Interactive effects of earthworms and climate change on soil organic carbon dynamics and sequestration

• Applicant: Dr. Gerrit Angst
• Subject Area: Soil Sciences
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 468483041

Soil represents the largest terrestrial carbon (C) reservoir and stores more C than the atmosphere and vegetation combined. Whether soil acts as C sink or source is co-determined by soil fauna, among which earthworms are particularly relevant. Yet, although present almost ubiquitously in ecosystems worldwide, the effects of earthworms on soil C sequestration have often been neglected. This hampers the advancement of ecological or biogeochemical models and, thus, the reliability as to which such models predict soil C storage across temporal and spatial scales.Earthworms have two major effects on soil C dynamics: they either increase the mineralization of C by stimulating microbial activity, biomass, and diversity, and they stabilize C by promoting the formation of macro- and microaggregate structures, in which C is protected against decomposition. The net effect of these processes, acting in opposite directions, on the soil C budget is widely unknown. Moreover, the role of a changing climate and different land uses in these processes has not been systematically investigated. Such knowledge, however, is indispensable in understanding and predicting soil C dynamics. Recent studies suggest that earthworms influence C stability and the composition of stable C pools on the molecular level, without necessarily leaving recognizable imprints on coarser measures, such as C contents in bulk soil.We will, thus, tackle the research gaps highlighted above by disentangling the effects of earthworms on C dynamics on the molecular level in realistic field experiments, under ambient and simulated future climates. Treatments without earthworms will serve as a control. We will test the interactive effects of climate change and earthworms in two different land use systems, representing heavily managed ecosystems (conventional agriculture) and ecosystems with minimal disturbance (extensively managed grassland). 13C-labeled litter will be supplied to the treatments, allowing us to trace the fate of C entering the soil. After one vegetation period, we will physically fractionate the soil from the treatments into differently stable C pools (specifically, aggregate- and mineral-associated C), measure C/13C and nitrogen contents, and extract biomarkers for microbial bio- and necromass. We will further employ a spatially resolved sampling design to test whether the effects of earthworms spatially manifest themselves on the pedon scale (i.e., on cm to dm) and on the nano scale (nm). Complementary laboratory incubations, examining the influence of individual earthworms and earthworm assemblages, round out the design of the proposed project. The proposed project will provide essential new insights into the interactive effects of earthworms, land use, and climate change on C dynamics and sequestration, information that is crucially needed for an effective C-related ecosystem management, but currently unavailable.

• DFG Programme: WBP Position