Desiccation Tolerance in Bryophytes: Evolutionary Origins, Poikilohydric Adaptation and Cellular Mechanisms

Abstract

Desiccation tolerance represents a fundamental adaptive strategy that enables Bryophytes to withstand fluctuations in water availability. Liverworts, mosses and hornworts predominantly exhibit poikilohydric water relations, whereby tissue hydration closely follows ambient environmental conditions. The present review synthesises the structural, physiological and cellular mechanisms associated with desiccation tolerance in Bryophytes and examines their evolutionary significance in the transition from aquatic to terrestrial environments. During dehydration, Bryophytes undergo progressive metabolic downregulation and cellular reorganisation, while structural characteristics such as cell wall elasticity and tissue water-retention properties help minimise mechanical injury. At the cellular level, protection involves maintenance of membrane integrity, accumulation of protective proteins and compatible solutes, dissipation of excess excitation energy, and activation of antioxidant mechanisms that limit photo-oxidative and cellular damage. The persistence of these mechanisms provides an ecologically effective strategy for survival under fluctuating and extreme moisture regimes. From an evolutionary perspective, desiccation tolerance may have provided an important alternative to complete internal water regulation during early terrestrialisation by enabling early land plants to survive periods of atmospheric water loss while retaining the capacity for rapid recovery following rehydration. Thus, Bryophytes provide valuable systems for understanding the integration of structural, physiological and cellular adaptations that underpin plant resilience to dehydration and illuminate key innovations associated with the evolution of life on land.