Global sea-level rise is anticipated to cause negative impacts on coastal terrestrial ecosystems, including reductions in plant productivity and forest mortality. However, the mechanisms driving salinity-induced tree death are poorly understood. Tree nonstructural carbohydrates (NSC), play an important role in tree survival, by acting as a resource to support growth, respiration and other metabolic functions. The aim of this study was to examine how recent seawater exposure influences NSC storage and tree death. To test this, we conducted work in a Pacific Northwest coastal watershed, where seawater exposure following dike failure in 2014 is resulting in significant Sitka-spruce (Picea sitchensis) mortality. We compared growth rates, tree-ring δ13C and water potential in declining and healthy trees, and investigated hydraulic function and seasonal NSC storage in different tissues along a gradient of crown health.
Results/Conclusions
We observed high tree mortality of trees in the forest (73% dead) within the first four years after dike removal. Declining and healthy trees suffered similar water stresses, with comparable salinities and water potential in soils and needles. Annual growth and wood δ13C decreased dramatically and consistently the year after seawater exposure, and no significant difference in these parameters was found between healthy and declining trees. These results suggest that neither growth nor gas exchange decline was directly related to tree death, but the inherent physiological functions in C metabolism (e.g., NSC storage) and hydraulic maintenance were responsible for crown health in Sitka-spruce. Our poster will present the correlations of carbon storage with tree crown greenness under salt water stress. Our study provides insight into the change of C balance in salinity-induced tree mortality, which will improve predictions of coastal vegetation dynamics under increasing seawater exposure.