Dynamics of belowground diffusion and diffusion and degradation

Authors: Som, Salina; Willett, Denis; Alborn, Hans

Submitted to: Rhizosphere 2004
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2017
Publication Date: 7/21/2017
Citation: Willett, D.S., Som, S., Alborn, H.T. 2017. Dynamics of belowground diffusion and diffusion and degradation. Rhizosphere 2004. 4:70-74. doi:10.1016/j.rhisph.2017.07.004.
DOI: https://doi.org/10.1016/j.rhisph.2017.07.004

Interpretive Summary: Many organisms use their sense of smell to navigate, even belowground. This is especially true of entomopathogenic nematodes (EPNs). These tiny roundworms are effective at infecting, killing and controlling many agricultural insect pests. However, belowground the chemicals that the nematodes use, or can use, to find and kill insect pests do not travel the way smells do aboveground. This might be a key factor in understanding how the nematodes find and sometimes fail to find their host insects. To understand how these chemicals move belowground, scientists at the USDA-ARS CMAVE Chemistry Research Unit measured diffusion and degradation of belowground signals under different environmental conditions. They discovered that belowground diffusion is nonlinear and can involve degradation of certain odors into rapidly moving belowground signals. These findings will be used to develop cost-effective management strategies that growers can use to control belowground insect pests.

Technical Abstract: It is well established that above ground herbivory induced plant volatiles (HIPVs) attract natural enemies of the herbivores. We now know that also roots can release HIPVs and that these compounds attract beneficial organisms such as entomopathogenic nematodes (EPNs). Unlike their aboveground counterparts, belowground volatile signals interact with solids, liquids, and gases as they move through soil pore spaces. This can result in non-linear diffusion profiles and even degradation in space and time and thus influence volatile signals used by EPNs for belowground navigation. We found that that in sandy Florida soil the diffusion and degradation profiles of E- ß -caryophyllene, d-limonene, pregeijerene, a-pinene, germacrene-d, and linalool were affected by moisture as well as pH levels. Furthermore, the common plant volatile linalool was non-diffusive below ground when tested at biologically relevant concentrations. In addition we discovered a novel pathway for the degradation of linalool into rapidly diffusing signals. These findings highlight the importance of considering abiotic factors when studying below ground semiochemically-based interactions such as attraction of beneficial EPNs to plant roots infected by host insects and suggest areas for future exploration.