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 WUEinst), which is defined as the ratio of the rate of net CO2 carbon assimilation (photosynthesis) to the rate of transpiration or stomatal conductance,[1] then called intrinsic water-use efficiency[2] (iWUE or Wi)
  • 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.[3]
  • field level : based on measurements of CO2 and water fluxes over a field of a crop or a forest, using the eddy covariance technique[4]

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.[5]

Intrinsic water-use efficiency Wi 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[3][6][7][8] 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.[9] 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.[10][11] 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[12] or forest trees,[13] and is still used today, for example related to a drought-induced limitation of tree growth[14]

  1. ^ 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.
  2. ^ 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. doi:10.21273/HORTSCI.26.11.1413.
  3. ^ a b Maximov, N. A. (1929). The plant in relation to water. George Allen & Unwin LTD London.
  4. ^ 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. Bibcode:2013AgFM..168...69T. doi:10.1016/j.agrformet.2012.07.008.
  5. ^ 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. PMID 24600020.
  6. ^ 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. Bibcode:1993Oecol..95..340E. doi:10.1007/BF00320986. ISSN 0029-8549. PMID 28314008.
  7. ^ 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. Bibcode:2014EcoEv...4.4505K. doi:10.1002/ece3.1270. ISSN 2045-7758. PMC 4264900. PMID 25512847.
  8. ^ 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. Bibcode:2016EcolL..19..424C. doi:10.1111/ele.12575. ISSN 1461-023X. PMID 26868103.
  9. ^ 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. PMID 15475373.
  10. ^ Bacon, M. Water Use Efficiency in Plant Biology. Oxford: Blackwell Publishing Ltd., 2004. ISBN 1-4051-1434-7. Print.
  11. ^ 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. Bibcode:2009FCrRe.112..119B. doi:10.1016/j.fcr.2009.03.009.
  12. ^ Iljin, V. (1916). "Relation of transpiration to assimilation in steppe plants". Journal of Ecology. 4 (2): 65–82. Bibcode:1916JEcol...4...65I. doi:10.2307/2255326. JSTOR 2255326.
  13. ^ Bates, C.G. (1923). "Physiological requirements of Rocky Mountain trees". Journal of Agricultural Research. 24: 97–164.[1]
  14. ^ 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. Bibcode:2012GCBio..18.1000L. doi:10.1111/j.1365-2486.2011.02566.x.