| With the increase of extreme weather events such as heavy rainfall and extreme drought,water cycle process and intensity of the ecosystem changes significantly,leading to intensive and frequent drying-wetting cycles in most terrestrial ecosystems,particularly agricultural ecosystems.The violent drying-wetting cycles in the soil surface have profound effects on soil physical and chemical properties in a short period,thus change the process and effectiveness of soil nitrogen mineralization and have an impact on plant growth.In this study,the effect of soil drying-wetting cycles on the net mineralization and availability of nitrogen and its relationship with soil texture and other properties were studied.A total of 26 farmland soil samples from different locations in China were incubated in the laboratory under the constant soil moisture and different intensities of drying-wetting cycles treatments.The dynamic changes of soil nitrogen mineralization and its rate were determined.The effects of soil physical and chemical properties on soil nitrogen mineralization were clarified.In addition,we used the first-order kinetics model to fit nitrogen mineralization.The quantitative relationship between the nitrogen mineralization rate and soil moisture,and the relationship between the parameters and soil physical and chemical properties were determined.The main conclusions were as follows:(1)Under the constant soil moisture treatments,the sample site,incubation time and soil moisture significantly affected soil nitrogen mineralization and its rate(P<0.05),and incubation time had significant interaction with water(P<0.05).During the incubation time,cumulative net nitrogen mineralization and nitrogen mineralization rate was significantly positively correlated with soil moisture content.Cumulative net nitrogen mineralization increased exponentially with incubation time,which was consistent with the first-order kinetics model fitting,and grew faster when the soil moisture content was higher.There was a significantly positive correlation between soil moisture content and k value(N mineralization rate constant)of the first-order kinetics model.The clay content was significantly negatively correlated with the first-order kinetic model parameter N0(nitrogen mineralization potential),the sand content was significantly positively correlated with N0,the soil organic carbon,total nitrogen concentration,pH and C/N were significantly positively correlated with k,and the initial ammonium,nitrate and mineral nitrogen concentration were significantly negatively correlated with k.The bivariate primary composite model can fit the response of nitrogen mineralization to soil moisture content and incubation time.The net mineralization was significantly positively correlated with the net nitrification and ammonification.The net ammoniation of soil decreased with the increase of initial ammonium and mineral nitrogen concentration.The net nitrification decreased with the increase of initial nitrate and mineral nitrogen concentration,and increased with the soil organic matter,total nitrogen concentration and C/N.The net mineralization decreased with the increase of initial ammonium,nitrate and mineral nitrogen concentration,and increased with the soil organic matter,total nitrogen concentration and C/N.(2)Under drying-wetting cycles treatments,the frequency and intensity of drying-wetting cycles significantly affected soil nitrogen mineralization and its rate(P<0.01),and had a significant interaction effect on soil net nitrification rate and mineralization rate(P<0.05).Cumulative net nitrogen mineralization increased exponentially with incubation time,which was in accordance with the first-order kinetics model fitting.The nitrogen mineralization of 100-20%FC was higher than that of 60-0%FC.There was a significantly positive correlation between soil organic carbon and total nitrogen concentration and the first-order kinetics model parameter N0.The net ammoniation increased with the clay content and C/N,and decreased with the increase of pH,sand content,initial ammonium,nitrate and mineral nitrogen concentration.The net nitrification decreased with the increase of clay content,and increased with the pH,sand content,organic matter,total nitrogen,initial nitrate and mineral nitrogen concentration.The net mineralization decreased with the increase of clay content,and increased with the soil organic matter,total nitrogen,initial nitrate and mineral nitrogen concentration.(3)The effect size of drying-wetting cycles on soil nitrogen mineralization was significantly affected by incubation time(P<0.05).Compared with the constant moisture treatment,drying-wetting cycles increased the cumulative net nitrogen mineralization and nitrogen mineralization rate on the spatial-temporal scale.Under the100-20%FC,the effect size on NH4~+decreased with the increase of soil pH.The effect size on NO3~-increased with the pH,soil organic matter and total nitrogen concentration.The effect size on mineral nitrogen increased with the total nitrogen concentration.While under the 60-0%,the effect size on NH4~+increased with the clay content,and decreased with the increase of soil pH,sand content and initial nitrate concentration.The effect size on NO3~-increased with the soil pH,sand content,initial nitrate and mineral nitrogen concentration,and decreased with the increase of clay content.The effect size on mineral nitrogen increased with the soil pH,sand content,initial nitrate and mineral nitrogen concentration,and decreased with the increase of clay content.The effect size of 100-20%FC on nitrogen mineralization was less dependent on soil properties than that of 60-0% FC. |
