Enhanced phosphorus availability and uptake in Salvia miltiorrhiza associated with humic-induced changes in soil...

Humic acid (HA) is known to improve phosphorus (P) availability in agricultural soils. Yet, the underlying mechanisms by which it influences the microbial community and subsequent P turnover remain unclear. In this study, a pot experiment was conducted using soil from a three-year Salvia miltiorrhiza (S. miltiorrhiza) cultivation system, in which the soil was amended with three HA concentrations (T1: 100-fold dilution, T2: 200-fold, T3: 400-fold) alongside an untreated control (CK). We determined P uptake by S. miltiorrhiza, soil P fractions, phosphatase activities, along with high-throughput sequencing of the microbial communities to specifically target those associated with P transformation. The results showed that HA application significantly enhanced root P uptake, with increases of 68.59% and 91.05% under T2 and T3, respectively. Consequently, soil Olsen-P content decreased by 19.19% and 15.20%, respectively, consistent with the depletion of available P under enhanced plant uptake. Soil P fractionation further revealed that HA application decreased inorganic P by 20.91% and 32.29%, respectively, under T2 and T3 treatments. Specifically, H₂O-P decreased by 62.1% and 73.61%, and NaHCO₃-Pi decreased by 53.21% and 50.48%, respectively, under the T2 and T3 treatments. In parallel, acid phosphatase activity was increased by 68.72% and 66.67% under the T2 and T3 treatments compared to CK. Comparative high-throughput sequencing between T2 and CK revealed that HA application enriched key microbial genera associated with P cycling, including Sphingomonas, Nitrospira, Ferruginibacter, and Hyphomicrobium. Collectively, these findings suggest that HA may promote P mobilization and mineralization through association with microbial communities, thereby potentially enhancing P bioavailability and plant uptake. These findings offer new perspectives on the associations between HA application, microbial community shifts, and P use efficiency, suggesting a potential approach that merits further evaluation for P management in agricultural systems.