Carbon balance under dual droughts: Disentangling the effects of soil and atmospheric moisture on tree sink and source dynamics in European forests.
Atmospheric drought (high vapor pressure deficit, VPD) and soil drought frequently co-occur, yet plants respond to these stressors through partially distinct physiological pathways, potentially altering source (photosynthesis) and sink (growth and respiration) activities. Despite significant advances in understanding drought impacts on photosynthesis and plant hydraulics, the independent and interactive effects of soil vs. atmospheric drought on whole-tree carbon balance, including non-structural carbohydrate (NSC) dynamics, allocation priorities, and growth, remain insufficiently understood.
This project aims to disentangle the effects of soil and atmospheric droughts on tree sink and source dynamics in European forests, by studying leaf-to-whole-tree ecophysiological processes that drive growth, carbon sequestration and tree mortality. Research will primarily be conducted in Pfynwald (Valais, Switzerland), as part of the VPDrought experiment, where mature Scots pines (Pinus sylvestris) are exposed to increased soil drought and reduced VPD. (https://vpdrought.wsl.ch/). Measurements will be taken on gas exchange and leaf water potential across treatments during fieldwork campaigns. In addition, monitored data of leaf area development, stem radial growth and sap flow will be utilized and integrated in a model to simulate carbon uptake and respiration of the forest throughout the year. Moreover, NSC concentrations will be measured across tree organs to study carbon transport and allocation priorities under dual droughts. Lastly, a ¹³C pulse-labelling experiment will trace the fate of newly assimilated carbon.
As part of the overarching FutureForest project (https://futureforests.uk), complementary measurements will be done at a comparable manipulation experiment in Estonia (FAHM, University of Tartu) to quantify the impacts of soil droughts and VPD on carbon assimilation, storage, transport and sink activity in temperate and boreal forests.
