A new snow module improves predictions of the isotope-enabled MAIDENiso forest growth model

Abstract

Abstract. The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module; consequently, their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in eastern and western Canada for black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The MAIDENiso model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates of cellulose isotopic composition. Future work may include the development of inverse modelling with this new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments.

Progressive enrichment in 18O and 2H in xylem water along sap flow paths in Fagus sylvatica trees

“…This kinetic isotope effect might have an important role in the isotopic exchange between metabolic intermediates and water during post‐photosynthetic metabolism, creating fractionation. This type of isotope exchange during plant biosynthetic pathways involves a preferential fractionation of light O–H isotopes into organic molecules and the consequent enrichment of heavy isotopes in the water, as shown for several biochemical processes such as lipid and carbohydrates biosynthesis (Cormier et al, 2018), including cellulose (Hermoso de Mendoza et al, 2022; Kagawa & Battipaglia, 2022; Sternberg et al, 1986). Post‐photosynthetic O–H isotopic exchange mainly occurs via carbonyl hydration, which is a good candidate reaction to explain xylem transformations, as it involves isotopic exchange between xylem water and metabolites during cellulose biosynthesis (Cheesman & Cernusak, 2017; Hill et al, 1995; Samuel & Silver, 1965; Sternberg & Deniro, 1983).…”

“…Moreover, water participates in biochemical reactions linked to the biosynthesis of many molecules, undergoing biochemical isotope fractionation (da Silveira Lobo Sternberg, 1988;Yakir & DeNiro, 1990). Some of these metabolic pathways involving xylem water may be responsible for the gradual enrichment observed, due to difference in chemical reaction rates between light and heavy as shown for several biochemical processes such as lipid and carbohydrates biosynthesis (Cormier et al, 2018), including cellulose (Hermoso de Mendoza et al, 2022;Kagawa & Battipaglia, 2022;Sternberg et al, 1986). Post-photosynthetic O-H isotopic exchange mainly occurs via carbonyl hydration, which is a good candidate reaction to explain xylem transformations, as it involves isotopic exchange between xylem water and metabolites during cellulose biosynthesis (Cheesman & Cernusak, 2017;Hill et al, 1995;Samuel & Silver, 1965;Sternberg & Deniro, 1983).…”