Allelopathic Exudates of Cogongrass (Imperata cylindrica): Implications for the Performance of Native Pine Savanna Plant Species in the Southeastern US

Abstract

We conducted a greenhouse study to assess the effects of cogongrass (Imperata cylindrica) rhizochemicals on a suite of plants native to southeastern US pine savanna ecosystems. Our results indicated a possible allelopathic effect, although it varied by species. A ruderal grass (Andropogon arctatus) and ericaceous shrub (Lyonia ferruginea) were unaffected by irrigation with cogongrass soil "leachate" (relative to leachate from mixed native species), while a mid-successional grass (Aristida stricta Michx. var. beyrichiana) and tree (Pinus elliottii) were negatively affected. For A. stricta, we observed a 35.7 % reduction in aboveground biomass, a 21.9 % reduction in total root length, a 24.6 % reduction in specific root length and a 23.5 % reduction in total mycorrhizal root length, relative to the native leachate treatment. For P. elliottii, there was a 19.5 % reduction in percent mycorrhizal colonization and a 20.1 % reduction in total mycorrhizal root length. Comparisons with a DI water control in year two support the possibility that the treatment effects were due to the negative effects of cogongrass leachate, rather than a facilitative effect from the mixed natives. Chemical analyses identified 12 putative allelopathic compounds (mostly phenolics) in cogongrass leachate. The concentrations of most compounds were significantly lower, if they were present at all, in the native leachate. One compound was an alkaloid with a speculated structure of hexadecahydro-1-azachrysen-8-yl ester (C23H33NO4). This compound was not found in the native leachate. We hypothesize that the observed treatment effects may be attributable, at least partially, to these qualitative and quantitative differences in leachate chemistry.

Experimental evidence that invasive grasses use allelopathic biochemicals as a potential mechanism for invasion: chemical warfare in nature

“…Determination of potential allelopathic biochemicals is difficult, as chemical isolation of compounds from soils or dead plant materials may differ substantially in form and function from compounds extracted from living tissues (Hagen et al 2013). It is also difficult to identify individual compounds as the driving allelopathic biochemical, as several compounds may work individually or in combination (Hierro and Callaway 2003).…”

Recent advances in allelopathy for weed control: from knowledge to applications

“…Simple phenolics also have relevant allelopathic functions as herbicides and fungicides . In many cases, the study of phenolics has involved total phenolic content analyses, with gas chromatography and/or HPLC as the principal techniques …”

Cogongrass (Imperata cylindrica) invasions in the US: Mechanisms, impacts, and threats to biodiversity

“…Given these definitions, only four studies in our database met the criteria for allelopathy. Of these, only Hagan et al (2013b) found a reduction in performance of co-occurring natives (wiregrass, Aristida stricta, and slash pine, Pinus elliottii). Therefore, although ''allelopathy'' is the most common invasion mechanism addressed in the cogongrass literature, additional studies aimed at evaluating soil-mediated inhibition of native species under realistic natural conditions are needed to determine if allelopathy is driving invasion success in ecologically relevant settings.…”

“…There are a wide variety of possible explanations for the invasive success of cogongrass. For example, the ability of the species to establish and persist in highly variable habitats has been attributed to dense rhizome formation (Dozier et al, 1998;MacDonald, 2004), allelopathy (Cerdeira et al, 2012;Hagan et al, 2013b), high rates of reproduction through both seeds and rhizomes (Holly and Ervin, 2007), exceptional phenotypic plasticity (Patterson, 1980), and tolerance of diverse growing conditions including shade, drought, and poor soil quality (Bryson et al, 2010;Patterson, 1980). In addition, fire, cultivation, or other anthropogenic disturbances are also thought to promote cogongrass invasions ( Fig.…”