Functional characterisation of plant leaf airspaces in 3D

Plant leaves are key components to the global carbon and water cycle, as virtually all terrestrial carbon going from the atmosphere to terrestrial ecosystems and ~70% of all terrestrial transpired water passes through them. Research on carbon and water fluxes at the leaf has primarily focused on how the pores on the surface of the leaf (stomata) and the cells where photosynthesis occurs (mesophyll cells) respond to changes in their environmental conditions. However, there is a space within the leaf that has often been overlooked or ignored when studying photosynthesis as this air-filled cavity barely limits the movement of CO2 in crop plants, which have most often been studied. However, this airspace was shown to limit the movement of CO 2 for certain leaf types found over a wide range of environments around the globe. Further, leaves of the flowering plants (angiosperms), the most diversified and recent plant group in terms of evolution, have improved stomatal control and water transport properties compared to their ancestors like ferns and gymnosperms such as conifers. Little is known on the diversity of the leaf airspace properties and whether or not the angiosperms have evolved improved traits similar to those related to water transport. The proposed project Functional characterisation of plant leaf airspaces in 3D will try to answer that question. The research, building from state-of-the-art three-dimensional leaf imaging through high resolution X-ray computed tomography, will allow to present the leaf airspace properties in their true volumetric nature. In combination with an in-depth analysis of photosynthesis and transpiration, the 3D representation of the leaf will make it possible to accurately describe the importance of the air space in carbon and water transport processes within the leaf, as well as the coordination of airspace properties with other related leaf traits. For this functional characterization, modelling at a small scale will be done using finite element analysis, a tool mostly used in engineering, that will accurately represent the physical processes within the diverse 3D leaf anatomies acquired. This modelling will be then used to build a leaf model that treats a canopy as a single big leaf in order to quantify the role of the leaf airspace in the plant carbon and water relations. This new knowledge is key to fully understand how leaves evolved, adapted, and optimized carbon acquisition and water loss in response to a changing environment, providing important information to reconstruct fossil leaf properties as well as to improve the prediction of plants responses to future climate.

Plant leaves are key components to the global carbon and water cycle, as virtually all terrestrial carbon going from the atmosphere to terrestrial ecosystems and ~70% of all terrestrial transpired water passes through them. Research on carbon and water fluxes at the leaf has primarily focused on how the pores on the surface of the leaf (stomata) and the cells where photosynthesis occurs (mesophyll cells) respond to changes in their environmental conditions. However, there is a space within the leaf that has often been overlooked or ignored when studying photosynthesis as this air-filled cavity barely limits the movement of CO2 in crop plants, which have most often been studied. This airspace was shown to limit the movement of CO2 for certain leaf types found over a wide range of environments around the globe. Further, leaves of the flowering plants (angiosperms), the most diversified and recent plant group in terms of evolution, have improved stomatal control and water transport properties compared to their ancestors like ferns and gymnosperms such as conifers. Little is known on the diversity of the leaf airspace properties and whether or not the angiosperms have evolved improved traits similar to those related to water transport. The project "Functional characterisation of plant leaf airspaces in 3D" answered those questions and showed that angiosperms, through smaller photosynthesising cells, were able to increase the surface area available for CO2 to diffuse and reach the photosynthesising chloroplasts. Hence, angiosperms were able to take full advantage of the increased number of pores at the leaf surface that provide more CO2 for photosynthesis by having more cell surface through which CO2 can diffuse and having an airspace that facilitates CO2 movement up to the photosynthesising cells. This restructuring of the whole leaf anatomy enabled angiosperms to dominate over the majority of the globe's biomes despite declining CO2 concentrations since the end of the Cretaceous. This research used state-of-the-art three-dimensional leaf imaging through high resolution X-ray computed tomography to present the leaf airspace properties in their true volumetric nature. This research combined an in-depth analysis of photosynthesis and transpiration with the 3D representation of the leaf to accurately describe the importance of the airspace in carbon and water transport processes within the leaf, as well as the coordination of airspace properties with other related leaf traits. This new knowledge is key to fully understand how leaves evolved, adapted, and optimized carbon acquisition and water loss in response to a changing environment, providing important information on how leaves are built, adapt to changing environmental conditions, and how they will respond to future climate.