Effects of different phosphorus supply levels on the organic acids, inorganic phosphorus, and microorganisms in the rhizosphere soil of switchgrass (Panicum virgatum L.)

This study aimed to explore the effects of different phosphorus supply levels on soil organic acids and inorganic phosphorus contents, and microbial communities, as well as to investigate the microbial ecological characteristics in the rhizosphere. The results are important for promoting soil phosphorus cycling. The experiment employed a randomized block design with ‘Alamo’ and ‘Pathfinder’ varieties of Panicum virgatum L. Three phosphorus levels were set: P0 (0 kg·hm^–2), P30 (30 kg·hm^–2), and P90 (90 kg·hm^–2), to study the composition and content of rhizosphere soil organic acids, inorganic phosphorus, and microbial population diversity. The results showed that phosphorus levels had a significant impact on rhizosphere soil organic acids and inorganic phosphorus contents, and microbial communities. At two phosphorus application levels, the ‘Alamo’ variety exhibited a greater increase in rhizosphere soil organic acid content and higher levels of rhizosphere soil inorganic phosphorus, compared with P0 treatments. In terms of microbial communities, both ‘Alamo’ and ‘Pathfinder’ varieties showed similar patterns of change. Under the P30 and P90 treatments, the succinic, malic, maleic, and malonic acid contents in the rhizosphere soil significantly increased, whereas the suberic acid content decreased. Additionally, the contents of Ca₂-P, Al-P, Fe-P, O-P, and Ca₁₀-P in the rhizosphere soil significantly increased after phosphorus application. Furthermore, the Chao1, ACE, Shannon, and Simpson indices of the bacterial communities significantly increased after phosphorus application, with the phyla Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi dominating at the phylum level. The comprehensive analysis found that under different phosphorus levels, the relationship between organic acids and inorganic phosphorus was not significant. The abundance and diversity of bacterial communities were jointly influenced by organic acids and inorganic phosphorus, and the relationships between the dominant bacterial phyla, organic acids, and inorganic phosphorus varied. In conclusion, the rhizosphere soil microecosystem, composed of organic acids, inorganic phosphorus, and microorganisms were a harmonious system that played a positive role in the efficient utilization of phosphorus resources.