Hydraulic impairment in early ontogenetic tree stages

Balanced water relations are crucial for the growth and survival of tree seedlings. Due to their small root system and limited water and carbon storage capacities, young stages are particularly prone to drought stress. In alpine regions, apart from summer droughts also frost drought and repeated freeze-thaw cycles in the cold season can impair plant hydraulics. Many temperate tree species are able to restore their hydraulic system in spring, but it is yet unknown if this also applies to young stages. Further, there are no studies if and how drought stress in summer and severe winter conditions, respectively can affect the ability for spring recovery. This project aims at analyzing the vulnerability of native tree seedlings to drought- and freeze-thaw induced embolism, and at estimating the impact of summer drought and different winter conditions on the repair of the hydraulic system in the following spring. Outcomes of this project are of great relevance for basic research on plant hydraulics, as they provide new insights in important, but hitherto largely neglected, stages. They are also relevant in applied research such as forestry; due to climate change more frequent and more severe drought events in summer, but also an increased risk for late frosts in spring and lack of a protecting snow cover in winter is expected. Future forestation programs should not only consider drought tolerance and acclimation capability of adult plants but particularly also that of youngest and most vulnerable tree stages.