Biochar Co-Applied with Lime Enhances Soil Phosphorus Availability via Microbial and Enzymatic Modulation of Paddy Soil.

Soil microorganisms play a crucial role in improving soil phosphorus (P) availability. However, few studies have explored the changes in microbial community structure and their underlying mechanisms for improving soil P availability with the application of biochar and lime. Three kinds of biochar, made from rice straw (SB), Chinese fir wood sawdust (WB), and pig manure (MB), alone and with lime (SBL, WBL, and MBL), were applied to paddy soil to reveal the biochemical mechanisms for enhancing soil P availability. High-throughput sequencing and real-time PCR were used to investigate soil microbial communities and P functional genes. The three biochars increased the soil's available P in the order of MB > SB > WB. Biochar co-applied with lime increased the available P (Olsen-P by 169-209%) and inorganic P (Al-P by 53.4-161%, Fe-P by 96.3-198%, and Ca-P by 59.0-154%) more than biochar alone, compared to the control (CK). Both biochar alone and co-applied with lime increased the activities of alkaline phosphomonoesterase (ALP), phosphodiesterase (PD), and inorganic pyrophosphatase (IPP) by 369-806%, 28.4-67.3%, and 37.9-181%, respectively, while it decreased the activity of acidic phosphomonoesterase (ACP) by 15.1-44.0%, compared to CK. Biochar, both alone and co-applied with lime, reduced the copy number of