Rapidly Changing Drylands and Consequences for the Microbial Carbon Cycle

Over the next century, climate change will have significant impacts on dryland ecosystems with some regions already experiencing elevated temperature and hydrological change. Drylands exist on every continent, cover ~46.2% (±0.8%) of the global land area and are home to 3 billion people[1]. Drylands are critical locations for climate change mitigation (via carbon sequestration) due to the high concentrations of soil inorganic carbon (SIC, 1237 Pg C) which exceeds soil organic carbon (SOC) in most drylands (Fig. 1) [2,3]. Despite drylands containing 80% of global SIC[3] (more than the individual permafrost, vegetation, and atmospheric reservoirs) this pool remains relatively understudied. The dryland SIC reservoir is considered relatively stable, however, growing evidence indicates SIC instability due to climate and land use change[4–6] contributing to the degradation of 5.43 million Km2 of drylands over the past 35 years[7]. Significant SIC degradation and desertification of drylands has occurred in the Mediterranean and European regions with some soils at the critical limit for providing ecosystem services. Therefore, quantifying the controls on dryland SIC/SOC is an immediate priority for the long-term stability of drylands. The impact of vegetation on dryland carbon cycling is relatively well studied with vegetation type and spatial distribution key controls. However, microbiology are the key drivers of the carbon cycle but the role of bacteria, archaea, and fungi in SIC/SOC synthesis and preservation remains elusive particularly in drylands that contain high biodiversity and are ecological hotspots. Microbes transfer carbon between the SOC and SIC pools through complex interactions between microbial communities, plant roots and mycorrhiza, and organo-mineral complexes and are controlled by biophysical parameters which may have non-linear and discontinuous influence across climate zones. Due to the spatial heterogeneity of drylands, the biophysical controls on SIC/SOC microbial carbon cycling could vary significantly in semiarid drylands due to the complexity of habitat types and differences in temperature and hydrological baselines. Therefore, the aim of this research is to establish the biophysical controls on microbial carbon cycling of the SOC and SIC pools in semiarid drylands. This proposal focusses on 3 semiarid dryland biodiversity hotspots: Makgadikgadi Basin (Botswana), and the islands of Lesvos and Samothraki (Greece). Using an interdisciplinary approach that bridges biology and chemistry, within a geographical context, this project will address the research questions: What are the key pathways of microbial carbon synthesis in semiarid dryland complexes? How is SOC and SIC degraded and preserved in semiarid dryland complexes? What impact do biophysical controls have on microbial carbon cycling in semiarid drylands? This project examines the full complement of biomolecules, including DNA/RNA (metagenomics/metatranscriptomics) to characterise the microbial community and metabolic potential, the speciation of carbon (geochemistry) to assess the SIC/SOC pools, and lipid distributions (lipidomics) to identify the transformation of carbon during synthesis and preservation. Using both environmental observation and laboratory experiments, the response of the microbial carbon cycle to individual and confounding climatic controls (temperature and hydrological change) will be tested. Combining “omics” based methodologies with geochemistry offers a novel approach and will be the first systematic analysis of microbial carbon cycling combined with omics in the Makgadikgadi Basin (Botswana), Lesvos, and Samothraki (Greece). This project will establish the diversity of bacterial, archaea and fungi and resolve the biophysical controls on the SIC/SOC carbon pools and establish the stability of SIC under changing environmental conditions.