Metagenomics Reveals the Effects of Organic Material Co-Application on Phosphorus Cycling Functional Genes and Bioavailable Phosphorus

Phosphorus is essential for crop growth, but excessive use of chemical fertilizers can lead to environmental issues. The incorporation of organic materials has the potential to enhance phosphorus availability and promote soil phosphorus cycling. This study investigated the effects of chemical fertilizer co-application with two organic materials on soil properties and functions. Four treatments were established: (1) chemical fertilizer alone (SC, consisting of urea, ammonium phosphate, and potassium sulfate), (2) chemical fertilizer with corn-straw-derived biochar (SCB), (3) chemical fertilizer with composted manure-based organic fertilizer (SCF), and (4) chemical fertilizer with both biochar and organic fertilizer (SCBF). This study focused on changes in soil properties, bioavailable phosphorus, phosphorus cycling functional genes, and related microbial communities. Compared to SC, the combined application of organic materials significantly increased available phosphorus (AP), alkaline hydrolysis nitrogen (AN), and available potassium (AK), with the SCBF exhibiting the highest increases of 78.76%, 47.47%, and 336.61%, respectively. However, applying organic materials reduced alkaline phosphatase (ALP) and acid phosphatase (ACP) activities, except for the increase in ACP in SCBF. Additionally, bioavailable phosphorus increased by up to 157.00% in SCBF. Adding organic materials significantly decreased organic phosphorus mineralization genes (phoA, phoD, phnP) and phosphate degradation genes (ppk2), while increasing inorganic phosphorus solubilization genes (pqqC, gcd), which subsequently increased CaCl2-P and Citrate-P contents in SCB and in SCBF. In summary, organic material application significantly enhances phosphorus bioavailability by improving soil physicochemical properties and phosphorus-related gene abundance. These findings provide new insights into sustainable soil fertility management and highlight the potential of integrating organic materials with chemical fertilizers to improve soil nutrient availability, thereby contributing to increased soybean yield. Moreover, this study advances our understanding of the underlying mechanisms driving phosphorus cycling under combined fertilization strategies, offering a scientific basis for optimizing fertilization practices in agroecosystems.