Effects of two-year nitrogen and phosphorus additions on nutrient release and enzyme activity during leaf litter decomposition in Larix principis-rupprechtii plantation

Aims Increasing global nitrogen (N) and phosphorus (P) deposition may affect the response mechanism of litter decomposition. We aimed to explore the responses of nutrient release and enzyme activities to exogenous N and P inputs. Methods We conducted a two‑year field litterbag experiment in larch ( Larix principis-rupprechtii ) plantation at the Saihanba Forest Farm in Hebei Province, China. Four treatments, i.e., N addition (+ N), P addition (+ P), N and P addition (N + P), and control (CK) were designed and examined the overall effect of the fertilization treatments on the remaining mass, nutrients, and enzymatic activity. Results In contrast to CK, the + N, + P, and N + P treatments significantly reduced the remaining leaf litter mass by 36.33%, 35.21%, and 38.50% at the end of the experiment, respectively. During the decomposition of leaf litter, + N had a significant effect on carbon (C) release and no significant effect on N and P release. + P promoted C release and significantly reduced the N remaining but increased the P remaining. Invertase activity decreased sharply in the early stage of decomposition. However, the activities of catalase, urease, and acid phosphatase declined in the middle stage in each treatment. The effect of + N on enzyme activities was not significant, while + P significantly increased urease activity. Conclusion The results reveal that continuous N and P deposition could promote the litter decomposition rate, while altered the nutrient release pattern in larch plantation.