Climate dependence of heterotrophic soil respiration from a soil-translocation experiment along a 3000 m tropical forest altitudinal gradient

Tropical ecosystems play a key role in the global carbon cycle, but their response to global warming is not well understood. Altitudinal gradients offer the unique possibility of undertaking in situ experimental studies of the influence of alterations in climate on the carbon (C) cycle. In a soil-translocation experiment we took replicate soil cores at 3030 m, 1500 m, 1000 m and 200 m above sea level along an altitudinal gradient in tropical forest in Peru, and exchanged (i.e. translocated) them among these sites to observe the influence of altered climatic conditions on the decomposition of soil organic matter under natural field conditions. Soil respiration rates of the translocated soil cores and adjacent undisturbed soils were measured twice a month from April 2007 to October 2007. The temperature sensitivity of heterotrophic respiration in each core was examined using a Lloyd & Taylor function and a simple modified third-order polynomial fit. Calculated Q ₁₀ values decreased with decreasing altitude using both mathematical functions (2.53-1.24 according to the Lloyd & Taylor function, and 2.56-0.63 using the polynomial fit). Soil organic C-stocks increased markedly and linearly with altitude, but surprisingly the average total soil respiration rate did not vary significantly with altitude along the transect (3.98-4.31 μmol CO₂ m^-2 s^-1). This implies an increase with elevation of absolute C allocation to below-ground allocation.