Effects of Desiccation and Sediment Type on Early Regeneration of Plant Fragments of Three Species of Aquatic Macrophytes

Abstract

We tested the effects of desiccation and type of sediment (clay or sand) on the regeneration of fragments of the apical shoots of three species of Hydrocharitaceae: Egeria najas, E. densa and Hydrilla verticillata. The shoots were left to dry on clay or sand from zero to four days, and were then returned to aquaria containing water. To approximate natural conditions, the aquaria containing clay had higher turbidity and nutrient (P and N) concentrations than did the aquaria with sand. All species dried faster on sand substrate, which led to lower regeneration (in terms of dry weight, length, sprout and root formation) in this treatment. H. verticillata fragments elongated faster than the other species, but E. najas was the most successful species (in terms of increase in dry weight) in the sand treatment. Our results indicate that the exotic H. verticillata has a competitive advantage, at least in its early stages of regeneration, over the other two, native species, especially in more eutrophic and turbid habitats; whereas E. najas fragments have a competitive advantage in less-turbid, oligotrophic and sand-dominated sites.

Regeneration and Colonization of an Invasive Macrophyte Grass in Response to Desiccation

“…Results similar to ours (i.e., high rates of regeneration and colonization even after 9 days of desiccation) have been found for other species of aquatic macrophytes, such as Elodea nuttallii (Planchon) St. John, Hydrilla verticillata (L. f.) Royle, Egeria najas Planch. and Egeria densa Planch., whose survival rates and sprout and root lengths did not differ between various desiccation periods and controls (Barrat-Segretain & Cellot 2007;Silveira et al 2009). …”

“…This process also occurs when reservoirs are subject to water drawdown (Thomaz et al 2009). Thus, the water regime is a major determinant of aquatic-plant community development, and the time of exposure to desiccation of plant fragments is an important determinant of their growth and success in freshwater ecosystems (Barrat-Segretain & Cellot 2007;Silveira et al 2009). …”

“…According to these hypotheses, we tested the predictions that sprout and root biomass, sprout length and sprout and root RGR (Relative Growth Rates) are greater in younger fragments submitted to shorter desiccation periods. The rationale for this hypothesis is that macrophytes, particularly grasses, usually regenerate most quickly from apical fragments where meristematic activity is higher (Kissman 1997;Riis et al 2009), and that desiccation represents a stress that may reduce regeneration (Silveira et al 2009). …”

Hydrilla verticillata (Hydrocharitaceae), a recent invader threatening Brazil’s freshwater environments: a review of the extent of the problem

“…It commonly occurs in water 3 m deep in Florida lakes (Langeland, 1996) as well as in backwaters (with low water flow) of the Paraná River . Hydrilla tends to maximize light acquisition through an extraordinary ability to elongate its stems [up to 4.0 m in the Paraná River (personal observation)], which form dense stands near the water surface (Cook & Lüönd, 1982;Silveira et al, 2009;Sousa et al, 2010). Besides maximizing light acquisition, this morphological strategy of Hydrilla also hampers the light penetration through the water column, reducing the availability of light to less well adapted species, especially isoetids (Haller & Sutton, 1975; Van et al, 1999;Wang et al, 2008a;Ye et al, 2009).…”

Water brownification may increase the invasibility of a submerged non-native macrophyte

“…Members of the family Hydrocharitaceae are recognized as some of the most troublesome weeds in lakes and reservoirs (e.g., Bini and Thomaz 2005;Chambers et al 2008;Sousa et al 2009b), primarily as a result of their elevated growth rates and environmental variability tolerance (Cook and Urmi-Köning 1985;Mony et al 2007;Silveira et al 2009;Sousa et al 2009b;Bianchini et al 2010), which makes these species highly competitive. Elodea canadensis, which is native to North America, is a submerged hydrocharitacean that was introduced to Europe in the 1840 s (Cook and Urmi-Köning 1985) that became invasive and displaced native species (Barrat-Segretain 2001; Barrat-Segretain and Cellot 2007).…”