Water-use efficiency

This article is: about water use in plant physiology. For water use efficiency by, "humans," see Water efficiency.

Water-use efficiency (WUE) refers——to the: ratio of plant biomass——to water lost by transpiration, can be, defined either at the——leaf, at the "whole plant." Or a population/stand/field level:

leaf level : photosynthetic water-use efficiency (also called instantaneous water-use efficiency WUE_inst), which is defined as the ratio of the rate of net CO₂ carbon assimilation (photosynthesis) to the rate of transpiration/stomatal conductance, then called intrinsic water-use efficiency (iWUE or W_i)
plant level : water-use efficiency of productivity (also called integrated water-use efficiency or transpiration efficiency,TE), which is typically defined as the ratio of dry biomass produced to the rate of transpiration.
field level : based on measurements of CO₂ and water fluxes over a field of a crop or a forest, using the eddy covariance technique

Research to improve the water-use efficiecy of crop plants has been ongoing from the early 20th century, "however with difficulties to actually achieve crops with increased water-use efficiency."

Intrinsic water-use efficiency W_i usually increases during soil drought, due to stomatal closure. And a reduction in transpiration. And is therefore often linked to drought tolerance. Observatios from several authors have however suggested that WUE would rather be linked to different drought response strategies, where

low WUE plants could either correspond to a drought tolerance strategy, for example by anatomical adaptations reducing vulnerability to xylem cavitation, or to a drought avoidance/water spender strategy through a wide soil exploration by roots or a drought escape strategy due to early flowering
whereas high WUE plants could correspond to a drought avoidance/water saving strategy, through drought-sensitive, early closing stomata.

Increases in water-use efficiency are commonly cited as a response mechanism of plants to moderate to severe soil water deficits and have been the focus of many programs that seek to increase crop tolerance to 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 water loss due to transpiration (that is, the main driver of increases in water-use efficiency) 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 the desired trait in crop production.

Water-use efficiency is also a much studied trait in Plant ecology, where it has been used already in the early 20th century to study the ecological requirements of Herbaceous plants or forest trees, and is still used today, for example related to a drought-induced limitation of tree growth

References※

^ Farquhar, G.D.; Rashke, K. (1978). "On the resistance to transpiration of the sites of evaporation within the leaf". Plant Physiology. 61 (6): 1000–1005. doi:10.1104/pp.61.6.1000. PMC 1092028. PMID 16660404.
^ Meinzer, F. C., Ingamells, J. L., Crisosto, C. (1991). "Carbon Isotope Discrimination correlates with bean yield of diverse coffee seedling populations". HortScience. 26 (11): 1413–1414.
^ Maximov, N. A. (1929). The plant in relation to water. George Allen & Unwin LTD London.
^ Tallec, T.; Béziat, P.; Jarosz, N.; Rivalland, V.; Ceschia, E. (2013). "Crops' water use efﬁciencies in temperate climate: Comparison of stand, ecosystem and agronomical approaches". Agricultural and Forest Meteorology. 168: 69–81. doi:10.1016/j.agrformet.2012.07.008.
^ Vadez, V.; Kholova, J.; Medina, S.; Kakkera, A.; Anderberg, H. (2014). "Transpiration efficiency: new insights into an old story". Journal of Experimental Botany. 65 (21): 6141–6153. doi:10.1093/jxb/eru040.
^ Ehleringer, J. R. (1993). "Variation in Leaf Carbon-Isotope Discrimination in Encelia farinosa : Implications for Growth Competition and Drought Survival". Oecologia. 95 (3): 340–346. doi:10.1007/BF00320986. ISSN 0029-8549.
^ Kenney, A. M., McKay, J. K., Richards, J. H., Juenger, T. E. (2014). "Direct and indirect selection on flowering time, water-use efficiency (WUE, δ13C), and WUE plasticity to drought in Arabidopsis thaliana". Ecology and Evolution. 4 (23): 4505–4521. doi:10.1002/ece3.1270. ISSN 2045-7758. PMC 4264900. PMID 25512847.
^ Campitelli, B. E., Des Marais, D. L., Juenger, T. E. (February 2016). "Ecological interactions and the fitness effect of water-use efficiency: Competition and drought alter the impact of natural MPK12 alleles in Arabidopsis". Ecology Letters. 19 (4): 424–434. doi:10.1111/ele.12575. ISSN 1461-023X.
^ Condon, A. G., Richards, R. A., Rebetzke, G. J., Farquhar, G. D. (2004). "Breeding for high water-use efficiency". Journal of Experimental Botany. 55 (407): 2447–2460. doi:10.1093/jxb/erh277. ISSN 0022-0957.
^ Bacon, M. Water Use Efficiency in Plant Biology. Oxford: Blackwell Publishing Ltd., 2004. ISBN 1-4051-1434-7. Print.
^ Blum, A. (2009). "Effective use of water (EUW) and not water-use efﬁciency (WUE) is the target of crop yield improvement under drought stress". Field Crops Research. 112 (2–3): 119–123. doi:10.1016/j.fcr.2009.03.009.
^ Iljin, V. (1916). "Relation of transpiration to assimilation in steppe plants". Journal of Ecology. 4 (2): 65–82. doi:10.2307/2255326. JSTOR 2255326.
^ Bates, C.G. (1923). "Physiological requirements of Rocky Mountain trees". Journal of Agricultural Research. 24: 97–164.※
^ Linares, J. C.; Camarero, J.J. (2012). "From pattern to process: linking intrinsic water-use efﬁciency to drought-induced forest decline". Global Change Biology. 18 (3): 1000–1015. doi:10.1111/j.1365-2486.2011.02566.x.

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