Recently, we found that across several C 4 grasses, leaf width (LW) correlated positively with g sw and negatively with iWUE. Here, using 48 field-grown genotypes of Sorghum bicolor, a C4 crop suited to dry and hot environments, we validated these correlations. Three times a day, we monitored leaf gas exchange and modeled leaf energy balance together with structural characteristics as possible iWUE predictors.
The underlying causes of variance in intrinsic water-use efficiency (iWUE = net photosynthesis/stomatal conductance for water vapors, gsw), particularly in C4 plants, are not well understood. Recently, we found that across many C4 grasses, leaf width (LW) associated negatively with iWUE and favorably with gsw. Here, using 48 field-grown genotypes of Sorghum bicolor, a C4 crop suited to hot and dry environments, we validated these correlations. Three times a day, we monitored leaf gas exchange and modeled leaf energy balance together with structural characteristics as possible iWUE predictors. LW associated favorably with gsw, interveinal distance of longitudinal veins, and the proportion of stomatal aperture relative to maximum while negatively with iWUE, stomatal density, and interveinal distance. Modeling of the energy balance revealed that broader leaves especially during noon when air temperatures approached 40°C, required to open their stomata more to produce a higher negative leaf-to-air temperature differential. These findings demonstrate the crucial part LW, which affects stomatal aperture and coordinates vein and stomatal characteristics, plays in forming iWUE. LW might therefore be used to forecast sorghum genotypes with greater iWUE.
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