Aeration treatment promotes transformation of soil phosphorus fractions to plant-available phosphorus by modulating rice rhizosphere microbiota

Microorganisms play an important role in affecting the content of available phosphorus (P) in plant rhizosphere soil. However, the effect of aeration on available P in rice rhizosphere soil and its microbial mechanism remain unclear. This study aimed to elucidate the effects of aeration strategies on available P and P-solubilizing microorganisms in rhizosphere soil, employing three different aeration methods (continuous flooding (CF), continuous flooding and aeration (CFA), and alternate wetting and drying (AWD)). We analyzed the bacterial and fungal community structures in rice rhizosphere soil via Illumina sequencing techniques and quantified the abundance of P transformation functional genes related to inorganic P solubilization (pqqC) and organic P mineralization (phoC, phoD, and appA) through quantitative PCR. Our findings revealed that the AWD treatment significantly increased soil pH and Eh; Both AWD and CFA treatments markedly increased soil Olsen-P content at the tillering and heading stages, as well as the microbial carbon-to-phosphorus ratio (MBC/MBP) at the heading and maturity stages. Cluster analysis showed distinct bacterial communities at the heading and maturity stages under AWD, which differed from those in other treatments. Fungal communities at the tillering and heading stages under CFA and AWD grouped together. AWD and CFA treatments consistently enhanced labile-P in the rhizosphere soil throughout the entire growth stages, while reducing moderately labile-P during the tillering and heading stages. Compared to CF, at the heading and maturity stages, the copy numbers of pqqC, phoD, phoC, and appA were higher under AWD compared to other treatments. In conclusion, this study posits that the increase in Olsen-P in paddy fields due to aeration results from improved oxygen conditions in the rhizosphere, alterations in pH and Eh, effects on microbial stoichiometry, and adjustments in the abundance and composition of P-solubilizing microorganisms, thereby promoting P transformation. This conclusion provides new insights into the conversion of soil P Fractions into plant-available forms.