Seeing light from a different angle: the effects of diffuse light on the function, structure, and growth of tomato plants

While considerable attention has been paid to how plants respond to changes in the spectral distribution and quantity of light, less attention has been paid to how plants respond to changes in the angular qualities of light. Evidence from both leaf- and ecosystem-scale measurements indicate that plants vary in their response to diffuse compared to direct light growing environments. Because of the significant implications for agricultural production, we quantified how changes in light quality affect the structure, function, and growth of Roma tomatoes in an open-air greenhouse experiment with direct and diffuse light treatments. Diffuse light conditions (ca. 50-60% diffuse) were created with a glass coating to diffuse light without significantly reducing the quantity of light. We measured leaf physiology and structure, as well as whole plant physiology, morphology, and growth. Light-saturated photosynthetic rates were set by the growing light environment and were unchanged by short-term exposure to the opposite light environment. Thus, after two months, plants in the diffuse light treatment demonstrated lower photosynthesis and had thinner leaves with higher chlorophyll concentration. However, relative growth rates did not differ between treatments and plants grown in diffuse light had significantly higher biomass at the conclusion of the experiment. While there was no difference in leaf or whole-plant water-use efficiency, plants in the diffuse light treatment demonstrated significantly lower leaf temperatures, highlighting the potential for diffuse light coatings and/or materials to reduce greenhouse energy use. Our results highlight the need to advance our understanding of the effects of diffuse light conditions on agricultural crops growing on a changing planet.