A04 - Carbon stock, turnover and functions in heavily weathered soils under lowland rainforest transformation systems
Strong decrease of organic carbon (C) stocks and degradation of soil properties after transformation of lowland rainforest to plantations was shown in Phase 1. In Phase 2, A04 Kuzyakov focused on C content, stocks and decomposability in riparian sites. The hypothesis was that C stocks in riparian sites are highly vulnerable by climate and land use changes, especially if water regime will be changed and ground water level drops. The results of Merten et al. (2016) indicated a drop of water level on mineral soils the decade after conversion to oil palm plantations. Consequently, we expected a fast mineralization of soil organic matter (SOM) and decrease of C stocks. To understand the past and recent SOM dynamics in mineral welldrained soils and riparian soils, depth profiles of natural 13C abundance were applied as tool to disentangle SOM mineralization (Alewell et al. 2011, Krüger et al. 2014, Guillaume et al. 2015, Drollinger et al. 2019) especially under anoxic or alternating conditions (Drollinger et al. 2019) and erosion-sedimentation processes. δ13C signature can be used as a suitable tool because SOM and litter decomposition lead to a 13C depletion by kinetic isotope fractionation (Ågren et al. 2010, Dawson et al. 2002, Werth and Kuzyakov 2010), but erosion brings the deeper 13C enriched soil horizons to the surface and so, leads to 13C enrichment. We tested the hypothesis that the comparison of δ13C signature of profile depths between riparian and well-drained soils will allow conclusions about the dominance of SOM mineralization or allochthonous C transport and deposition.