Distinct temperature sensitivity of soil carbon decomposition in forest organic layer and mineral soil

The roles of substrate availability and quality in determining temperature sensitivity (Q(10)) of soil carbon (C) decomposition are still unclear, which limits our ability to predict how soil C storage and cycling would respond to climate change. Here we determined Q(10) in surface organic layer and subsurface mineral soil along an elevation gradient in a temperate forest ecosystem. Q(10) was calculated by comparing the times required to respire a given amount of soil C at 15 and 25 degrees C in a 350-day incubation. Results indicated that Q(10) of the organic layer was 0.22-0.71 (absolute difference) higher than Q(10) of the mineral soil. Q(10) in both the organic layer (2.5-3.4) and the mineral soil (2.1-2.8) increased with decreasing substrate quality during the incubation. This enhancement of Q(10) over incubation time in both layers suggested that Q(10) of more labile C was lower than that of more recalcitrant C, consistent with the Arrhenius kinetics. No clear trend of Q(10) was found along the elevation gradient. Because the soil organic C pool of the organic layer in temperate forests is large, its higher temperature sensitivity highlights its importance in C cycling under global warming.