Genotypic variation in whole-plant transpiration efficiency in sorghum only partly aligns with variation in stomatal conductance

Abstract

Water scarcity can limit sorghum (Sorghum bicolor (L.) Moench) production in dryland agriculture, but increased whole-plant transpiration efficiency (TEwp, biomass production per unit of water transpired) can enhance grain yield in such conditions. The objectives of this study were to quantify variation in TEwp for 27 sorghum genotypes and explore the linkages of this variation to responses of the underpinning leaf-level processes to environmental conditions. Individual plants were grown in large lysimeters in two well-watered experiments. Whole-plant transpiration per unit of green leaf area (TGLA) was monitored continuously and stomatal conductance and maximum photosynthetic capacity were measured during sunny conditions on recently expanded leaves. Leaf chlorophyll measurements of the upper five leaves of the main shoot were conducted during early grain filling. TEwp was determined at harvest. The results showed that diurnal patterns in TGLA were determined by vapour pressure deficit (VPD) and by the response of whole-plant conductance to radiation and VPD. Significant genotypic variation in the response of TGLA to VPD occurred and was related to genotypic differences in stomatal conductance. However, variation in TGLA explained only part of the variation in TEwp, with some of the residual variation explained by leaf chlorophyll readings, which were a reflection of photosynthetic capacity. Genotypes with different genetic background often differed in TEwp, TGLA and leaf chlorophyll, indicating potential differences in photosynthetic capacity among these groups. Observed differences in TEwp and its component traits can affect adaptation to drought stress.

Drivers of Natural Variation in Water-Use Efficiency Under Fluctuating Light Are Promising Targets for Improvement in Sorghum

“…This points to a tradeoff between leaves with more numerous, smaller stomata which show high steady-state g s but rapid g s responses to PPFD, and leaves with fewer, larger stomata which show low steady-state g s but slow g s responses to PPFD. The finding that steady-state iWUE 2000 was mainly associated with g s 2000 rather than A 2000 is consistent with prior observations in sorghum (Geetika et al, 2019) and other C 4 grasses (Leakey et al, 2019), but the tradeoff with non-steadystate g s identified here (Figure 6) is not widely recognized.…”

Automated discretization of ‘transpiration restriction to increasing VPD’ features from outdoors high-throughput phenotyping data

“…a limited maximum transpiration rate (TR) value in the high VPD hours of the day) described in a crop model [4] is also partially featured. Only few measurements have been done under natural conditions [12][13][14][15][16], with both temperature and relative humidity changing simultaneously over the course of the day. Those studies measured the expression of genotypic differences in the transpiration response to VPD only from the maximum transpiration values under high VPD conditions, and also had low throughput.…”

Designing crops for adaptation to the drought and high‐temperature risks anticipated in future climates

“…This trait provides insight into the genetics of TE, especially from the perspective of plant hydraulics, probably with close involvement of aquaporins (Vadez et al, 2014). However, recent studies (Geetika et al, 2019) have shown that while genetic variation in TE aligned with differences in stomatal conductance under high demand conditions, some of the remaining residual variation reflected differences in photosynthetic capacity. Further, Shekoofa, Sinclair, Messina, and Cooper (2015) demonstrated that the expression of the limited transpiration trait could be jeopardized under high temperatures.…”