Effect of Phopshate Fertilizer and Manure on Crop Yield, Soil P Accumulation, and the Environmental Risk Assessment

Phosphorus （P） applied from fertilizer and manure is important in increasing crop yield and soil fertility; however, excessive uses of phosphate fertilizer and manure may also increase P loss from agricultural soils, posing environmental impact. A long term experiment was conducted on a calcareous soil （meadow cinnamon） in Hebei Province, China, from 2003 to 2006 to investigate the effects of phosphate fertilizer and manure on the yield of Chinese cabbage, soil P accumulation, P sorption saturation, soluble P in runoff water, and P leaching. P fertilizer （P2O5） application at a rate of 360 kg ha^-1 or manure of 150 t ha^-1 significantly increased Chinese cabbage yield as compared to the unfertilized control. However, no significant yield response was found with excessive phosphate or manure application. Soil Olsen-P, soluble P, bioavailable P, the degree of phosphorus sorption saturation in top soil layer （0-20 cm）, and soluble P in runoff water increased significantly with the increase of phosphate fertilizer and manure application rates, whereas the maximum phosphorus sorption capacity （Qm） decreased with the phosphate fertilizer and manure application rates. Soil Olsen-P and soluble P also increased significantly in the sub soil layer （20-40 cm） with the high P fertilizer and manure rates. It indicates that excessive P application over crop demand can lead to a high environmental risk owing to the enrichment of soil Olsen-P, soluble P, bioavailable P, and the degree of phosphorus sorption saturation in agricultural soils.

Vertical patterns in plant diversity and their relations with environmental factors on the southern slope of the Tianshan Mountains(middle section)in Xinjiang(China)

The investigation of distribution patterns of species diversity is significant for successful biodiversity conservation. The spatial patterns of vegetation and different life-forms species diversity along an elevation gradient in the middle section of the southern slope of the Tianshan Mountains in Xinjiang, China were explored, using the detrended canonical correspondence analysis （DCCA） and the generalized additive model （GAM） methods based on a field survey of 53 sampling plots. In this work 158 species of seed plants were recorded, including 141 herbaceous, 14 shrub, and 2 tree species, in which the woody plants are very limited. 53 sampling plots were classified into 9 major plant communities. The results indicate that the herb communities were the most sensitive to changes in elevation gradient. The diversity indices of the community as a whole presented bimodal patterns. The peak values for the species diversities were found in the transition region between mountain steppe desert and mountain desert steppe （2,200-2,300m）, and in the alpine grassland region （2,900-3,100m）, while maximum species diversities were in the areas of intermediate environmental gradient. The main environmental factors on the distribution patterns in plant diversity were the elevation, soft water, total nitroeen, available nitrogen, organic matter, and total salt. The response tendency of the four diversity indices for the whole community to the soil environment was the same as that of the herb layers.

Ammonia Volatilization and Nitrogen Utilization Efficiency in Response to Urea Application in Rice Fields of the Taihu Lake Region,China

Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 （control）, 100, 200, 300, or 350 kg N ha^-1. After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate, and the two higher N application rates （300 and 350 kg N ha^-1） showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surplus N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields. Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha^-1 for the type of paddy soil in the Taihu Lake region. However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.

Treated wastewater irrigation effect on soil,crop and environment:Wastewater recycling in the loess area of China

A study was carded out at the Loess Plateau in Dongzhi, China, to test the feasibility of using secondary treatment sewage effluent and to determine whether the water quality would then meet the recommended irrigation norm. Seven crops, including celery, wheat, maize, millet, apples, rapeseed and yellow beans, were tested in the study. Physical and chemical properties of the soil, crop yield and quality and leachate at different soil depths were measured. In most cases, the quality of the crops that made use of treated sewage was not distinctively different from those that did not use treated sewage. However, yields for the former were much higher than they were for the latter. Leachates at different soil depths were analyzed and the results did not show alarming levels of constituents. For a period of approximately 14 months, the treated sewage irrigation had no significant effect on the loess soil and no cases of illness resulting from contact with the treated sewage were reported. With treated sewage irrigation, a slight increase in the organic content of the soil was observed.

