The soil microbial respiration rate and its influencing factors in different forest belts of Taibai Mountain, Qinling Mountains

Soil microbial respiration is a major source of CO2 efflux to the atmosphere from forest ecosystems and plays a decisive role in predicting future global climate change. A typical temperate forest ecosystem, the Taibai Mountain contains a mosaic of stands with various attitudes. The objective of the present study was to investigate the trends and influencing factors of microbial respiration in temperate forest soils without external carbon input. In the Taibai Mountain, 0-10 cm topsoil of typical forest belts of different altitudes（Quercus aliena var. acuteserrata, Q. liaotungensis, Betula albosinensis, and B. albosinensis var. septentrionalis） were sampled and incubated at 15 ℃, 25 ℃, and 35 ℃. The microbial respiration rate showed a fluctuating downward trend and a slowly decreasing trend at Days 1-20 and Days 20-72, with a 68% and 90% decrease compared to the initial rate, respectively. Thus, high temperature promoted soil respiration in the short term whereas it retarded soil respiration in the long term. The temperature sensitivity index(Q10) of the soil in the Taibai Mountain decreased with warming. Microbial biomass increased initially and then decreased during the incubation at 15 ℃ and 25 ℃, whereas it decreased throughout the incubation at 35 ℃. Furthermore, BG（β-1,4-glucosidase） was the most important extracellular enzyme affecting microbial respiration. After 72 days of incubation, BG failed to provide adequate carbon for microbial growth and reproduction. At 25 ℃ and 35 ℃, the carbon provided by BX（β-1,4-xylosidase） became one of the most important carbon sources for microbial growth and reproduction. At 15 ℃ and 25 ℃, N was the limiting factor for soil respiration during the early incubation stage and C was the limiting factor for the later stage; at 35 ℃, N was the limiting factor of soil respiration throughout the incubation. At 15 ℃ and 35 ℃, there was no P limitation for soil respiration; however, P was a limiting factor for soil respiration during the early incubation stage at 25 ℃. The results of this study demonstrated that the key to limiting soil carbon emissions is to retard soil microbial respiration, with extracellular enzymes significantly influencing soil microbial respiration.