Improving forest drought resilience through tree xylem eco-physiological mechanisms

Introduction

Trees play a major role in Earth’s water and carbon cycles. Climate change puts trees under a growing threat of drought-induced mortality. This already happens in Europe, where summers are becoming hotter and drier, and across global forest biomes. Due to their large size and long lifespan, trees need time to adapt and migrate, time they lack under the fast rate of global change. On the other hand, forests are among the most important ecosystems we simply cannot afford to lose.

Xylem Embolism

Loss of xylem hydraulic conductivity due to the eruption of air bubbles is termed xylem embolism. Despite many years of studying tree responses to drought, it is still debated whether xylem embolism actually kills trees.

Challenges in Understanding

Simultaneous processes like carbon starvation, leaf desiccation, and heat damage make it harder to pinpoint the direct effects of drought on xylem embolism. Further, while the extent of embolism avoidance has been characterized in many tree species, embolism tolerance has been rarely studied, and recovery processes are mostly unknown.

Research Gaps

Finally, a wide research gap exists between eco-physiological mechanisms at the tree scale and implications at the forest scale. This research proposal portrays a clear roadmap to resolving the open questions in tree hydraulic mechanisms under drought and to integrating them at the forest scale.

Objectives

Increasing drought resilience in forests through eco-physiological mechanisms requires:

1. In-situ field measurements
2. Controlled experiments to decipher tree mechanisms
3. Advanced modeling to upscale tree-level measurements into the forest scale and support future forest management

Methodology

We will combine novel techniques, including:

• Custom-made micro-CT
• Field detection of xylem embolism and water potential
• Spatial mass spectrometry imaging
• And more

Additionally, we will conduct field measurements and manipulations on mature trees, greenhouse experiments on diverse tree species, and computational modeling to test new hypotheses aimed at increasing the drought resilience of forests.