Variations in belowground carbon use strategies under different climatic conditions

Abstract

Belowground carbon is important to the terrestrial carbon cycle, and altitudinal gradients in mountainous areas provide natural experiment sites for analysing the carbon cycle under different climatic conditions. Therefore, to better understand belowground carbon use strategies under different climatic conditions, we quantified soil respiration (RS) and its components (heterotrophic respiration (RH) and autotrophic respiration (RA)) and evaluated the belowground carbon use efficiency (CUE) at 8 sites along an altitudinal gradient (from 2017 to 3665 m asl) during the wet season (May to October) in 2015 and 2016. The results showed that the rates of RS, RH, and RA and the ratios of RH to RS were all negatively correlated with elevation. The contribution of RH to RS was larger than that of RA, ranging from to 66% to 86%. Soil temperature had a stronger relationship with RH than RA, although we note that the latter was not measured directly in this study. The microbial CUE tended to decrease from the mid-elevation sites to the lower- and higher-elevation sites. The root CUE exhibited an increasing trend from the mid-elevation site to the higher-elevation sites. These results suggest that (1) when considering changes in RS values in response to changes in soil temperature, the dominant contributor is RH, not RA; (2) from the areas with moderate temperature and precipitation to the high temperature and low precipitation areas, more belowground carbon (both organic and root carbon) tend to be consumed, whereas more root carbon tend to be retained from the moderate climatic areas to the low temperature and high precipitation areas.