Abstract
The phenomenological expression showing crop yield to be directly dependent on crop transpiration use efficiency (TE) has encouraged continued focus on TE as a viable approach to increasing crop yields. The difficulty in the phenomenological perspective is that research tends not to match up with the underlying mechanistic variables defining TE. Experimental evidence and the mechanistic derivation of TE by Tanner and Sinclair showed that the common focus on increasing the intrinsic ratio of leaf CO2/H2O exchange has limited opportunities for improvement. On the other hand, the derivation showed that daily vapor pressure deficit (VPD) weighted for the daily cycle of transpiration rate has a large, direct impact on TE. While VPD is often viewed as an environmental variable, daily weighted VPD can be under plant control as a result of partial stomatal closure during the midday. A critical feature of the partial stomatal closure is that transpiration rate is decreased resulting in conservation of soil water. The conserved soil water allows late-season, sustained physiological activity during subsequent periods of developing water deficits, which can be especially beneficial during reproductive development. The shift in the temporal dynamics of water use by water conservations traits has been shown in simulation studies to result in substantial yield increases. It is suggested from this analysis that effective water use through the growing season is more important for increasing crop yield than attempts focused on improving the static, intrinsic TE ratio.
Highlights
There continues to be great interest in increasing crop transpiration efficiency (TE), which is often defined as crop mass production per unit of crop transpiration
Stability in TE was fully illustrated in the analysis of C.T. deWit (1958) in which results from experiments worldwide were combined and plotted for each species as growth vs. transpiration normalized by evaporation from an open water surface
If a genotype with a low plant hydraulic conductance is paired with low soil conductance resulting from soil drying, the threshold of extractable soil water at which transpiration decrease is likely initiated is at a higher soil water content than the usual one third transpirable soil water (Sinclair, 2017a)
Summary
There continues to be great interest in increasing crop transpiration efficiency (TE), which is often defined as crop mass production per unit of crop transpiration. This interest seems to be sustained in spite of the fact that more than a century of research has shown little progress in improving basic TE. The one noted exception has been the development from carbon isotope discrimination observations of the wheat cultivar ‘Drysdale’ in Australia for rainfed conditions (Rebetzke et al, 2002). The carbon isotope discrimination approach in itself did not resolve the exact physiological advantage of this variety. The percent yield increase of Drysdale was found to be less than 11% at a base yield of about 1 t ha−1 (i.e., yield improvement of 0.11 t ha−1) and the percent yield increase declined linearly with higher base yields
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
