As it is illustrated by the loss and reappearance of chlorophyll-fluorescence signals in drying and rewetting cycles performed in the laboratory on a rock sample with cyanobacterial crusts from an inselberg in Ivory Coast (with the cyanobacteria Stigonema mamillosum, Scytonema lyngbioides and Gloeocapsa sanguinea, and traces of Stigonema ocellatum) desiccation and recovery can occur very rapidly (Fig. 11.12). Triggered by sensing the loss of a small amount of water a rapid deactivation of photosynthetic activities is essential to avoid oxidative stress during desiccation (Hirai et al. 2004). Recovery from desiccation may occur within a few minutes up to several hours after rewetting and recovery of photosystem I activity is faster than that of photosystem II (Jones 1977; Coxson and Kershaw 1983; Lüttge et al. 1995; Satoh et al. 2002; Rascher et al. 2003). It depends on the duration of the dormant state of desiccation, and frequent drying and wetting cycles maintain stability (Scherer and Zhong 1991). The sequence of events during recovery is firstly, reappearance of respiration, followed by photosynthesis and finally N2-fixation (Scherer et al. 1984). Rapid recovery is associated with rapid repair mechanisms, e.g. of the D1-protein (see Sect. 4.1.5) of photosystem II (Harel et al. 2004).
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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.