@article{HirlOgeeOstleretal.2021, author = {Hirl, Regina T. and Og{\´e}e, J{\´e}r{\^o}me and Ostler, Ulrike and Sch{\"a}ufele, Rudi and Baca Cabrera, Juan C. and Zhu, Jianjun and Schleip, Inga and Wingate, Lisa and Schnyder, Hans}, title = {Temperature-sensitive biochemical 18O-fractionation and humidity-dependent attenuation factor are needed to predict δ18O of cellulose from leaf water in a grassland ecosystem}, series = {New Phytologist}, volume = {229}, journal = {New Phytologist}, number = {6}, publisher = {Wiley}, issn = {0028-646X}, doi = {10.1111/nph.17111}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:eb1-opus-5700}, pages = {3156 -- 3171}, year = {2021}, abstract = {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 per mille) 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.}, language = {en} }