Amending intensively fertilized soils with manure for 40 years increases inorganic and organic phosphorus pools and promotes microbe-mediated phosphorus mobilization

Soil phosphorus (P) pools are affected by the quantity and quality of fertilizer applications, with phosphatases produced by soil microbes playing an important role in the transformation of organic P. In this study, the effect of different fertilization practices on soil P forms, microbial community and mineralization processes was investigated in a long-term field experiment in northeast China (initiated in 1979). P K-edge X-ray absorption near-edge and Illumina MiSeq high-throughput sequencing, soil phosphatase activity (acid, alkaline and neutral phosphomonoesters) and soil chemical properties were analyzed to determine the processes and main factors influencing P transformations with different levels of organic P addition. Our result showed that total N, total C, total P, and Olsen-P affected soil P forms. Although all P forms increased at the highest level of fertilization, surplus P was accumulated mainly in the form of inorganic dibasic calcium phosphate and hydroxyapatite, as well as organic myo-inositol. The highest bacterial richness and diversity increased and coincided with high levels of dibasic calcium phosphate and Al-P, typically retained in bacterial genera. Soil total C and phosphatase activity were positively related to bacterial richness, although with weaker relationships than with DCP and Al-P. The bacterial community was also closely related to Olsen P, which in turn was affected by all tested organic and inorganic soil P pools, with the exception of hydroxyapatite. Therefore, it appears that hydroxyapatite may not contribute to available P and can be viewed as a sink of P in intensively fertilized soils. Sphingomonas showed a robust positive correlation with inorganic and organic P forms, possibly related to their capacity to increase alkaline phosphatase production in high pH and organic C rich soils. In conclusion, the results suggested that P added in manures in intensively fertilized soils accumulates in different inorganic P and organic P pools and increased alkaline phosphatase activity.