Abstract: Soil microbes are an important component of soil ecosystems that influence material circulation and are involved in the energy flow of ecosystems. The increase in atmospheric nitrogen (N)depositionaffectsalltypesofterrestrialecosystems,includingsubalpineforests. Ingeneral,alpine and high-latitude ecosystems are N limited. Increased N deposition could therefore affect microbial activity and soil respiration. In this study, four levels of N addition, including CK (no N added), N1 (2 g m−2 a−1),N2(5gm−2 a−1),andN3(10gm−2 a−1),werecarriedoutinaSichuanredwoodforest at the eastern edge of the Tibetan Plateau. The dynamics of soil respiration, major microbial groups, ecoenzymaticstoichiometry,andmicrobialbiomasscarbonandnitrogen(MBCandMBN,respectively) were investigated over a year. The results showed that N application significantly increased soil respiration (11%–15%), MBC (5%–9%), MBN (23%–34%), N-acetylglucosidase (56.40%–204.78%), and peroxidase (42.28%–54.87%) activities. The promotion of soil respiration, N-acetylglucosidase, and peroxidase was highest under the N2 treatment. The carbon, nitrogen, and phosphorus metabolism of soil microbes in subalpine forests significantly responded to N application. In the latter stages of N application, microbial metabolism changed from being N restricted to phosphorus restricted, especially under the N2 treatment. Soil bacteria (B) and gram-positive (G+) bacteria were the dominant microbial groups affecting soil respiration. Structural equation modelling indicated that N application significantly promoted soil respiration and microbial biomass, whereas the main microbial groups did not significantly respond to N application. Therefore, we conclude that short-term N addition alleviates microbial nitrogen limitation and promotes soil respiration in the subalpine forest ecosystem that accelerates soil carbon (C) and N cycling. Continuous monitoring is needed to elucidate the underlying mechanisms under long-term N deposition, which may help in forecasting C, N, and P cycling in the alpine region under global climate change.
Keywords: ecoenzymaticstoichiometry;nitrogenaddition;subalpineconiferousforest;soilmicrobial nitrogen restriction; soil respiration; soil microbial groups
