Decomposition of C-13-labelled plant material in a European 65-40 degrees latitudinal transect of coniferous forest soils: simulation of climate change by translocation of soils

Standard C-13-labelled plant material was exposed over 2-3 yr at 8 sites in a north-south climatic gradient of coniferous forest soils, developed on a cid and calcareous parent materials in Western Europe. In addition to soils exposed in their sites of origin, replicate units containing labelled mate rial were translocated in a cascade sequence southwards along the transect, to simulate the effects of climate warming on decomposition processes. The current Atlantic climate represented the most favourable soil temperature and moisture conditions for decomposition. Northward this climatic zone, wh ere the soil processes are essentially temperature-limited, the prediction for a temperature increase of 3 degrees C estimated a probable increase of C mineralisation by 20-25% for the boreal zone and 10% for the cool tempera te zone. Southward the cool Atlantic climate zone, (the Mediterranean clima te), where the processes are seasonally moisture-limited, the predicted inc rease of temperature by 1-2 degrees C little affected the soil organic matt er dynamics, because of the higher water deficit. A significant decrease of C mineralisation rates was observed only in the superficial layers recogni sed in Mediterranean forest soils as 'xeromoder' and subject to frequent dr y conditions. In the deeper Mediterranean soil organic horizons (the mull h umus types), representing the major C storage in this zone, C mineralisatio n was not affected by a simulated 2 degrees C temperature increase. The tem perature effect is probably counteracted by a higher water deficit. (C) 200 0 Elsevier Science Ltd. All rights reserved.