Novel use of PDMS tubing for in-soil capture of plant natural products

The extraction of small lipophilic molecules (SLMs) in the soil-root interface that play a role in belowground ecological interactions between plants and insect herbivores was investigated. Polydimethylsiloxane (PDMS) microtubing has been shown to absorb root SLMs selectively in low disturbance setups, where analytes were extracted from the polymer with methanol. This technique was adapted to isolate SLMs that diffuse in the vapour phase in soil and sand and under various experimental parameters, extracting with a plug of diethyl ether pushed through the length of the silicon tubing. Moisture level had a substrate-dependent effect on the recovery rate of analytes that were applied as synthetic blends of known belowground SLM semiochemicals in the media. Higher amounts of two selected SLMs, (E)-caryophyllene and (-)-thujopsene, were extracted from sand, and increased polymer and solvent volume, as well as sampling duration, resulted in more of these two SLMs recovered by extraction. It was also shown that PDMS tubes lose no extraction capacity after repeated use. The signature compound (E)-caryophyllene was successfully isolated from the rhizosphere of maize plants infested with Diabrotica v. virgifera larvae by extracting the silicon tubing with diethyl ether. Because the tubes are preconditioned to reduce the presence of contaminants, such extracts can be directly analysed by GC and GC-MS and used in electrophysiological and behavioural assays. After further modifications, non-invasive, in situ PDMS probes can be developed that extract SLMs from plant rhizosphere for the study of belowground chemical ecology processes.