Warming causes variability in SOM decomposition in N‐ and P‐fertiliser‐treated soil in a subtropical coniferous forest

Abstract

AbstractBoth temperature and nutrient availability have essential roles in regulating the decomposition of soil carbon (C) and nitrogen (N), the main controls on organic matter accumulation in forest ecosystems. However, there is a lack of information about how N deposition and phosphorus (P) additions might impact soil C and N decomposition rates in subtropical forests under climate warming. We measured soil organic C and N mineralisation rates and corresponding exoenzyme activities in a subtropical forest soil that had received N and/or P additions for six years in experimental conditions at a range of temperatures between 10 and 40°C. Our results showed that soil organic C and N decomposition rates were positively correlated with the activities of their corresponding enzymes, which suggests that the extracellular enzyme activities could be the main influence on soil organic matter (SOM) decomposition rates. N additions had a significant positive effect on soil organic C mineralisation and enhanced oxidase and hydrolase activities. P additions had little effect on soil organic C and N decomposition rates. These results challenge the assumptions that soil microorganisms are N‐rich and P availability restricts organic matter decomposition, and provides additional evidence that N, not P, regulates organic matter decomposition in subtropical forests. While N additions significantly influenced the soil C and N decomposition rates, they had little effect on their sensitivity to temperature. In contrast, P additions had a significant effect on the temperature sensitivities of SOM decomposition and the βG and NAG Vmax. Overall, our results show that SOM decomposition is vulnerable to both N and P additions, and both should be considered when predicting how SOM decomposition and C cycling might change under warming.Highlights The effect of N and/or P additions on the temperature sensitivity of SOM decomposition was explored. N stimulated soil organic C decomposition rates and corresponding enzyme activities. P promoted the sensitivity of SOM decomposition to temperature changes. N and P additions could affect the stability of SOM in subtropical forests in the future.