Phosphorus addition enhances gross microbial N cycling in phosphorus-poor soils: a 15N study from two long-term fertilization experiments
The tight coupling between nitrogen (N) and phosphorus (P) suggests that P availability may affect soil microbial N dynamics in terrestrial ecosystems. However, how P addition affects the internal N transformations in P-deficient agricultural soil remains poorly understood. We hypothesized that an increase in gross microbial N rates in P-deficient soil should occur after long-term P inputs in agricultural soils. We thus conducted a 15N pool dilution experiment to quantify the gross microbial N transformation rates after long-term mineral fertilizer applications in an upland fluvo-aquic soil (from Fengqiu with pH 8.55) and upland red soil (from Qiyang with pH 5.49) in China. We found that P addition significantly enhanced the gross N mineralization and immobilization rates when N and K were also applied, probably due to the increased soil total C and N concentrations at both soils. Also, gross nitrification rate was stimulated by P addition, perhaps because of enhanced gross N mineralization rates and associated NH4+ substrate availability. Our results showed that long-term P addition may stimulate soil gross N dynamics and hence increase overall N availability for crops in P-deficient agricultural soils.
KeywordsPhosphorus deficiency P availability N dynamics Gross N mineralization 15N recovery
This work was financially supported by the National Natural Science Foundation of China (grant numbers 41671231, 41571294), the High-Level Talent Start-Up Research Project of Nanjing Forestry University (grant numbers GXL2018012), and the National Key Research and Development Program of China (grant numbers 2017YFD0200103, 2017YFD0800106).
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