The effects of Epichloe endophytes on the growth and competitiveness of Achnatherum sibiricum are mediated by soil microbe diversity

Many grasses are infected by systemic fungal endophytes that occur in aboveground plant tissues. Both aboveground endophytic fungi and belowground soil microbes can influence plant growth, but studies on their simultaneous effects on plant growth and competitiveness are limited. This study aims to investigate whether the role of aboveground endophytic fungi in the growth and competitive ability of the host grasses was influenced by soil microbes. In this study, we used Epichloe endophyte-infected and endophyte-free Achnatherum sibiricum as plant materials. A wet sieving method was adopted to obtain microbial inocula with different diversities (com, combined microbe fraction, high diversity; sm, small microbe fraction, low diversity). A three-factor randomized block design was used. The first factor was the endophyte infection status of A. sibiricum. The second factor was the microbial composition of the soil inocula. The third factor was the planting type. Growth and competitive characters were measured after 16 weeks. The results showed that a soil microbe inoculation was detrimental to the growth of A. sibiricum. Epichloe endophytes significantly mitigated the inhibitory effect of soil microbes on A. sibiricum planted alone. When A. sibiricum was planted with Stipa grandis, there was a significant interaction between Epichloe endophytes and soil microbes on the interspecific competition of A. sibiricum. When inoculated with small microbial community fraction, Epichloe endophytes significantly improved the interspecific competitive ability of host plants. When inoculated with combined microbial community fraction, however, Epichloe endophytes had no significant effect on host competition. The results showed that the interaction between Epichloe endophytes and soil microbes contributed more to the interspecific competitive ability than either Epichloe endophytes or soil microbes alone.

Automated summary

This study investigates the role of soil microbes in the growth and competitive ability of grasses infected with aboveground endophytic fungi. The results show that soil microbial inoculation is detrimental to the growth of the grass, but the presence of the endophytic fungi mitigates this inhibitory effect. When the grass is planted with another species, there is a significant interaction between the endophytic fungi and soil microbes on interspecific competition. The improvement of competitive ability by the endophytic fungi depends on the diversity of soil microbes.