Carbon isotopic composition reflects intrinsic water use efficiency and not its component traits in sugarcane

Authors: Ellsworth, Patrick; White, Paul

Submitted to: Tropical Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2024
Publication Date: 9/25/2024
Citation: Ellsworth, P.Z., White Jr, P.M. 2024. Carbon isotopic composition reflects intrinsic water use efficiency and not its component traits in sugarcane. Tropical Plant Biology. https://doi.org/10.1007/s12042-024-09367-z.
DOI: https://doi.org/10.1007/s12042-024-09367-z

Interpretive Summary: Insufficient water for agriculture is a major problem worldwide. Decreasing how much water crops use without decreasing crop productivity can be done by increasing water use efficiency (WUE). At the leaf level WUE is the photosynthetic rate relative to transpiration or stomatal conductance, which is the water loss from the leaf. At the plant level, WUE is plant weight relative the water transpired from the plant. At the field level, WUE is yield or crop productivity relative the volume of water used by the crop. Because gas exchanged measurements, which are used to measure leaf WUE, are laborious, leaf carbon isotopic composition (d13Cleaf) theoretically can be used as proxy for leaf WUE. In this study WUE and d13Cleaf were measured in 55 varieties of sugarcane. Both d13Cleaf and WUE varied significantly across varieties (genetic effect). Variation in WUE was largely due to variation in transpiration than photosynthetic rate. WUE was significantly correlated with d13Cleaf, but not with the component traits of WUE (photosynthetic rate and transpiration), showing that d13Cleaf was specifically a proxy for WUE. This significantly relationship between WUE and d13Cleaf show that d13Cleaf has potential to be a proxy for WUE in sugarcane.

Technical Abstract: Water is the most important resource in plant growth and is a major limiting factor in sugarcane productivity worldwide. Improving water use efficiency (WUE) can increase sugarcane productivity relative to available water resources by increasing photosynthetic capacity relative to transpiration and stomatal conductance instead of decreasing stomatal conductance. Leaf carbon stable isotopic composition (d13Cleaf) can serve as a proxy for intrinsic WUE (WUEi) because WUEi and d13Cleaf are theoretically related through the link between intracellular and ambient CO2 concentrations (Ci/Ca) and leaf CO2 discrimination ('13Cleaf). In this study we surveyed 55 sugarcane genotypes for WUEi, leaf WUE (WUEleaf), Ci/Ca, and d13Cleaf by gas exchange measurements and stable isotope analysis. We hypothesized that significant genotypic variation was found in WUEi, WUEleaf, and d13Cleaf within the sugarcane population in Louisiana. We also hypothesized that both WUEi and d13Cleaf and '13Cleaf and Ci/Ca were correlated and that d13Cleaf could be used as a proxy for WUEi in sugarcane. Here WUEi and WUEleaf had a genetic effect and were controlled mostly by water loss (stomatal conductance or transpiration). WUEi, WUEleaf, Ci/Ca, and d13Cleaf were correlated, but d13Cleaf was not correlated with the component traits of WUEi (photosynthetic rate and stomatal conductance). d13Cleaf shows promise as a proxy for WUEi to at least be able to select the tails of the distribution, but the relationship between WUEi and d13Cleaf may not be sufficiently strong to select WUE at a finer scale.