On 28 November at 9:15 Gristin Rohula-Okunev will defend her doctoral thesis „Effects of endogenous and environmental factors on night-time water flux in deciduous woody tree species“.
Senior Research Fellow Priit Kupper, University of Tartu, Estonia
Associate Professor Teemu Hölttä, University of Helsinki, Finland
It is well-known fact that plants will open the stomata for photosynthetic carbon gain during the daytime. However in the last decade the night-time transpiration phenomenon has been intensively studied and it has been observed the incomplete stomatal closure at night in many different plant species. Nevertheless it is still no commonly accepted mechanism for stomatal regulation during periods of darkness. The aim of the studies was to investigate the impact of different environmental and plant endogenous factors on night-time and predawn water relations and gas exchange in deciduous woody tree species. We found that many species appeared to increase the aperture of their stomata prior to dawn. It could be that high predawn stomatal conductance may reduce diffusional limitation to photosynthesis during the early daylight hours and promote increased carbon assimilation and enhanced growth. Furthermore, we found that predawn stomatal conductance was significantly correlated with predawn leaf sucrose content. Thus, soluble sugars as an important osmoticums is related to the nocturnal gas exchange. Furthermore, the elevated air humidity may also promote the predawn stomatal opening. Additionally, the higher air humidity may increase the important mineral nutrients uptake for the growth. Our studies showed that nutrients availability partially regulates the night-time water relations. It could be that intensive night-time transpiration may increase the nutrient uptake or nutrient transport in nutrient-poor habitats. Our studies showed that also wind speed is an important driver of night-time sap flow in species characterised by larger leaves. In summary, the night-time transpiration is an important adaptation for the plants and it may not vary only due to the differences in environmental conditions, but also due to the physiological differences between species as well within species.