Overlooked Sunfleck Properties and Potential Implications for Crop Improvement

Sunflecks are ubiquitous in crop canopies, yet their properties are understudied. Recent data indicates that on sunny days, wind-induced sunflecks within crop canopies (windflecks) occur roughly twice per second and at amplitudes of roughly 10% of full sunlight. However, studies on the effects of fluctuating light on photosynthesis and plant growth often use fluctuations that do not resemble sunflecks, possibly resulting in irrelevant crop improvement targets. In this review, first, we quantify this mismatch between experiments and reality, showing that most studies measuring light intensities in crop canopies did so too infrequently to capture all sunfleck properties, while studies either simulating dynamic photosynthesis or growing plants under fluctuating light did so using much slower fluctuations than those often encountered in the field. Second, we attempted to estimate the losses of photosynthesis due to sunflecks: using light intensity fluctuations recorded inside a rice canopy at high frequency (100 Hz) on a sunny day, a dynamic photosynthesis model based analysis calculated minimal losses (0.85%-1.24% diurnally; relative to steady-state simulations), suggesting that sunflecks are too frequent, short, and weak to cause substantial losses due to slow dynamics of photosynthesis. We found that the choice of light intensity pattern matters enormously, as estimated losses reached 13% diurnally when using a less realistic light intensity pattern. We also introduce a framework for determining photosynthesis under windflecks based on pulsed light experiments. Thirdly, we present an overview of effects of global climate change on dynamic photosynthesis and crop growth under fluctuating light, concluding that likely, rising [CO₂] will benefit photosynthesis under sunflecks, whereas heat, VPD and drought may be detrimental. Finally, we suggest future research directions, noting that new targets for crop improvements under sunflecks will require a much better characterization of sunflecks, their windfleck and cloudfleck components, and their effects on photosynthesis and plant growth.