Elemental allelopathy: processes, progress, and pitfalls

Abstract

Allelopathic interference between plants has generally been discussed in terms of the production of toxic complex biochemicals; however, complex biochemicals may not be the only substances plants use to interfere with one another. It has also been suggested that inorganic elements may be used in an allelopathic manner. If, through phytoenrichment or root exudates, a plant is able to increase the bioavailable levels of a particular element and tolerate the levels better than its neighbors, it can produce an allelopathic effect. Elemental allelopathy has been implicated as the cause for the success of a number of invasive weeds, including Acroptilon repens, Tamarix spp., Halogeton glomeratus, Salsola iberica, and Mesambryenthemum crystallinum. Phytoenrichment of elements can occur through hyperaccumulation and litter deposition and by altering rhizosphere chemistry. Reported cases of elemental allelopathy have involved three types of elements: heavy metals and soluble salts in terrestrial systems and elemental S in aquatic systems. For the most part, studies that have reported elemental allelopathy have been inconclusive. In order to prevent overreaching conclusions in the study of biochemical allelopathy, criteria were set that can be adapted to the study of elemental allelopathy. Of the studies reviewed, the most common criteria left uninvestigated were whether the plant was actually responsible for changing the concentration of the element and whether the increased levels of an element negatively affected other species. If the study of elemental allelopathy is to avoid the same problems often associated with the study of biochemical allelopathy, these criteria should be included in investigations of elemental allelopathy.

Establishment of Tamarix ramosissima under different conditions of salinity and water availability: Implications for its management as an invasive species

“…, 2000;Glenn and Nagler, 2005). This fact might be supporting previous evidence indicating that once established, saltcedars causes an increase in the salinity of the soil due to leaf litter (De Loach et al, 2000), which in turn would generate elemental allelopathy (Morris et al, 2009) and interfere with native vegetation growth (Di Tomaso, 1998;Lesica and De Luca, 2004;Landerburger et al, 2006). Therefore, mature saltcedars might be found growing at higher levels of salinity than they were able to tolerate during the colonization process as a consequence of their own action on the soil.…”

Ecological mechanisms of invasion success in aquatic macrophytes

“…For plants, weapons are often manifested through allelopathic chemicals (Ervin & Wetzel, 2003). Morris et al (2009) noted that dilution is a major hurdle for allelopathy in aquatic systems indicating that its effects may be less than those in terrestrial systems. Allelopathy has, however, been implicated in aquatic macrophytes (Gopal & Goel, 1993) such as C. demersum (Wium-Anderson et al, 1983), and Gross (2003) noted that allelopathy does occur in all aquatic habitats and is especially common in fully aquatic species.…”

The role of biotic interactions in determining metal hyperaccumulation in plants

“…Another hypothesis suggested to explain MH is the ‘elemental allelopathy hypothesis’, which proposes that hyperaccumulation evolved as a strategy to reduce performance of competing neighbour species via release of heavy metals (Boyd, ). Allelopathy has usually been studied in the context of organic compounds (Morris, Grossl, & Call, ), but the concept can also apply to the release of inorganic elements by metal hyperaccumulators (El Mehdawi, Quinn, & Pilon‐Smits, , ). Such elemental allelopathy can be achieved either by the decomposition of leaf litter or by the extraction of elements from leaves through rain water, both of which can result in enrichment of the soil in toxic compounds (El Mehdawi, et al, ).…”