Quantifying and manipulating the angles of light in experimental
measurements of plant gas exchange
Abstract
Diffuse light has been shown to alter plant leaf photosynthesis,
transpiration, and water-use efficiency. Despite this, the angular
distribution of light for the artificial light sources used with common
gas exchange systems is unknown. Here we quantify the angular
distribution of light from common gas exchange systems and demonstrate
the use of an integrating sphere for manipulating those light
distributions. Among three different systems, light from a 90° angle
perpendicular to the leaf surface (± 5.75°) was <25% of the
total light reaching the leaf surface. The integrating sphere resulted
in a greater range of possible distributions from predominantly direct
light (i.e., > 40% of light from a 90 ± 5.75° angle
perpendicular to the leaf surface) to almost entirely diffuse (i.e.,
light from an even distribution drawn from a nearly 0° horizontal angle
to a perpendicular 90° angle). The integrating sphere can thus create
light environments that more closely mimic the variation in sunlight
under both clear and cloudy conditions. In turn, different proportions
of diffuse light increased, decreased, or did not change photosynthetic
rates depending on the plant species observed. This new tool should
allow the scientific community to explore new and creative questions
about plant function within the context of global climate change.