Work

The Stem of the Mediterranean Species Quercus ilex : a Forgotten Source of BVOCs

Year: 2026

Type: article

Abstract: Biogenic Volatile Organic Compounds (BVOCs) fulfil key ecological functions and have a significant impact on climate and air quality. However, research into BVOC fluxes from tree compartments other than the foliage remains limited and mainly restricted to conifers. In this study, we examined the stem emissions from Quercus ilex, an oak species that, despite lacking terpene storage pools, emits significant quantities of monoterpenes through its leaves. BVOC fluxes were measured using purpose-built dynamic stem chambers on four field-grown adult trees from spring to autumn. Q. ilex stems were found to be a net source of BVOCs, comprising mainly oxygenated and non-oxygenated monoterpenes and sesquiterpenes. Emissions fluctuated throughout the season with peak emissions in the summer. During summer months, the daily mean emission rate of monoterpenes ranged between 0.7 and 37 pmol·m-2·s-1stem surface (0.1 - 5.1 ng·m-2·s-1) whereas that of sesquiterpene ranged from 0.1 and 22 pmol·m-2·s-1 (0.02 - 4.5 ng·m-2·s-1) and even up to 95 pmol·m-2·s-1 (19 ng·m-2·s-1) for one of the trees. Deposition of BVOCs, primarily the major monoterpenes emitted by Q. ilex leaves and their secondary oxidation products, were occasionally observed but in minor quantities. Stem emissions were mainly driven by temperature with positive exponential relationships. Furthermore, they increased with lower predawn leaf water potential values, meaning with increasing drought stress, but they decreased with air humidity and stem transpiration. Significant emission differences were also observed between individual trees, possibly related to biotic stress. Overall, the results demonstrate that stems of non-coniferous trees such as oaks can be a net source of BVOCs, particularly of highly reactive terpenoids, which should be taken into account in emission inventories. Further research is needed to truly understand the mechanisms behind stem emissions, as well as their role in the forest ecosystem.

Source: Tree Physiology

DOI: 10.1093/treephys/tpag161