Differences in leaf water use efficiency among soybean cultivars not well correlated with carbon isotope ratios

Authors: BUNCE, JAMES - Retired ARS Employee

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2019
Publication Date: 5/10/2019
Citation: Bunce, J.A. 2019. Differences in leaf water use efficiency among soybean cultivars not well correlated with carbon isotope ratios. Plants. 8(5):123. https://doi.org/10.3390/plants8050123.
DOI: https://doi.org/10.3390/plants8050123

Interpretive Summary: With increasing scarcity of water, and projected increased frequency of drought, increasing the ratio of crop yield to water consumed, termed water use efficiency, is an important objective. This study tested whether there were consistent differences among cultivars of soybeans in leaf water use efficiency under field conditions, and whether the ratio of carbon isotopes in plant tissue was a reliable indicator of water use efficiency. The results indicated that there were consistent differences in leaf water use efficiency among the soybean cultivars studied, but that carbon isotope ratios were not a useful short-cut for determining leaf water use efficiency in this case.

Technical Abstract: High intrinsic water use efficiency, the ratio of leaf photosynthesis to stomatal conductance, may be a useful trait in adapting crops to water-limited environments. Carbon isotope ratios can be a useful indicator of intrinsic water use efficiency but might not be well correlated with it if the plants compared differ substantially in mesophyll conductance. In this study, six cultivars of soybeans previously shown to differ in water use efficiency in indoor experiments were grown in the field in Beltsville, Maryland, and mid-day intrinsic water use efficiency was measured on nine clear days during mid-seasons of two years. Measurement dates were chosen for diverse temperatures. Carbon isotope ratios were determined on mature, upper canopy leaves harvested during early pod filling each year. Intrinsic water use efficiency differed among cultivars both years and the differences were quite consistent across measurement dates. Correlations between intrinsic water use efficiency and carbon isotope ratios were not significant in either year. It is concluded that consistent cultivar differences in intrinsic water use efficiency exist in these soybean cultivars under field conditions, but that carbon isotope ratios may not be useful in identifying them.