Soil alkaline phosphatase activity and bacterial phoD gene abundance and diversity under regimes of inorganic fertilizer reduction with straw

Alkaline phosphatase (ALP), which was encoded by bacterial phoD genes, hydrolyzes organic phosphorus (P) into dissolved phosphorus in soils and is therefore vital for absorbing phosphorus (P) in vegetation. However, the unreasonable application of chemical fertilizer will inhibit this process of dissolving phosphorus. Until now, although the fact that straw is the optimal C source has been recognized, its impact on phoD-harboring bacteria under decreasing chemical fertilizer is not clear. A field experiment was established with chemical fertilizer only (F) and the gradient inorganic fertilizer reduction with straw: inorganic fertilizer with straw (FS), 70% inorganic fertilizer with straw (0.7FS), 60% inorganic fertilizer with straw (0.6FS), and 50% inorganic fertilizer with straw (0.5FS). Mixed treatments received equal amounts of straw. Integrated high-throughput absolute abundance quantification (iHAAQ) was used to investigate the phoD bacterial community structure. From the correlation between the plant-total P of three vegetables and microbial variables, only the plant-total P of chili was significantly related to ALP and the abundance of phoD gene. Although the total vegetable yield was significantly increased by the addition of straw, no correlation with ALP and phoD bacterial community was found. In addition, the abundance of the phoD bacterial community and the levels of ALP activity were both higher in a regime featuring 70% inorganic fertilization with straw (0.7FS), but the ability of phoD bacteria ALP release was strongly activated in a regime featuring 50% inorganic fertilization with straw (0.5FS). Distance-based redundancy analysis (db-RDA) indicated that the community of phoD bacteria clustered four groups and suggested that a number of soil factors played key roles in shaping the entire phoD bacterial community, including soil organic carbon, total nitrogen, available phosphorus, Ca2+-Ex, and total potassium. The correlation between the absolute abundance of ALP-regulating bacteria and ALP activity suggests that Amycolatopsis may predominantly account for ALP activity, especially in the 0.5FS regime. In the reduction of chemical fertilizer, the straw substitution did not reshape the structure of the phoD bacterial community but strongly activated phoD bacteria to release ALP.