Plant Adaptation in a Changing Climate: From Molecular Mechanisms to Ecosystem Resilience

Hotter droughts expose a central coordination problem in terrestrial plants: water loss must be limited before xylem dysfunction becomes irreversible, yet excessive stomatal closure suppresses carbon acquisition and evaporative cooling at the same time that high temperature raises respiratory demand and accelerates tissue heating. This critical narrative review integrates evidence from plant hydraulics, stomatal physiology, carbon metabolism and thermal biology to evaluate how plants negotiate that coupled constraint and why commonly used single-axis drought or heat traits often fail to predict performance under compound stress. Literature published from 1 January 2000 to 15 July 2026 was selected through searches of major open scholarly databases and citation-based follow-up, with emphasis on mechanistic experiments, field manipulations, cross-species syntheses and recent meta-analyses. The strongest evidence identifies hydraulic dysfunction as a recurrent proximate axis of severe drought injury, but the timing and consequences of hydraulic decline are modified by stomatal regulation, access to water, phloem transport and the accessibility of non-structural carbohydrate reserves. Stomatal closure can protect hydraulic integrity during soil and atmospheric drought, whereas extreme heat can favour sustained or increased conductance for leaf cooling even after photosynthesis has declined, creating a water–carbon–temperature conflict. Carbon starvation is therefore better treated as a dynamic, organ-specific process coupled to transport and maintenance than as a simple depletion of bulk carbohydrate concentration. Thermal resilience likewise depends on realised leaf temperature, not air temperature alone, and drought can erode thermal safety by restricting transpirational cooling. Across these domains, compound heat and drought responses are non-additive and strongly contingent on stress sequence, rate of onset, hydraulic strategy, rooting depth and recovery capacity. The review proposes an integrated framework in which survival emerges from the duration for which plants can remain within coupled hydraulic, carbon and thermal safety margins. Progress now depends on experiments and models that measure these margins simultaneously, preserve realistic stress dynamics and connect cellular protection to whole-plant function and field performance.