Effect of minor water depth treatments on competitive effect and response of eight wetland plants

Abstract

Two facets of plant competition, competitive effect (CE) and competitive response (CR), can be used to explain plant community composition but our understanding of abiotic factors that may differentially affect species’ competitive ability is incomplete. We tested whether water-depth affected CE (ability to suppress neighbour) and CR (avoid suppression from neighbour), and if so whether there was consistence in the rank order of both measures of competition under different water depth treatments. CE and CR were measured and compared for eight wetland plant species (Carex lurida, Carex tribuloides, Elymus virginicus, Juncus tenuis, Lythrum salicaria, Phalaris arundinacea, Rumex orbiculatus and Verbesina alternifolia) at five different waterdepth treatments (+2, 0, -2, -4 and -6 cm relative to the substrate). Overall, we found that mean CE was at its lowest value at +2 cm water depth, while mean CR was highest at +2 and -6 cm compared to the other water treatments. There was a significant variation of CE between species, with a defined hierarchical order. Pairwise CE rank order correlations between water depth treatments were significant but CR correlations were generally not. There was no significant correlation between CE and CR. CE was significantly correlated with biomass of species grown alone but CR was not. These findings indicate that CE may be used as a general measure to predict wetland species performance, and thus community assemblage, across a range of water depths. CR does not seem to demonstrate predicable patterns between species and water depth treatments. Our results suggest that competition intensity may be reduced in a non-resource-stressed flooded environment by a reduction in CE, but the corresponding increase in CR could dampen this effect on overall competitive ability.Peer reviewedCompetitive effect and responseFreshwater wetlandsNon-resource stressPhalaris arundinaceaPhytometerWater dept

Plant competitive ability and the transitivity of competitive hierarchies change with plant age

“…This is strong evidence that the relative competitive effect abilities among species do not vary strongly through plant development, and is consistent with studies showing that competitive effect ability is generally independent of both target plant identity and nutrient conditions (Fraser and Miletti 2008;Goldberg and Landa 1991;Wang et al 2010). Competitive effect ability is correlated with traits such as plant height and size, leaf shape, and relative growth rate (Goldberg 1996;Goldberg and Fleetwood 1987;Goldberg and Landa 1991;Keddy et al 2002).…”

“…Importantly, other studies have shown a lack of correlation between competitive effect and response abilities (Fraser and Miletti 2008;Goldberg and Landa 1991;Keddy et al 1994). We suggest that the form of competition occurring is important in determining whether there is a positive relationship between competitive effect and response.…”

“…Competitive hierarchies are known to change depending on resource identity and availability (Fortner and Weltzin 2007;Fraser and Miletti 2008;Keddy et al 2000) and disturbance (Suding 2001;Suding and Goldberg 2001), which may provide mechanisms for the coexistence of multiple species (Crain et al 2004).…”

Using three pairs of competitive indices to test for changes in plant competition under different resource and disturbance levels

“…Relative competitive index (RCI), relative neighbour effect Brooker et al (2005), Grace (1995), Turkington et al (1993), Campbell & Grime (1992), Wilson & Tilman (1995), Fraser & Miletti (2008), Markham & Chanway (1996) …”

Mechanisms of dominance by the invasive hybrid cattail Typha × glauca

“…We expected Typha treatments to lower light penetration and temperature at the soil surface (Angeloni et al 2006;Hager 2004) and to decrease native plant Herman et al (2001) and P values calculated using two-tailed t tests species' abundances (Frieswyk et al 2007;Tuchman et al 2009;Zedler and Kercher 2004). We anticipated negative, intraspecific effects of Typha density and Typha litter on the biomass of individual Typha plants and overall Typha biomass (Gurevitch et al 1992;Holly and Ervin 2006) and hypothesized that waterlevel treatments would have species-specific effects on native plant biomass (Fraser and Miletti 2008;Weiher and Keddy 1995).…”