Ecophysiology of Plants in Dry Environments

Abstract

Drought is a meteorological term which indicates a long period when there is not enough rain for the successful growth of crops or replenishment of water supplies (see also Chap. 1). The expression water stress is frequently used to indicate the complex series of effects that are triggered in plants by drought. The term drought stress is more appropriate to specify when the stress status occurs only over a long period of time. However, because it is often difficult to separate the two phenomena, the definitions of water stress, drought stress, and water deficit are often used interchangeably. Drought leads to water deficit in the soil and plant tissues, which in turn alters physiological processes and can have ultimate consequences for growth, development, and survival of plants. Among the many biochemical and developmental processes that are affected by water stress, decrease of photosynthesis (Cornic and Massacci 1996; Flexas et al. 2002; Sperlich et al. 2016), changes in water relations (Gorai et al. 2015; Reinhardt et al. 2015; Yousfi et al. 2016), reduction of both cell division and expansion (Avramova et al. 2016; Clauw et al. 2015, 2016), abscisic acid (ABA) synthesis (Du et al. 2018; Linster et al. 2015; Teng et al. 2014), and accumulation of sugars (Srivastava et al. 2018; Zandalinas et al. 2018) play a fundamental role in reducing productivity. The concept of stress cannot be separated from that of stress tolerance (sometimes indicated with the less appropriate term of stress resistance), which is the plant’s ability to survive in an unfavorable environment. Such an ability can derive either from adaptation or acclimation to the stress condition. Both terms indicate an increase in tolerance and are sometimes erroneously used interchangeably. The difference is in the cause of the increased tolerance: in acclimated plants, it is the result of a previous stress condition, while in adapted plants, the tolerance is fixed in the genome and derives from selection processes that have occurred over many generations.