Estimation of As and Cu Contamination in Agricultural Soils Around a Mining Area by Reflectance Spectroscopy:A Case Study

Concentrations of Iron (Fe), As, and Cu in soil samples from the fields near the Baoshan Mine in Hunan Province, China, were analyzed and soil spectral reflectance was measured with an ASD FieldSpec FR spectroradiometer (Analytical Spectral Devices, Inc., USA) under laboratory condition. Partial least square regression (PLSR) models were constructed for predicting soil metal concentrations. The data pre-processing methods, first and second derivatives (FD and SD), baseline correction (BC), standard normal variate (SNV), multiplicative scatter correction (MSC), and continuum removal (CR), were used for the spectral reflectance data pretreatments. Then, the prediction results were evaluated by relative root mean square error (RRMSE) and coefficients of determination (R 2 ). According to the criteria of minimal RRMSE and maximal R 2 , the PLSR models with the FD pretreatment (RRMSE = 0.24, R 2 = 0.61), SNV pretreatment (RRMSE = 0.08, R 2 = 0.78), and BC-pretreatment (RRMSE = 0.20, R 2 = 0.41) were considered as the final models for predicting As, Fe, and Cu, respectively. Wavebands at around 460, 1 400, 1 900, and 2 200 nm were selected as important spectral variables to construct final models. In conclusion, concentrations of heavy metals in contaminated soils could be indirectly assessed by soil spectra according to the correlation between the spectrally featureless components and Fe; therefore, spectral reflectance would be an alternative tool for monitoring soil heavy metals contamination.

Carbon and Oxygen Isotopic Compositions: How Lacustrine Environmental Factors Respond in Northwestern and Northeastern China

Surface lake sediments, 28 from Hoh XU, 24 from northeastern China, 99 from Lake Bosten, 31 from Ulungur and 26 from Heihai were collected to determine δ13C and δ18O values. Considering the impact factors, conductivity, alkalinity, pH, TOC, C/N and carbonate-content in the sediments, CI, P, S, and metal element ratios of Mg/Ca, Sr/Ca, Fe/Mn of bulk sediments as environmental variables enable evaluation of their influences on δ13C and δ18O using principal component analysis （PCA） method. The closure and residence time of lakes can influence the correlation between δ13C and δ18O. Lake water will change from fresh to brackish with increasing reduction and eutrophication effects. Mg/Ca in the bulk sediment indicates the characteristic of residence time, Sr/Ca and Fe/Mn infer the salinity of lakes. Carbonate formation processes and types can influence the 6~3C--~1So correlation. ~180 will be heavier from Mg-calcite and aragonite formed in a high-salinity water body than calcite formed in freshwater conditions. When carbonate content is less than 30%, there is no relationship with either 613C or 6180, and also none between δ13C and δ18O. More than 30%, carbonate content, however, co-varies highly to δ13C and δ18O, and there is also a high correlation between δ13C and δ18O. Vegetation conditions and primary productivity of lakes can influence the characteristics of δ13C and δ18O, and their co-variance. Total organic matter content （TOC） in the sediments is higher with more terrestrial and submerged plants infilling. In northeastern and northwestern China, when organic matter in the lake sediments comes from endogenous floating organisms and algae, the δ13C value is high. δ13C is in the range of-4‰ to 0‰ when organic matter comes mainly from floating organisms （C/N〈6）; in the range of-4‰ to 8‰ when organic matter comes from diatoms （C/N=6 to 8）; and -8‰ to -4‰ when organic matter comes from aquatic and terrestrial plants （C/N〉8）.

