植物间相互作用对非生物环境的响应已受到广泛关注，但有关其对生物因子响应方面的研究较少。内生真菌在禾草中广泛存在，其与禾草宿主的互利共生已被大量的研究所证实，那么内生真菌是否能够增强宿主相对于非宿主植物的竞争力呢？目前仅有的报道存在明显的不确定性。我们推测：内生真菌宿主与非宿主之间的相互作用不仅与内生真菌对宿主生长和抗性的直接作用有关，也与内生真菌通过影响宿主植物土壤反馈而对非宿主植物产生的间接作用有关，而且直接和间接作用的强度会随宿主植物本身的竞争力和环境变化发生改变。本研究选取内蒙古中东部草原感染内生真菌的、优势种羊草和伴生种羽茅为宿主植物，群落中不感染内生真菌的其它植物作为非宿主植物，探讨内生真菌对宿主和非宿主植物相互作用的直接和间接影响及其对全球变化的响应。本研究不仅有助于阐明内生真菌在决定宿主与非宿主植物关系方面的关键作用，而且有助于预测内生真菌宿主所在群落的发展和演替方向。

The responses of plant-plant interactions to abiotic factors have been well studied, while their responses to biotic factors remain unclear. Fungal endophytes are widely distributed in grasses, and their mutualism has been demonstrated in many studies. Can endophyte infection improve competitive ability of host over non-host plants? The limited publications are varied in results. We suggest that this variation is at least partly resulted from the following reasons. The interactions between host and non-host plants are not only related to direct contributions of endophytes by improving the growth and resistance of host grasses, but also related to indirect contributions of endophytes by inhibiting the growth of non-host plants through plant soil feedback. Certainly, both direct and indirect contributions of endophytes can be affected by environmental conditions. In this study, both endophyte-infected, dominant species, Leymus chinensis, and endophyte-infected, companion species, Achnatherum sibiricum, in the Inner Mongolia steppe will be chosen as target host species. Endophyte-free, neighboring plants in the community will be chosen as non-host plants. Both direct and indirect effects of endophyte infection on the interactions between host and non-host plants will be studied, and their responses to global change will be investigated. We aim not only to understand the important contributions of endophytes to the interactions between host and non-host plants, but also to predict the development and succession dynamics of endophyte associated grasslands.