Despite its importance for crop productivity in drought-affected
environments, the underlying mechanisms of variation in intrinsic water
use efficiency (iWUE) are not well understood, especially in C4 plants.
Recently, Cano et al. (2019) discovered that leaf width (LW) correlated
negatively with iWUE and positively with stomatal conductance for water
vapour (gsw) across several C4 grasses. Here, we analysed these
relationships within 48 field-grown genotypes that cover a broad range
of variation in LW in Sorghum bicolor, a well-adapted C4 crop to xeric
and hot conditions, by measuring and modelling leaf gas exchange and
leaf energy balance three times a day, using anatomical traits as
potential drivers for iWUE. LW correlated negatively with iWUE and
stomatal density, but positively with gsw, interveinal distance of
longitudinal veins (IVDL) and the percentage of stomatal aperture
relative to maximum. Energy balance modelling showed that wider leaves
opened the stomata more to generate a more negative leaf-to-air
temperature difference especially at midday, when air temperatures
exceeded 40ºC. These results highlight the important role that LW plays
in shaping iWUE through modification of vein and stomatal traits and by
regulating stomatal aperture. Therefore, LW could be used as a predictor
for higher iWUE among sorghum genotypes.
Coordination of stomata and vein patterns with leaf width underpins water use efficiency in a C4 crop