Heat and drought: Stress and recovery responses of Aleppo pine seedlings

Aleppo pine trees growing at the arid timberline (Yatir forest, Israel) are facing extreme seasonal drought combined with hot temperatures during summer and short heat wave periods in spring. These heat waves have large effects on the forest carbon and water exchange, and might likely increase in severity with predicted climate change scenarios. To better understand the trees’ physiology during stress and subsequent ability to recover from heat and drought, we performed a greenhouse experiment on one-year-old Pinus halepensis. Soil moisture was kept close to the winter optimum in the control and heat treatment and close to summer values in the drought and heat-drought treatment. The trees of the heat treatment were exposed to two short heat waves (4-days each) with temperature maxima of 43°C, about 15°C above the control and drought trees. Aboveground carbon exchange, transpiration and emissions of selected volatile organic compounds (VOC) were measured continuously using automated tree chambers (n=4 per treatment). To detect changes in biomass allocation and carbohydrate pools, additional trees were sampled before, during and at the end of the stress periods. We will present first results of stress and recovery responses of carbon and water exchange including VOC emissions. In combination with changes in biomass allocation and carbohydrate pool analysis, this can give us a better view on pine seedling performance during periodic combined environmental stress.