Continuous Cropping Regulates Fungal Community Structures and Functional Groups in Rhizosphere Soil of Tibet Barley

Continuous cropping regulates the community structure of rhizosphere soil microbes; however, the effects of continuous cropping on the community structure and function of rhizosphere fungal communities of plants cultivated in high-altitude regions are not well understood. In this study, 18S rRNA gene high-throughput sequencing was applied to examine the rhizosphere fungal community structure during continuous cropping of Tibet barley (a principal cereal cultivated on the Qinghai-Tibetan Plateau). The results showed that the Chao1 and phylogenetic diversity (PD) indices declined as cropping years increased. Additionally, relative abundance of the genera Cystofilobasidium, Mucor, and Ustilago increased, whereas the abundance of Fusarium decreased during continuous cropping. Furthermore, identification of ecological groups using FUNGuild revealed that saprotrophs, pathogens, and symbiotrophs were the dominant groups in rhizosphere soil, and these three trophic modes all increased significantly with continuous cropping. During continuous cropping, the fungal plant-pathogens Parastagonospora and Ustilago also increased remarkably, as did the endophyte fungi Verticillium. Collectively, continuous cropping of Tibet barely increased the potential for plant-pathogenic and endophyte fungi in rhizosphere soil. Thus, the development of sustainable farming practices to reduce the abundance of harmful fungi is vital to Tibet barley growth and production during continuous cropping of plants cultivated in high-altitude regions.