Leaf angle as a leaf and canopy trait: Rejuvenating its role in ecology with new technology

Life on Earth depends on the conversion of solar energy to chemical energy
by plants through photosynthesis. A fundamental challenge in optimizing
photosynthesis is to adjust leaf angles to efficiently use the intercepted
sunlight under the constraints of heat stress, water loss, and
competition. Despite the importance of leaf angle, until recently, we have
lacked data and frameworks to describe and predict leaf angle dynamics and
their impacts from leaves to the globe. We review the role of leaf angle
in studies of ecophysiology, ecosystem ecology, and earth system science
and highlight the essential yet understudied role of leaf angle as an
ecological strategy to regulate plant carbon-water-energy nexus and to
bridges leaf, canopy, and earth system processes. Using two models, we
show that leaf angle variations have significant impacts on not only
canopy-scale photosynthesis, energy balance, and water use efficiency but
also light competition within forest canopy. New techniques to measure
leaf angles are emerging, opening opportunities to understand the
rarely-measured intraspecific, interspecific, seasonal, and interannual
variations of leaf angles and their implications to plant biology and
earth system science. We conclude by proposing three directions for future
research.