**1. Introduction**

Presently, there is a rising concern regarding the extreme changes in climatic conditions and their related impact on the living (biotic) and non-living (abiotic) components of our ecosystems. The recent cases of flooding, drought, cyclones and hurricanes have caused an alarm and called for us to review the way in which we understand and interact with our biosphere. These situations arise not only due to anthropogenic activities but also due to natural phenomenon. A vital factor that contributes to climatic fluctuation is upsurge and accumulation of greenhouse gases which eventually cause a rise in global temperature [1–5]. There has been a significant increase in the amount of research pertaining to the mechanisms for and development of abiotic stress tolerance in plants over the past couple of decades. This is because plants are the beings most readily and deeply affected by climate change issues due to their immobile nature.

Under environmental stress conditions, arising from temperature extremes, fluctuations in rainfall and wind patterns, heat, salinity, pH variations, drought, electromagnetic radiation, etc., plants show numerous symptoms of stress-induced phytotoxicity. This ranges from modifications in metabolic and physiological activities to depletion in overall productivity. Consequently, this becomes a raging concern in case of crop plants and other plant beings that are crucial for providing ecosystem services (such as pulpwood, timber, ecotourism and natural habitat for wildlife). Due to loss in growth and productivity, there is an issue of global food shortage and also the deeply worrying aspect of oxygen depletion [6–15]. Therefore, among all the effects of the current trend of climate change on our planet, the ones on plant systems are of utmost importance.

In the backdrop of climate change, some abiotic elements of our biosphere are more susceptible to variations than the others. These include drought, salinity and UV-B. These factors influence plant life forms in solitary or in combined ways, whereby morphological, physiological and biochemical attributes of plants are effectively altered. Simultaneously, there are revelled modifications in the epigenetic codes of the plant genome, leading to what is known as chromatin-based 'epigenetic memory'. This memory may help the plant in future when it is exposed to similar kinds of stress, wherein there is elevation of plant defence activities. Plants can also respond to environmental stressors by adapting and acclimatising using various strategies. However, the climate-influenced rise in abiotic stressors continues to hamper plant growth and productivity on a larger scale and also draw in the biotic or pathogenic stress challenge into the picture.

As such, we have discussed in the present chapter some key issues related to climate change and its impact, such as the nature and origin of climate variability, its expected trend in near future, how the climate change conditions affect the sessile plant beings, the strategies adapted by plants to overcome the stress created due to the increasingly challenging environment, and the role of epigenetic mechanisms in helping the plants adapt and acclimatise better to these conditions. Moreover, the role of friendly bacteria also termed as 'plant growth-promoting rhizo-bacteria' in alleviating the negative effects of climate change on plants has also been delineated. With a clear understanding of the issue at hand, we can equip ourselves better to face the testing times that lay ahead of us.
