ASHLEY, NATALIE* and GARY K. GREER. Department of Biology, West Virginia State College, Institute, WV 25112-1000. - Effects of above-ground injury on the ability of Ailanthus altissima to effect neighbors via soil properties.
Ailanthus altissima (Tree-of-Heaven, TOH) is a widespread invasive common to disturbed
habitats and an increasing component of near urban forests in eastern North America. An allelopathic
compound (ailanthone) has been previously isolated from TOH, however, production is greatest in
seedlings. We investigated the effects of above-ground injury on the ability of reproductively
mature TOH to effect neighbors via soil properties. Five small TOH trees at the edge of each of
three populations received the following injury treatments: 0% (control) 10%, 20% 40%, and 100%
removal of above-ground biomass, based on height. Moderate injury treatments were designed to
simulate those that may occur naturally, whereas more severe injury simulated frequently used
roadside management. Soil from the top 20 cm was collected each week, 0.5 meters from each TOH,
dried, and an extract made by pouring 5.0 L water through the soil suspended in a cheesecloth.
The extract was used to water seeds of Fagopyrum esculentum (buckwheat) for germination
and radicle growth studies and to water seedlings for studies of growth and reproduction. Seed
germination rates were reduced in the 40% and 100% injury treatments, relative to control, only
during the second of three weeks. Patterns of radicle growth across treatments were complex
and changed in sign (increased vs. decreased growth) between weeks, however, most treatments
were associated with increases in radicle growth. In the seedling experiment, no differences
in total dry weight biomass (DWB) were detected. In contrast, root: shoot DWB ratio was reduced,
whereas height and reproductive effort (reproductive DWB ÷ total DWB) were elevated in the more
severe (30%, 40% and 100%) injury treatments. In general, a trend of increasing release from TOH
effects with increasing injury was observed. Loss of leaf tissue, which has been previously
associated with ailanthone production, may be responsible for these trends.
Key words: allelopathy, injury-induced response, Invasive species