Evaluation of trap discs for root exudate eco-friendly sampling using rhizoboxes: Application to untargeted screening of organic compounds by gas chromatography hyphenated with high resolution mass spectrometry

In the present paper, an unusual sampling method, called EcoRoot, was investigated for sampling directly in soil, root exudates of Poa annua L., belonging to the Poaceae family. Using a rhizobox, sorption filters were placed directly onto roots to serve as traps for root exudates. Various trap compositions, namely, cellulose nitrate, glass microfiber and nylon, were evaluated for their ability to adsorb/desorb a standard mixture of known exuded compounds and for recovery yield. Cellulose nitrate supports exhibited better yields for compounds known to be exudated by plants of the Poaceae family. Then, two crucial parameters were investigated: the contact and extraction times. The most suitable methodology for extracting the target compounds was a cellulose nitrate support with a contact time of 60 min and 30 min in an ultrasonic bath using a mixture H₂O/MeOH. Soil and root sampling was carried out under the optimized conditions. Then, silylation of extracts was performed, and GC-HRMS was used to demonstrate that this sampling method could be used to efficiently trap compounds from soil and roots. Moreover, among the 6,136 compounds detected in extracts, 516 appeared to be specific to root exudates. This Ecoroot methodology allows root exudates to be collected in conditions as close as possible to natural growth environment, limiting the environmental impact with a 0.59 score (AGREEprep) compared to hydroponic methods. Ecoroot offers interesting perspectives for studying root exudate metabolome and their temporal and spatial dynamics in the rhizosphere, with important issues in both Ecology and Plant biology.