C 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 grasses adapted to habitats with different mean annual precipitation (MAP) and measured leaf-level structural and anatomical traits associated with mesophyll conductance (g ) and leaf hydraulic conductance (K ). The C grasses adapted to lower MAP showed greater mesophyll surface area exposed to intercellular air spaces (S ) and adaxial stomatal density (SD ) which supported greater g . These grasses also showed greater leaf thickness and vein-to-epidermis distance, which may lead to lower K . Additionally, grasses with greater g and lower K also showed greater photosynthetic rates (A ) and leaf-level water-use efficiency (WUE). In summary, we identify a suite of leaf-level traits that appear important for adaptation of C grasses to habitats with low MAP and may be useful to identify C species showing greater A and WUE in drier conditions.