Abstract

Photosynthetic carbon gain and stomatal behaviour is dependent upon light intensity. In the field plants experience a range of light intensities and over the long term modify their growth through changes in leaf anatomy and morphology (e.g. sun and shade leaves). In a naturally fluctuating environment, stomata and photosynthesis are continually experiencing and adjusting to a variable light intensity. However, these responses are not always synchronized, as stomatal movements can be an order of magnitude slower than the more rapid photosynthetic response. Therefore over the diel period, short term fluctuations in light (sun/shade flecks) drive temporal and spatial dynamics of carbon gain and water loss, meaning that under natural fluctuating environmental conditions water use efficiency is far from optimal. A consequence of CO2 diffusion limitation is a decrease in photochemical sink capacity for excitation energy that can lead to photoinhibition under high light. Non-photochemical quenching processes are vital for dissipating excess excitation pressure, particularly in a dynamic light environment. However, in the laboratory we generally grow plants under square wave lighting regimes that do not mimic the natural environment. Little is known about the effect of a fluctuating growth light environment on plant photosynthesis or stomatal behaviour; for example, do stomata respond faster and/or photosynthetic capacity differ when compared to conventionally grown square wave plants? Photosynthetic and stomatal response data from plants that have been grown under LEDs in a fluctuating or ‘constant’ square wave lighting regimes of identical photoperiods and total daily light intensity.