Phycokey - Aquatic macrophytes -- Wolffia

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Morphology:
Emergent foliage aquatic macrophytes in this key have the majority of their photosynthetic foliage above the water surface, connected by their stem(s) to roots anchored in the benthic substrate. Because of the low to non-existent dissolved oxygen in many sediments, the roots have to both be tolerant of such conditions, and have oxygen pumped to them from the overlying plant. Much of the biomass of plants with emergent foliage is in their underground rhizomes and roots. Most species have >40% underground, and Scirpus lacustris as much as 90% (Westlake 1966).
Carbon uptake:
Emergent leaves have the same advantage as their predecessor land plants – stomates that allow rapid gas exchange between their internal gasses and atmospheric gasses. The rate of diffusion of CO₂, for example, is 10⁴ greater in air than underwater (Osmond et al. 1981).
Methane release:
Emergent foliage of aquatic vascular plants are responsible for 80-90% of methane release from most wetlands, and the diurnal pattern varies from light increase during early morning to temperature increase in the afternoon (Whiting and Chanton 1996).
Preservation importance:
While most studies of aquatic plants stress their adverse affects, a statistical study of 24 lakes in northcentral Minnesota USA demonstrates the adverse affects of plant loss on three sports fish: northern pike (Esox lucius), bluegill (Lepomis macrochirus), and pumpkinseed (Lepomis gibbosus) that suffer from loss of nesting sites, food, and cover from sun and predators (Radomski and Goeman 2001).
Habitat :
Freshwater to brackish water shallow sites. In some cases the maximum depth of growth is limited by hydrostatic pressure, in others by high light attenuation.

References:
Osmond, C.B., N. Valaane, S.M. Haslam, P. Uotila, and Z. Roksandie 1981. Comparisons of δ¹³C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants. Oecologia (Berl) 50:117-124. Radmoski, P., and T.J. Goeman 2001. Consequences of human lakeshore development on emergent and floating-leaf vegetation abundance. North American Journal of Fisheries Management 21:46-61. Westlake, D.F. 1966. Some basic data for investigations of the productivity of aquatic macrophytes. In: Primary productivity in aquatic environments (International Biological Programme):229-248. University of California Press; Cambridge University Press. Whiting, G.J., and J.P. Chanton 1996. Control of the diurnal pattern of methane emission from emergent aquatic macrophytes by gas transport mechanisms. Aquatic Botany 54:237-253.

Morphology:

Emergent leaves have the same advantage as their predecessor land plants – stomates that allow rapid gas exchange between their internal gasses and atmospheric gasses. The rate of diffusion of CO2, for example, is 104 greater in air than underwater (Osmond et al. 1981).

Habitat :

References:

Emergent leaves have the same advantage as their predecessor land plants – stomates that allow rapid gas exchange between their internal gasses and atmospheric gasses. The rate of diffusion of CO₂, for example, is 10⁴ greater in air than underwater (Osmond et al. 1981).