C(4)grasses adapted to low precipitation habitats show traits related to greater mesophyll conductance and lower leaf hydraulic conductance

In habitats with low water availability, a fundamental challenge for plants will be to maximize photosynthetic C-gain while minimizing transpirational water-loss. This trade-off between C-gain and water-loss can in part be achieved through the coordination of leaf-level photosynthetic and hydraulic traits. To test the relationship of photosynthetic C-gain and transpirational water-loss, we grew, under common growth conditions, 18 C(4)grasses adapted to habitats with different mean annual precipitation (MAP) and measured leaf-level structural and anatomical traits associated with mesophyll conductance (g(m)) and leaf hydraulic conductance (K-leaf). The C(4)grasses adapted to lower MAP showed greater mesophyll surface area exposed to intercellular air spaces (S-mes) and adaxial stomatal density (SDada) which supported greater g(m). These grasses also showed greater leaf thickness and vein-to-epidermis distance, which may lead to lower K-leaf. Additionally, grasses with greater g(m)and lower K(leaf)also showed greater photosynthetic rates (A(net)) and leaf-level water-use efficiency (WUE). In summary, we identify a suite of leaf-level traits that appear important for adaptation of C(4)grasses to habitats with low MAP and may be useful to identify C(4)species showing greater A(net)and WUE in drier conditions.