TY - JOUR A1 - Hirl, Regina T. A1 - Ogée, Jérôme A1 - Ostler, Ulrike A1 - Schäufele, Rudi A1 - Baca Cabrera, Juan C. A1 - Zhu, Jianjun A1 - Schleip, Inga A1 - Wingate, Lisa A1 - Schnyder, Hans T1 - Temperature-sensitive biochemical 18O-fractionation and humidity-dependent attenuation factor are needed to predict δ18O of cellulose from leaf water in a grassland ecosystem JF - New Phytologist N2 - We explore here our mechanistic understanding of the environmental and physiological processes that determine the oxygen isotope composition of leaf cellulose (δ18Ocellulose) in a drought-prone, temperate grassland ecosystem. A new allocation-and-growth model was designed and added to an 18O-enabled soil–vegetation–atmosphere transfer model (MuSICA) to predict seasonal (April–October) and multi-annual (2007–2012) variation of δ18Ocellulose and 18O-enrichment of leaf cellulose (Δ18Ocellulose) based on the Barbour–Farquhar model. Modelled δ18Ocellulose agreed best with observations when integrated over c. 400 growing-degree-days, similar to the average leaf lifespan observed at the site. Over the integration time, air temperature ranged from 7 to 22°C and midday relative humidity from 47 to 73%. Model agreement with observations of δ18Ocellulose (R2 = 0.57) and Δ18Ocellulose (R2 = 0.74), and their negative relationship with canopy conductance, was improved significantly when both the biochemical 18O-fractionation between water and substrate for cellulose synthesis (εbio, range 26–30‰) was temperature-sensitive, as previously reported for aquatic plants and heterotrophically grown wheat seedlings, and the proportion of oxygen in cellulose reflecting leaf water 18O-enrichment (1 – pexpx, range 0.23–0.63) was dependent on air relative humidity, as observed in independent controlled experiments with grasses. Understanding physiological information in δ18Ocellulose requires quantitative knowledge of climatic effects on pexpx and εbio. KW - canopy conductance KW - grassland KW - isotope-enabled soil–vegetation–atmosphere transfer model (MuSICA) KW - 18O-enrichment of cellulose oxygen isotope composition of cellulose KW - perennial ryegrass (Lolium perenne) KW - relative humidity KW - temperature Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:eb1-opus-5700 SN - 0028-646X SN - 1469-8137 VL - 229 IS - 6 SP - 3156 EP - 3171 PB - Wiley ER -