Many mechanisms respond simultaneously when plants are under drought stress. We examined physiological traits across six Zea mays genotypes varying in grain productivity under water limitation to identify plant strategies associated with greater productivity under limited water. Data were collected on diurnal stomatal conductance (gs), maximum shoot hydraulic conductivity, pressurized root flow, light-adapted chlorophyll fluorescence, and gas exchange on well-watered and water-limited plants in the field and greenhouse to identify traits and general strategies associated with grain production under water limitations in the field. Results indicated that greater grain production was associated with greater peak gs among genotypes and treatments, and, when grown under limited water, maximum whole shoot hydraulic conductivity and pressurized root flow, the last of which may be linked to refilling of capacitance tissues to support plant gas exchange under limited water availability. Additionally, genotypes with greater grain production under limited water availability had reduced effective quantum yield of chlorophyll fluorescence relative to lower-yielding genotypes, suggesting trade-offs limiting maximum electron transport for the safety of photosynthetic apparatuses aligned with a productive strategy under limited water availability. Because both photosynthesis and gs declined similarly among genotypes grown with limited water, instantaneous WUE determined under limited water in the greenhouse was similar among genotypes and did not show any relationship with grain production under limited water availability in the field. A successful strategy for maize under cyclic water limitation appears to be to maintain growth with greater stomatal conductance and hydraulic conductivity, while protecting photosynthetic apparatuses. Finding a strong linkage between grain productivity and pressurized root flow, with its potential connection to capacitance tissues, emphasizes the need to explore hydraulic mechanisms that have received little attention to date but could provide a crucial mechanism for maintaining productivity when water availability is limited.
Comas et al. (Sat,) studied this question.