中国科学院水利部水土保持研究所机构知识库

  随着暴雨和干旱等极端天气事件的增加，生态系统水分循环过程和强度发生显著变化，导致多数陆地生态系统，特别是农业生态系统中出现密集而频繁的干湿交替现象。土壤表层剧烈的干湿交替会在短时间内对土壤物理化学性质产生重要影响，从而改变土壤氮素矿化过程和有效性，对植物生长产生影响。本研究围绕土壤干湿交替对氮素净矿化和有效性的影响及其与土壤质地等性质的关系开展研究，以全国26个不同地点农田土壤样品为对象，通过设置恒定水分处理以及不同强度的干湿交替处理进行室内培养试验，以确定恒定水分与干湿交替条件下土壤氮矿化量与速率变化规律，明确土壤理化性质对土壤氮素矿化的影响，并利用氮素矿化一阶动力学模型，分析氮矿化速率与土壤水分的定量关系，确定参数与土壤理化性质的关系。取得的主要结论如下：

  （1）在恒定水分条件下，采样地点、培养周期与水分处理显著影响土壤氮素矿化以及矿化速率（P<0.05），并且培养周期与水分处理之间具有显著的交互作用（P<0.05）。在培养周期内，土壤累积净氮矿化量和土壤净氮矿化速率与土壤水分含量呈显著正相关关系。土壤累积净氮矿化量随时间的延长而呈现指数增加，符合一阶动力学模型拟合，并且水分含量越高增长越快。土壤水分含量与一阶动力学模型参数k值（氮矿化速率常数）显著正相关。粘粒含量与一阶动力学模型参数N₀（氮矿化势）显著负相关，砂粒含量与N₀显著正相关，土壤有机碳含量、全氮含量、pH和C/N与k呈显著正相关关系，初始铵态氮、硝态氮和矿质氮含量与k呈显著负相关关系。二元一次复合模型可以拟合土壤累积净氮矿化量对培养周期和土壤水分含量的响应关系。土壤净矿化量与净硝化量和净氨化量显著正相关。土壤净氨化量随初始铵态氮和矿质氮含量的增加而降低。净硝化量随初始硝态氮和矿质氮含量的增加而降低，随土壤有机质、全氮含量和C/N增加而增加。净矿化量随初始铵态氮、硝态氮和矿质氮含量的增加而降低，随土壤有机质、全氮含量和C/N增加而增加。

  （2）在干湿交替处理条件下，干湿交替次数与强度的增加显著增加土壤氮矿化以及矿化速率（P<0.01），并且对净硝化速率和矿化速率具有显著交互影响（P<0.05）。土壤累积净氮矿化量随时间的延长而呈现指数增加，符合一阶动力学模型拟合，并且100-20% FC干湿交替处理氮矿化高于60-0% FC处理。土壤有机碳和全氮含量与一阶动力学模型参数N₀呈显著正相关关系。土壤净矿化量与净硝化量成显著正相关，而与净氨化量关系不显著。土壤净氨化量随土壤粘粒含量和C/N的增加而增加，随土壤pH值、砂粒和初始铵态氮、硝态氮和矿质氮含量的增加而降低。净硝化量随粘粒含量的增加而降低，随pH、土壤砂粒、有机质、全氮、初始硝态氮和矿质氮含量增加而增加。净矿化量随粘粒含量的增加而降低，随土壤有机质、全氮、初始硝态氮和矿质氮含量增加而增加。

  （3）培养时间显著影响土壤氮素矿化对干湿交替的响应（P<0.05）。相比于恒定水分处理，干湿交替处理在时空尺度上增加土壤累积净氮矿化量和净氮矿化速率。在100-20% FC干湿交替处理条件下，NH₄⁺差异随着土壤pH值的增加而降低，NO₃^-差异随pH、土壤有机质和全氮含量增加而增加，总矿质氮差异随土壤全氮含量增加而增加；而60-0% FC干湿交替处理条件下，NH₄⁺差异随粘粒含量的增加而增加，随土壤pH值、砂粒和初始硝态氮含量的增加而降低。NO₃^-差异随土壤pH值、砂粒、初始硝态氮和矿质氮含量的增加而增加，随粘粒含量的增加而降低。总矿质氮差异随土壤pH值、砂粒、初始硝态氮和矿质氮含量的增加而增加，随粘粒含量的增加而降低。100-20% FC干湿交替处理土壤氮素矿化差异对土壤性质依赖性小于60-0% FC处理。

    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 the 100-20% 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.