Journal
JOURNAL OF EXPERIMENTAL BOTANY
Volume 62, Issue 8, Pages 2875-2887Publisher
OXFORD UNIV PRESS
DOI: 10.1093/jxb/erq461
Keywords
Breeding strategies; drought stress; intrinsic water use efficiency; photosynthesis; soybean; stomatal conductance
Categories
Funding
- USDA-CREES [2006-35100-17263]
- CID
- Italian Ministry for Land, Environment and Sea
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Intrinsic water use efficiency (WUEintr), the ratio of photosynthesis to stomatal conductance to water, is often used as an index for crop water use in breeding projects. However, WUEintr conflates variation in these two processes, and thus may be less useful as a selection trait than knowledge of both components. The goal of the present study was to determine whether the contribution of photosynthetic capacity and stomatal conductance to WUEintr varied independently between soybean genotypes and whether this pattern was interactive with mild drought. Photosynthetic capacity was defined as the variation in WUEintr that would occur if genotypes of interest had the same stomatal conductance as a reference genotype and only differed in photosynthesis; similarly, the contribution of stomatal conductance to WUEintr was calculated assuming a constant photosynthetic capacity across genotypes. Genotypic differences in stomatal conductance had the greatest effect on WUEintr (26% variation when well watered), and was uncorrelated with the effect of photosynthetic capacity on WUEintr. Thus, photosynthetic advantages of 8.3% were maintained under drought. The maximal rate of Rubisco carboxylation, generally the limiting photosynthetic process for soybeans, was correlated with photosynthetic capacity. As this trait was not interactive with leaf temperature, and photosynthetic capacity differences were maintained under mild drought, the observed patterns of photosynthetic advantage for particular genotypes are likely to be consistent across a range of environmental conditions. This suggests that it is possible to employ a selection strategy of breeding water-saving soybeans with high photosynthetic capacities to compensate for otherwise reduced photosynthesis in genotypes with lower stomatal conductance.
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