Dynamics of the water extractable organic carbon pool during mineralisation in soils from a Douglas fir plantation and an oak-beech forest-an incubation experiment

In the context of land use change, the dynamics of the water extractable organic carbon (WEOC) pool and CO2 production were studied in soil from a native oak-beech forest and a Douglas fir plantation during a 98-day incubation at a range of temperatures from 8A degrees C to 28A degrees C. The soil organic carbon, water contents and mineralisation rates of soil samples from the 0-5 cm layer were higher in the native forest than in the Douglas fir plantation. During incubation, a temperature-dependent shift in the delta C-13 of respired CO2 was observed, suggesting that different carbon compounds were mineralised at different temperatures. The initial size of the WEOC pool was not affected by forest type. The WEOC pool size of samples from the native forest did not change consistently over time whereas it decreased significantly in samples from the Douglas plantation, irrespective of soil temperature. No clear changes in the delta C-13 values of the WEOC were observed, irrespective of soil origin. The fate of the WEOC, independent of soil organic carbon content or mineralisation rates, appeared to relate to forest types. Replacement of native oak-beech forest with Douglas fir plantation impacts carbon input to the soil, mineralisation rates and production of dissolved organic carbon.