Nitrogen depositions increase soil respiration and decrease temperature sensitivity in a Moso bamboo forest.

Highlights • Nitrogen depositions significantly increase soil respiration (Rs) rates. • Nitrogen depositions significantly decrease the temperature sensitivity of Rs. • Soils emit 470 kg CO 2 ha−1 yr−1 per 1 kg N ha−1 yr−1 added to Moso bamboo forests. • Models based on temperatures of soil and air may quantify annual soil CO 2 effluxes. • The N saturation threshold of Moso bamboo forests may be 60 kg N ha−1 yr−1. Abstract Nitrogen (N) deposition plays an important role in regulating forest productivity and microbial biomass and activities, ultimately influencing soil respiration (Rs). However, the effects of increasing atmospheric N depositions on Rs in subtropical Moso bamboo forests remain poorly understood. Here, we conducted a 4-year field experiment in a subtropical Moso bamboo forest to quantify the effect of simulated N depositions at four rates (0, 30, 60 and 90 kg N ha−1 yr-1) on Rs. The mean Rs rate of the control was 353.17 ± 53.23 mg CO 2 m-2 h-1 or 30.75 ± 2.38 t CO 2 ha-1 yr-1. Soil respiration showed significantly higher sensitivity (Q 10) to soil temperature than to air temperature, and the Rs rate was significantly positively related to soil microbial biomass carbon, soil temperature, and NO 3 -. In response to N addition treatments of 30, 60, and 90 kg N ha-1 yr-1, the mean annual Rs increased by approximately 45.7%, 37.7%, and 13.0%, respectively, compared with the control. Nitrogen depositions decreased the temperature sensitivity of Rs, leading to predictions that they may be able to mitigate the priming effects of future climate warmings on Rs in Moso bamboo forests in the coming decades. Combined models based on the significant relationships between Rs rates, daily mean air temperatures, and hourly soil temperatures at a depth of 5 cm may reliably and feasibly estimate annual soil CO 2 efflux. On average, soil emitted 470 kg CO 2 ha-1 yr-1 per 1 kg N ha-1 yr-1 added, which declined when N addition surpassed the N saturation threshold of 60 kg N ha-1 yr-1. Our findings provide a method for estimating annual soil CO 2 efflux and new insights into the effects of N deposition rates on soil CO 2 efflux in Moso bamboo forests. [ABSTRACT FROM AUTHOR]