土壤线虫作为土壤食物网的重要组分，通过取食植物根系和加快物质循环等生态过程影响着植物的生长发育和群落动态。土壤线虫群落的组成和功能也会因植物群落物种组成和多样性的改变而变化。植物和土壤线虫群落紧密联系且相互作用，共同维持着陆地生态系统的物种多样性和功能。然而, 这种相互作用如何受到气候变化、养分输入和其他生物干扰的影响还不清楚。
青藏高原是对全球变化响应最敏感的区域之一，其生态系统脆弱，易受气候和环境变化的影响。已有研究表明青藏高原高寒草甸土壤线虫数量丰富、种类繁多，在凋落物分解、养分矿化及生物地球化学循环过程中发挥重要作用。氮素和温度是影响高寒草甸土壤线虫群落重要的环境因子，而病原真菌不仅是影响植物群落的重要生物因子，也会激发植物启动防御机制，进而对土壤线虫群落产生间接影响。
本研究利用在青藏高原东缘高寒草甸设置的多因子（包括氮添加（+12 g N m-2 yr-1）、增温（+~1.5℃）和施加叶面病原真菌抑制剂（阿西米达））试验，调查了土壤线虫群落对上述因子及其交互作用的响应，揭示了土壤线虫与植物群落、微生物性质和土壤理化性质的联系。并结合盆栽试验，探究高寒草甸不同植物物种和功能群对土壤线虫和微生物的响应。主要研究结果如下：
1. 病原真菌抑制剂、氮添加和增温没有改变土壤线虫群落的总丰度。与对照相比，在施用病原真菌抑制剂和氮添加处理下，食细菌线虫的相对丰度分别增加了7.5%和7.9%，且施用病原真菌抑制剂时植食线虫的相对丰度减少了22.3%。
2. 病原真菌抑制剂的施用不仅显著增加了土壤线虫群落的物种多样性（p = 0.01），同时改变了土壤线虫群落结构。病原真菌抑制剂的施用会削弱氮添加对土壤线虫群落物种多样性的促进作用。增温会削弱施用病原真菌抑制剂和氮添加对各营养类群水平和土壤线虫群落物种多样性的效应。氮添加促使土壤食物网向依赖细菌的快速分解途径（线虫通道指数 = 0.45）靠近，加速土壤养分矿化。
3. 土壤微生物对禾类草和杂类草的生长有抑制作用，对菊科植物生长无显著影响；而土壤线虫能够促进菊科植物生长，但对禾类草和杂类草的生长无显著影响。土壤线虫群落中食细菌线虫的占比越高，越有利于植物生长。叶片干物质含量低（资源获取型）的植物物种在生长过程中更容易受到土壤线虫群落的积极影响。
       综上，土壤线虫群落对氮添加和病原真菌的响应更大，而对温度变化并不敏感。三个处理因子之间存在显著的交互作用，多数情况下增温会削弱病原真菌抑制剂和氮添加的效应。本研究还发现在高寒草甸生态系统中，不同植物物种对土壤生物的响应存在差异，其中禾类草和杂类草的生长易受到土壤微生物的抑制作用，而菊科植物的生长更易受到土壤线虫的促进作用。本研究为预测未来全球变化下青藏高原高寒草甸土壤线虫群落的动态变化和对植物群落构建的反馈，以及草地生态系统的适应性管理提供理论依据。

    As an important component in the soil food network, soil nematodes affect plant growth and community dynamics through feeding on plant roots and accelerating ecological processes, such as nutrient and carbon cycling. The composition and function of soil nematodes communities also change with varying plant diversity and community composition. Plant and soil nematode communities are closely linked and interact with each other, playing a critical role in maintaining species diversity and the functions of terrestrial ecosystems. However, how the interactions between plants and nematodes will be affected by climate changes, nutrients input and other disturbances remains unclear. 
The Tibetan Plateau is one of the most sensitive and fragile regions in response to global change. Studies have found that the soil nematodes are abundant in number and variety in the alpine meadows of the Tibetan Plateau, and play an important role in regulating litter decomposition, nutrient mineralization and biogeochemical cycling. While nutrient and temperature represent important environmental factors affecting the soil nematode community, pathogenic fungi are important biological factors driving changes in nematode community via altering plant community and stimulating plant to defend themselves. However, few studies have focused on the effects of foliar pathogenic fungi, nutrients and temperature simultaneously, and it is unclear whether the changes in soil nematode community will in turn affect plant performance and community structure and functioning.
     We conducted a filed experiment to examine the effects of fungicides application (Amistar), nitrogen addition (+12 g N m-2 y-1) and warming (OTCs, +~1.5℃) on soil nematodes in an alpine meadow ecosystem in the Tibetan plateau. The relationships between soil nematode and plant community, microbial properties and soil properties were examined. Combined with a potting experiment, we also explored the responses of different plant species or functional groups to soil nematodes and microorganisms. The main results are as follows：
1. Fungicide application, nitrogen addition and warming did not alter the abundance of soil nematode community. Compared with the control, the relative abundance of bacterivores increased by 7.5% and 7.9% under fungicide application and nitrogen addition, respectively. The relative abundance of herbivores decreased by 22.3% under fungicide application.
2. Fungicide application significantly increased species diversity of soil nematode community (p = 0.01), and changed the soil nematode community structure. Fungicide application weakened the nitrogen effects on the species diversity of soil nematode community. Warming weakened the interactive effects of fungicide application and nitrogen addition on trophic group and species diversity of soil nematode community. Under nitrogen addition, the soil food web moved closer to the rapid decomposition pathway which relies on bacteria (nematode channel index = 0.45), accelerating the mineralization of soil nutrients.
3. Soil microorganisms had significant negative effects on grasses and forbs, but had no effect on the growth of Compositae plants. While promoting the growth of Compositae plants, soil nematodes showed no effect on the growth of grasses and forbs. Moreover, the higher proportion of bacterivores is favorable for plant growth. We also found that soil nematode community can promote the growth of species with low leaf dry matter content (i.e., resource-acquisitive).
     In summary, nitrogen addition and pathogenic fungi had greater disturbance to soil nematode community, whereas soil nematodes were not sensitive to changes in temperature. There was a significant interaction among the three treatment factors. In most cases, warming weakened the interactive effects of fungicide and nitrogen treatments. This study also showed that plant species responded differently to soil organisms. Soil microorganisms had inhibitory effects on the growth of grasses and forbs, and soil nematodes could promote the growth of plants in the Compositae plants. This study provides the theoretical basis for predicting the dynamic changes of soil nematode community and their feedback to plant community assembly in Tibetan alpine ecosystems and is of important implications for grassland management under future global change.

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