Vegetation NPP Distribution Based on MODIS Data and CASA Model——A Case Study of Northern Hebei Province

Net Primary Productivity （NPP） is one of the important biophysical variables of vegetation activity, and it plays an important role in studying global carbon cycle, carbon source and sink of ecosystem, and spatial and temporal distribution of CO2. Remote sensing can provide broad view quickly, timely and multi-temporally, which makes it an attractive and powerful tool for studying ecosystem primary productivity, at scales ranging from local to global. This paper aims to use Moderate Resolution Imaging Spectroradiometer （MODIS） data to estimate and analyze spatial and temporal distribution of NPP of the northern Hebei Province in 2001 based on Carnegie-Ames-Stanford Approach （CASA） model. The spatial distribution of Absorbed Photosynthetically Active Radiation （APAR） of vegetation and light use efficiency in three geographical subregions, that is, Bashang Plateau Region, Basin Region in the northwestern Hebei Province and Yanshan Mountainous Region in the Northern Hebei Province were analyzed, and total NPP spatial distribution of the study area in 2001 was discussed. Based on 16-day MODIS Fraction of Photosynthetically Active Radiation absorbed by vegetation （FPAR） product, 16-day composite NPP dynamics were calculated using CASA model; the seasonal dynamics of vegetation NPP in three subreglons were also analyzed. Result reveals that the total NPP of the study area in 2001 was 25.1877 × 10^6gC/（m^2.a）, and NPP in 2001 ranged from 2 to 608gC/（m^2-a）, with an average of 337.516gC/（m^2.a）. NPP of the study area in 2001 accumulated mainly from May to September （DOY 129-272）, high NIP values appeared from June to August （DOY 177-204）, and the maximum NPP appeared from late July to mid-August （DOY 209-224）.

Surfactant-Enhanced Phytoremediation of Soils Contaminated with Hydrophobic Organic Contaminants:Potential and Assessment

Phytoremediation is becoming a cost-effective technology for the in-situ clean up of sites polluted with hydrophobic organic contaminants （HOCs）. The major factors limiting phytoremediation are the mass transfer, rate of plant uptake, and microbial biodegradation of HOCs. This article discusses the potential of surfactants to enhance desorption, plant uptake, and biodegradation of HOCs in the contaminated sites. Positive effects of surfactants on phytoremediation have been recently observed in greenhouse studies. The presence of some nonionic surfactants including polyoxyethylene sorbltan monooleate （Tween 80） and polyoxyethylene（23）dodecanol （Brij35） at relatively low concentrations resulted in significant positive effects on phytoremediation for pyrene-contaminated soil. However, the anionic surfactant （sodium dodecyl sulfate, SDS） and the cationic surfactant （cetyltrimethylammonium bromide, CTMAB） were not useful because of their phytotoxicity or low efficiency for surfactant-enhanced phytoremediation （SEPR）. The mechanisms of SEPR for HOC-contaminated sites were evaluated by considering experimental observations. In view of concerns about the cost effectiveness and toxicity of surfactants to plants, more research is needed to enhance the use of SEPR technology.

Decomposition characteristics of organic materials and their effects on labile and recalcitrant organic carbon fractions in a semi-arid soil under plastic mulch and drip irrigation

Labile organic carbon （LC） and recalcitrant organic carbon （RC） are two major fractions of soil organic carbon （SOC） and play a critical role in organic carbon turnover and sequestration. The aims of this study were to evaluate the variations of LC and RC in a semi-arid soil （Inner Mongolia, China） under plastic mulch and drip irrigation after the application of organic materials （OMs）, and to explore the effects of OMs from various sources on LC and RC by probing the decomposition characteristics of OMs using in-situ nylon mesh bags burying method. The field experiment included seven treatments, i.e., chicken manure （CM）, sheep manure （SM）, mushroom residue （MR）, maize straw （MS）, fodder grass （FG）, tree leaves （TL） and no OMs as a control （CK）. Soil LC and RC were separated by Huygens D＇s method （particle size-density）, and the average soil mass recovery rate and carbon recovery rate were above 95%, which indicated this method was suitable for carbon pools size analysis. The LC and RC contents significantly （P〈0.01） increased after the application of OMs. Moreover, LC and RC contents were 3.2%-8.6% and 5.0%-9.4% higher in 2016 than in 2015. The applications of CM and SM significantly increased （P〈0,01） LC content and LC/SOC ratio, whereas they were the lowest after the application of TL. However, SOC and RC contents were significantly higher （P〈0.01） after the applications of TL and MS. The correlation analysis indicated the decomposition rate of OMs was positively related with LC content and LC/SOC ratio. In addition, lignin, polyphenol, WOM （total water-soluble organic matter）, WHA （water-soluble humic acid）, HSL （humicdike substance） and HAL （humic acid-like） contents in initial OMs played important roles in SOC and RC. In-situ nylon mesh bags burying experiment indicated the decomposition rates of CM, SM and MS were significantly higher than those of MR, FG, and TL. Furthermore, MS could result in more lignin derivatives, WHA, and HAL polymers in shorter time during the decomposition process. In conclusion, the application of MS in the semi-arid soil under a long-term plastic mulch and drip irrigation condition could not only improve soil fertility, but also enhance soil carbon sequestration.

