Differences in stomatal sensitivity to CO2and light influences variation in water use efficiency and leaf carbon isotope composition in two genotypes of the C4plantZea mays

Abstract

AbstractThe ratio of net CO2uptake (Anet) and stomatal conductance (gs) is an intrinsic measurement of leaf water use efficiency (WUEi) however its measurement can be challenging for large phenotypic screens. Measurements of leaf carbon isotope composition (δ13Cleaf) may be a scalable tool to approximateWUEifor screening because it in part reflects the competing influences ofAnetandgson the CO2partial pressure (pCO2) inside the leaf over time. However, in C4photosynthesis the CO2concentrating mechanism complicates the relationship between δ13CleafandWUEi. Despite this complicated relationship, several studies have shown genetic variation in δ13Cleafacross C4plants. Yet there has not been a clear demonstration of whetherAnetorgsare the causal mechanisms controllingWUEiand δ13Cleaf. Our approach was to characterize leaf photosynthetic traits of twoZea maysrecombinant inbred lines (Z007E0067 and Z007E0150) which consistently differ for δ13Cleafeven though they have minimal confounding genetic differences. We demonstrate that these two genotypes contrasted inWUEidriven by differences in the speed of stomatal responses to changes inpCO2and light that lead to unproductive leaf water loss. These findings provide support that differences in δ13Cleafin closely related genotypes do reflect greaterWUEiand further suggests that differences in stomatal kinetic response to changing environmental conditions is a key target to improveWUEi.