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 13.9°C. 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 μ mol CO 2 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 ( Q 10 of 2.07 and 2.94 at 1500 and 1000 m asl, respectively) than at the highest and lowest sites of the gradient ( Q 10 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.