Beyond The Cellulose: Quantifying Plant To Ecosystem Level Water Balance Using Isotopic Composition Of Plant Lipids.

Cellulose δ¹⁸O is a well-established proxy for hydrological processes, with numerous applications in ecological and environmental research. Cellulose does not, however, persist after organic matter deposition, which limits its application. Here we compare plant hexane-extractable compounds with cellulose, testing whether lipid δ¹⁸O can be used as a proxy for hydrological processes. We use C₃ and C₄species to show that manipulations of evapotranspiration (ET) replenishment yield unequivocal isotopic signals, of similar magnitude and direction, in cellulose and plant lipids. Large differences in isotopic composition are observed between C₃ and C₄ plants, but linear relationships between cellulose and lipid δ¹⁸O hold in both groups, irrespective of variations in productivity and molecular composition of extracts. Oxygen enrichments match changes in water use efficiency, reflected by carbon isotope ratios (δ¹³C), demonstrating that lipids are suitable for assessing plant to ecosystem level water balance, with potential for measuring long-term biophysical forcings in managed and natural ecosystems.