Community assembly of endophytic bacteria and fungi differs in soil-root continuum of Carex cepillacea

Endophytic microbes in nutrient-impoverished soils have unique adaptive mechanisms through the dual selection of plants and soil, which is of great research value for exploring the nutritional strategies of nonmycorrhizal plants. However, the assemblage of endophytic microbes associated with Cyperaceae plants in phosphorus-deficient soil remains unclear. We examined fungal and bacterial communities associated with Carex cepillacea in bulk soil, rhizosphere soil and root endosphere, in the alpine grassland of Qinghai-Tibet Plateau. Diverse endophytes were identified, among which some unique endophytes were enriched in the roots. Specifically, 100 % of rhizosphere bacterial dominant taxa and 85 % of rare taxa reached the root endosphere through the root barrier, while only 65.5 % of rhizosphere fungal dominant taxa and 30.1 % of the rare taxa reached the root endosphere. Thus, in the soil-plant continuum, host appears to have a stronger influence on plant-fungal community assembly than on plant-bacterial community assembly. Moreover, pH and soil available phosphorus (AP) were the primary drivers of the microbial structure in the rhizosphere soil and root endosphere, while MAP mostly influenced microbial structure in the rhizosphere soil. Network analyses further found that endophytic fungi tend to have a higher number of network connections than bacteria, suggesting that fungi are more central than bacteria to the community structure of root microbiomes. Solirubrobacterales and Hypocreales contained most of core groups in the root microbiome, including many plants growth-promoting microbes such as phosphate-dissolving and nitrogen-fixing bacteria. These results indicate that Carex cepillacea roots are colonized by diverse and unique endophytes, including some core microbiota that are potentially important in driving the plant adaptability and nutrient uptake. The findings also highlight the different community assembly patterns of fungi and bacteria in the root-soil continuum. Further exploration of the roles of endophytes is of great significance for understanding the nutrient strategies of nonmycorrhizal plants in alpine environments.