Soil phosphorus availability alters the effects of straw carbon on microbial mediated phosphorus conversion

Aims Crop straw return promotes microbial mediated phosphorus (P) cycling in soils, thereby increasing soil P availability. However, it remains unclear whether straw carbon (C) regulated organic phosphorus (Po) conversion is affected by soil P availability. Methods Here, the responses to straw addition of soil microbial biomass, extracellular enzyme stoichiometry, bacterial community composition and P fractions were studied in soils with different available P contents. Results Straw addition increased the organic P (Po) mineralization in the medium P (MP) soil, while decreased it in the low P (LP) and high P (HP) soils, respectively. Microbial nutrient limitation and community composition were co-regulated by soil C and P availability. LP and HP soils had the highest P and C limitations, respectively. In the MP soil, microbial P and C limitations lie between those of LP and HP soils. Straw addition decreased microbial P limitation in the LP and MP soils, while little change occurs in the HP soil. In addition, species number, diversity and the synergy of microbial communities were high in the MP soil. Straw addition induced a greater increase in the relative abundance of P-solubilizing microorganisms (e.g., Rhizobiales and Bradyrhizobium ) in the MP soil compared to in the LP and MP soils. Conclusions We concluded that straw addition promotes Po mineralization when the soil Olsen-P content was between 8.1–18.9 mg kg –1 and the corresponding MBC:P ratio was between 25.6–36.9. Our results highlight that the changes in microbial nutrient limitation and community composition caused by straw addition drive different soil P conversions.