Soil heterotrophic respiration in response to rising temperature and moisture along an altitudinal gradient in a subtropical forest ecosystem, Southwest China.

Globally, one-third of the terrestrial carbon (C) is stored in tropical soils. The warming predicted for this century is expected to increase microbial decomposition in soil and escalate climate change potential by releasing more carbon dioxide (CO) into the atmosphere. Understanding the response of soils to warming is a key challenge in predicting future climate change trajectories. Here we examined the combined effect of soil temperature (T) and soil water content (VWC) on soil heterotrophic respiration (R) and its temperature sensitivity across different altitudes (2400, 1900, and 1450 m ASL) in the Ailaoshan subtropical forest ecosystem, Southwest China. Along the elevation gradient, soil C stocks in the top 10 cm soil layer increased significantly from 10.7 g/ kg at 1480 m ASL to 283.1 g/ kg at 2480 m ASL. Soil cores from various elevations were translocated to the same, and lower elevations and R from those cores were measured every month from February 2010 to January 2014. Temperature sensitivity (Q) of R for the period was highest at the highest (H) elevation (Q = 5.3), decreased significantly towards the middle (M, Q = 3.1) and low (L, Q = 1.2) elevation. Q at M and L elevation did not differ between the place of origin and translocated cores. For the cores within each elevation, Q did not vary across the years. Our models suggest that R increased significantly in response to an increase in T at each elevation under an intermediate VWC. Hence, the rate of emission was higher in lower elevations due to a higher T range. Our findings highlight that the predicted warming over the 21st century will have the greatest impact of T on R especially on the soils at the highest elevations, and will lead towards positive feedback to the climate system.