Temporal variation and climate dependence of soil respiration and its components along a 3000 m altitudinal tropical forest gradient

To simulate the effect of temperature on soil respiration rates, we translocated soil cores among four sites (3030, 1500, 1000, and 200 m asl) along an altitudinal tropical forest gradient in the Peruvian Andes, traversing a difference in mean annual temperature of 13.9C. Rates of total (R_s) and heterotrophic (R_sh) respiration were measured twice a month from April 2007 to March 2009 and additionally for full 24 h periods. The diurnal range in R_s increased with altitude; this variation was mainly root and litter derived, whereas R_sh varied only slightly over full 24 h periods. Although mean annual daytime R_s rates were not significantly different among the four sites (4.45-4.05 mol CO₂ m^-2 s^-1), the annual amount of respired C decreased with increasing altitude from 1639 g C m^-2 yr^-1 at 200 m asl to 1064 g C m^-2 yr^-1 at 3030 m asl. The contribution of R_sh to R_s was not correlated with elevation and ranged from 25% to 60%. The temperature dependence of R_s was lower at the midelevation sites (Q₁₀ of 2.07 and 2.94 at 1500 and 1000 m asl, respectively) than at the highest and lowest sites of the gradient (Q₁₀ of 4.33 and 6.92 at 3030 and 200 m asl, respectively). The temperature sensitivity of R _sh was higher for the sites at 3030 and 200 m asl and increased with time, i.e., with the loss of the most labile C pools.