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Days of anoxia

Fig. 6.17 Tolerance of anoxia in high-latitude grasses using (Left) a subarctic Icelandic population of pseudo-viviparous plantlets of Festuca vivipara and (Right) seedlings from an arctic population of Deschampsia beringensis. The plants were kept under total anoxia for different lengths of time at 5 °C and then allowed to recover in a cold room at 10 °C. With F. vivipara 6 plants per treatment were used and with D. beringensis 25 per individual time treatment.

dangerous. Throughout the period under ice there is a total deprivation of oxygen and all aerobic metabolism ceases. After months of encasement in ice, the arrival of spring and snowmelt exposes plants to the full oxygen concentration of the air, often within a matter of hours. Plants that have survived months of oxygen deprivation then face the additional hazard of post-anoxic injury. This is exactly the same situation that is faced by temperate plants that have been subjected to flooding, where plant survival requires an ability to overcome the double stress of first oxygen deprivation through flooding followed by the dangers of post-anoxic injury when tissues that have endured anoxia for a prolonged period are returned suddenly to air (Fig. 6.17; see also Chapter 8).

Tolerance of anoxia is energetically expensive, particularly in the carbohydrate reserves that have to be conserved to support overwintering anaerobic metabolism and provide the antioxidants for defence in spring against post-anoxic injury. In an area with limited resources as in the Arctic, it would be advantageous for those species that inhabit areas such as slopes and ridges where ice encasement is less likely to occur not to use their limited overwintering reserves for protection against ice encasement, and its associated anoxic and post-anoxic stresses.

Examples such as these demonstrate the evolutionary responses of plants to the less immediately obvious aspects of habitat diversity within a landscape that seems at first sight to offer minimal potential for habitat differentiation. Although the Arctic may not be rich in species it nevertheless possesses considerable diversity within populations. Furthermore the juxtaposition of contrasting habitats, wet and dry, cold and warm, is very immediate at high latitudes. The minute stature and sparse nature of the vegetation does not allow for the buffering of the climate elements and the creation of mesic habitats. Consequently, populations inhabiting contrasting environments may be only metres from each other as the transition from one type of habitat to another is often very abrupt.

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