Weakening of the 'enzymatic latch' mechanism following long-term fertilization in a minerotrophic peatland

Despite the global importance of understanding the effects of nitrogen (N) and phosphorus (P) deposition on carbon (C) cycling in northern peatlands, the control of N and P interactions through the 'enzymatic latch' mechanism has been largely overlooked. A long-term fertilization experiment in a moderate-rich fen in northeast China was conducted to evaluate the underlying mechanisms of how continuous N and P addition regulate key extracellular enzymes and their interactions, and the subsequent influences on organic C storage in peatlands. The results demonstrated that the growth of Sphagnum moss and vascular plants were both reduced by N addition but enhanced by P addition. Phenolic concentrations were higher in P addition treatments, as were phenol oxidase activities. In general, N addition played a critical role in regulating the stoichiometry of beta-D-glucosidase, N acetyl-beta-glucosaminidase and phosphatase, while P addition was more important in regulating their activities. The direct and indirect effects due to fertilization and shifts in vegetational composition, respectively, weakened the 'enzymatic latch' mechanism that controls the decomposition of organic matter after long-term fertilization. Our results indicate that P likely plays a more important role than N in controlling microbial extracellular enzymatic activities and organic matter decomposition in northern minerotrophic peatlands. Consequently, the interactions between N and P is likely of primary significance in regulating the biogeochemical cycling of peatlands.