S5 Stress physiology
Editor: De Boeck HJ
Ecophysiology integrates biology, chemistry, and physics to study how individual organisms sense and respond to changes in their environment. Because they are largely immobile, plants are restricted to responding to changing conditions through phenotypic plasticity. This has led to a series of adaptations, often through adjustments in gene expression leading to changes in hormone synthesis, osmotic balance, etc. (Larcher, 2003; Schulze et al., 2005). Some responses to changes in the environment are slow and these often relate to morphological adjustments such as increased root growth in response to drought via abscisic acid. Other responses are much faster, among which many adjustments (such as stomatal conductance) are to the large fluctuations in temperature, radiation, and air humidity plants experience within a single day.
In uncovering how climate- and other global-change drivers will affect plants and ecosystems, studying ecophysiology provides a mechanistic way to predict when tolerance limits are exceeded and therefore when changes can be expected in the functioning of individual plants, species, and entire ecosystems. Measuring tools and analytical procedures have become increasingly sophisticated, yet the interpretation can be challenging as physiological responses may vary considerably with context-dependent factors such as microclimate and acclimation. For example, heat stress effects may be misinterpreted if tissue temperature is not directly determined and only air temperatures are used (De Boeck et al., 2016; Michaletz et al., 2016), and if measurements are made on plants that have been exposed to relatively high temperatures earlier in their growing season (leading to hardening and muted responses to heat) as opposed to plants that were not exposed (Neuner & Buchner, 2012). Moreover, many ecophysiological measurements are made at the leaf level and scaling up to whole organisms or even ecosystems is usually not straightforward.
In the stress physiology chapter (5), we describe a series of physiological or related measurements useful in climate-change biology. These focus mostly on their use as indicators of stress, be it through the determination of compounds (e.g. chlorophyll and carotenoid content, non-structural carbohydrates), traits and variables such as reflectance, leaf hydraulic conductivity, and leaf thermal properties, to measurements that directly assess stress (through Fv/Fm) and general approaches for determining tolerance.
De Boeck, H. J., Velde, H. V. D., Groote, T. D., & Nijs, I. (2016). Ideas and perspectives: Heat stress: more than hot air. Biogeosciences , 13(20), 5821-5825.
Larcher, W. (2003). Physiological Plant Ecology: Ecophysiology and Stress Physiology of Functional Groups. Springer Science & Business Media.
Michaletz, S. T., Weiser, M. D., McDowell, N. G., Zhou, J., Kaspari, M., Helliker, B. R., & Enquist, B. J. (2016). The energetic and carbon economic origins of leaf thermoregulation. Nature Plants, 2, 16147.
Neuner, G., & Buchner, O. (2012). Dynamics of tissue heat tolerance and thermotolerance of PS II in alpine plants. In C. Lütz (Ed.), Plants in Alpine Regions: Cell Physiology of Adaption and Survival Strategies (pp. 61-74). Vienna: Springer.
Schulze, E. D., Beck, E., & Müller-Hohenstein, K. (2005). Environment as stress factor: stress physiology of plants. In Plant Ecology (pp. 7-22). Berlin: Springer.