Summary
The effects of leaf hairs on photosynthesis, transpiration, and leaf energy balance were measured on the desert shrub Encelia farinosa in order to determine the adaptive significance of the hairs. The pubescence reduces leaf absorptance resulting in a reduced heat load, and as a consequence lower leaf temperatures and lower transpiration rates. In its native habitat where air temperatures often exceed 40° C, the optimum temperature for photosynthesis in E. farinosa occurs at 25° C, and at leaf temperatures above 35° C net photosynthesis declines precipitously. An advantage of leaf pubescence is that it allows a leaf temperature much lower than air temperature. As a result, leaf temperatures are near the temperature optimum for photosynthesis and high, potentially lethal leaf temperatures are avoided. However, there is a disadvantage associated with leaf pubescence. By reflecting quanta that might otherwise be used in photosynthesis, the presence of leaf hairs reduces the rate of photosynthesis. A tradeoff model was used to assess the overall advantage of possessing leaf hairs. In terms of the carbon gaining capacity of the leaf, the model predicted that for different environmental conditions different levels of leaf pubescence were optimal. In other words, under aird conditions and/or high air temperatures, leaves of E. farinosa would have a higher rate of photosynthesis by being pubescent than by not being pubescent. The predictions from this model agreed closely with observed patterns of leaf pubescence in the field.
Similar content being viewed by others
References
Billings, W.D., Morris, R.J.: Reflection of visible and infrared radiation from leaves of different ecological groups. Am. J. Bot. 38, 327–331 (1951)
Björkman, O.: Comparative studies on photosynthesis in higher plants. In: Photophysiology, Vol. 8, pp. 1–63. New York: Academic Press 1973
Björkman, O., Holmgren, P.: Adaptability of the photosynthetic apparatus to light intensity in ecotypes from exposed and shaded habitats. Physiol. Plant. 16, 889–914 (1963)
Björkman, O., Nobs, M., Berry, J., Mooney, H.A., Nicholson, F., Catanzaro, B.: Physiological adaptation to diverse environments: approaches and facilities to study plant responses to contrasting thermal and water regimes. Carnegie Inst. Wash. Yb. 72, 393–403 (1973)
Clausen, J.D., Keck, D., Hiesey, W.M.: Experimental studies on the nature of species. I. The effect of varied environments of western North American plants. Carnegie Inst. Washington Publ. 520 (1940)
Coulter, J.M., Barnes, C.R., Cowles, H.C.: A test book of botany for Colleges and Universities, Vol. II. Ecology. New York: Amer. Book 1911
Cunningham, G.L., Strain, B.R.: Ecological significance of seasonal leaf variability in a desert shrub. Ecology 50, 400–408 (1969)
Ehleringer, J.: The adaptive significance of leaf hairs in a desert shrub. Ph.D. thesis, Stanford University (1977)
Ehleringer, J., Björkman, O.: Quantum yields for CO2 uptake in C3 and C4 plants: dependence on temperature, carbon dioxide, and oxygen concentration. Plant Physiol. 59, 86–90 (1977)
Ehleringer, J., Björkman, O.: Pubescence and leaf spectral characteristics in a desert shrub, Encelia farinosa. Oecologia (Berl.) 36, 137–148 (1978a)
Ehleringer, J., Björkman, O.: A comparison of photosynthetic characteristics of Encelia species possessing glabrous and pubescent leaves. Plant Physiol. 62, 185–190 (1978b)
Ehleringer, J., Björkman, O., Mooney, H.A.: Leaf pubescence: effects on absorptance and photosynthesis in a desert shrub. Science 192, 376–377 (1976)
Ehleringer, J., Miller, P.C.: A simulation model of plant water relations and production in the alpine tundra of Colorado. Oecologia (Berl.) 19, 177–193 1975)
Gates, D.M.: Energy echange in the biosphere. New York: Harper and Row 1962
Gates, D.M.: Energy, plants, and ecology. Ecology 46, 1–13 (1965)
Gausman, H.W., Cardenas, R.: Effect of leaf pubescence of Gynura aurantiaca on light reflectance. Bot. Gaz. 130, 158–162 (1969)
Gausman, H.W., Cardenas, R.: Light reflectance by leaflets of pubescent, normal, and glabrous soybean lines. Agron. J. 65, 837–838 (1973)
Hare, C.L.: The arborescent Senecios of Kilimanjaro: a study in ecological anatomy. Trans. Royal Soc. Edinburgh 60, 355–371 (1941)
Medina, E.: Relationships between nitrogen level, photosynthetic capacity, and carboxydismutase activity in Atriplex patula leaves. Carnegie Inst. Wash. Yb. 69, 655–662 (1970)
Oppenheimer, H.R.: Adaptation to drought: xerophytism. In: Plant-water Relationships in Arid and Semi-arid Conditions, pp. 105–138. Paris: UNESCO 1960
Pearman, G.I.: The reflection of visible radiation from leaves of some western Australian species. Aust. J. Biol. Sci. 19, 97–103 (1966)
Rabideau, G.S., French, C.S., Holt, A.S.: The absorption and reflection spectra of leaves, chloroplast suspensions, and chloroplast fragments as measured in an Ulbricht sphere. Am. J. Bot. 33, 769–777 (1946)
Raschke, K.: Heat transfer between the plant and the enivonment. Ann. Rev. Plant Physiol. 11, 111–126 (1960)
Schimper, A.F.W.: Plant geography upon a physiological basis. Oxford: Clarendon (1903)
Sellers, W.D., Hill, R.H.: Arizona Climate 1931–1972. Tucson: Univ. of Arizona 1974
Shreve, E.B.: Factors governing seasonal changes in transpiration of Encelia farinosa. Bot. Gaz. 77, 432–439 (1924)
Shreve, F., Wiggins, I.L.: Vegetation and flora of the Sonoran Desert. Stanford: Stanford University Press 1964
Shull, C.A.: A spectrophotometric study of reflection of light from leaf surfaces. Bot. Gaz. 87, 583–607 (1929)
Sinclair, R., Thomas, D.A.: Optical properties of leaves of some species in arid South Australia. Aust. J. Bot. 18, 261–273 (1970)
Skene, M.: The biology of flowering plants. New York: MacMillan 1924
Smith, W.K., Nobel, P.S.: Influences of seasonal changes in leaf morphology on water-use efficiency for three desert broad leaf shrubs. Ecology 58, 1033–1043 (1977)
Strain, B., Chase, V.: Effect of past and prevailing temperature on the carbon dioxide exchange capacities of some woody desert perennials. Ecology 47, 1043–1045 (1966)
Warming, E.: Oecology of Plants: An introduction to the study of plant communities. London: Oxford University Press 1909
Wooley, J.T.: Water relations of soybean leaf hairs. Agron. J. 56, 569–571 (1964)
Wuenscher, J.E.: The effect of leaf hairs of Verbascum thapsus on leaf energy exchange. New Phytol. 69, 65–73 (1970)
Author information
Authors and Affiliations
Additional information
C.I.W.-D.P.B. Publication No. 613
Rights and permissions
About this article
Cite this article
Ehleringer, J.R., Mooney, H.A. Leaf hairs: Effects on physiological activity and adaptive value to a desert shrub. Oecologia 37, 183–200 (1978). https://doi.org/10.1007/BF00344990
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00344990