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Hence, it appears fairly straightforward that the different nocturnal temperature regimes in the two regions led to evolution of the two different strategies, one taking the risk and obtaining more productivity and the other one avoiding the risk on account of the loss of some productivity. Indeed Table 12.2 suggests that the African Senecio keniodendron has a much lower annual productivity than the Andean Es-peletias (Rada et al. 1985).

Interestingly, Lipp et al. (1994) note that in species growing at high elevations in Hawai'i features of both adaptive strategies are combined and a complete suite of

Fig. 12.16A-C Plants of high altitudes on Haleakala volcano, Maui island, Hawai'i. Styphelia tameiameiae (A), Dubautia menziesii (B), Argyroxiphium sandwicense (C)

characteristics with either strict tolerance or avoidance of extracellular ice formation is not expressed. Five species were studied, namely Argyroxiphium sandwicense and Dubautia menziesii (both Asteraceae), Sophora chrysophylla (Fabaceae), Vaccinium reticulatum (Ericaceae) and Styphelia tameiameiae (Epacridaceae) (Fig. 12.16). Typical freezing tolerance is not fully expressed possibly due to a more recent evolutionary status of these taxa. A combination of the two possible adaptive strategies is given in that a period of supercooling occurs prior to ice nucleation. Four of the five species could tolerate extracellular ice formation to a certain degree. For example, in S. tameiameiae in the laboratory there was considerable supercooling prior to ice formation at - 9.4 °C, and the latter did not cause tissue injury.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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