Rhizosphere soil fertility and microbial community characteristics of Arundo donax cv. Lvzhou No.1 in coastal saline-alkali soils

Saline-alkali soils are widespread in ecologically fragile regions and are characterized by high salinity and alkalinity, leading to soil degradation and reduced productivity. To evaluate the potential of <i>Arundo donax</i> cv. Lvzhou No.1 for improving coastal saline-alkali soils, this study was conducted on Pingtan Island, Fujian Province, China. Three treatments were established: a blank control (CK), rhizosphere soils from one-year cultivation (R1), and five-year cultivation (R5). Soil physicochemical properties and microbial community structure were assessed using soil chemical analyses and high-throughput sequencing. Cultivation of <i>A. donax</i> cv. Lvzhou No.1 alleviated saline-alkali stress by reducing soil pH and salinity, with stronger effects under long-term cultivation. Soil fertility increased markedly, with organic matter (OM) and total nitrogen (TN) rising by 91.00% and 70.00%, respectively. Microbial diversity also increased, with fungal communities dominated by Ascomycota and bacterial communities by Proteobacteria. Functional predictions showed higher abundances of saprophytic genera (<i>Acremonium, Fusarium</i>) and enhanced bacterial metabolic pathways, including fatty acid synthesis and the tricarboxylic acid cycle, indicating increased microbial metabolic activity. These changes promoted organic matter turnover and nutrient release. Canonical correspondence analysis identified OM, TN, available nitrogen (AN), and available phosphorus (AP) as the primary drivers shaping microbial community structure. Overall, long-term cultivation of <i>A. donax</i> cv. Lvzhou No.1 improves coastal saline-alkali soils by enhancing physicochemical properties and optimizing microbial community composition. These findings provide a scientific basis for ecological restoration and sustainable utilization of coastal saline-alkali lands.