Final Report Summary - SOLCA (Carbonic anhydrase: where the CO2, COS and H2O cycles meet)
One of the grand challenges in Earth system science is to understand how the biosphere and atmosphere interact with one another and how changes in biosphere function will respond to, and potentially alter carbon-climate feedbacks in the future. As seasonal and inter-annual variations in atmospheric CO2 concentrations are strongly influenced by changes in the gross fluxes of photosynthesis and respiration from the biosphere, the atmospheric CO2 concentration responds dynamically to large-scale changes in climate and hydrology across the land surface. However, it is difficult to measure photosynthesis and respiration at large scales and thus interpreting changes in atmospheric CO2 concentrations requires the use of process-based Land Surface Models (LSM). As LSMs are one of the most powerful tools society has to provide guidance on present and future carbon-climate feedbacks, it is important to validate that the key processes described within LSMs behave as we expect them to.
In this context, variations in the concentrations of atmospheric COS and CO18O at large scales can be used as independent tracers of biosphere carbon and water cycling and could be used to constrain the magnitude of terrestrial biosphere CO2 fluxes in the future. However, critical gaps in our understanding of certain processes that govern COS and CO18O biosphere-atmosphere exchange currently prevent us from using oxygen stable isotopes and COS routinely in Land Surface Models (LSMs) and atmospheric inversions. In particular, an understanding of how the activity of the enzyme carbonic anhydrase (CA) varies across the land surface and how this enzymes activity is regulated by environmental drivers is necessary before we can attribute changes in atmospheric COS and CO18O concentrations confidently to changes in biosphere productivity.
In response to this challenge the ERC project SOLCA set out to unleash the potential of COS and CO18O as large scale tracers of biosphere activity by developing vital understanding of CA activity and biosphere COS and CO18O gas exchange. To achieve this we built a unique gas exchange system capable of measuring simultaneously CO18O and COS fluxes from climate-controlled microcosms for the first time. Using soils collected from a range of biomes across the world, CA activity was estimated for both tracers using the new climate-controlled gas exchange system. In particular, the SOLCA project demonstrated that the amount of CA in soils was linked to changes in microbial biomass and certain CA genes across different biomes and that the activity of CA was strongly modulated by changes in temperature and soil moisture content that could be derived from soil texture. In addition we observed that the cytoplasmic pH of soil microbes had a very strong influence on the CA-catalysed CO2 hydration rate and oxygen isotope exchange rate with soil water pools [CO2+H218O<>H2O+CO18O]. In addition, the project also demonstrated that all the soils (and some plants) investigated in SOLCA released COS to the atmosphere. For the first time we showed that the magnitude of COS released from soils can be predicted by the total amount of N in soils and the rate modulated by soil temperature. Collectively, this new understanding has been consolidated in a unique theoretical modelling framework that has been successfully implemented in an isotope-enabled LSM. For the first time ever it is now possible to predict how soil CA activity varies across the land surface and estimate the exchange of COS and CO18O between soils, plants and the atmosphere. This breakthrough is now providing opportunities to attribute the impact of soils and plants to the seasonal variability of CO2, COS and CO18O at atmospheric stations and provide independent constraints on biosphere productivity with changes in climate and hydrology across the Earths surface.
In this context, variations in the concentrations of atmospheric COS and CO18O at large scales can be used as independent tracers of biosphere carbon and water cycling and could be used to constrain the magnitude of terrestrial biosphere CO2 fluxes in the future. However, critical gaps in our understanding of certain processes that govern COS and CO18O biosphere-atmosphere exchange currently prevent us from using oxygen stable isotopes and COS routinely in Land Surface Models (LSMs) and atmospheric inversions. In particular, an understanding of how the activity of the enzyme carbonic anhydrase (CA) varies across the land surface and how this enzymes activity is regulated by environmental drivers is necessary before we can attribute changes in atmospheric COS and CO18O concentrations confidently to changes in biosphere productivity.
In response to this challenge the ERC project SOLCA set out to unleash the potential of COS and CO18O as large scale tracers of biosphere activity by developing vital understanding of CA activity and biosphere COS and CO18O gas exchange. To achieve this we built a unique gas exchange system capable of measuring simultaneously CO18O and COS fluxes from climate-controlled microcosms for the first time. Using soils collected from a range of biomes across the world, CA activity was estimated for both tracers using the new climate-controlled gas exchange system. In particular, the SOLCA project demonstrated that the amount of CA in soils was linked to changes in microbial biomass and certain CA genes across different biomes and that the activity of CA was strongly modulated by changes in temperature and soil moisture content that could be derived from soil texture. In addition we observed that the cytoplasmic pH of soil microbes had a very strong influence on the CA-catalysed CO2 hydration rate and oxygen isotope exchange rate with soil water pools [CO2+H218O<>H2O+CO18O]. In addition, the project also demonstrated that all the soils (and some plants) investigated in SOLCA released COS to the atmosphere. For the first time we showed that the magnitude of COS released from soils can be predicted by the total amount of N in soils and the rate modulated by soil temperature. Collectively, this new understanding has been consolidated in a unique theoretical modelling framework that has been successfully implemented in an isotope-enabled LSM. For the first time ever it is now possible to predict how soil CA activity varies across the land surface and estimate the exchange of COS and CO18O between soils, plants and the atmosphere. This breakthrough is now providing opportunities to attribute the impact of soils and plants to the seasonal variability of CO2, COS and CO18O at atmospheric stations and provide independent constraints on biosphere productivity with changes in climate and hydrology across the Earths surface.