As a graduate student, I do recall reading some research on the subject. I have reviewed my files but so far have not found my reprints. I seem to recall them coming from Australian researchers who also proposed using it as an indicator of soil quality. I will keep looking for them for you.

What I did manage to recover is the following:

1)Ethylene is normally produced by root tips and controls lateral root branching and root morphology (E.Curl & B.Truelove, The Rhizosphere, 1986, page 187).

2)Ethylene is produced by known soil fungal species and has anti-fungal properties (A.Martin, Introduction to Soil Microbiology, 1977, pages 207-208).

3)Ethylene has plant allelopathic potential (E.L.Rice, Allelopathy, 1984, pages 103, 323). In fact, elevating soil levels of ethylene gas is a proposed control for Striga in Africa (L.Butler, 1995, "Chemical communication between the parasictic weed Striga and its crop host", pages 158-168, In Inderjit, Dakshini & Einhellig (eds.) Allelopathy: Organisms, Processes and Applications).