Water-use efficiency
Water-use efficiency refers to the ratio of water used in plant metabolism to water lost by the plant through transpiration. Two types of water-use efficiency are referred to most frequently:
- photosynthetic water-use efficiency, which is defined as the ratio of the rate of carbon assimilation to the rate of transpiration, and
- water-use efficiency of productivity, which is typically defined as the ratio of biomass produced to the rate of transpiration.
Increases in water-use efficiency are commonly cited as a response mechanism of plants to moderate to severe soil water deficits, and has been the focus of many programs that seek to increase crop tolerance of drought. However, there is some question as to the benefit of increased water-use efficiency of plants in agricultural systems, as the processes of increased yield production and decreased transpirational water loss are fundamentally opposed. If there existed a situation where water deficit induced lower transpirational rates without simultaneously decreasing photosynthetic rates and biomass production, then water-use efficiency would be both greatly improved and a desired trait in crop production.
