Changes in soil total nitrogen (N) content would affect wetland function and the global N cycle. Determination of spatial heterogeneity controlling factors of wetland soil total N content per unit mass is essential to assess responses of ecosystem N cycle to global change. However, such information is limited in permafrost zones because few soil profiles have been acquired and methods to predict spatial distributions of wetland soil total N content in large areas are inefficient, which increase uncertainty in evaluations of N cycle at national or global scales. To determine the spatial heterogeneity of wetland soil total N content at different soil depths and frozen zones and the factors controlling wetland soil total N content in the frozen zones of Northeast China, the spatial pattern of wetland soil total N content was investigated by using a random forest method that combined field samples with environmental factors. Vertically, wetland soil total N content decreased with increasing soil depth, with the highest content in the top soil layer (0–30 cm). Spatially, wetland soil total N content decreased from northwest to southeast, with relatively high total N content in a continuous permafrost zone and relatively low total N content in a seasonally frozen zone. The overall coefficient of variation of wetland soil total N content in the frozen zones of Northeast was 29.58 %, indicating moderate variation. Land surface temperature, mean annual temperature, and mean annual humidity significantly affected total N content in 0–30 and 30–60 cm soil layers, suggesting that variations in temperature and humidity altered sequestration processes of wetland soil total N content. In the 60–100 cm soil layer, compared with other environmental factors, mean annual humidity, altitude, and mean annual precipitation had the greatest influence on the spatial distribution of wetland soil total N content. The study unravels the spatial pattern of soil total N content in frozen zones of Northeast China and reflects the direct and indirect effects of environmental factors on total N content. This provides a basis for the management and protection of wetland ecosystems.

中文翻译：

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冻土区温度与湿地土壤全氮含量空间异质性的关系


土壤全氮（N）含量的变化会影响湿地功能和全球氮循环。确定单位质量湿地土壤全氮含量的空间异质性控制因素对于评估生态系统氮循环对全球变化的响应至关重要。然而，在多年冻土区，此类信息有限，因为获得的土壤剖面很少，而且预测大面积湿地土壤全氮含量空间分布的方法效率低下，这增加了国家或全球尺度氮循环评估的不确定性。为明确不同土层、不同冻土带湿地土壤全氮含量的空间异质性及控制东北冻土带湿地土壤全氮含量的因素，采用随机抽样方法研究了湿地土壤全氮含量的空间格局。森林法将现场样本与环境因素相结合。垂直方向上，湿地土壤全氮含量随着土层深度的增加而降低，其中表层土层（0~30 cm）含量最高。空间上，湿地土壤全氮含量由西北向东南递减，连续多年冻土区全氮含量相对较高，季节性冻土区全氮含量相对较低。东北冻土区湿地土壤全氮含量总体变异系数为29.58%，呈中等变异。地表温度、年平均温度和年平均湿度显着影响0-30和30-60 cm土层的全氮含量，表明温度和湿度的变化改变了湿地土壤全氮含量的固存过程。 在60~100 cm土层中，与其他环境因子相比，年平均湿度、海拔高度和年平均降水量对湿地土壤全氮含量的空间分布影响最大。该研究揭示了东北冻土区土壤全氮含量的空间格局，反映了环境因素对全氮含量的直接和间接影响。这为湿地生态系统的管理和保护提供了依据。