Drought legacy responses of growth and carbon relations of evergreen and deciduous trees

Background

Drought has been shown to reduce tree carbon uptake and to have lagged effects on tree radial growth. To date we lack an understanding on above- versus belowground responses of tree growth to drought, and on the role of respiration versus non-structural carbohydrate (NSC) storage. These are not only important for tree growth and survival, but have the potential to alter tree recovery, to induce lagged responses during recovery and to modulate tree responses to subsequent drought. Consequences of recurrent drought events for tree species typical of current and future mountain forests are still poorly understood.

Research questions and hypotheses

The aim of the project is to unravel drought legacy responses of above- and belowground growth, NSCs and respiration of evergreen and deciduous tree species. The hypotheses will be tested that deciduousness and the drought effects on above- versus belowground growth and on respiration versus NSC storage will alter legacy effects of drought on recovery and on responses to a subsequent drought event, and that these effects and responses are modulated by nitrogen (N) availability. The project will also test whether effects of recurrent droughts will be more pronounced for saplings than for mature trees.

Approach and methods

In a common garden experiment, saplings growing under low versus higher N supply will be subjected to (i) ambient conditions with ample water supply, (ii) severe summer drought, (iii) severe summer drought following (i) or (ii). Selected trees will be pulse-labelled with 13CO2 and 15N to detect shifts in above- versus belowground carbon and nitrogen allocation and trade-offs between respiration and storage. In an ongoing multi-year experiment mature trees and saplings will be compared.

Time frame