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. Therefore, on few weeks old tree seedlings, embolism resistance will be analysed using the optical vulnerability method, ultrasonic emission analyses, synchrotron-based micro-CT, the evaporative flux method, as well as staining of functioning conduits. With regard to induction and reversal of winter embolism, juvenile plants will be subjected to different growth conditions (summer drought, shade) and exposed to either mild or strong winter conditions, and native embolism and starch content will be regularly measured from autumn to 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. The project is carried out in cooperation with Kathy Steppe (University of Ghent) and Georg von Arx (Swiss Federal Institute for Forest, Snow and Landscape research).