Physiology of Algae: An Insight

Introduction

Algae are the key primary producers present in aquatic and terrestrial environments and are a representative of several emerging genetic model systems (Armbrust et al., 2004; Hopes et al., 2016; Nymark et al., 2016). They also play progressively more significant role in human nutrition (FAO, 2014). Algal photosynthesis provides about one-half of the total oxygen that we breathe, and their genomes revealed the story of a tangled past that traverses the tree of life through processes of endosymbiosis and the horizontal gene transfer (HGT) (Price et al., 2012; Cenci et al., 2017).

They are known to demonstrate a wide range of morphological diversity and inhabit the diverse aquatic systems. Algae frequently occur in extreme environments, and this reflects their remarkable ability to endure a variety of natural as well anthropogenic stresses. They need to survive with low concentrations of few essential nutrients (particularly carbon, nitrogen, phosphorus and trace elements) in natural water and, low availability of light and temperature. Besides withstanding such limiting factors, they have to survive and grow in the adverse habitats that are enriched with salts, toxic metals and pesticides, elevated temperature, pH, UV–B radiation and light intensity. Algae are known to be the principal primary producers of water bodies – from a rain pond to the oceans. Therefore, the tolerance range of algae to diverse stress factors assumes tremendous significance from an ecological standpoint. The basic metabolic mechanism of algae is similar to that of higher plants.

Cyanobacteria and microalgae present in the atmosphere, are exposed to a range of stress factors such as, humidity, temperature, oxidative stress, nitrogen starvation, radiation, and osmotic stress (Fröhlich–Nowoisky et al., 2016, Després et al., 2012, Tesson et al., 2016, Wiśniewska et al., 2019). There is one theory suggesting that this stress is a result of evolutionary force that causes selection pressure and hence affects spread and the evolution of organisms (Fröhlich–Nowoisky et al.,2016). Their atmospheric survival capability depends totally on the adaptability of the cyanobacteria and microalgae towards the ever changing environmental condition (Fröhlich–Nowoisky et al., 2016; Tesson et al., 2016; Wiśniewska et al., 2019). The stress response generated is of great importance to their capability to colonize the new habitats and also to survive. They also endure the ever demanding environmental conditions such as irradiance, temperature, and humidity gradients. According to Tesson et al., (2012), there may be a possibility that microalgae may change the stage of life e.g., into dormant cell stage, during their stay in the unfavourable environmental conditions. Therefore, the further investigation of physiological modifications that affects microalgae as they disperse is quintessential. The diversity of algae includes such genotypes that can, through evolution, grow over a large range of mean and extreme value of flux in photo-synthetically active radiation (PAR) of both low and high concentration of dissolved nutrients and of extensive ranges in temperature (Raven & Geider, 1988).