The Biology of Alpine Habitats pp. 59-61 (2009)
Laszlo Nagy and Georg Grabherr

4.3 Other atmospheric physical and chemical factors related to climate

4.3.1 Atmospheric pressure

Atmospheric pressure and the partial pressure of gases in the air decrease with altitude, the only environmental factor specific to mountains. The rate of decrease is related to altitude (Fig. 3.2). While the partial pressure of component gases in the air decreases, their ratio to each other remains unchanged. The impacts of a decrease in atmospheric pressure on living organisms have been investigated in detail, especially on animal and human physiology and adaptation (Table 4.3). A variety of physiological and evolutionary adaptations have helped the colonization of high-altitude habitats by flying insects (Dillon et al. 2006), anurans and reptiles (Navas 2002, 2006), birds (Altschuler and Dudley 2006), and mammals (Hayes and O'Connor 1999). For plants it has been observed that some biophysical-physiological phenomena are connected to air pressure, such as transpiration, which increases with a decrease in atmospheric pressure Körner (2003). Low atmospheric pressure has also been related to putative morphological adaptations in the form of mucilage production and low stomata numbers in high Andean plants (González 1985). There has been some recent experimental work on plant physiology in extreme hypobaric environments (e.g. Paul et al. 2004). The interesting finding from these studies was that low pressure caused the expression in Arabidopsis of about 200 genes, of which less than half were prompted by hypoxia alone, too. This indicates that hypobaria has its own impact, largely related to plant water economy, irrespective of the partial pressure of oxygen. However, as the above experiments used one-tenth of the pressure at sea level-much lower than any plant growing at extreme alpine altitudes can experience-results are difficult to relate to real-life high mountain conditions. There are some complex and less well explained phenomena related to low atmospheric pressure and related hypoxic conditions, such as the high survival rate of common garden lettuce (Lactuca sativa) at 6000 m, as observed by Halloy and González (1993). Frost damage, appeared to decrease under low atmospheric pressure (approximately 472 hPa versus 1013 hPa pressure at sea level) at temperatures (night-day) that would have prevented the plants from surviving at normal atmospheric pressure. Halloy and Gonzalez (1993) explained the increased frost/cold tolerance by the reduced oxidative damage to cells after thaw at a low ambient oxygen partial pressure, less than half of that experienced at sea level. The question remains, however, as to what extent cold tolerance is shaped by selection of taxa, or physiological adaptation in hypobaric (and hypoxic) high mountain environments.

Michurin: High Atmospheric Pressure (1929)

Atmospheric Pressure, Plant Growth & Development