Effect of Temperature, pH and Salt on Fluorescent Quality of Water Extractable Organic Matter in Black Soil

Water erosion is the major reason for the loss of soil organic carbon in the Northeast China, which leads to the soil quality deterioration and adjacent water pollution. In this study, the effect of extraction temperature, pH value, and salt on the water extractable organic matter （WEOM） was determined by means of the UV absorbance, fluorescence excitation-emission matrix, and derived fluorescence indexes. In general, the carbon content and aromaticity of WEOM increased with the increasing of extraction temperature, with the exception that there was no significant difference in the amount at 0 and 20℃. More fluorophores, especially microbially-derived organic matter were extracted at high temperature. The pH values of extractant, including 5, 7, and 10, showed no effect on the carbon amount of WEOM, whereas the aromaticity and microbially-derived component gradually increased with the increasing of pH values. The fluorescence intensity of humic acid-like fluorophore was stronger in neutral and alkali condition than that in acidic condition. The addition of 10 mmol L-1 CaCl2 significantly decreased the carbon amount of recovered WEOM. Moreover, it significantly decreased the aromaticity of WEOM and the quantity of fulvic acid-like and humic acid-like fluorophores, whereas increased the percentage of tyrosine-like and tryptophan-like fluorophores in the total fluorophores and the amount of microbially-derived organic matter. Generally, 10 mmol L-1 KCl showed the same influence trend, but with low influence degree.

Accumulation and Fractionation of Rare Earth Elements in Soil-Rice Systems

Accumulation and fractionation of rare earth elements （REEs） were studied through applications of exogenous REEs in soils with pot-cultured rice for 2 years. The results show that the biomass of rice consistently decreases at sprouting and maturity stages when the amount of exogenous REEs are over 400 mg· kg^- 1. It illustrates that the endurance of rice to exogenous REE exposure is much weaker than that of wheat. The distribution patterns of REEs in rice of the control are similar to that in the soil, both exhibiting light REE （LREE） enrichment and positive Tb in the roots and the aboveground parts. Applications of exogenous REEs ranging from 400 to 1200 mg· kg^- 1 have significant effects on the distribution patterns of REEs in roots, some effects in stems and leaves, and almost no effects in grains. Accumulation rates of REEs in different organs follow the order of roots 〉 leaves 〉 stems 〉 panicle axes and crusts 〉 grains. The roots take up different REEs at almost the same rates, except for the selective accumulation of Th. In the aboveground parts, the accumulation rates of middle REEs （MREEs） and heavy REEs （HREEs） are higher than those of LREEs, there are significant selective accumulations of Eu and Tb. Accumulation rates of REEs in the roots, stems and leaves increase with the increasing applications of exogenous REEs, but they change slightly in the panicle axes, crusts and grains, demonstrating that it is easier for the roots, stems and leaves to accumulate exogenous REEs. Selective accumulation and fractionation of exoge nous Nd are also observed in rice organs including grains.

