Embracing 3D Complexity in Leaf Carbon–Water Exchange

Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants

“…In fact, doing so has significantly expanded our understanding of g m across diverse species and under numerous environmental conditions (Evans and von Caemmerer, ; Flexas et al ., , ; Warren, ; Evans et al , ). However, new insights are likely to be gained from a better understanding of how the complex 3‐D arrangement of stomata, cells, organelles, and intercellular airspaces of the leaf integrate to impact the variation in g m observed between plant types, and how g m responds to different measurement and growth conditions (Earles et al , ). Measurements of leaf gas exchange, isotope exchange and, to a lesser extent, chlorophyll fluorescence (Evans and Vogelmann, ; Evans, ; Cernusak et al , ; Ho et al , ; Theroux‐Rancourt and Gilbert, ) integrate across the 3D space of the leaf that is held within the measurement chamber.…”

“…The development and merging of these two emerging areas of research is likely to provide new insights into how the complexity of leaf tissue cellular and subcellular properties influences the diffusive properties of CO 2 within the leaf as well as the apparent differences in g m that occur between species, growth environments, and measurement conditions. The 3‐D reaction‐diffusion models and image analysis are briefly introduced and discussed below, but a more detail description can be found in several recent reviews and manuscripts (Tholen and Zhu, ; Ho et al , , ; Berghuijs et al ., , ; Theroux‐Rancourt et al , ; Xiao and Zhu, ; Earles et al ., , ).…”

“…There are several imaging techniques that have been recently utilized to estimate the 3‐D structure of the leaf (e.g. X‐ray computed tomography, focused ion beam scanning electron microscopy, serial block‐face scanning electron microscopy; see review by Earles et al , for additional details). The few publications comparing 2‐D versus 3‐D leaf structure suggest that 2‐D projections maybe underestimating key traits.…”

“…These authors suggest that 2‐D methods generally underestimate S mes , but use of a curvature correction factor with a 2‐D cross‐sections (Thain, ) improved the relationship to that of the 3‐D microCT analysis. The application of these 3‐D technologies to leaf traits associated with g m has the potential to further our understanding of the structure–function relationship of leaf anatomy and g m (Earles et al , ). The various tools for 3‐D leaf analysis are likely to continue to provide new insights, but they are not yet readily available to the larger plant science community and as previously pointed out the downstream data analysis can be computationally demanding (Theroux‐Rancourt et al , ; Earles et al , ).…”

“…The application of these 3‐D technologies to leaf traits associated with g m has the potential to further our understanding of the structure–function relationship of leaf anatomy and g m (Earles et al , ). The various tools for 3‐D leaf analysis are likely to continue to provide new insights, but they are not yet readily available to the larger plant science community and as previously pointed out the downstream data analysis can be computationally demanding (Theroux‐Rancourt et al , ; Earles et al , ). As discussed throughout this review there are still plenty of unanswered questions about the relationship of g m and leaf anatomy that can be addressed with proper comparison with 2‐D leaf analysis and extrapolation with geometric models to construct 3‐D representations of the leaf (Figure ).…”