Soil respiration along an altitudinal gradient in a subalpine secondary forest in China

The subalpine forest ecosystems in the Miyaluo Forest District in western Sichuan (China) could be very sensitive to global climate change, with important consequences for the regional carbon (C) balance. In a birch secondary forest in this area, we measured plots with (Control) and without (No Litter) leaf litter to explore variation in soil respiration and its relationship with environmental factors along an altitudinal gradient, and to quantify the litter contribution to soil respiration. Soil respiration rate decreased with elevation. The average of soil respiration rates along the elevation gradient during the measurement period was 2.83 +/- 0.14 mu mol CO2 m(-2) s(-1) in the Control treatment and 2.35 +/- 0.16 mu mol CO2 m(-2) s(-1) in the No Litter treatment, with an average proportion of litter layer contribution to soil respiration of 17%. A significant linear relationship between soil respiration and soil temperature along the altitudinal gradient was found, while soil respiration was not significantly correlated with soil water content in both treatments. Soil temperature accounted for 94.9% and 95.6% of the total variation in soil respiration in Control and No Litter treatments, respectively. At altitudes of 2910 m, 3135 m, 3300 m and 3492 m a.s.l., soil respiration had a significant exponential relationship with soil temperature (p<0.05), but it was not significantly correlated with soil water content in both treatments (p>0.05). Soil temperature accounted for more than 92% and 81% of the total variation in soil respiration in Control and No Litter treatments, respectively, at all altitudes except at 3135 m a.s.l. Our results suggest that the expected temperature increases by global warming might enhance soil respiration in the birch secondary forest.