Yong Zhou, Xia Li, Yuan Gao, Hui Liu, Yu-Bao Gao, Marcel G. A. van der Heijden, An-Zhi Ren

 

In nature, plants can take part in a variety of symbiotic microbial interactions throughout their lifetimes. Some microbial symbionts, such as root-associated arbuscular mycorrhizal fungi (AMF) and fungal endophytes found in the above-ground tissues of grasses, can simultaneously form associations with the same host. In this symbiosis, the host grasses provide carbon resources and nutrients to both AMF and endophytes, the AMF benefit grasses through increasing the acquisition of limited soil resources such as phosphorus, and endophytes may enhance host resistance to biotic and abiotic stresses. Endophytes can also alter the functioning of different groups of soil microorganisms, including AMF. Previous studies showed that endophytes and AMF can interact additively, antagonistically or neutrally regarding host plant growth, depending on the species of these fungi and the host grass. But little is known about the influence these multiple symbioses on plant competition.

Here, we used a microcosm experiment to investigate the role of endophyte infection and AMF colonization on competition between two grass species (Achnatherum sibiricum and Stipa grandis). We grew one plant species in monoculture or mixture with the competitor species and manipulated the presence of one of two AMF species as well as a non-AMF control. For A. sibiricum, we also manipulated the presence of the endophyte infection.

We found that endophyte infection significantly enhanced the competitive ability of the subordinate plant species (A. sibiricum) compared to the dominant plant species (S. grandis). The effects of AMF on plant competition were variable and depended on the identity of the AMF species. One AMF species gave A. sibiricum plants a higher competitive ability, while the other AMF species gave S. grandis a higher competitive ability. Simultaneous infection with both endophytes and AMF in A. sibiricum also altered the competitive relationships with S. grandis, indicating that endophytes 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. These results may help to explain the coexistence of a subordinate plant species with a dominant plant species in nature.

Photograph provided by authors.

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