A multiple time scale modeling investigation of leaf water isotope enrichment in a temperate grassland ecosystem

Abstract

Understanding the controls on temporal variation in plant leaf δ²H and δ¹⁸O values is important for understanding carbon–water dynamics of the biosphere and interpreting a wide range of proxies for past environments. Explaining the enrichment mechanisms under field conditions is challenging. To clarify the leaf water isotopic enrichment process at the ecosystem scale, four models with a range of complexities that were previously conducted at the leaf scale have been tested to simulate canopy foliage water in a multispecies grassland ecosystem. Although the exact importance of considering non‐steady‐state or/and isotopic diffusion in bulk leaf isotopic simulations has been reported in previous studies, our findings suggested that the steady‐state assumption (SSA) is practically acceptable as a first‐order approximation. The SSA two‐pool model was the best option for reproducing seasonality of the bulk‐leaf‐water isotopic ratio for a grassland ecosystem. Relative humidity at canopy layer as the most controlling factor for canopy foliage water stable isotope composition because of its high sensitivity and variation. The results highlighted that canopy foliage water was a well‐behaved property that was predictable for a multispecies grassland ecosystem at hourly or daily time‐scales.