Morphological adaptations of emergent plants to water flow: a case study with Typha angustifolia, Zizania latifolia and Phragmites australis

Abstract

1. Water velocity plays an important role in shaping plant community structure in flowing waters although few authors have yet attempted to explain the adaptation of plants to flow. 2. We aimed to test two hypotheses, that: (i) some emergent macrophytes reconfigure their shoot distribution in fast currents and form clumps, and (ii) the shape and morphology of such clumps minimises drag caused by the current. The study focuses on three emergent macrophytes that co-occur along a gradient of water velocity. 3. The species showed a clear zonation in response to water depth and current velocity. Phragmites australis occupied shallower and more slowly flowing water than Typha angustifolia and Zizania latifolia, which had similar preferences. 4. Both T. angustifolia and Z. latifolia shoots were more clumped at high velocity, whereas they were more randomly distributed at low flow or in stagnant water. Because of the low shoot density, water flowed more easily through T. angustifolia clumps, whereas Z. latifolia clumps had a high shoot density and large amounts of trapped litter, causing stagnant water in the centre of the clump. The clumps of Z. latifolia with a high density of shoots were longer and narrower than T. angustifolia clumps. Phragmites australis was less tolerant of flow than the other two species and large amounts of litter trapped in the clumps impaired flow. 5. The shoot distribution of both T. angustifolia and Z. latifolia is reconfigured at high flow and this minimises drag on the clumps.

Spatial and temporal tree colonization in a midstream sediment bar and the mechanisms governing tree mortality during a flood event

“…If there is deep root penetration, such as in Salix spp., localized scouring around an individual tree can be less influential (Asaeda et al, 2005). No significant localized scouring was noticed in the sediment bar.…”

Fine sediment retention as affected by annual shoot collapse: Sparganium erectum as an ecosystem engineer in a lowland stream

“…The current velocity is highly reduced inside dense patches, however, for patches with scarce shoot density, flow penetrates into the stand crossing between shoots, producing tiny eddies behind them. Contrastingly, for dense patches, currents flow around the patches (Asaeda et al, 2005). Therefore, turbulence intensity does not always diminish in the emergent macrophyte bed; however, the most dominant factor affecting sedimentation is the secondary helical current forming behind the patches, which accumulates sediments trailing behind the patches (Sand-Jensen, 2003).…”

“…In running waters, standing macrophytes can enhance the sedimentation of fine particles in vegetated areas by reducing flow velocity (Sand-Jensen, 1998;Elliot, 2000;Schultz et al, 2003;Asaeda et al, 2004) and forming turbulence inside the stands (Ennabili et al, 1998;Schultz et al, 2003;Asaeda et al, 2005). The decomposition is another source of fine sediments in streams (Hietz, 1992;Ennabili et al, 1998;Asaeda et al, 2002).…”

“…Emergent macrophytes produce patchy ramet distributions with various densities in flowing waters (Asaeda et al, 2005). The current velocity is highly reduced inside dense patches, however, for patches with scarce shoot density, flow penetrates into the stand crossing between shoots, producing tiny eddies behind them.…”

Using multiple scales to estimate the projected frontal surface area of complex three‐dimensional shapes such as flexible freshwater macrophytes at different flow conditions

“…Reference area can be total area, either estimated from body biomass (Schutten and Davy 2000;Barrat-Segretain et al 2002;Sand-Jensen 2003), body morphometrics (García-March et al 2007), or directly measured from scanned and image-analyzed plan-form areas (Puijalon et al 2005;Haring and Carpenter 2007). It can also be frontal surface area, either estimated from body length and width (Waringer 1993;Asaeda et al 2005;Green 2005) or directly measured on photographs using image analysis procedures (Gaylord et al 1994;Niklas and Spatz 2000;Suren et al 2000;Rudnicki et al 2004;Boller andCarrington 2006, 2007;O'Hare et al 2007). As previously discussed (Alexander 1990;Statzner et al 2006), C d values obtained for these differently estimated reference areas are not comparable.…”