AOBPreview originally published online on June 30, 2004
Annals of Botany 2004 94(2):199; doi:10.1093/aob/mch143
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Annals of Botany 94/2, © Annals of Botany Company 2004; all rights reserved
VIEWPOINT |
Plants and Altitude — Revisited
Department of Plant Sciences, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
* For correspondence. E-mail galej{at}vms.huji.ac.il
Received: 24 November 2003 Returned for revision: 3 March 2004 Accepted: 28 April 2004 Published electronically: 30 June 2004
ABSTRACT
The importance of modelling and the integration of all environmental factors as they change with time is emphasized in relation to the evaluation of plant response to altitude.
Key words: Altitude, carbon dioxide, oxygen, photosynthesis, transpiration
The physiological ecology, and particularly the leaf gas exchange (mainly CO2 and O2) of plants growing at high altitude, has been receiving renewed attention (e.g. Smith and Donahue, 1991
; Terashima et al., 1995; Sakata and Yokoi, 2002).
In considering the effect of altitude on whole plant physiology and ecology all factors of the environment must be taken into account, not only leaf gas exchange under saturating light and otherwise optimal conditions. For example, shortwave solar radiation increases with altitude while air temperatures usually, but not always, fall (Gale, 1972a, b). For many hours of the day at high elevation the maximum solar radiation may indeed be well above the saturation levels for photosynthesis of C3 plants. Even so, on clear sky summer days, plants are exposed to less than saturating light for most of the daylight hours of the day. At such times of the day, plants growing at high elevations have a relative advantage, as incident sunlight increases with altitude.
Gale (1972b, 1973) predicted and demonstrated a potential increase of transpiration with altitude when there is less than the average lapse rate of ambient temperature (about 0.6 °C/100 m at mid-latitudes). This results from the higher total radiation absorbed by leaves, the increase in the diffusion coefficient of water vapour in air at reduced barometric pressure and the increased density gradient of H2O vapour from the leaf to the ambient air. This is contrary to the case of CO2 influx into leaves, where the two diffusion factors tend to cancel out (Gale, 1972a). Consequently, transpiration rates at high altitude may be very high, as for example in Mediterranean climates where temperature inversions are common (Cohen et al., 1981). Under such conditions and where water is available and stomata remain open, a 1000 m elevation above sea level may bring about a doubling of transpiration rates. von Caemmerer and Farquhar (1981) showed how vapour efflux through the stomata may impede CO2 diffusion influx and hence photosynthesis. Consequently, the effect of transpiration on photosynthesis should also be studied and included in the analysis of the effect of altitude on leaf gas exchange. Moreover, exposure to conditions that induce high rates of transpiration may exhaust available water. This results in closure of stomata and hence reduction in photosynthesis and may also bring about a more xeromorphic plant species composition (Cohen et al., 1981).
A comprehensive analysis of altitude effects on plants would include radiation and other meteorological conditions over the course of the day and growing season. Exceptional, if not unusual events, such as temperature inversions, would also be considered. Apart from the above, other important factors to be taken into account are the physiological type of the plants (e.g. meso- or xeromorphic, C3 or C4) response of the whole plant and the edaphic environment. Cohen et al. (1981) and Friend and Woodward (1990) described early work in this direction, combining field and laboratory experimentation and modelling.
LITERATURE CITED
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Cohen SS, Gale J, Poljakoff-Mayber A, Shmida A, Suraqui S. 1981. Transpiration and the radiation climate of the leaf on Mt. Hermon: a Mediterranean mountain. Journal of Ecology 69: 391–403.
Friend AD, Woodward FI. 1990. Evolutionary and ecophysiological responses of mountain plants to the growing season environment. Advances in Ecological Research 20: 59–124.
Gale J. 1972a. The availability of carbon dioxide for photosynthesis at high altitudes: theoretical considerations. Ecology 53: 494–497.[CrossRef]
Gale J. 1972b. Elevation and transpiration. Some theoretical considerations, with special reference to Mediterranean type climates. Journal of Applied Ecology 9: 691–702.[CrossRef]
Gale J. 1973. Experimental evidence for the effect of barometric pressure on photosynthesis and transpiration. Ecology and Conservation (UNESCO) 5: 289–293.
Sakata T, Yokoi Y. 2002. Analysis of the O2 dependency in leaf-level photosynthesis of two Reynoutria japonica populations growing at different altitudes. Plant Cell and Environment 25: 65–74.[CrossRef]
Smith WA, Donahue RA. 1991. Simulated influence of altitude on photosynthetic CO2 uptake potential in plants. Plant Cell and Environment 14: 133–136.
Terashima I, Masuzawa T, Ohba H, Yokoi Y. 1995. Is photosynthesis suppressed at higher elevation due to low CO2 pressure? Ecology 76: 2663–2668.[CrossRef]
von Caemmerer S, Farquhar GD. 1981. Some relationships between the biochemistry of photosynthesis and the gas exchange of leaves. Planta 153: 376–387.[CrossRef][Web of Science]
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