Symbiotic relationships with microbes may influence how plants respond to environmental change. Here, we investigated how fungal endophyte infection affected the growth of a native grass under altered water and nutrient availability. In a two-month field experiment, we compared the performance of endophyte-infected (EI) and endophyte-free (EF) Achnatherum sibiricum subjected to four treatments comprised of a factorial combination of two levels of water availability and two levels of fertilization. The greatest benefits of endophyte infection occurred in the well-watered fertilized treatment. With reduced water and/or nutrient availability, the benefits declined. EI plants subjected to drought and fertilization had higher root:shoot ratios and allocated more nitrogen to photosynthetic machinery and thus had a higher net photosynthetic rate than EF counterparts. In the wellwatered unfertilized treatment, EF plants allocated more nutrients to photosynthetic machinery, while EI plants allocated more resources to defense. Thus EI plants were superior to EF plants in terms of nutrient conservation. In the drought unfertilized treatment, no significant difference occurred between EI and EF plants. Our results support the idea that the endophytegrass interactions are dependent on available resources. However, we did not find a clear cost of endophyte infection. For A. sibiricum, fertilizer addition resulted in greater benefits of the symbiosis for plant growth, but this advantage decreased under drought.

In nature, grasses simultaneously establish multiple symbiotic associations with endophytic fungi and arbuscular mycorrhizal fungi (AMF). The effect of these multiple interactions on competitive interactions between plants remains poorly understood. In this study, we tested whether endophytes and AMF (Glomus mosseae or Glomus etunicatum) alter plant competition between a subordinate plant species that associates with both symbionts (Achnatherum sibiricum) and a dominant plant species, Stipa grandis, that only associates with one symbiont (AMF). And we hypothesized that endophytes can facilitate the coexistence of the subordinate plant species (A. sibiricum) and the dominant plant species (S. grandis). The results demonstrated that endophyte infection significantly enhanced the competitive ability of the subordinate plant species compared to the dominant plant species. The effects of AMF on plant competition were variable and depended on the identity of the AMF species. Glomus etunicatum gave A. sibiricum plants a higher competitive ability, while G. mosseae gave S. grandis a higher competitive ability. Simultaneous infections of both endophytes and AMF in A. sibiricum also altered the competitive relationships with S. grandis. In conclusion, these results suggest that endophytic fungi can facilitate the coexistence of a subordinate plant species with a dominant plant species. Moreover, endophytes could not only affect the competitive ability of the host plant directly but also indirectly by interacting with different AMF to change the growth of competing plant species. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13084/suppinfo is available for this article.

Trade-off between vegetative growth and reproduction is an important plant adaptive strategy to environmental variability. The study investigated the Stipa grandis resource allocation and the relationship between its sexual reproduction and climate factors among three sites located along a typical environmental gradient in the Inner Mongolian Plateau. The results show that different climatic characteristics among three habitats cause the growth differentiation of S. grandis. S. grandis exhibits a prominent change on the resource allocation patterns. The number of reproductive tillers and panicles biomass allocation are significantly increased along the gradient of water availability and temperature whereas the number of vegetative tillers and root biomass allocation are reduced. The rate of the percentage increase is prominently reduced although the foliage allocation increased. It suggests that under the environments with drought and high temperature, S. grandis allocates more resources to sexual reproduction but reduces the investment in vegetative growth and asexual reproduction. Moreover, the amount of precipitation in April and May are significantly correlated with the sexual reproductive allocation of S. grandis.