Acacia trees in the Arava desert: higher activity of photosynthesis during noon and summer times

Among living tree species, Acacia raddiana (Savi) and Acacia tortilis (Forssk), species of the legume family populate some of the hottest and driest places on earth. Trees that live under these environmental conditions are a major point of interest in light of ongoing climate change. My research investigates the physiological processes underlying this unique plant strategy. We performed measurements of Acacia trees in their natural habitat once a month for a year in order to follow the water relations dynamics of the trees. Leaf gas-exchange and water potential were measured, as well as atmospheric and soil parameters. Daily and annual gas-exchange curves showed a pattern of higher activity during noon and in summer, when temperature and radiation is maximal (44°C, 1800 µmol m^-2 s^-1) but the air is drier (relative humidity of 21%). Gas exchange activity seasonally in summer and diurnally at noon, suggesting that light and temperature are the primary driver, and that water availability does not influence carbon assimilation. Additionally, even after five months of drought, pre-dawn water potential was practically zero (between -0.2 and -0.8 MPa), together with high soil water potential of the soil (0.4 Mpa) and soil water content (5.1%). Our results suggest that Acacia trees growing in this hyper arid environment do not experience a severe water stress, in spite of the harsh conditions. Next, we aim at identifying their water sources in situ.