Non-Photochemical Fluorescence Quenching Across Scales: From Chloroplasts to Plants to Communities

Non-photochemical quenching (NPQ) of chlorophyll fluorescence, as a measure of photoprotective thermal dissipation of excess excitation energy (from singlet state chlorophyll a), is usually studied at the molecular, organelle, and leaf scale over relatively short time periods, where it is most readily and easily quantified. The focus has been more on the mechanism(s) of the rapid component (energy-dependent quenching or qE) of NPQ and its basic modulation, rather than on the diversity in capacity and dynamics of NPQ (although see, e.g., Adams and Demmig-Adams, Chap. 2, Adams et al. Chap. 23, and Demmig-Adams et al. Chap. 24 for discussion of continuously sustained NPQ). In the past, it has also been difficult to measure levels of NPQ continually and at scales that reach whole plant or even community levels. This has resulted in a lack of understanding of how NPQ affects plant productivity and what may drive the adaptation and acclimation of NPQ kinetics and capacity. Thus, the role of thermal dissipation (assessed via its indicator NPQ) at the whole plant and even community scale is an understudied, albeit important topic. Thermal dissipation is by definition a protective process, and yet subject to tight metabolic control. How does regulation of thermal dissipation impact the operational state of photosynthesis? How efficient are the regulatory processes preventing photoinhibition and photooxidative stress? How does the large variation in NPQ dynamics and capacity relate to plant fitness and productivity? Does thermal dissipation impose a cost on photosynthetic rate in fluctuating environments? In this chapter, we address these questions by (1) describing the processes that give rise to thermal dissipation and the measurement of NPQ, (2) the role of thermal energy dissipation at different scales within the plant system, (3) the modulation of thermal energy dissipation capacity according to growth environment, and (4) the development of approaches for understanding how the dynamics of thermal dissipation determine plant fitness and productivity