Rhizosphere Mediation of Biosphere-Climate Feedbacks – Assessing Blue Carbon Cycling under Climate Change

• Applicant: Dr. Peter Mueller
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 502681570

Climate-driven alterations in soil abiotic conditions can directly affect microbial communities and thereby carbon and greenhouse-gas (GHG) fluxes to the atmosphere. In addition to direct climate-change effects (CCEs) on soil microbial carbon cycling, plant responses to climate change can act as a strong –sometimes overriding– mediator of CCEs on soil microbial communities. These plant-mediated effects are most pronounced in the rhizosphere and are determined by plant physiological and morphological trait expressions. However, the link between plant traits, soil microbial functioning, and carbon fluxes is poorly developed, which represents a key knowledge gap in informing models of ecosystem-climate feedbacks. I argue that plant-mediated effects on soil microbial carbon cycling are particularly important in wetland ecosystems because here plants not only control the microbial substrate supply, they also regulate the availability of electron acceptors by providing oxygen to an reducing soil system. At the same time, wetland soil microbial carbon cycling plays a disproportionately large role in the climate system, because low rates of microbial activity have caused wetlands to sequester the largest soil organic carbon (SOC) stock in the biosphere, representing a vast potential source of GHG to the atmosphere if unlocked by climate change. The central objective of this Emmy Noether project is to understand the mechanisms by which plants mediate CCEs on wetland SOC stock stability and GHG emissions through investigations of plant-trait responses and their interactions with soil microbial communities. Studies will be focused on tidal wetlands, semi-terrestrial ecosystems at the interface of land and sea that have been increasingly recognized for their outsized leverage over the global carbon cycle under the term ‘blue carbon’. The work comprises four complementary subprojects (SPs) that assess soil microbial carbon cycling from a plant-trait perspective. SP1 will provide the mechanistic basis by identifying the plant traits that control wetland SOC decomposition via rhizosphere priming effects, and determine how priming effects relate to overall wetland GHG emissions. This knowledge will be applied to address the project’s central question in SP2: How do plants mediate the effects of climate change on wetland SOC stock stability and GHG emissions? SP2 will quantify the interactions between plant traits and microbial carbon cycling along climate-sensitive environmental gradients, focusing on individual plant-level responses (i.e. phenotypic plasticity) and community-level responses. SP3 will complement this work by exploring population-level responses (i.e. intraspecific genotypic variation) as a yet overlooked additional level of plant-mediated CCEs on soil microbial carbon cycling. The synthesis, SP4, will compare and summarize the findings of the experimental SPs and advance their future integration into numerical models on wetland carbon cycling.

• DFG Programme: Independent Junior Research Groups
• International Connection: USA
• Cooperation Partner: Professor James Patrick Megonigal, Ph.D.