Into the depths: the challenge of belowground VOC sampling

Volatile organic compounds (VOCs) serve pivotal functions in the intricate interactions within
plant ecosystems, facilitating communication among plants and other b i o t i c constituents such
as pollinators and soil organisms. While airborne VOCs have garnered considerable scientific
attention, belowground VOCs remain comparatively understudied. Nevertheless, these
belowground compounds intricately mediate signaling pathways between plants, soil bacteria,
fungi, belo wground insects, nematodes, and bacterial consortia. The primary limitation to
understanding subterranean VOC dynamics lies in technical challenges. Various methodologies
exist for their investigation, including ex situ non destructive extraction of plants from their
substrate for root VOC analysis (emi tted VOCs) VOCs), or root tissue grinding for VOC profiling VOC s
contained ther ein)ein). In situ approaches encompass static methods such as Solid Phase
Microextraction (SPME) (placed in an inert tube) and dynamic techniques like Dynamic
Headspace Sampling (DHS), employing either air extraction (pull) or injection (push) for
sampling (or both in push pull device) device). The heterogeneous and complex nature of soil poses
challenges in identifying the precise origins of sampled VOCs, which may emanate from
bacterial, fungal, root, insect, or organic matter sources. Furthermore, sampling efficacy is
contingent upon soil physicochemical parameters such as pH, temperature, and pore size .
While controlled environment studies or inert substrate replacements (e.g. glass beads) offer
experimental control, they may deviate from ecological realism. We will present the advantages
and disadvantages of the different strategies, indicating which scientific questions they are best
suited to answer. Additionally, we showcase home made devices developed in our laboratory,
designed to sample belo w ground VOCs and elucidate their role in plant plant interactions or
allelopathic phenomena