Long-term effects of temperature on carbon mineralisation processes

The long-term effects of temperature on soil C mineralisation were investigated in two experiments using 14C labelled wheat straw incubated in organic soils from five coniferous forests located in different climate zones of Western Europe. In the first experiment, samples were incubated in the laboratory at 4, 10, 16, 23 or 30°C, with constant moisture, and the loss of 14C was monitored for 550 days. Double negative exponential functions fitted to the 14C loss data at different temperatures were used to define the relative proportions of labile and recalcitrant components in the original straw. The estimated proportions of these constituents were related to incubation temperatures with the amount of C reflecting the labile fraction increasing with increasing temperature. In the second experiment samples mixed with the labelled straw were incubated at 4, 16 or 30°C until the same percentage of 14C loss was reached. The samples were then incubated again at a common temperature for 30 days and CO2 production was measured to assess the lability of the remaining material. For all the soils, the amount of readily decomposed material was higher in samples conditioned at 4° than at 30°C. It was concluded that in addition to temperature controlling rates of C mineralisation in soil it also affects the processes of decomposition so that material produced at higher temperatures was more recalcitrant than at lower temperatures.