Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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Proton and Copper Binding to Humic Acids Analyzed by XAFS Spectroscopy and Isothermal Titration Calorimetry
No full textProton and copper (Cu) binding to soil and lignite-based humic acid (HA) was investigated by combining X-ray absorption fine structure (XAFS) spectroscopy, isothermal titration calorimetry (ITC), and nonideal-competitive-adsorption (NICA) modeling. NICA model calculations and XAFS results showed that bidentate and monodentate complexation occurred for Cu binding to HA. The site-type-specific thermodynamic parameters obtained by combining ITC measurements and NICA calculations revealed that copper binding to deprotonated carboxylic-type sites was entropically driven and that to deprotonated phenolic-type sites was driven by entropy and enthalpy. Copper binding to HA largely depended on the site-type and coordination environment, but the thermodynamic binding mechanisms for Cu binding to the specific site-types were similar for the different HAs studied. By comparing the site-type-specific thermodynamic parameters of HA-Cu complexation with those of low molar mass organic acids, the Cu coordination could be further specified. Bidentate carboxylic Cu complexes made the dominating contributions to Cu binding to HA. The present study not only yields molecular-scale mechanisms of ion binding to carboxylic- and phenolic-type sites of HA but also provides the new insight that the universal nature of site-type-specific thermodynamic data enables quantitative estimation of the binding structures of heavy metal ions to humic substances
Formation of litter crusts and its multifunctional ecological effects in a desert ecosystem
No full textDesertification is one of the major issues in global environmental change, and it is of great concern to scientists and policy-makers in the world. Litter crusts can be of great importance for the restoration and management of desert ecosystems. The formation of litter crusts and its ecological effects on desert surface microhabitats were studied in a wind-water erosion crisscross desert region. It was found that litter crusts, especially the four-year litter crusts, exhibited a better soil storage capacity and temperature regulating ability when compared to the bare land, biocrusts, and two-year litter crusts; the four-year litter crusts significantly increased soil total porosity, soil water storage, and soil organic carbon content, but reduced soil bulk density. Furthermore, species richness, coverage, and plant height of seedlings in litter crusts were significantly greater than those in bare land and biocrusts. Although the bare land had the greatest total number of seedlings, the survival rate of seedlings was lowest there. Our findings revealed that litter crusts had significantly positive effects on soil moisture, soil temperature, soil physicochemical properties, and seedling establishment. The multifunctional ecological effects of litter crusts are more positive than lichenand moss-dominated biocrusts in desert ecosystems
Simulating the potential distribution of Elaeagnus angustifolia L. based on climatic constraints in China
No full textElaeagnus angustifolia L. has considerable ecological value and plays an important role in windbreak and sand fixation, soil and water conservation, vegetation restoration and afforestation in Asia. Understanding the potential distribution and the limiting climatic factors is the first step for sustainable use of this species at regional scale. Here, we simulated the potential distribution of E. angustifolia and evaluated its limiting climatic factors using a maximum entropy model (MaxEnt) and geographical information system (GIS) in China, based on 190 occurrence grid cells and 13 climatic variables in China. The results show that: (1) annual range of temperature (ART), annual mean temperature (AMT), humidity index (HI), and coldness index (CI) are the dominant climatic factors limiting its potential distribution range; (2) low temperature is an important climatic factor that limits both southern and northern distribution boundaries, and high rainfall is another climatically limiting factor for the southern boundary, and (3) the potential distribution areas are mainly located in the warm temperate and middle temperate zone with cold and dry winters, and in the arid and semi-arid regions of China between 30 degrees N and 50 degrees N. The simulating results can improve our understanding of the geographical and ecological characteristics of E. angustifolia, and provide references for the introduction of this species for control and restoration of degraded land in China
Positive responses of belowground C dynamics to nitrogen enrichment in China
