Global climate change has resulted in precipitation regimes exhibiting an increasing trend in rainfall intensity but a reduction in its frequency. Nitrogen (N) deposition is a crucial component of the global N cycling. Nematode body size is a trait that responds to climate change and is used as a standard trait-based indicator in soil community analysis. Variations in body size influence metabolic carbon (C). We examined the ways by which body size and metabolic C of nematodes respond to changing precipitation regimes and how N deposition regulates these responses by an 8-year manipulative experiment. Nematode body size was indicated by the community-weighted mean (CWM) mass. We quantified C metabolism components of soil nematodes including production C, respiration C, and corresponding C use efficiency (CUE) under different precipitation intensities and N addition in a semi-arid steppe on the Mongolian Plateau. The Mantel test was used to determine the correlations between CWM, CUE and environmental factors. The partial least squares path modeling (PLS-PM) was conducted to quantify direct or indirect contributions among latent variables. We found that heavy precipitation intensity increased the CWM mass of total nematodes and omnivores-predators without N addition. N addition decreased CWM mass of bacterivores across all the precipitation intensity treatments. Stronger precipitation intensities might be favorable for nematode production and respiration C. Variations in the nematode CWM mass drove the CUE to change with N addition. Our findings provide new insights into the mechanisms underlying nematode body size and C metabolism, and highlight that explorative studies, such as manipulative experiments, are needed to identify traits underlying size-related effects and to investigate how they affect CUE of nematodes. These efforts may increase our understanding of how changes in precipitation regimes and N deposition may alter soil nematode communities in grassland ecosystems.

中文翻译：

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温带草原氮沉降和降水格局变化下体型引起的土壤线虫代谢碳变化

全球气候变化导致降水状况呈现出降雨强度增加但频率减少的趋势。氮（N）沉降是全球氮循环的重要组成部分。线虫体型是一种响应气候变化的性状，被用作土壤群落分析中基于标准性状的指标。体型的变化会影响代谢碳 (C)。我们通过为期 8 年的操纵实验研究了线虫的体型和代谢碳对降水模式变化的反应方式，以及氮沉降如何调节这些反应。线虫体大小由群落加权平均（CWM）质量表示。我们量化了蒙古高原半干旱草原不同降水强度和施氮量下土壤线虫的碳代谢组成，包括生产碳、呼吸碳和相应的碳利用效率（CUE）。 Mantel检验用于确定CWM、CUE和环境因素之间的相关性。进行偏最小二乘路径建模（PLS-PM）来量化潜在变量之间的直接或间接贡献。我们发现，在不添加氮的情况下，强降水强度会增加线虫和杂食性捕食者的 CWM 质量。添加氮降低了所有降水强度处理中食菌动物的 CWM 质量。较强的降水强度可能有利于线虫的生产和呼吸 C。线虫 CWM 质量的变化驱动 CUE 随着氮的添加而变化。我们的研究结果为线虫体大小和碳代谢的机制提供了新的见解，并强调需要进行探索性研究，例如操作实验，以确定与大小相关的影响的特征，并研究它们如何影响线虫的 CUE。这些努力可能会增加我们对降水状况和氮沉降的变化如何改变草原生态系统中土壤线虫群落的理解。