Characteristics of Caragana korshinskii and Hippophae rhamnoides stemflow and their significance in soil moisture enhancement in Loess Plateau, China

Stemflow of xerophytic shrubs represents a significant component of water replenishment to the soil-root system and influences water utilization of plant roots at the stand scale,especially in water-scarce semi-arid ecosystems.The stemflow of two semi-arid shrubs(Caragana korshinskii and Hippophae rhamnoides)and its effect on soil moisture enhancement were evaluated during the growing season of 2011 in the semi-arid loess region of China.The results indicated that stemflow averaged 12.3%and 8.4%of the bulk precipitation for C.korshinskii and H.rhamnoides,respectively.Individual stemflow increased in a linear function with increasing rainfall depth.The relationship between funneling ratios and rainfall suggested that there existed a rainfall depth threshold of 11 mm for both C.korshinskii and H.rhamnoides.Averaged funneling ratios were 156.6±57.1 and49.5±30.8 for C.korshinskii and H.rhamnoides,respectively,indicating that the canopy architecture of the two shrubs was an effective funnel to channel stemflow to the root area,and C.korshinskii showed a greater potential to use stemflow water in the semi-arid conditions.For individual rainfall events,the wetting front depths were approximately 2 times deeper in the rooting zone around the stems than in the bare area outside canopy for both C.korshinskii and H.rhamnoides.Correspondingly,soil water content was also significantly higher in the root area around the shrub stem than in the area outside the shrub canopy.This confirms that shrub stemflow conserved in the deep soil layers may be an available moisture source for plant growth under semi-arid conditions.

Spatiotemporal evolution and driving forces of changes in rural settlements in the poverty belt around Beijing and Tianjin： a case study of Zhangjiakou city, Hebei Province

The rural settlement is one of important aspects to understand regional human-environment relationships. Zhangjiakou city, located in the poverty belt around Beijing and Tianjin, was used as an example to analyze the evolution of rural settlements during 1985–2010 through the use of statistical and spatial analysis methods. The results demonstrate the following:(1) the area of rural settlements expanded from 665.76 to 928.14 km2 during 1985–2010. Rural settlements in prefecture city of Zhangjiakou were significantly agglomerated in terms of their spatial distribution, which presented an approximately normal distribution over the entire period. Rural settlements were usually distributed within regions where the terrain niche had an elevation of between 900 and 1500 m, and a slope from 5? to 20?;(2) there were significant regional differences in the density and size distribution of rural settlements in Zhangjiakou. The density of rural settlements in 2010 was higher than that in 1985, while there was a clustered distribution of rural settlements in 2010. There was a significant high value cluster in the size distribution, and a local negative correlation between the size and density distribution of rural settlements in Zhangjiakou;(3) rural economic development, investment in agricultural technology, and infrastructure improvement played important roles in the evolution of rural settlements. There were spatial differences in the relationship between the distribution of rural settlements and socio-economic factors in Zhangjiakou. This study provides practical guidance for the achievement of urban and rural integration development and the promotion of a new form of countryside construction.

Zircon U-Pb Age and Geochemistry of the Ore-hosting Ultramafic Complex of Zhou'an PGE-Cu-Ni Deposit,Henan Province,Central China

The Zhou＇an PGE-Cu-Ni deposit was recently discovered in the Qinling orogenic belt bound by the Yangtze and the North China Cratons. It is a blind deposit thoroughly covered by the Cenozoic alluvial sediments in the Nanyang Basin. As the first large PGE-Cu-Ni deposit discovered in the Qinling-Dabie-Sulu orogenic belt, its geological and geochemical characteristic, isotope age, genesis and tectonic setting are of wide concern in both scientific studies and ore exploration. In this contribution, we report the results obtained from a pioneering study. The Zhou＇an ultramafic complex is ferruginous, with m/f = 4.79-5.08, and shows the nature of tholeiite series. It is rich in light rare earth elements, Rb, Th, U, La, Sm, Zr and Hf, and poor in heavy rare earth elements, Nd and Ta, suggesting an intraplate setting. It has high S7Sr/S6Sr and low 143Nd/144Nd ratios. The ratios of Zr/Nb, La/Nb, Ba/ Nb, Rb/Nb, Th/Nb, Th/La and Ba/La, suggest the magma originated from lithosphere mantle. The Fo values of olivine and Pd/Ir-Ni/Cu diagram suggest primary magma was High Mg basalt. The laser ablation inductively coupled plasma atomic emission spectroscopy zircon U-Pb age is 641.5 ± 3.7 Ma.

Effective remediation of aged HMW-PAHs polluted agricultural soil by the combination of Fusarium sp, and smooth bromegrass (Bromus inermis Leyss.)