No full textDetermining how nitrogen (N) impacts ecosystem carbon (C) cycling is critical to using C sequestration to offset anthropogenic CO2 emissions. The N deposition rate in China is higher than the global average; however, many results of N enrichment experiments in China have not been included in global syntheses. In this study, we assembled a large dataset that comprised 124 published studies concerning N addition experiments, including 570 observations at 127 sites across China, to quantify the responses of belowground C dynamics to N enrichment in terrestrial ecosystems in China by a meta-analysis. The results showed that overall soil organic C, dissolved organic C (DOC) and soil microbial biomass C (MBC) increased by 1.8, 7.4, and 8.8%, respectively (P < 0.05), in response to N enrichment; belowground biomass and litter increased by 14.6 and 24.4%, respectively (P < 0.05); and soil respiration increased by 6.1% (P < 0.05). N enrichment promoted C inputs into the soil mainly by increasing litter and belowground biomass inputs. Additionally, N enrichment increased C output by increasing soil respiration. Land use type and N addition level had different impacts on the soil C pool and on soil respiration. DOC, MBC, and litter exhibited more positive responses to N deposition in cooler and more arid regions than in other regions. The meta-analysis indicated that N enrichment had a positive impact on belowground C cycles in China. Climate played a greater role than did N deposition level in affecting processes of ecosystem C cycling. Moreover, belowground C cycle processes are determined by complicated interactions among land use type, N enrichment, and climate. (c) 2017 Elsevier B.V. All rights reserved
Partial Least Squares Regression for Determining Factors Controlling Winter Wheat Yield
No full textWheat (Triticum aestivum L.) yield is influenced by many independent factors including precipitation, fertilization, soil nutrients, and crop variety. Due to high correlations of these factors, it is difficult to analyze their relative importance on wheat yield. This study quantified the effects of independent factors on wheat yield and identified the most important control factors through a long-term experiment on the Loess Plateau, China. The experiment consisted of 17 treatments, including five different levels of N and P fertilizer. Partial least squares regression (PLSR) was used to evaluate the factors on wheat yield in four variety groups-Qinmai4 (1985-1986), Changwu131 (1987-1996), Changwu134 (1997-2015), and 31-yr planting across the three varieties (1985-2015). Variable importance in projection (VIP) value revealed that N fertilizer had the greatest effect on wheat yield in all four groups (VIP = 1.266-2.313). The second most important factors were climate factors for Qinmai4 (VIP = 1.060), precipitation (February, annual, and fallow season) for Changwu131 (W-1 = 0.335-0.351, VIP = 1.381-1.474), and soil nutrients (total nitrogen [TN], soil organic matter [SOM], and available potassium [AK]) for Changwu134 (W-1 = -0.231-0.514, VIP = 1.084-2.317). When tested across varieties, TN and SOM were the second most important factors for 31-yr planting (W-2 = 0.455 and 0.313; VIP = 1.908 and 1.370, respectively). These results indicate that PLSR can reveal the control factors on wheat yield in the study area and provide a reference tool for analyses in other crops or areas
Regulated Deficit Irrigation Effect of Winter Wheat as Affected by Different Fertilizer Application Treatments
No full textField and pot experiments were conducted to evaluate the effect of fertilizers (no fertilizer (F0), compound fertilizer (F1) and organic fertilizer+compound fertilizer (F2) on wheat under water stress (RD1 (waterdeficit at flowering-milking stage), RD2 (water deficit at returning green-jointing stage) and RD3 (water deficit at returning green-jointing and flowering-milking stage). The control plants (CK) were subjected to 60-75% field water capacity (FWC) in the whole growing stage. The results showed that different fertilizer treatments had different effects on winter wheat with RDI treatments. At flowering stage, RD2 and RD3 lowered significantly population quantity, leaf area, plant height and dry weight per shoot of winter wheat in both F0 and F1 treatments. In F2 treatment, RD2 and RD3 lowered significantly plant height and leaf area and but had no significant effects on population quantity and dry weight per shoot of winter wheat. At jointing stage, RD2 and RD3 lowered significantly water use efficiency of leaf level (WUEleaf) in F0 treatment, but increased WUEleaf of winter wheat in F1 and F2 treatments. At flowering stage, RD2 had no effect on photosynthetic rate (P-N), transpiration rate (Tr) and WUEleaf of winter wheat. RD3 lowered significantly P-N and Tr of wheat, but had no effect on WUEleaf in F0 treatment. In F1 treatment, RD2 and RD3 had similar P-N, Tr and WUEleaf with CK. In F2 treatment, RD2 increased significantly P-N, but had no effect on WUEleaf of winter wheat. RD3 had no effect on P-N and but improved WUEleaf by lowering Tr of winter wheat. RD2 lowered grain yield of winter wheat in F0 and F1 treatments, but had no effect on grain yield in F2 treatment. RD3 significantly reduced the grain yield in 3 fertilizer treatments. In addition, grain yield stability (GYS) of winter wheat in F2 treatment was higher than those in F0 and F1 treatments under the same RDI treatment. In conclusion, appropriate RDI and fertilizer treatment can significantly increase WUEleaf and grain yield stability of winter wheat. (C) 2018 Friends Science Publisher
Ecoenzymatic stoichiometry and microbial nutrient limitation in rhizosphere soil in the arid area of the northern Loess Plateau, China
