Ever Changing Seasonal Phenological Patterns of Physiological Stress! What’s the Road Ahead?

Ongoing climate change continues to increase the intensity and frequency of extreme events, including heat waves, false spring damage and droughts across the globe. Immobile terrestrial plants must withstand these environmental stressors to complete their life cycle. Although many physiological studies have shown that the characteristics endowing stressors are not static in time and experience periodic changes, they are often disregarded as such. Understanding and utilizing the seasonal occurring patterns of physiological stress acclimation can promote better adaptation and mitigation in the face of climate change.

Diverse phenotypic measurements can be used to observe tissue necrosis and estimate physiological ability to withstand environmental stress. These include cold hardiness, drought tolerance and thermotolerance (Grossman 2023). More specifically, measurements include low-temperature exotherm (LTE) and critical electrolye leakage (LT50) for cold hardiness, turgor loss point (ΨTLP) and vulnerability to xylem cavitation (Px) for drought tolerance, as well as, critical temperature of chlorophyll fluorescence (Tc) for thermotolerance.

A recent study shows physiological tolerance to freezing damage, droughts and heat waves varies periodically over the course of a year (Figure 1). In cold winter, tolerance to freezing is gained or lost over a period of days to weeks. Plants reach their maximum acclimation in mid-winter, when even unusually cold temperatures are unlikely to cause freeze-induced damage. By contrast, the maximum state of de-acclimation is usually achieved during the growing season, when freezing periods are less common (Kovaleski et al., 2022). The mechanical driving factor for drought tolerance is sublethal water deficit. It follows a roughly sinusoidal acclimation and de-acclimation pattern (Northing PC. 2022), which is consistent with cold resistance. The temporal scale of drought acclimation in seasonal perennials may last weeks or months since drought itself occurs over longer timescales (months to years or decades) than false springs (days to weeks). Unlike other tolerances, the rapid acclimation of heat tolerance is a response to ambient warming. In different natural systems, this pattern shows higher heat resistance in hot and dry seasons than in cold and humid seasons (Froux et al., 2004).

Figure 1: Physiological tolerance to heat waves, freezing damage typical of false springs, and droughts varies periodically over a year, producing a distinct phenological signal for each stress tolerance trait (Adapted from Grossman 2023).

The synthesis of existing evidence indicates that seasonal perennial plants adapt to environmental stress periodically, producing a distinct phenological signal for each trait. A priority to integrate global change ecology and plant ecology is to treat these repeated patterns of physiological changes from a phenological perspective. At the same time, a comprehensive framework for understanding seasonal patterns of plant adaptation across species to abiotic stress in the natural environment needs to be further developed.


Froux F et al. 2004. Seasonal variations and acclimation potential of the thermostability of photochemistry in four Mediterranean conifers. Annals of Forest Science 61: 235–241.

Grossman, J. J. 2023. Phenological physiology: seasonal patterns of plant stress tolerance in a changing climate. New Phytologist 237: 1508-1524.

Kovaleski AP. 2022. Woody species do not differ in dormancy progression: differences in time to budbreak due to forcing and cold hardiness. Proceedings of the National Academy of Sciences, USA 119: e2112250119

Northing PC. 2022. Acclimation to drought and cold stress in holly (Ilex): evergreen tolerance and deciduous escape. Haverford, PA, USA: Bryn Mawr College.


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