Untangling root and microbial volatile organic compound emissions from soils of two different temperate tree species

The main sources of volatile organic compounds (VOCs) emitted from forest soils are roots and soil microorganisms. However, quantifying the relative contributions of these sources to net soil VOC emissions and the proportion of root VOCs degraded by soil microorganisms is challenging.

In order to partition soil VOC emissions into root and microbial VOC emissions, we conducted a controlled mesocosm experiment using Picea abies and Fagus sylvatica saplings, as well as soil (Cambisol) collected from a temperate forest dominated by these two species. VOC emissions from the soil surface (combined root and soil emissions), as well as from excavated roots and root-free bulk soil (sieved to 2 mm), were analyzed using PTR-TOF-MS and GC-MS. To evaluate the role of microorganisms as a source or sink of VOCs in the rhizosphere, microbial colonization of roots was modified by applying three washing treatments: (1) no washing (intact rhizosphere, high colonization), (2) water washing (partial removal of root microbiome, intermediate colonization), and (3) washing with 70% (v/v) ethanol (disinfection, reduced colonization), with 6 replicates per species and treatment.

This study aims to improve our understanding of the soil VOC fluxes in forest ecosystems by quantifying the contributions of roots and microorganisms to net soil VOC emissions, as well as the uptake of root VOCs by soil microorganisms.