Abstract Nematodes are a crucial component of the soil food web, and play a key role in maintaining biodiversity and regulating soil nutrient cycling. Many studies have been done on the effects of N addition on the soil biota, but the effects of N addition on nematodes in plant litter versus in soil are not well understood, especially in semi-arid steppe ecosystems. Here we investigated the composition of nematode communities in plant litter versus in surface soil in two climatically contrasting years in a simulated N enrichment experiment with four N levels (0, 25, 50 and 100 kg N ha−1 yr−1) in a temperate semi-arid grassland. We found that nematodes in plant litter were more sensitive to N addition than that in surface soil, that is, the abundance and generic richness of nematodes in plant litter, but not in surface soil, manifest a significant difference among N addition rates at both community and guild levels. The abundance and generic richness of nematodes were significantly higher in 2015 (a year with relatively wet weather) than 2016 (a year with relatively dry weather) in soil, but the opposite was true on the abundance of nematodes in litter. The plant parasites and omnivores-predators were more abundant, whereas the bacterivores and fungivores were less abundant, in 2015 than 2016. Our results also indicate that litter C/N ratio and soil moisture have greater impact than litter biomass and plant species richness on the abundance of nematodes in litter layer, while soil moisture and resource availability have greater impact than soil N availability and pH on the abundance of nematodes in the top soil. These results provide new insights into the dynamics of nematode communities, and suggest that the litter layer is very important to maintain a stable nematode community in the steppe ecosystem under the fluctuating climate.

中文翻译：

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半干旱草地植物凋落物与表土层线虫对氮添加的不同反应

摘要 线虫是土壤食物网的重要组成部分，在维持生物多样性和调节土壤养分循环方面发挥着关键作用。已经对 N 添加对土壤生物群的影响进行了许多研究，但 N 添加对植物凋落物与土壤中线虫的影响尚不清楚，尤其是在半干旱草原生态系统中。在这里，我们在温带四种 N 水平（0、25、50 和 100 kg N ha−1 yr−1）的模拟 N 富集实验中，研究了植物凋落物与表层土壤中线虫群落的组成。半干旱草原。我们发现植物凋落物中的线虫比表层土壤中的线虫对 N 添加更敏感，即植物凋落物中线虫的丰度和一般丰富度，而不是表层土壤中的线虫，表明社区和公会级别的 N 添加率之间存在显着差异。土壤中线虫的丰度和一般丰度在 2015 年（天气相对潮湿的年份）显着高于 2016 年（天气相对干燥的年份），但凋落物中线虫的丰度则相反。与 2016 年相比，2015 年植物寄生虫和杂食性捕食者数量较多，而食菌动物和食真菌动物较少。凋落物层中线虫的丰度，而土壤水分和资源可用性对表层土壤中线虫丰度的影响大于土壤 N 可用性和 pH 值。