Evaluation of elemental allelopathy in Acroptilon repens (L.) DC. (Russian Knapweed)

Abstract

Although Acroptilon repens (L.) DC. (Russian knapweed) is known to concentrate zinc (Zn) in upper soil layers, the question of whether the elevated Zn has an allelopathic effect on restoration species has not been addressed.

Elemental allelopathy: processes, progress, and pitfalls

“…In both cases, the effect has been reported on species of phytoplankton. Although phytoplankton vary from vascular plants in some aspects, they function similarly both physiologically and ecologically (Morris 1980). Wium-Andersen et al (1982) clearly demonstrated the effect of elemental S on the photosynthesis of a species of epiphytic phytoplankton, however, as is often the case, the concentrations of S used in the experiments did not necessarily represent levels found in nature.…”

“…Isolate and characterize toxin Vivrette and Muller (1977), Morris et al (2006) Determine toxin levels found naturally in accumulator species, rates of deposition, and accumulation in soils Sharma and Tongway (1973), Vivrette and Muller (1977), Boyd et al (1999), Boyd and Jaffre (2001), Zhang et al (2005Zhang et al ( , 2007 Select proper bioassay based on Vivrette and Muller (1977), Lesica and Deluca (2004), Morris et al (2006) growth form species phenology Determine uptake and symptoms of the toxin in affected species Vivrette and Muller (1977), Morris et al (2006) Source: Adapted from Fuerst and Putnam (1983) Plant Ecol (2009) 202:1-11 5 which concentrate their roots at the soil surface, may be better candidates. For species which are thought to phytoenrich elements through acidification or other modifications of the rhizosphere, root architecture may not be as important.…”

“…Morris et al (2006) showed that germinating and developing seedlings of three grass species were unaffected by accumulations of Zn associated with surface soils underneath stands of A. repens. The authors concluded that older plants with lower relative growth rates and longer exposure to the elevated soils would have been more likely to accumulate toxic tissue concentrations of Zn.…”

“…However, the Zn levels used in the solutions were not representative of levels found in nature and therefore did not provide conclusive evidence. Morris et al (2006) attempted to address the question of whether phytoenrichment of Zn in soil by A. repens negatively impacted associated grasses by applying chemical treatments for the alleviation of Zn toxicity to plants grown in soils collected from both within a stand of A. repens and in soil collected adjacent to A. repens. The addition of Fe-oxides and bioavailable Fe and P helped to reduce uptake of Zn or offset the negative effects of ion substitution, thus isolating any effect of Zn toxicity and minimize confounding factors, such as from biochemical allelopathy or differences in available nutrients.…”

“…The use of chemical amendments by Morris et al (2006) is another promising technique that may help to isolate the effects of elemental allelopathy from other factors, although it probably won't be effective in cases of osmotic stress caused by saline soils. Application of chemical amendments to soils must be done carefully in order to avoid unintended chemical or biological alterations of the soils and can be avoided by using foliar applications when possible (Morris et al 2006). As other elements are implicated in elemental allelopathy and new mechanisms of toxicity are included, the adaptation of additional chemical amendments may be possible.…”