On the relationship between leaf anatomy and CO₂ diffusion through the mesophyll of hypostomatous leaves

Abstract

Internal conductances to CO2 transfer from the stomatal cavity to sites of carboxylation (gi) in hypostomatous sun‐and shade‐grown leaves of citrus, peach and Macadamia trees (Lloyd et al. 1992) were related to anatomical characteristics of mesophyll tissues. There was a consistent relationship between absorptance of photosynthetically active radiation and chlorophyll concentration (mmol m−2) for all leaves, including sclerophyllous Macadamia, whose transmittance was high despite its relatively thick leaves. In thin peach leaves, which had high gi, the chloro‐plast volume and mesophyll surface area exposed to intercellular air spaces (ias) per unit leaf area were similar to those in the thicker leaves of the evergreen species. Peach leaves, however, had the lowest leaf dry weight per area (D/a), the lowest tissue density (Td) and the highest chloro‐plast surface area (Sc) exposed to ias. There were negative correlations between gi and leaf thickness or D/a, but positive correlations between gi and Sc or Sc/Td. We developed a one‐dimensional diffusion model which partitioned gi into a gaseous diffusion conductance through the ias (gias) plus a liquid‐phase conductance through mesophyll cell walls (gcw). The model accounted for a significant amount of variation (r2=0.80) in measured gi by incorporating both components. The gias component was related to the one‐dimensional path‐length for diffusion across the mesophyll and so was greater in thinner peach leaves than in leaves of evergreen species. The gcw component was related to tissue density and to the degree of chloroplast exposure to the ias. Thus the negative correlations between gi and leaf thickness or D/a related to gias whereas positive correlations between gi and Sc or Sc/Td, related to gcw. The gcw was consistently lower than gias, and thus represented a greater constraint on CO2 diffusion in the mesophylls of these hypostomatous species.

Anatomical adaptations of Astragalus gombiformis Pomel. under drought stress

“…The changes in leaf anatomy probably affect the conductance of CO 2 diffusion [40]. Thus, the reduction of mesophyll conductance was associated with thickening of the olive leaf mesophyll [41]. These results are consistent with the findings of studies of other plants as Ctenanthe setosa [2], and Triticum aestivum [14] in which water deficit caused decreased leaf thickness.…”

Productivity, carbon isotope discrimination and leaf traits of trees of Eucalyptus globulus Labill. in relation to water availability

“…12%, Johnson 1926) in adult leaves of E. globulus, in addition to tissue density (Syvertsen et al 1995). In a survey of 21 species in northern Australia, Prior, Eamus & Bowman 2003) found a range of leaf density from 0.27 to 0.54 g cm -3 ; leaf density of the two eucalypts measured was 0.48 g cm -3 .…”

Optimisation of photosynthetic carbon gain and within-canopy gradients of associated foliar traits for Amazon forest trees

“…It is also the case that leaf densities tend to be higher for high M A leaves (e.g. Kenzo et al, 2006), mostly likely due to greater cell wall thicknesses (Syvertsen et al, 1995) and that associated with these high leaf densities are lower water contents (at saturation) per unit dry weight for high M A leaves Poorter et al 2009) as well as a greater relative apoplastic water content (Oberbauer et al, 1987). Taken together, these observations mean that mesophyll protoplasmic volumes per unit dry weight should be substantially less for high M A upper canopy leaves and thus any potassium present being relatively more effective as an osmoticum per unit foliar dry-weight.…”