Different Responses of Soil Respiration and Its Components to Nitrogen and Phosphorus Addition in a Subtropical Secondary Forest

Background Nitrogen (N) and phosphorus (P) deposition have largely affected soil respiration ( R s ) in forest ecosystems. However, few studies have explored how N and P individually or in combination to influence R s and its components (autotrophic respiration, R a ; heterotrophic respiration, R h ), 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. Results We found that N addition on average reduced R s , R a , and R h by 15.2%, 15%, and 11.7%, respectively during 2-year field study. P addition had an inconsistent effect on R a , with R a increasing by 50.5% in the first year but reducing by 26.6% in the second year. Moreover, P addition on average decreased R h by 8.9%–30.9% and R s by 6.7%–15.6% across 2 years. In contrast, N and P co-addition on average increased R s , R a , and R h by 1.9%, 7.9%, and 2.1% during the experimental period. Though R s and R h were significantly correlated with soil temperature, their temperature sensitivities were not significantly changed by fertilization. R a was predominantly regulated by soil nitrogen availability (NH 4 + and NO 3 − ), soil dissolved organic carbon (DOC), and enzyme activities, while the variation in R h was mainly attributable to changes in soil microbial community composition and soil β-D-Cellubiosidase (CB) and β-Xylosidase (XYL) activities. Conclusion Our findings highlight the contrasting responses of R s 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.