Predominant effects of soil organic carbon quality on phosphatase activity in upland Ultisols under long-term fertilizations

Abstract

Understanding phosphorus (P) mobilization in “legacy P”-rich croplands is critical for sustainable agricultural P management. However, the role of soil organic carbon (SOC) quality (i.e., biochemical recalcitrance) in regulating the enzyme activity associated with microbial mineralization of organic P in such environments has not been extensively investigated. Therefore, in this study, upland Ultisols subjected to seven different fertilization regimens (i.e. no fertilizer, chemical N, P, NP, and NPK fertilizer, swine manure, and NPK plus swine manure) for 35 years were collected to clarify and quantify the effect of SOC quality on acid (ACP) and alkaline phosphatase (ALP) activities. The ratio between labile and recalcitrant C, an index of SOC quality, increased by 15.5 %– 22.9 % with manure application compared with the non-fertilized control, whereas it decreased by 1.94 %–18.5 % under chemical fertilizations. ACP activity was determined to be 3–6-fold greater than ALP activity in the same soil, and both were significantly greater under manure fertilization than the other regimens. A significant positive correlation was observed among SOC quality, phosphatase activities, the abundances of their encoding genes, and the compositional dissimilarities of corresponding functional bacterial communities. Soil nutrient content, SOC quality, and functional gene abundance were the predominant influencing factors regulating ACP activity rather than soil pH, nutrient stoichiometry, and the composition of functional bacterial community. This finding suggests that the increased ACP activity was strongly associated with the proliferation of functional taxa dominated by copiotrophs. In contrast, soil pH and the composition of functional bacterial community were the primary regulators of ALP activity, suggesting a mitigation of acidity-induced inhibition that promoted its enhancement. The findings of this study provide an empirical basis for manipulating microbial mineralization of organic P through the application of labile organic materials to maintain P bioavailability in fertilized croplands.