Structural and Functional Responses of Rhizosphere Microbial Communities to Pennisetum giganteum Cultivation in a Dry-Hot Valley: Differential Shifts in Prokaryotic Versus Fungal Communities
Understanding the ecological adaptability of Pennisetum giganteum (JUJUNCAO) and its long-term effects on rhizosphere microecology is critical for vegetation restoration in fragile ecosystems. In this study, we investigated the soil physicochemical properties and microbial community structure and function in the rhizosphere of P. giganteum cultivated for 1 and 3 years (Y1, Y3), alongside pre-planting soil (Y0), in a dry-hot valley in Chuxiong, Yunnan, China. Following three years of cultivation, the soil total carbon (TC), organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO3−-N), total phosphorus (TP), and available phosphorus (AP) showed significant increases of 84.18%, 96.09%, 61.32%, 212.47%, 24.71%, and 22.19%, respectively, whereas the soil pH remained stable. Fungal communities showed significant declines in diversity and richness and a fundamental structural shift as early as one year after planting. In contrast, prokaryotic communities showed a relatively stable structure. Soil carbon and nitrogen variables were the factors most strongly associated with microbial community composition, and long-term cultivation concurrently enriched the arbuscular mycorrhizal fungi Septoglomus and genera containing potential plant pathogens such as Fusarium and Nectria. The relative abundance of Nectria was positively correlated with the soil carbon and nitrogen contents (p < 0.05), suggesting a potential ecological trade-off between beneficial symbiosis and disease risk. Predicted functional pathway composition indicated a shift in microbial metabolism from basal pathways of phospholipid and nucleotide synthesis toward carbon-nitrogen metabolism via PWY-3781 and the glyoxylate shunt, with fungal community turnover more pronounced. Consequently, P. giganteum demonstrates considerable potential for ecological restoration in dry-hot valleys; however, long-term cultivation deserves attention due to potential nitrate loss and the accumulation of taxa containing potential pathogens, with fungal communities serving as sensitive bioindicators of soil health.