Fusarium sp. strain ZH-H2 is capable to degrade high molecular weight polycyclic aromatic hydrocarbons （HMW-PAHs）, smooth bromegrass （Bromus inermis Leyss.） can also degrade 4- to 6-ring PAHs. Pot experiments were conducted to investigate how bromegrass and different inoculum sizes of ZH-H2 clean up HMW-PAHs in agricultural soil derived from a coal mine area. The results showed that, compared with control, different sizes of inocula of ZH-H2 effectively degraded HMW-PAHs, with removal rates of 19.01, 34.25 and 29.26% for 4-, 5- and 6-ring PAHs in the treatment with 1.0 g kg-1ZH- H2 incubation after 90 d. After 5 mon of cultivation, bromegrass reached degradation rate of these compounds by 12.66, 36.26 and 36.24%, respectively. By adding strain ZH-H2 to bromegrass, HMW-PAHs degradation was further improved up to 4.24 times greater than bromegrass （W）, in addition to the degradation rate of Bbf decrease. For removal rates of both 5- and 6-ring PAHs, addition of 0.5 g kg-1 Fusarium ZH-H2 to pots with bromegrass performed better than addition of 0.1 g kg-1, while the highest concentration of 1.0 g kg-1 Fusarium ZH-H2 did not further improve degradation. Degradation of4-ring PAHs showed no significant difference among different ZH-H2 incubations with bromegrass treatments. We found that the degradation rates of 4-, 5- and 6-ring PAHs in all treatments are significantly correlated in a positive, linear man- ner with activity of lignin peroxidase （LIP） （t=0.8065, 0.9350 and 0.9165, respectively）, while degradation of 5- and 6-ring PAHs is correlated to polyphenoloxidase （PPO） activity （r=0.7577 and 07806）. Our findings suggest that the combination of Fusarium sp. ZH-H2 and bromegrass offers a suitable alternative for phytoremediation of aged PAH-contaminated soil in coal mining areas, with a recommended inoculation size of 0.5 g Fusarium sp. ZH-H2 per kg soil.

Pivotal roles of artificial oxygen vacancies in enhancing photocatalytic activity and selectivity on Bi_2O_2CO_3 nanosheets

There is an increasing interest in bismuth carbonate(Bi2O2CO3,BOC)as a semiconductor photocatalyst.However,pure BOC strongly absorbs ultraviolet light,which drives a high recombination rate of charge carriers and thereby limits the overall photocatalysis efficiency.In this work,artificial oxygen vacancies(OV)were introduced into BOC(OV-BOC)to broaden the optical absorption range,increase the charge separation efficiency,and activate the reactants.The photocatalytic removal ratio of NO was increased significantly from 10.0%for pure BOC to 50.2%for OV-BOC because of the multiple roles played by the oxygen vacancies.These results imply that oxygen vacancies can facilitate the electron exchange between intermediates and the surface oxygen vacancies in OV-BOC,making them more easily destroyed by active radicals.In situ DRIFTS spectra in combination with electron spin resonance spectra and density functional theory calculations enabled unraveling of the conversion pathway for the photocatalytic NO oxidation on OV-BOC.It was found that oxygen vacancies could increase the production of active radicals and promote the transformation of NO into target products instead of toxic byproducts(NO2),thus the selectivity is significantly enhanced.This work provides a new strategy for enhancing photocatalytic activity and selectivity.

Effects of Elevated Air Temperatures on Soil Thermal and Hydrologic Processes in the Active Layer in an Alpine Meadow Ecosystem of the Qinghai-Tibet Plateau

