Livestock grazing and atmospheric nitrogen (N) deposition have been reported as important factors affecting soil communities. However, how different large herbivore grazing and N addition may interact to affect soil biota in grassland ecosystems is unclear. Nematodes are the most abundant metazoan in soil ecosystems, play critical roles in regulating carbon and nutrient dynamics, and are valuable bioindicators. We examined the independent and interactive effects of grazing regimes (no grazing; sheep grazing; cattle grazing; mixed grazing of sheep and cattle) and N addition (ambient N; N addition) on soil nematodes in a meadow steppe. We found that grazing and N addition interacted to influence total nematode abundance, trophic group abundance, generic richness, diversity and several nematode-based indices (maturity index, channel ratio, enrichment index). In cattle grazing treatment, N addition significantly increased total nematode abundance, and the abundance of bacterial feeders, plant feeders, and omnivore-predators, and generic richness. By contrast, in the sheep and mixed grazing treatments, N addition had a negative effect on the same variables. Moreover, N addition reduced nematode maturity, enrichment and structure indices, and enhanced nematode channel ratio, in most grazing treatments, except mixed grazing where N addition had no effect on these variables. Structural equation modeling (SEM) revealed that N addition indirectly reduced nematode abundance and richness through increased soil NO₃⁻-N content, whereas the effects of grazing were associated with increased relative biomass of grasses. Our results suggested that the response of soil nematodes to N addition strongly depended on herbivore assemblages. Nitrogen addition enhanced soil nematode diversity and maintained a relatively complex and mature soil food web in the presence of cattle rather than sheep grazing. Furthermore, our study highlighted that under N deposition, cattle grazing could benefit the soil nematode community.

据报道，牲畜放牧和大气氮 (N) 沉积是影响土壤群落的重要因素。然而，不同的大型食草动物放牧和氮添加可能如何相互作用影响草地生态系统中的土壤生物群尚不清楚。线虫是土壤生态系统中最丰富的后生动物，在调节碳和养分动态方面发挥着关键作用，是有价值的生物指标。我们研究了放牧制度（不放牧；绵羊放牧；牛放牧；绵羊和牛混合放牧）和 N 添加（环境 N；N 添加）对草甸草原土壤线虫的独立和交互影响。我们发现放牧和氮添加相互作用影响线虫总丰度、营养群丰度、一般丰富度、多样性和几个基于线虫的指数（成熟度指数、通道比、浓缩指数）。在牛放牧处理中，添加 N 显着增加了线虫总丰度，以及细菌饲养者、植物饲养者和杂食性捕食者的丰度以及一般丰富度。相比之下，在绵羊和混合放牧处理中，氮添加对相同变量具有负面影响。此外，在大多数放牧处理中，除氮添加对这些变量没有影响的混合放牧外，N 添加降低了线虫成熟度、富集和结构指数，并提高了线虫通道比率。结构方程模型 (SEM) 表明，N 添加通过增加土壤 NO 间接降低了线虫的丰度和丰富度 和一般的丰富性。相比之下，在绵羊和混合放牧处理中，氮添加对相同变量具有负面影响。此外，在大多数放牧处理中，除氮添加对这些变量没有影响的混合放牧外，N 添加降低了线虫成熟度、富集和结构指数，并提高了线虫通道比率。结构方程模型 (SEM) 表明，N 添加通过增加土壤 NO 间接降低了线虫的丰度和丰富度 和一般的丰富性。相比之下，在绵羊和混合放牧处理中，氮添加对相同变量具有负面影响。此外，在大多数放牧处理中，除氮添加对这些变量没有影响的混合放牧外，N 添加降低了线虫成熟度、富集和结构指数，并提高了线虫通道比率。结构方程模型 (SEM) 表明，N 添加通过增加土壤 NO 间接降低了线虫的丰度和丰富度₃ ^- -N 含量，而放牧的影响与草的相对生物量增加有关。我们的结果表明土壤线虫对 N 添加的反应强烈依赖于食草动物组合。添加氮增强了土壤线虫的多样性，并在有牛而不是羊放牧的情况下维持了相对复杂和成熟的土壤食物网。此外，我们的研究强调，在氮沉积下，放牧可以使土壤线虫群落受益。