Project 6: Global change and biodiversity feedbacks as drivers of the carbon cycle in the plant–soil system

Michael Schmidt
Samuel Abiven
Moritz Reisser

Research aims - The aim of this project is to demonstrate whether increased biodiversity and net primary production lead to increased carbon storage in the ecosystem, especially in the largest carbon pool, the mineral soil, and thus reduces the release of greenhouse gases.

Climate change (nitrogen deposition, summer droughts, vegetation fire) – We will analyse plant–soil feedbacks in laboratory experiments, using our newly build Multi Isotope labelling in Controlled Environment (MICE) facility, and in three of the field sites (tropical, temperate, boreal) using transplanted model mini-ecosystems. Global change includes many processes, and we focus on three processes, key to the terrestrial carbon cycle, i.e. increasing chronic atmospheric nitrogen deposition (Hagedorn et al., 2011), widespread summer droughts, and more frequent wildfires (Schmidt, 2004; Preston & Schmidt, 2006), with yet unknown consequences for the carbon cycle (e.g. Schmidt et al. 2011). We will use the MICE facility to manipulate mini-ecosystems (plants and soil from the three field sites) and expose them to four climatic scenarios: today’s equivalent climate (corresponding to the site), increased nitrogen deposition, drought and post-fire conditions (by pyrolising the plant biomass). The plant–soil system will be labelled with stable isotopes (¹³C, ¹⁵N) in order i) to investigate the changes in organic matter dynamics when climate changes are applied and ii) to produce highly labelled experimental material that could be traced in the field. We will transplant the manipulated mini-ecosystem, from the MICE facility to the three URPP GCB sites Siberia, Laegeren and Borneo (tropical, temperate, boreal). The mini-ecosystems will contain highly labelled material (¹³C and ¹⁵N in fresh biomass and charred biomass) in order to follow fluxes related to C losses from the soil (CO₂ and organic matter dissolved in water), as well as processes involved in the stabilisation of soil C (microbial, physical and chemical mechanisms). Using a large number of replicates will allow us to follow the underlying processes of C stabilisation in soil and vegetation at a high spatial and temporal precision.

Biodiversity experiment – We will use the MICE chambers to grow different species of trees and grasses labelled with ¹³C (and potentially ¹⁵N, ¹⁸O and ²H) under today’s climatic conditions. Then we recombine the different species (1, 2, 4, 8 species) and transplant them to the temperate site at Laegeren. In the field we can follow the total carbon fluxes and the contributions from the isotopically labelled decomposing biomass, and the living biomass.

Expected contributions to research theme – This project will contribute to a better understanding of global change–biodiversity–ecosystem functioning relationships by identifying underling pathways and mechanisms and by quantifying processes of soil carbon stabilization after carbon input from vegetation. These mechanisms and processes will be fed into more comprehensive mechanistic models developed within the URPP GCB. This will eventually allow us to predict how potential scenarios of global change and biodiversity responses affect, and feed back to, terrestrial biogeochemical cycles, and eventually to the climate system. Developing and implementing a new generation of mechanistic soil carbon models should better reflect observations and inform predictions and policies.