Biochar amendment shifts bacterial keystone taxa regulating soil phosphorus dynamics

Abstract

Biochar amendment can improve soil phosphorus (P) availability, yet the influence of microbial community structure, especially certain keystone taxa on P dynamics remains uncertain. A pot experiment was conducted on a highly weathered Ferralsol to investigate how the amendment with biochar and P-fertilizer (CK, no biochar and P addition; PP, 30 kg P ha−1 addition; BC, 4 % biochar addition and BP, 30 kg P ha−1 combined with 4 % biochar addition) affect soybean (Glycine max (L.) cv. Huaxia-9) P uptake, soil P dynamics and its association with bacterial community structure and keystone taxa. The biochar-amended treatments (BC and BP) led to a 50–130 % increase in P uptake and a ten-fold rise in labile P proportion compared to treatments without biochar (CK and PP). This could be associated with the incorporation of P from biochar, as well as the altered soil P availability by elevated soil pH, soil organic carbon (SOC), microbial biomass P and alkaline phosphatase activity. Furthermore, biochar amendments altered bacterial community composition by increasing the relative abundance of Gemmatimonadetes, Bacteroidetes and Verrucomicrobia phylum by over three-fold, while decreasing the relative abundance of Chloroflexi and Acidobacteria phylum by over 50 %, compared to the non-biochar treatments. Additionally, the elevated C:P ratio following biochar amendment played a dominant role in shaping the keystone taxa, which was identified as the primarily microbial predictor of soil labile P. Specifically, biochar amendment increased microbial network complexity, inducing a shift in keystone taxa from oligotrophs to copiotrophs, such as Rhizobiales, Sphingomonadales and Rhodospirillales, which are wildly recognized for their roles in soil P mobilization. Taken together, our findings suggested that biochar-induced shift in keystone taxa is one of the major predictors of soil P dynamics, highlighting the potential of harnessing specific keystone taxa for improving soil P availability.