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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 plain language summary is available for this article.

Aims Achnatherum sibiricum plants were infected by fungal endophytes Neotyphodium and Epichloe and high infection rates have been found in our experimental field. Our objective was to determine the effects of Neotyphodium and Epichloe on growth and physiological characteristics in A. sibiricum. Methods In a field experiment, we measured plant growth and physiological characteristics of A. sibiricum with a LI-6400 portable photosynthesis system and determined the contents of carbon (C%) and nitrogen (N%) and other physiological variables in 2011 and 2012. Achnatherum sibiricum plants were successfully infected with Neotyphodium and Epichloe. Important findings Neotyphodium infection had a significant positive effect on both leaf length and plant height in A. sibiricum, whereas Epichloe infection had a significant negative effect on the two variables. Maximum net photosynthetic rate was significantly higher in the endophyte-free plants than in plants infected by Neotyphodium and Epichloe; whilst Neotyphodium infected plants had significantly higher maximum net photosynthetic rate than Epichloe infected plants. Moreover, Neotyphodium infection significantly increased stomatal limitation and water use efficiency (WUE) of the host grass. Epichloe infection had a negative effect on photosynthetic variables except intercellular CO2 concentration in the first year. Neotyphodium infection resulted in greater accumulation of soluble sugars in host plants than Epichloe infection and endophyte-free treatment. The N% in Epichloe infected plant was significantly higher than in Neotyphodium infected plants in both years and in endophyte-free plants in the second year.

Background and Aims The fungal endophytes in grasses grow intercellularly and systemically in aboveground plant tissues. Vertically transmitted asexual endophytes (Neotyphodium) forming asymptomatic infections of cool-season grasses have been repeatedly derived from sexual species (Epichlo) that abort host inflorescences. The phylogenetic distribution of seed-transmitted endophytes is strongly suggestive of cocladogenesis with their hosts. Endophytes are considered plant mutualists: they receive nutrition and protection from the host plant while the host plant may benefit from enhanced competitive abilities and increased resistance to herbivores, pathogens, and various abiotic stresses. Most studies of grass-endophyte associations have been undertaken with two economically important plant species, Lolium perenne and Festuca arundinacea. The interactions between endophytes and other grasses in natural plant communities, however, are seldom concerned. Much less attention has been paid to native grasses in Inner Mongolia Steppe, which lies in the north of China and is an important part of Steppe in Eurasia, and only limited published symbiosis studies are available in this natural ecosystem. Thereby, a more comprehensive view of the ecology, diversity of endophytes and their interactions with host plants becomes essential. Methods Our research of grass (Achnatherum sibiricum) associated with Neotyphodium endophyte (a new grass-endophyte association) was carried out in the Inner Mongolia Steppe, China. Twenty-seven endophyte strains were isolated from four A. sibiricum populations including Hulingol (H), Xi Ujimqin Qi (X), Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences (IMGERS-CAS) (I), and the Leymus chinensis plot of the IMGERS-CAS (L), respectively. Colony morphology, growth rate on potato dextrose agar (PDA) and conidial measurements of isolates were used to characterize diversity of endophytes hosted by A. sibiricum. The genetic polymorphisms of Neotyphodium species from the four A. sibiricum populations were also analyzed using random amplified polymorphic DNA (RAPD) markers. Key Results Four morphological groups of Neotyphodium species and five individual morphological types were described based on the colony morphology, growth rate, and conidial shape and size. A total of 463 bands were obtained using 20 RAPD primers, of which 461 bands were polymorphic. A total of 93 unique loci were obtained, accounting for 20.1% of the total amplified loci. Nei's diversity index (h) and Shannon's diversity index (I) were 0.238 and 0.387, respectively. In the four populations (H , X , I, and L), the value of h was 0.122 0, 0.180 4, 0.146 3 and 0.210 7, respectively. The four populations may be ranked in a descending order as L X I H, and the I of the four populations had a similar trend. The fixation index (F ST ), the coefficient of gene differentiation (G ST ), and the genetic differentiation (Hsp-Hpop)/Hsp (estimated by Shannon's diversity index) were 0.205 1, 0.300 4, and 0.355 0, respectively. The genetic variation of Neotyphodium species mainly existed within populations. Genetic similarities within each population were found to be in the range of 0.647 9-0.943 8 in similarity, and the average genetic distance among the four populations was 0.285 8, varying from 0.057 8 to 0.433 9. Clustering analysis based on Nei's unbiased genetic distance and UPGMA method showed that there were seven distinct RAPD genetic groups. Conclusions The high incidence of endophytic infection in A. sibiricum was indicative that the presence of the endophyte gave the grass a competitive advantage over non-infected grasses. The study also indicated that there were higher genetic diversity based on morphological and RAPD results, and that there were relatively high genetic variations among the four populations and higher genetic differentiation of Neotyphodium sp. within a geographical region. Most of the genetic groups were related to geographical origins of the strains. The dendrogram of genetic distance matched rather well with the morphological data, as reflected by the four morphotypes.