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 degrees 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 mu 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 (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.