049 mg Hg kg(-1), 24.12 mg Pb kg(-1), and 68.5 mg Zn kg(-1). The concentration of As was mostly due to parent materials, whereas the source of Pb was mainly due to vehicle exhaust. The high concentration of Cd was resulted from agricultural practices and parent materials. The concentrations of Cr, Cu, Hg, and Zn were associated with parent materials and human activities.

Response of CH4 emission of paddy fields to land management practices at a microcosmic cultivation scale in China

The terrestrial ecosystem may be either a source or a sink of CH4 in rice paddies, depending, to a great extent, on the change of ecosystem types and land use patterns. CH4 emission fluxes from paddy fields under 4 cultivation patterns (conventional plain culture of rice (T1), no-tillage and ridge culture of rice (T2), no-tillage and ridge culture of rice and wheat (T3), and rice-wheat rotation (T4)) were measured with the closed chamber technique in 1996 and 1998 in Chongqing, China. The results showed that differences existed in CH4 emission from paddy fields under these land management practices. In 1996 and 1998, CH4 emission was 71.48% and 78.82% (T2), 65.93% and 57.18% (T3), and 61.53% and 34.22% (T4) of that in T1 during the rice growing season. During the non-rice growing season, CH4 emission from rice fields was 76.23% in T2 and 38.69% in TI. The accumulated annual CH4 emission in T2, T3 and T4 in 1996 decreased by 33.53%, 63.30% and 65.73%, respectively, as compared with that in T1. In 1998, the accumulated annual CH4 emission in T1, T2, T3 and T4 was 116.96 g/m2, 68.44 g/m2, 19.70 g/m2 and 11.80 g/m2, respectively. Changes in soil physical and chemical properties, in thermal and moisture conditions in the soil and in rice plant growth induced by different land use patterns were the dominant causes for the difference in CH4 emission observed. The relative contribution of various influencing factors to CH4 emission from paddy fields differed significantly under different land use patterns. However, the general trend was that chlorophyll content in rice leaves, air temperature and temperature at the 5 cm soil layer play a major role in CH4 emission from paddy fields and the effects of illumination, relative humidity and water layer depth in the paddy field and CH4 concentration in the crop canopy were relatively non-significant. Such conservative land use patterns as no-tillage and ridge culture of rice with or without rotation with wheat are thought to be beneficial to reducing CH4 emission from paddy fields and are, therefore, recommended as a significant solution to the problems of global (climatic) change.

[Synthesis and spectroscopic properties of rare earth complexes with o-phthalate and 1,10-phenanthroline]

The complexes of rare earth ions (Nd3+, Sm3+) with o-phthalate and 1,10-phenanthroline have been synthesized and characterized by elemental analysis, 1H NMR, IR, and DTA-TG. The compositions of complexes have been confirmed to be RE2L3.2H2O and RE2L3 phen.2H2O (RE: rare earth ions, L: o-phthalic, phen: 1,10-phenanthroline), their far-IR and FT-Raman spectra have been discussed and studied.