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Micromorphological changes within foliage of two xerophytes in response to varying water and nutrient availability


As a consequence of ongoing climate change, dry forests throughout the world have experienced elevated drought stress and the dominant trees higher rates of mortality. In Switzerland, these trends have been observed for the last 20 years in low elevation pine (Pinus sylvestris) stands of Central Wallis.

The CaNuPine project has been designed to analyze the interactions between carbon starvation, as a consequence of drought, and varying soil nutrient availability. During two experimental years, pine and oak saplings are being exposed to irrigation shortages (4 levels) and varying nutrient supplies (2 levels) - with or without removal of a part of pre-existing foliage (pine) - within an ecosystem facility simulating the growth conditions in a young afforestation.


The specific and main objectives in the present sub-project are to 1) assess how interactions between spring drought and elevated nutrient availability affect the tissue composition of pine versus oak foliage during foliage elongation, 2) analyze circadian micromorphological changes in foliage of pine and oak under drought stress and 3) microlocalize NSC (starch and sucrose) and thus relate the changes in patterns of carbon assimilation and translocation within droughted plants to adaptive, defense and stress responses in tissues and cells.

Therefore, different morphological (needle/leaf biomass, water content, leaf mass per area), histological (leaf blade tissue area/thickness, veinlet network density, intercellular space volume), cytological (cuticula thickness, organelle size and frequency) and ultrastructural (microlocalization of 13C-labeled starch and sucrose pools) parameters are assessed in leaves and needles. Methodological and technological developments needed with a view to microlocalizing 13C-labeled compounds will be achieved in the framework of a collaboration with the Forest Growth and Climate research team and the Luxembourg Institute of Science and Technology (LIST).

The expected results should advance our mechanistic understanding of 1) drought and mineral nutrition interplay with regard to the formation of xeromorphic traits, 2) circadian dynamics of cell-level changes in response to drought and 3) NSC dynamic and translocation in droughted foliage. On a larger scale and in the context of replacement of pine by downy oak at low elevation in the Central Alps, the expected findings should provide insights on the morphological and physiological adaptation specificities in these two drought-tolerant xerophytes.