Final Report Summary - CDREG (Carbon dioxide regulation of Earth’s ecological weathering engine: from microorganisms to ecosystems)
The ultimate goal of CDREG was to provide a new synthesis in which the role of atmospheric CO2 in regulating the ‘global ecological weathering engine’ across scales from root-associated microorganisms to terrestrial ecosystems would be mechanistically understood and comprehensively assessed in the context of Earth’s Cenozoic CO2 and climate history and our current climate crisis. It aimed to provide timely opportunities for policy interface because mechanistic understanding of CO2-mediated land ecosystem weathering and feedbacks between the biosphere, geosphere, atmosphere and oceans may lead to technologies and land-use management practices for enhancing this route to sequestering fossil fuel emitted CO2 and neutralizing ocean acidification. Over the course of the 5 year programme, CDREG full-filled and extended these goals through the execution of four interdisciplinary work packages (WPs) in collaboration with our project partners in Southampton, Exeter and Bristol. Key outcomes have been advancement of the careers of four post-doctoral researchers and the training of three PhD students. The CDREG team have published a steady stream of manuscripts in learned academic journals, given talks and presented posters at numerous conferences in Europe and further overseas. Key scientific outcomes from WP1 has been to discover empirical evidence for a negative feedback across a declining Cenozoic atmospheric CO2 regulated through the action of CO2 starvation on host tree productivity and mycorrhizal fungi on rates of biological weathering that may provide an important contributory mechanism stabilizing Earth’s CO2 minimum over the past 24 million years. By employing techniques of molecular biology, we were able to combine results from transcriptomic and metabolomic analyses to develop a new molecular genetic model for weathering by the mycorrhizal fungus associated with the roots of pine seedlings. Savannas are a major global ecosystem that expanded under Miocene low atmospheric CO2 levels 8–10 Myr ago. The cause of this rise is much debate with most explanations proposing a role of fire in keeping tree cover low. Key scientific outcomes from WP2 have been show that starch dynamics are important given they affect trees and grasses differently under drought and low CO2. This overlooked factor may represent a new driver of savanna biome expansion and the ongoing woody encroachment of open savanna with increasing atmospheric CO2 over the 20th and 21st centuries. The geological history of savannas is inferred from ocean sediment cores, and in analyses cores from the Atlantic off the west African coast, WP3 showed the Sahara desert had repeatedly expanded and contracted paced by orbital variations in the African monsoon. We further showed that the present-day Sahara desert was periodically transformed to an area of savanna vegetation for hundreds of thousands of years – a phenomenon we call the ‘mega-green Sahara’ events – during the past 8 million years. Human actions in managing the landscape are crucial to sustainability removing the greenhouse gas carbon dioxide from the atmosphere will be critical to limiting future climate change. WP4 showed how by modelling interactions described by experiments in WP1 and WP2, we could develop strategies involving the application of crushed silicate rocks to terrestrial managed agricultural lands may be able to capture CO2 whilst simultaneously improving food and soil security.