Presentation_1_Temperature-Dependent Oxygen Isotope Fractionation in Plant Cellulose Biosynthesis Revealed by a Global Dataset of Peat Mosses.pdf

The oxygen isotope composition (δ¹⁸O) of plant cellulose has been widely used to study ecohydrological processes of ecosystems as well as to reconstruct past climate conditions in terrestrial climate archives. These applications are grounded on a key assumption that the biochemical fractionation during cellulose synthesis is a constant around +27‰ and is not affected by environmental factors. Here we revisit the influence of temperature on biochemical fractionation factor during cellulose synthesis using a global compilation of Sphagnum cellulose δ¹⁸O data. Sphagnum (peat mosses) are known for inhabiting waterlogged peatlands and possessing unique physiological strategy in that their cellulose δ¹⁸O could closely reflect growing-season precipitation δ¹⁸O. Although within-site cellulose δ¹⁸O variability shows a median standard deviation of 0.7–0.8‰ resulting from different degrees of evaporative enrichment of ¹⁸O in metabolic leaf water, this evaporative enrichment should be a small quantity due to the external capillary “water buffer” in Sphagnum mosses. Using site-specific minimum cellulose δ¹⁸O data that most likely reflect the signal of unevaporated source water, we show that the apparent enrichment factor between cellulose and precipitation δ¹⁸O increases with decreasing air temperature. In particular, the apparent enrichment factor could reach values as high as +32‰ when growth temperature is below 5°C. This observational dataset extends the support for the temperature-dependent oxygen isotope fractionation in plant cellulose synthesis previously demonstrated in laboratory experiment, with implications for paleoclimate and plant physiology studies that employ cellulose δ¹⁸O measurements, particularly in alpine regions.