Influences of N deposition on soil microbial respiration and its temperature sensitivity depend on N type in a temperate forest

Abstract

Knowledge on temperature sensitivity (Q10) of soil microbial respiration is crucial to improving the accuracy in predicting soil organic carbon (C) dynamics in climate–C models. However, the responses of soil microbial respiration and its Q10 to nitrogen (N) deposition, particularly different N types, remain unclear. Therefore, we incubated surface soils collected from a temperate forest receiving simulated N deposition under 15 °C and 25 °C for 150 days to examine the effects of different types of N deposition on soil microbial respiration and its Q10 and reveal their underlying mechanisms. A mixture of inorganic and organic N had the highest suppression on soil microbial respiration, followed by organic N and inorganic N. This suggested that the suppression effect of atmospheric N deposition on microbial respiration was underestimated by previous studies based on single inorganic N. Q10 values in all soils ranged from 1.96 to 2.76 with a mean of 2.41 at the end of incubation. Inorganic N significantly increased the averaged Q10 values, suggesting that inorganic N caused soil microbial respiration to become more sensitive to climate warming than organic N. Across the incubation period, Q10 values exhibited substantial temporal variation, which depended on the N type. Soil microbial respiration was negatively controlled by NO3−-N and bacteria:fungi and gram-positive:gram-negative bacteria ratios. However, Q10 was positively controlled by soil NH4+-N. Our results highlighted the effects of inorganic and organic N deposition on microbial respiration and its potential mechanisms and implied the necessity of considering the N type when predicting soil C cycling and dynamics in increasing N deposition scenario.