Absorption of visible light by floral anthocyanins increases flower temperatures: implications for a warmer world

With rising global temperatures, understanding the mechanisms that influence plant thermal energy balance are critical to forecasting plant and pollinator responses. Flower temperatures impact visitation by insect pollinators, and several temperature-sensitive processes central to plant reproduction. Anthocyanin pigments absorb strongly in visible and ultraviolet wavebands, but clear support for a warming effect of pigments on flowers has remained elusive. We used infrared imaging to measure petal temperatures of horticultural varieties of plants differing in floral anthocyanin content. Excised sets of flowers were mounted perpendicularly to the sun, and exposed to direct ambient sunlight filtered either through Aclar (UV-transparent) or Courtguard (UV-opaque) under low-wind (