Effects Of Drying-wetting Cycles And Additional Nitrogen Source On Soil Carbon And Nitrogen Transformation And Microbial Diversity

Frequent drought and extreme rainfall events cause soil to undergo frequently drying-wetting cycles under the context of climate change,which altering the water,carbon and nitrogen cycles of the ecosystem,while the mechanism of the influence of drying-wetting cycles on soil carbon and nitrogen cycling is unclear.Therefore,the sandy and clay loam in the fluvo-aquic soil region in the Huang-Huai-Hai Plain was selected in this study,the effects of drying-wetting cycles?drying-wetting frequency:0,2,6 and 12 cycles?and additional nitrogen source(the total amount of nitrogen application was 0,110 and 220 mg-N·100 g^-1·dry soil)on soil carbon and nitrogen mineralization and soil microbial diversity were investigated under laboratory controlled conditions.The results will be useful in providing theoretical and data supports on maintaining soil carbon and nitrogen balance and optimizing irrigation and fertilizer management.The main results were as follows:?1?The drying-wetting cycles and additional nitrogen source significantly increased the CO₂ and N₂O release rate from the sandy and clay loam.There was similar response pattern of soil CO₂ and N₂O release rate to the drying-wetting cycle between the two soils.The longer the drying period,the stronger the excitation effect of additional nitrogen source on soil CO₂ release rate,whereas the shorter the drying period,the stronger the excitation effect of additional nitrogen source on soil N₂O release rate.?2?The drying-wetting cycles and additional nitrogen source significantly increased the organic carbon mineralization rate.In the rewetting and humidity stage,the DOC and TOC content of soil under the three nitrogen concentration levels showed a trend of N2>N1>N0,indicating a long-term effect of additional nitrogen source on the organic carbon mineralization.The subsequent effects of drying-wetting cycles on soil carbon mineralization were different between sandy loam and clay loam.?3?Under the condition of drying-wetting cycles,additional nitrogen source significantly increased the inorganic nitrogen?NO₃^--N and NH₄⁺-N?content in the sandy and clay loam soil,The net mineralized nitrogen accumulation increased gradually with the increase in the frequency of drying-wetting cycles,and with the increase of nitrogen application amount,and the nitrogen mineralization rate of the sandy loam presented more intense response to the drying-wetting cycles and additional nitrogen source compared with the clay loam.In the rewetting and humidity stage,the total nitrogen?TN?and NO₃^--N content of each treatment decreased to some extent;the decrease of TN content in the sandy loam was more than that in the clay loam.The correlation analysis indicated that the CO₂ release rate of sandy loam and clay loam was significantly positively correlated with the N₂O release rate and soil NH₄⁺-N content.The N₂O release rate in sandy loam and clay loam was positively correlated with the NH₄⁺-N and NO₃^--N content.?4?The drying-wetting cycles and additional nitrogen source significantly increased the urease,sucrase and cellulase activity in the sandy loam and clay loam.The catalase activity in the constant moisture treatment showed a decreasing trend.The higher the drying-wetting frequency and nitrogen concentration,the higher the catalase activity.The phosphatase activity presented a slow upward trend in sandy loam and clay loam,and increased with the increase of nitrogen concentration.In the rewetting and humidity stage,the activities of urease,sucrase,cellulase and catalase in all treatments decreased slowly,and the higher the frequency of drying-wetting cycles.The ureases activity was positively related to the CO₂ release rate,NH₄⁺-N,DOC and NO₃^--N content.The ureases activity was significantly and positively correlated with the N₂O release rate.Both the cellulose activity and sucrase activity was significantly correlated with the CO₂ release rate,DOC content.?5?The drying-wetting cycles and additional nitrogen source increased the soil microorganisms index of Shannon and Richness.The maximum Evenness index was measured in the constant moisture treatment in both sandy loam and clay loam.There was significant difference in soil microbial community structure between the constant moisture treatment and drying-wetting cycles.The higher the frequency of drying-wetting cycles in sandy loam,the more significant the correlation between the microbial functional diversity and the DOC?AP?available phosphorus?and TN content,while the lower the frequency of drying-wetting cycles,the more significant the correlation between the microbial functional diversity and the NO₃^--N,soil moisture content?SMC?and NH₄⁺-N content.The higher the frequency of drying-wetting cycles in clay loam,the more significant the correlation between the microbial functional diversity and the NO₃^--N,DOC and AP content,while the lower the frequency of drying-wetting cycles,the more significant the correlation between the microbial functional diversity and the SMC,NH₄⁺-N and TN content.In the re-wetting and humidity stage,the correlation between 2drying-wetting cycles and AP increased,while the correlation between 6,12 cycle and TN decreased,the correlation between the TN content and the microbial functional diversity in the 6 and 12drying-wetting cycles weakened with the consumption of additional nitrogen source.