Non-native plant species often bring traits with them to their newly occupied ranges that potentially change the nature of interaction among species within communities.  The possibility of biochemical exudates that act as toxic “Novel Weapons” has been explored and documented, but the possibility that root exudates, typical for some invading plant species, can act as means to cope with allelopathic compounds exuded by native competitors, received much less attention. Phenolic compounds are allelopathic signal molecules exuded by the roots of many plants and detected by the roots of other plants. Invasive plants – plants that often were introduced from far-away regions - may not respond appropriately to these interspecies signals. Root enzymes that destroy phenolic compounds may be involved in the process of permitting an invasive plant to (a) ignore the signal molecules exuded by plants in the native community and (b) to render such allelopathic compounds ineffective. We screened and assayed roots of a wide range of invasive and native grasses for polyphenolic oxidases and peroxidase enzymes and tested whether grasses with differing levels of such oxidase activity also differ in performance in environments enriched in phenolics and in competition with allelopathic, native species.

Results/Conclusions

An analysis of large number of grass genera and species showed that all members of the genus Bromus exhibit elevated levels of phenolics-oxidizing enzymes in their root zone. Species from that genus are known to be problematic invaders in many parts of North America and other parts of the world. Other grass genera, regardless of their life form and tendency to invasion, typically have lower levels of these enzymes. In greenhouse studies we found that seedlings of Bromus inermis showed increased growth and higher allocation to roots when grown in soils enriched with a range of phenolics, while species from other grass genera did not show such reaction towards phenolics in the soil.  When grown in competition with Ambrosia artemisiifolia, an allelopathic, native North American plant, Bromus inermis was not reduced in growth while in contrast another, non-native grass (Dactylis glomerata) was. The presence of high concentrations of root enzymes capable of reducing the potential negative effect of released polyphenols present in grasses of the genus Bromus but largely absent in other grass genera suggest that these enzymes act as “Novel Defenses” in the invaded range of brome species and might explain some of their competitive success in new range.