Stomatal acclimation to dynamic light: implications for photosynthesis and water use efficiency

Although stomata typically occupy only a small portion of the leaf surface (0.3-5%), stomata control approximately 95% of all gas exchange between the leaf interior and external environment.Therefore, stomatal behaviour has major consequences for photosynthetic CO2fixation and water loss from leaf to canopy levels, influencing carbon and hydrological cycles at global scales. Plant acclimation to growth light environment has been studied extensively; however, the majority of these studies have focused on constant light intensity and photo-acclimation, with few studies exploring the impact of dynamic growth light on stomatal acclimation and behaviour. Initially, in this thesis natural variation in the response of stomatal conductance (gs) to light was assessed in the model tree species Populus nigra. Dynamic growth light regimes (varying in intensity and pattern) were subsequently used, to explore how stomatal acclimation to growth light impacts stomatal behaviour, photosynthesis (A) and water use efficiency (Wi). The rate, magnitude and diurnal behaviour of the response of gs to light varied significantly between genotypes and growth light treatments, which promoted differences in A and therefore Wiover the course of the day. The findings in this study illustrate the impact of growing plants in dynamic light regimes, similar to those experienced by plants in the natural environment, on the physiology and performance of model species Populus nigraand Arabidopsis thaliana. Furthermore, it emphasizes that growing plants under laboratory conditions and square-wave illumination does not accurately represent plant acclimation anddevelopment under a natural environment. Highlighting the need to potentially rethink how we grow plants as a community if we are to infer results from the lab to the field. Finally, this study highlights the importance of considering plant acclimation togrowth light, and the impact this has on the functional response of stomata, when attempting to model the response of gsacross leaf to ecosystem and global scales.