How does varying water supply affect oxygen isotope variations in needles and tree rings of Scots pine?

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Timofeeva , G , Treydte , K , Bugmann , H , Salmon , Y , Rigling , A , Schaub , M , Vollenweider , P , Siegwolf , R & Saurer , M 2020 , ' How does varying water supply affect oxygen isotope variations in needles and tree rings of Scots pine? ' , Tree Physiology , vol. 40 , no. 10 , pp. 1366-1380 .

Title: How does varying water supply affect oxygen isotope variations in needles and tree rings of Scots pine?
Author: Timofeeva, Galina; Treydte, Kerstin; Bugmann, Harald; Salmon, Yann; Rigling, Andreas; Schaub, Marcus; Vollenweider, Pierre; Siegwolf, Rolf; Saurer, Matthias
Other contributor: University of Helsinki, Department of Forest Sciences

Date: 2020
Language: eng
Number of pages: 15
Belongs to series: Tree Physiology
ISSN: 0829-318X
Abstract: In many regions, drought is suspected to be a cause of Scots pine decline and mortality, but the underlying physiological mechanisms remain unclear. Because of their relationship to ecohydrological processes, delta O-18 values in tree rings are potentially useful for deciphering long-term physiological responses and tree adaptation to increasing drought. We therefore analyzed both needle- and stem-level isotope fractionations in mature trees exposed to varying water supply. In a first experiment, we investigated seasonal delta O-18 variations in soil and needle water of Scots pine in a dry inner Alpine valley in Switzerland, comparing drought-stressed trees with trees that were irrigated for more than 10 years. In a second experiment, we analyzed twentieth-century delta O-18 variations in tree rings of the same forest, including a group of trees that had recently died. We observed less O-18 enrichment in needle water of drought-stressed compared with irrigated trees. We applied different isotope fractionation models to explain these results, including the Peclet and the two-pool correction, which considers the ratio of unenriched xylem water in the needles to total needle water. Based on anatomical measurements, we found this ratio to be unchanged in drought-stressed needles, although they were shorter. The observed lower O-18 enrichment in needles of stressed trees was therefore likely caused by increased effective path length for water movement within the leaf lamina. In the tree-ring study, we observed lower delta O-18 values in tree rings of dead trees compared with survivors during several decades prior to their death. These lower values in declining trees are consistent with the lower needle water O-18 enrichment observed for drought-stressed compared with irrigated trees, suggesting that this needle-level signal is reflected in the tree rings, although changes in rooting depth could also play a role. Our study demonstrates that long-term effects of drought are reflected in the tree-ring delta O-18 values, which helps to provide a better understanding of past tree physiological changes of Scots pine.
Subject: 11831 Plant biology
1184 Genetics, developmental biology, physiology

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