The impact of an inverse climate–isotope relationship in soil water on the oxygen‐isotope composition of Larix gmelinii in Siberia

• DOI: 10.1111/nph.13759
• Publication Date: 2015-11-26T15:58:48Z
• Authors: Matthias Saurer; Alexander V. Kird...; Anatoly S. Prokus...; Katja T. Rinne; Rolf T. W. Siegwolf
• Keywords: 0106 biological sciences; 570; Climate; Carbohydrates; soil water; Larix; Oxygen Isotopes; Plant Roots; 01 natural sciences; Soil; oxygen isotope; Craig-Gordon model; leaf water enrichment; Ecosystem; Probability; 0105 earth and related environmental sciences; Water; Humidity; Microclimate; 15. Life on land; cellulose; 6. Clean water; Droughts; Plant Leaves; Siberia; Solubility; 13. Climate action; permafrost

Summary

Stable oxygen isotope ratios (δ18O) in trees from high latitude ecosystems are valuable sources of information for recent and past environmental changes, but the interpretation is hampered by the complex hydrology of forests growing under permafrost conditions, where only a shallow layer of soil thaws in summer. We investigated larch trees (Larix gmelinii) at two sites with contrasting soil conditions in Siberia and determined δ18O of water from different soil depths, roots, twigs, and needles as well as δ18O of soluble carbohydrates regularly over two growing seasons. A comparison of results from the 2 yrs revealed an unexpected ‘inverse’ climate‐isotope relationship, as dry and warm summer conditions resulted in lower soil and root δ18O values. This was due to a stronger uptake of isotopically depleted water pools originating from melted permafrost or previous winter snow. We developed a conceptual framework that considers the dependence of soil water profiles on climatic conditions for explaining δ18O in needle water, needle soluble carbohydrates and stem cellulose. The negative feedback of drought conditions on the source isotope value could explain decreasing tree‐ring δ18O trends in a warming climate and is likely relevant in many ecosystems, where a soil isotope gradient with depth is observed.