| The world has been undergoing a significant climate change with temperature rising as main characteristics. Global average surface temperature has increased by0.74℃in the last100years (i.e.,1906to2005). The global warming caused the rising of sea level, precipitation change, the increased occurrence frequencies of extreme weather events etc. Agricultural production closely depends on the natural conditions, especially climatic conditions (including changes of temperature, precipitation, wind speed and atmospheric [CO2](carbon dioxide concentration), etc.), hence climate change has a great influence on it. Soil water and soil nutrients which are indispensable for crop growth would be affected by climate change. For the sake of determining the influence of the uncertainties of climate change on agriculture production, the hydraulics characteristic and water environmental condition in study area were analyzed, and the T-FACE system platform was built to simulate the meteorological conditions (including elevated [CO2] and temperature) in the coming50years and to study the effects of these conditions on the changes of soil total nitrogen (TN), soil organic carbon, ammonium, nitrate, available phosphorus (P) and soil water content at different wheat growth stages in the Taihu Lake region based on the typical paddy soil-wushan soil. The simulation and prediction of soil water were made with three models and the variation trend of soil water and soil nutrients under the future climate changing scenario were clarified, which provided theoretical reference for the management of irrigation and fertilization.The results were as follows:The bulk density and clay content were the main factors affecting the water characteristics curves. While soil water content in plough layer was relatively higher under a lower water suction, the available water content had a significant negative correlation with bulk density and clay content, and had a significant positive correlation with porosity. The bulk density and total porosity were the main impact factors to the saturate hydraulic conductivity, whereas the other factors such as the capillary porosity and pH took the second place. The total reservoir capacity of wushan soil in plough layer (0-14cm) was91.48mm. The available water reservoir capacity was22.02mm, and the flood detention reservoir capacity was20.50mm. Therefore, this soil was in good water condition, which not only guaranteed the realization of stable and high soil productivity but also had a regulatory function of water storage. The data of the water characteristic curve and soil reservoir capacity in this soil will provide the scientific basis for soil water management under the condition of climate change.Under elevated atmospheric [CO2] and temperature conditions, there were obvious differences in the average water content at the depth of0-14cm among different experimental plots. Soil water content increased in the following order:CT(elevated [CO2] and temperature), T(elevated temperature), C(elevated [CO2]) and CK. There were significant differences in soil water content among0-14cm,14-33cm and33-59cm soil layers, with the soil water content in0-14cm soil layer higher than that in14-33cm and33-59cm soil layers.The soil water content of plough layer in C ring and CK ring was273.62g·kg-1and279.87g·kg-1, respectively, accounting for72.10%and73.75%of water holding capacity in study area, and that in CT ring and T ring was253.98g·kg-1and259.72g·kg-1, being65.93%and67.44%of water holding capacity correspondingly, which showed that elevated temperature could significantly reduce soil water content in plough layer and Elevated [CO2] had a little influence on it.The analysis and comparison of temporal stability of soil water content in three soil layers (0-14cm,14-33cm and33-59cm) showed that the temporal stability of soil water increased with the deepening of soil depth. Three measuring points of temporal stability in three soil layers (0-14cm,14-33cm and33-59cm) were determined using the relative mean difference method, which were appropriate to simulate the changes of average soil water in the corresponding soil layers with the RMSE between observed value and simulated value lower than3.52%.When the simulation of climate change was performed, the contents of ammonium decreased significantly with rising [CO2] during the wheat growth season (from tillering to ripening stage) in2011to2012; Therefore, under the condition of climate change, increasing nitrogen fertilizer to ensure meet the nitrogen absorption. Soil NO3--N content showed no clear variation under different [CO2] and temperature conditions; elevated [CO2] enhanced available P in0-14cm soil layer. With elevated [CO2] and temperature, C/N ratio decreased as follows:O CT>CK>T. The correlation between soil water content and nitrate in C ring was highly significant, and that between soil water and ammonium was significant in C ring. There was a significant correlation between soil water and ammonium under the interaction of elevated [CO2] and temperature (CT). No significant correlation was observed between soil moisture and soil nutrients under elevated [CO2].The three treatments of elevated [CO2], elevated temperature, and their interaction (i.e., C, T and CT ring) all decreased the content of ammonium in plough layer during the wheat growth season (from tillering to ripening stage), but the variation of ammonium in farmland leaching water was not consistent with that of soil in plough layer and in plowpan, indicating that there was no significant influence of elevated [CO2] and temperature on ammonium content in farmland leaching water. Elevated [CO2] and temperature treatments all had no obvious effect on nitrate content either in soil or in farmland leaching water.Sensitivity analyses of soil moisture and meteorological factors based on BP neural network were conducted. Models of Auto Regressive Integrated Moving Average (ARIMA), Back Propagation Artificial Neural Network (BP-ANN), and Least Squares Support Vector Machine (LS-SVM) were used to simulate the soil water in soil layers of0-14cm and14-33cm. The results showed that:there were satisfied results when meteorological factors were taken as input variables, and the simulation accuracy of LS-SVM was the highest.The analysis of soil water and nutrient during the whole wheat growth period shows that increased temperature could offset the positive effect on biomass increment which was caused by increased [CO2] under the climate change. The application amount of nitrogen fertilizer should be increased properly in order to meet the need of crops. The output of LS-SVM model has the best simulation precision. In addition, the N, P transformation mechanism under climate change need further study. |
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