Date of this Version
Agrosyst Geosci Environ. 2020;3:e20110.
Quantitative evidence of light use efficiency (LUE) controls on water use effi- ciency (WUE) is lacking, especially comparatively across row crops. Field research experiments (2016–2018) were set up for maize (Zea mays L.), soybean [Glycine max (L.) Merr.], sorghum [Sorghum bicolor (L.) Moench], and winter wheat (Triticum aestivum L.), under optimal growth conditions in dry sub-humid conditions. Overall, LUE was able to explain 52% of variance in WUE, and were related as WUE = 1.73 LUE, although crop-specific variation was observed. High- est sensitivity of WUE to changes in LUE was found in sorghum, followed by soybean, winter wheat, and maize. Evapotranspiration per unit light absorbed by crop canopy, which is a measure of canopy conductance (gc) ranged from a min- imum of 0.45 kg H2O MJ−1 in sorghum to a maximum of 0.68 kg H2O MJ−1 in maize. Slopes of WUE vs. LUE relationship were limited by energy-limited upper ceiling of latent heat of vaporization and characterized distribution of absorbed energy into latent heat of vaporization and sensible heat. Vapor pressure deficit (VPD) accounted for 41% of variability in the WUE vs. LUE relationship, and the relationship was subject to change with VPD conditions higher or lower than 0.85 kPa. Seasonal evolution of crop-specific gc was modeled and communicated as a function of heat accumulation during the growing season. The research find- ings contribute to quantification of critical parameters that bridge water and light use efficiency, and better understanding of the resource use in C3 and C4 agricul- tural row crops.