Seasonal and diurnal variations in soil respiration rates at a treeline ecotone and a lower distribution limit of subalpine forests

Abstract

This study examined the seasonal and diurnal variations in soil respiration rates (R_S) during a growing season at the treeline ecotone (2,800 m) and the lower distribution limit (1,600 m) of subalpine forests on a volcanic mountain in Japan. The aboveground biomass, the total R_S during the growing season, and the R_S per day during the growing season were lower at 2,800 m than those at 1,600 m. Seasonal R_S variations positively correlated with those of soil and air temperatures at both elevations, and this tendency was more apparent at 1,600 m than 2,800 m. The mean volumetric soil water content (W_S) during the growing season was much lower at 2,800 m than 1,600 m because of the scoria substrate at 2,800 m. The monthly mean diel cycle of R_S was positively correlated with the soil temperature at each elevation every month, whereas that at 1,600 m was negatively correlated with that of the W_S. The R_S at 2,800 m decreased during the daytime especially in August, despite no changes in the W_S. The decrease in R_S after precipitation at 1,600 m was higher than that at 2,800 m. Seasonal and diurnal R_S variations could be reproduced from soil and air temperatures, and W_S. Estimating soil respiration rate from these variables will help understand the future carbon budget of forests due to global warming.