iTREE-Long-term variability of tree growth in a changing environment – identifying physiological mechanisms using stable C and O isotopes in tree rings


Trees play are a critical role in the carbon cycle – their photosynthetic assimilation is one of the largest terrestrial carbon fluxes and their standing biomass represents the largest carbon pool of the terrestrial biosphere. Understanding how tree physiology and growth respond to long-term environmental change is pivotal to predict the magnitude and direction of the terrestrial carbon sink.

iTREE is an interdisciplinary research framework to capitalize on synergies among leading dendro-climatologists, plant physiologists, isotope specialists, and global carbon cycle modellers with the objectives of reducing uncertainties related to tree/forest growth in the context of changing natural environments. Cross-cutting themes in our project are tree rings, stable isotopes, and mechanistic modelling.


We will (i) establish a European network of tree-ring based isotope time-series to retrodict inter-annual to long-term tree physiological changes, (ii) conduct laboratory and field experiments to adapt a mechanistic isotope model to derive plant physiological variables from tree-ring isotopes, (iii) implement this model into a dynamic global vegetation model, and perform subsequent model-data validation exercises to refine model representation of plant physiological processes and (iv) attribute long-term variation in tree growth to plant physiological and environmental drivers, and identify how our refined knowledge revises predictions of the coupled carbon-cycle climate system.

Hence iTREE will result in a seamless understanding of the responses of terrestrial ecosystems to long-term environmental change, and ultimately help reduce uncertainties of the magnitude and direction of the past and future terrestrial carbon sink.



Gharun M, Klesse S, Tomlinson G, Waldner P, Stocker B, Rihm B, Siegwolf R, Buchmann N (2021) Effect of nitrogen deposition on centennial forest water-​use efficiency. Environmental Research Letters 16: 114036, doi: external page10.1088/1748-​9326/ac30f9


Lehmann MM, Egli M, Brinkmann N, Werner RA, Saurer M, Kahmen A (2020) Improving the extraction and purification of leaf and phloem sugars for oxygen isotope analyses. Rapid Communications in Mass Spectrometry 34: e8854, doi: external page10.1002/rcm.8854external page


Brinkmann N, Eugster W, Buchmann N, Kahmen A (2018) Species-specific differences in water uptake depth of mature temperate trees vary with water availability in the soil. Plant Biology 21: 71-81 doi: external page10.1111/plb.1290

Brinkmann N, Seeger S, Weiler M, Buchmann N, Eugster W, Kahmen A (2018) Employing stable water isotopes to estimate residence times of soil water and temporal origin of xylem water in a temperate forest. New Phytologist 219: 1300-1313 doi: external page10.1111/nph.15255


Brinkmann N, Eugster W, Zweifel R, Buchmann N, Kahmen A (2016) Temperate tree species how identical response in tree water deficit but different sensitivities in sap flow to summer soil dryings. Tree Physiology 36: 1508–1519 external pagedoi: 10.1093/treephys/tpw062


Rinne KT, Saurer M, Kirdyanov AV, Loader NJ, Bryukhanova MV, Werner RA, Siegwolf RTW (2015) The relationship between needle sugar carbon isotope ratios and tree rings of larch in Siberia. Tree Physiology 35: 1192-1205 doi:external page10.1093/treephys/tpv096

Roden J, Kahmen A, Buchmann N, Siegwolf R (2015) The enigma of effective pathlength for 18O enrichment in leaf water of conifers. Plant, Cell and Environment 38: 2551–2565 doi:external page10.1111/pce.12568


Gessler A, Ferrio JP, Hommel R, Treydte K, Werner RA, Monson RK (2014) Stable isotopes in tree rings: towards a mechanistic understanding of isotope fractionation and mixing processes from the leaves to the wood. Tree Physiology 34: 796-818 doi:external page10.1093/treephys/tpu040

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