Differences in mechanical and structural properties of surface and aerial petioles of the aquatic plant Nymphaea odorata subsp. tuberosa (Nymphaeaceae)

Abstract

Lily pads (Nymphaea odorata) exhibit heterophylly where a single plant may have leaves that are submerged, floating, or above (aerial) the surface of the water. Lily pads are placed in a unique situation because each leaf form is exposed to a distinctly different set of mechanical demands. While surface petioles may be loaded in tension under conditions of wind or waves, aerial petioles are loaded in compression because they must support the weight of the lamina. Using standard techniques, we compared the mechanical and morphological properties of both surface and aerial leaf petioles. Structural stiffness (EI) and the second moment of area (I) were higher in aerial petioles, although we detected no differences in other mechanical values (elastic modulus [E], extension ratio, and breaking strength). Morphologically, aerial petioles had a thicker rind, with increased collenchyma tissue and sclereid cell frequency. Aerial petioles also had a larger cross-sectional area and were more elliptical. Thus, subtle changes in the distribution of materials, rather than differences in their makeup, differentiate petiole forms. We suggest that the growth of aerial petioles may be an adaptive response to shading, allowing aerial leaves to rise above a crowded water surface.

Prolonged buoyancy and viability of Zostera muelleri Irmisch ex Asch. vegetative fragments indicate a strong dispersal potential

“…(lacunae accounted for 27% of rhizome volume) (Connell et al 1999). A high proportion of lacunae within leaf tissue has been found to provide greater buoyancy to both submerged and emergent aquatic species (Etnier & Villani 2007;Hemminga & Duarte 2000;Stewart 2004). Therefore, considering the high proportion of lacunae within both the leaves (24.8% of total leaf area) (Grice et al 1996), and rhizomes of Z. muelleri, these air spaces are likely to play a critical role in the buoyancy of the species, enabling for greater dispersal of vegetative fragments.…”

“…A high proportion of lacunae within leaf tissue also provides greater buoyancy to both submerged and emergent aquatic species including seagrasses (Hemminga & Duarte 2000) the water lily, Nymphaea odorata Ait. (Etnier & Villani 2007) and species of marine macroalgae (Stewart 2004). The increased buoyancy that lacunal spaces provide also facilitates dispersal of detached fragments via water currents.…”

Nutrient enrichment affects the mechanical resistance of aquatic plants

“…At low nutrient levels, the central cylinder area relative to the cross-sectional area is higher, which results in a more peripheral positioning of the sustaining tissue, particularly the endodermis rich in lignified cell walls. Having supporting tissues nearer the periphery has been shown to increase stem stiffness (Schulgasser and Witztum, 1997; Usherwood et al , 1997; Etnier and Villani, 2007): when stems are exposed to bending, the outer fibres endure maximal forces (Niklas, 1992; Vogel, 2003) thus, having more rigid tissues in a peripheral position maximizes stem rigidity.…”

Under pressure: biomechanical limitations of developing pneumatocysts in the bull kelp (Nereocystis luetkeana, Phaeophyceae)

“…Other biological materials are known to similarly specialize in either compression (mammalian bone, Reilly and Burstein , cetacean heart valves, Lillie et al. ) or tension (mussel byssus, Bell and Gosline , aquatic plants, Etnier and Villani ). Future work should examine the histological differences that may exist between Nereocystis pneumatocyst tissue, which resists compression, and Nereocystis stipe tissue, which is known to resist tension (Johnson and Koehl , Denny et al.…”

“…This strategy ensures that pneumatocyst tissue can specialize in resisting compression and never tension, which would only occur if internal pressure exceeded hydrostatic pressure during development. Other biological materials are known to similarly specialize in either compression (mammalian bone, Reilly andBurstein 1974, cetacean heart valves, Lillie et al 2013) or tension (mussel byssus, Bell andGosline 1996, aquatic plants, Etnier andVillani 2007). Future work should examine the histological differences that may exist between Nereocystis pneumatocyst tissue, which resists compression, and Nereocystis stipe tissue, which is known to resist tension (Johnson and Koehl 1994, Denny et al 1997, Hale 2001, Denny and Gaylord 2002, Denny and Hale 2003.…”