Effects of Soil Bacterial Taxa under Different Precipitation Gradients on the Multi-Functionality of the Rhizosphere Soils under Caragana intermedia Forests

Abstract

Elucidating the impact of rhizosphere microbial communities in the Caragana intermedia forest on soil polyfunctionality can significantly enhance our understanding of the microbial mechanisms underpinning soil multi-functionality, which is crucial for sustainable land management. The rhizosphere soils under Caragana intermedia forests in different regions with variable precipitation gradients (MAP500 (precipitation ≥ 500 mm), MAP450 (400~500 mm), MAP300 (300~400 mm), MAP250 (200~300 mm)) were investigated in the research object. The interrelationships among soil properties, particularly the soil bacterial taxa and soil multi-functionality, were examined using metagenomic analysis, sequencing techniques, redundancy analysis, and partial least squares path modeling. The results show that (1) concurrent with escalating precipitation, Rhizosphere Soil Multi-functionality Index (SMI) exhibited a significant increase (p < 0.05); (2) the community structures of the Always Abundant Taxa (AAT), Always Rare Taxa (ART), Moderate Taxa (MT), Conditionally Abundant Taxa (CAT), Conditionally Rare group (CRT), and Conditionally Abundant Taxa (CRAT) varied significantly across precipitation gradients. Mean annual precipitation (MAP), soil moisture content (SMC), and pH were identified as the most critical environmental factors influencing the overall bacterial community and various taxa; (3) precipitation predominantly exerts indirect effects on AAT, MT, CAT, and CRAT by modulating soil moisture. Bacterial taxa that are conditionally rare or abundant in arid and semi-arid regions are the principal drivers of soil multi-functionality alterations within the rhizosphere of the Caragana intermedia forest. In the stewardship of Caragana intermedia plantations, microbial community composition can be optimized through the regulation of soil moisture and pH, as well as the strategic introduction of conditional microbial taxa, thereby enhancing the plantation’s resilience to climate change. This research contributes to sustainable land use practices by providing insights into microbial management strategies that enhance soil health and ecosystem resilience.