Biochar regulates putative keystone microbial taxa to drive phosphorus cycling and increase availability in urban greenspace soils

The quality of soil in urban green spaces often deteriorates due to poor design practices, insufficient maintenance, and environmental pressures associated with urbanization. Although biochar, as an effective soil additive, can significantly improve the soil quality in greenspace, it significantly influences the phosphorus (P) cycling processes through functional regulation of microbial community; however, further analysis is essential to validate this mechanism. Therefore, this study reported pot experiments using Euonymus kiautschovicus, a typical urban greenspace plant, followed by metagenomic analysis for investigating microbial-driven P cycle mechanisms. Four treatment groups were established according to the dosage of biochar, including 0% (CK), 4% (BC4), 8% (BC8), and 12% (BC12). Biochar application significantly increased soil available P (AP) and total P (TP) content, with BC12 demonstrating maximum AP and TP content of 21.79 mg kg−1 and 0.62 g kg−1, respectively. On the one hand, biochar serves as a direct source of P. On the other hand, it enhances AP by regulating P-cycling functional microorganisms. Random forest model identified phnP, phoA, relA, ppnK, pstA, phnD, and pstS as the putative keystone genes regulating soil P cycling. Microbial co-occurrence network analysis and partial least squares path modeling (PLS-PM) demonstrated that the biochar application improved soil AP by regulating putative keystone microbial taxa (Modules 1 and 2) involved in P cycling. This study elucidates the microbial mechanisms underlying biochar-mediated P cycling in greenspace soils, providing a scientific basis for biochar application for improved soil quality in urban greenspace.