After grazing exclusion, is there any modification of strategy for two guerrilla species: Elymus repens (L.) Gould and Agrostis stolonifera (L.)?

Abstract

Elymus repens (L.) Gould and Agrostis stolonifera (L.), are competitive grasses with guerrilla strategy that invade grasslands with a low stocking rate. In this work, we tested the hypotheses that grazing exclusion facilitates vegetative development of rhizomes and stolons of these clonal grasses and that such change is a key mechanism for their abundance in set-aside grasslands. The competitive capacities of these two guerrilla species were characterised by samples in plant community (species richness and biomass) and on the level of individual species (morphometric measurements on stolons and rhizomes) during a growing season. Compared to grasslands where grazing was excluded for three years, species richness was higher in grazed site and the plant community structure differed. Indeed, with grazing exclusion, a shift from annual species with a diversified growth-form to perennial species with a tall tussock and graminoid growth-form was monitored. In ungrazed situation, Elymus repens and Agrostis stolonifera were the dominant grasses, and the standing biomass for the lowland community showed a significant increase compared to the grazed site. Vegetative development increased competitive capacities of these two guerrilla species and led by phenomenon of competitive exclusion to the disappearance of annuals species. With grazing cessation, Elymus repens was found to increase the size of aerial traits (shoot length and the number of leaves per shoot) and this may both be propitious for achieving dominance within plant communities and also maintaining its competitive local advantage. By contrast, Agrostis stolonifera showed an increase in a root trait, i.e. rhizome length, in the fenced site, which provide good ability for spatial propagation and then to explore adjacent patches. We concluded that Elymus repens presented a morphological capacity to change its colonising strategy from a guerrilla strategy to a phalanx strategy, by morphological variability of aerial organs, when it was submitted to competitive stress and environment modifications. Agrostis stolonifera showed a capacity to escape aerial competition resulting from grazing cessation, than to increase underground propagation capacity. The present study highlighted the capacities of Elymus repens to respond in an adaptative way to competitive pressure.

Botanical composition, production and nutrient status of an originally Lolium perenne-dominant cut grass sward receiving long-term manure applications

“…The increase in content of stoloniferous/rhizomatous grasses suggests that the smothering effect of slurry dry matter may have been implicated in the decline of perennial ryegrass. The content of creeping bent and couch grass increased in response to slurry application and are considered to be 'guerrilla species' in that they creep into and colonise gaps in vegetation due their ability to produce rhizomes or stolons (Amiaud et al 2008). Potentially this could confer advantages over tussock type grasses when herbage is covered in solid matter as a result of treatment with high rates of slurry.…”

Does disturbance enhance the competitive effect of the invasive Solidago canadensis on the performance of two native grasses?

“…Elymus repens (L.) Gould (couch grass) is a strongly rhizomatous perennial grass with a guerrilla strategy, having prolific vegetative expansion by means of few ramets with longer spacers, creating a large clonal patch (Amiaud et al 2008). E. repens is an aggressive weed in arable lands, but also widespread along road-sites and pastures, and according to Grime's ecological strategies is a competitive-ruderal species (C/CR strategist) (Grime 2001).…”

“…'*' denote significant differences at p\0.05 between burned and unburned conditions, while capital letters show significant differences between the performance of American and European populations of S. canadensis Disturbance enhance the competitive effect of the invasive Solidago canadensis patches due to high tiller density and productivity (Carson and Barrett 1988), high phenotypic plasticity (Mojzes et al 2003), and a vigorous rhizome system that allows rapid vegetative propagation after disturbances (de Kroon and Bobbink 1997). Similarly, E. repens is also reported to have strong competitive abilities because it can respond to competitive pressure by shifting from a guerrilla strategy towards a phalanx strategy by producing dense canopy and long aerial shoots (Amiaud et al 2008;Pottier and Evette 2010). This is achieved by reducing the length of rhizome internodes, increasing branch frequency, and preferential allocation to aerial shoots and leaves (Amiaud et al 2008).…”

“…Similarly, E. repens is also reported to have strong competitive abilities because it can respond to competitive pressure by shifting from a guerrilla strategy towards a phalanx strategy by producing dense canopy and long aerial shoots (Amiaud et al 2008;Pottier and Evette 2010). This is achieved by reducing the length of rhizome internodes, increasing branch frequency, and preferential allocation to aerial shoots and leaves (Amiaud et al 2008). Despite these abilities, both species suffered large reductions in biomass in the presence of S. canadensis, perhaps due to the competitive advantage of the higher statured invasive species over the shorter grass species.…”

“…As the growth of rhizomes is negatively dependent on the quantity of light received by the leaves in E. repens (Palmer 1958), shading by S. canadensis could induce the prolific vegetative growth in this species, thus higher allocation to belowground tissues. Increased belowground biomass can enhance resource acquisition by root extension (perhaps the case of B. pinnatum), and also allow the colonization of surrounding gaps by elongation of vegetative organs (rhizomes and stolons) to avoid competition with a superior competitor (Amiaud et al 2008). This intense root competition can be an effect of resource depletion by the larger invasive species; but also the effect of allelopathy of S. canadensis (Abhilasha et al 2008;Yuan et al 2012) which might inhibit the access of the other competitor's roots to resources (Schenk 2006).…”