Different responses of soil respiration and its components to nitrogen and phosphorus addition in a subtropical secondary forest

Nitrogen (N) and phosphorus (P) deposition have largely affected soil respiration (Rs) in forest ecosystems. However, few studies have explored how N and P individually or in combination to influence Rs and its components (autotrophic respiration, Ra; heterotrophic respiration, Rh), especially in highly P-limited subtropical forests. To address this question, we conducted a field manipulation experiment with N and/or P addition in a 50-year-old subtropical secondary forest. We found that N addition on average reduced Rs, Ra, and Rh by 15.2%, 15%, and 11.7%, respectively during 2-year field study. P addition had an inconsistent effect on Ra, with Ra increasing by 50.5% in the first year but reducing by 26.6% in the second year. Moreover, P addition on average decreased Rh by 8.9%–30.9% and Rs by 6.7%–15.6% across 2 years. In contrast, N and P co-addition on average increased Rs, Ra, and Rh by 1.9%, 7.9%, and 2.1% during the experimental period. Though Rs and Rh were significantly correlated with soil temperature, their temperature sensitivities were not significantly changed by fertilization. Ra was predominantly regulated by soil nitrogen availability (NH4+ and NO3−), soil dissolved organic carbon (DOC), and enzyme activities, while the variation in Rh was mainly attributable to changes in soil microbial community composition and soil β-D-Cellubiosidase (CB) and β-Xylosidase (XYL) activities. Our findings highlight the contrasting responses of Rs and its components to N or P addition against N and P co-addition, which should be differentially considered in biogeochemical models in order to improve prediction of forest carbon dynamics in the context of N and P enrichment in terrestrial ecosystems.