In this study,effects of elevated air temperatures on thermal and hydrologic process of the shallow soil in the active layer were investigated. Open-top chambers(OTCs)were utilized to increase air temperatures 1-2℃ in OTC-1 and 3-5℃ in OTC-2 in the alpine meadow ecosystem on the Qinghai- Tibetan Plateau.Results show that the annual air temperatures under OTC-1 and OTC-2 were 1.21℃ and 3.62℃ higher than the Control,respectively.The entirely-frozen period of shallow soil in the active layer was shortened and the fully thawed period was prolonged with temperature increase.The maximum penetration depth and duration of the negative isotherm during the entirely-frozen period decreased, and soil freezing was retarded in the local scope of the soil profile when temperature increased.Meanwhile, the positive isotherm during the fully-thawed period increased,and the soil thawing was accelerated.Soil moisture under different manipulations decreased with the temperature increase at the same depth. During the early freezing period and the early fully- thawed period,the maximum soil moisture under the Control manipulation was at 0.2 m deep,whereas under OTC-1 and OTC-2 manipulations,the maximum soil moisture were at 0.4-0.5 m deep. These results indicate that elevated temperatures led to a decrease of the moisture in the surface soil.The coupled relationship between soil temperature and moisture was significantly affected by the temperature increase.During the freezing and thawing processes, the soil temperature and moisture under different manipulations fit the regression model given by the equationθV=a/{1+exp[b(TS+c)]}+d.

Variations of Microbial Communities and the Contents and Isotopic Compositions of Total Organic Carbon and Total Nitrogen in Soil Samples during Their Preservation

Semi-sealed preservation of soil samples at different moisture of 4% and 23 %, respectively, was simulated to observe the variations of soil microbial communities and determine the contents and isotopic compositions of the total organic carbon and total nitrogen on the 7th and 30th day, respectively. The results show that during preservation, the quantity of microbial communities tended to increase first and then decrease, with a wider variation range at higher moisture （23%）. At the moisture content of 23 %, the microbial communities became more active on the 7th day, but less after 30 days, and their activity was stable with little fluctuation at the moisture content of 4%. However, there were no significant changes in the contents and isotopic compositions of the total organic carbon and total nitrogen. During preservation, the responses of soil microbes to the environment are more sensitive to changes in the total nitrogen and organic carbon contents. It is thus suggested that the variations of microbial communities have not exerted remarkable impacts on the isotope compositions of the total nitrogen and total organic carbon.

Litter Decomposition of Emergent Plants along an Elevation Gradient in Wetlands of Yunnan Plateau,China

The decomposition of plant litter is a key process of litter decomposition to global climate warming in plateau in the flows of energy and nutrients in ecosystems. However, the response wetlands remains largely unknown. In this study, we conducted a one-year litter decomposition experiment along an elevation gradient from 1891 m to 3260 m on the Yurman Plateau of Southwest China, using different litter types to determine the influences of climate change, litter quality and microenvironment on the decomposition rate. The results showed that the average decomposition rate （K） increased from 0.608 to 1.152, and the temperature sensitivity of litter mass losses was approximately 4.98%/℃ along the declining elevation gradient. Based on a correlation analysis, N concentrations and C ： N ratios in the litter were the best predictors of the decomposition rate, with significantly positive and negative correlations, respectively. Additionally, the cumulative effects of decomposition were clearly observed in the mixtures of Scirpus tabernaemontani and Zizania caduciflora. Moreover, the litter decomposition rate in the water was higher than that in the sediment, especially in high-elevation areas where the microenvironment was significantly affected by temperature. These results suggest that future climate warming will have significant impacts on plateau wetlands, which have important fimctions in biogeochemical cycling in cold highland ecosystems.

Preconcentration of Ultra-trace Cadmium with Nanometer-size TiO_2 Colloid and Determination by GFAAS with Slurry Sampling

A novel method of ultra-trace Cd（Ⅱ） preconcentration with nanometer-size TiO2 colloid and determination by graphite furnace atomic adsorption spectrometry（GFAAS） with slurry sampling was first advanced in this paper. The adsorption efficiency of nanometer-size TiO2 colloid for ultra-trace Cd（Ⅱ） could reach above 96% in a short time when the pH value was between 5 and 6. Other problems were also studied, such as adsorption capacity, nanometer-size TiO2 colloid dosage, effect of coexistent ions. The detection limit（3σ） and the relative standard deviation （R.S.D） of this method were 4.46.103 μg/L and 1.30%（n=7）, respectively. The method was successfully applied to the analysis of environmental samples with recoveries between 93.8% and 96.4%.