The desert plant Calotropis procera maintains C3 photosynthetic metabolism under salt stress

The C-3 plant Calotropis procera is native to arid desert zones with a pan-tropical distribution. For this species, the leaf mesophyll conductance (g(m)) and stomatal limitation (l(s)) represent significant constraints on the photosynthetic rate (A), and leaf anatomical and structural traits have a direct influence on the maintenance of photosynthetic activity under water deficit conditions. In this study, g(m), l(s), A, stomatal conductance (g(s)), and the anatomical and structural leaf traits of C. procera were measured to clarify their responses under salt stress conditions. We found that leaf anatomical and structural traits varied significantly i.e. stomatal density, mesophyll thickness, trichome density and epidermal thickness. At the beginning of the stress imposition, g(m) was maintained, l(s) increased, and mesophyll limitation (l(mc)) decreased. In salt-stressed plants reduced g(s) did not represent an immediate decrease in A. Anatomical and structural features of new leaves attenuate the effects of l(s) on CO2 conductance inside the leaves and maintain water status. C. procera maintains photosynthetic metabolism even when showing high leaf Na+ concentration, which does not damage the photosynthetic apparatus.