No full textArid ecosystems are characterized as having stressful conditions of low energy and nutrient availability for soil microorganisms and vegetation. The rhizosphere serves as the one of most active microorganism habitats, however, the general understanding of the ecoenzymatic stoichiometry (exoenzymes) and microbial nutrient acquisition in rhizosphere soil is limited. Here, we investigated the vegetation communities and determined the soil physicochemical properties, microbial biomass, and enzymatic activities in rhizosphere under different vegetation and soil types in the arid area of the northern Loess Plateau. Type II standard major axis (SMA) regression analysis showed that the plants played a more important role than soil properties in determining ecoenzymatic stoichiometry. Linear regression analysis displayed a microbial stoichiometric homeostasis (community-level) in rhizosphere. The Threshold Elemental Ratio (TER) revealed that the microbial nutrient metabolisms of rhizosphere were co-limited by N and P in the A. ordosica and A. cristatum communities of loess, and A. cristatum communities of feldspathic sandstone weathered soil. Binding spatial ordination analysis (RDA and CCA) demonstrated that soil physical properties (e.g., soil moisture, silt and clay contents) have more contribution to ecoenzymatic stoichiometry than the other investigated soil parameters, whereas soil nutrients (e.g., total organic carbon, nitrogen, and phosphorus) predominantly controlled microbial nutrient ratios. Therefore, the ecoenzymatic stoichiometry in rhizosphere is greatly regulated by plants and soil physical properties. The microbial N and P are co-limited under Gramineae plant in loess and feldspathic sandstone weathered soil regions. Meanwhile, the microbial nutrient limitation is mainly affected by soil nutrient supply. These findings could be crucial for illuminating rhizosphere microbial metabolism and revealing the nutrient cycling of root-soil interface under arid and oligotrophic ecosystems
Evaluation of shear stress and unit stream power to determine the sediment transport capacity of loess materials on different slopes
No full textThis study aims to evaluate the relationship between loess soil-based sediment transport capacity and the most well-known and extensively used shear stress and unit stream power for different steep slopes. This study also determined the suitability of shear stress- and unit stream power-based transport capacity functions for rill flow on non-erodible bed. Loess soil was collected from Ansai County, which is located in a typical loessial region in China's Loess Plateau. The median diameter of the loess soil was 0.04 mm. The experiment was conducted in a rill flume with a soil-feeding hopper. The slope gradients in this study ranged from 10.51 to 38.39%, and the flow discharges per unit width varied from 1.11 x 10(-3) to 3.78 x 10(-3) m(2) s(-1). The sediment transport capacity was measured for each combination. Results showed that T-c can be effectively described by the power function shear stress-based equations for various slope gradients with R (2) > 0.94 and P 0.95 and P < 0.01. Unit stream power was a good predictor of T-c for different slope gradients with NSE that ranged from 0.95 to 0.99. The unit stream power predicted T-c better when the slope gradient was above 26.79%. Unit stream power was more satisfied than shear stress for predicting T-c under different slope gradients. The unit stream power-based LISEM, which was multiplied by 0.62 (i.e., the correction coefficient), predicted well the sediment transport capacity of the rill flow in our experiment, where NSE = 0.93. The shear stress-based Zhang model, which was multiplied by the correction coefficient of 0.77, adequately predicted the sediment transport capacity of rill flow in our experiment, where NSE = 0.81. By performing the controlled rill flume experiments, this study showed that shear stress and unit stream power strongly influenced T-c for certain slope gradients under non-erodible conditions
Feldspathic sandstone addition and its impact on hydraulic properties of sandy soil
No full textFeldspathic sandstone could be used as an effective conditioner to improve the physical quality of sandy soil, and increase the crop yield there. To determine the effects of feldspathic sandstone content on soil hydraulic properties in a sandy soil, the present study added 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% (no sandy soil) of feldspathic sandstone to sandy soil. Changes in hydraulic parameters were investigated and the results showed addition of feldspathic sandstone increased saturated water content by 37%–61% and field capacity by 29%–44%, and decreased saturated hydraulic conductivity from 10.19 to 0.58 cm h−1 of the sandy soil. Further data analysis demonstrated that with increasing content of feldspathic sandstone, the parameter n of soil water retention curve in Van Genuchten model dropped from 1.807 to 1.333. The same decreasing trend is detected in parameter a of infiltration rate (3.841–0.703) in Kostiakov formula (i = at−b) and parameter a1 of wetting front (6.901–1.174) in the empirical equation (X = a1tb1). In terms of hydraulic parameters, 40% feldspathic sandstone and 60% sandy soil, optimally matching indices of loess soil, were the best mixing ratio for sandy land restoration.</p
