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

Abstract

Abstract 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, H 2 O-P decreased by 62.1% and 73.61%, and NaHCO 3 -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.