Leaves: anatomically similar to terrestrial bottom of leaves have stomata cuticle present Cell walls heavily thickened by cellulose (rigidity) New growth must respire anaerobically until leaves reach surface, then lacunae increase in size Structural Support Emergents

Structural Support Floating Leaf Leaf shape: circular with entire margins - resistance to tearing large surface area yet reduced resistance to current support tissues drastically reduced or absent lack of rigidity prevents mechanical damage Leaf texture tough and leathery - withstand wind, rain, hail waxy cuticle on upper surface only Petioles long and thin - rapid elongation when necessary

Structural Support Submersed Leaf shape: ribbon-like large surface area yet reduced resistance to current support tissues drastically reduced or absent lack of rigidity prevents mechanical damage Vascular elements generally lacking in lignin support provided by water that surrounds the leaf and aerenchyma within the blade

Heterophylly A form of polymorphism where more than one kind of leaf on the same plant Occurs among aquatic plants that grow in shallow, submersed habitats that undergo fluctuations in water levels Figure from Reimer, Donald N Introduction to Freshwater Vegetation, Krieger Publ. Co. p Myriophyllum humile A B

Part III Macrophytes effects on the wetland environment : 1. Productivity 2.Habitat Structure 3.Water column 4.Sediment composition & chemistry

Primary Productivity Among the highest of any community Emergents 1500 to 4500 g C m -2 yr -1 Submersed 50 to 1000 g C m -2 yr -1 Phytoplankton 50 to 450 g C m -2 yr -1

Below ground Biomass Below ground biomass can be more than half of total Portion of biomass in roots and rhizomes by plant type: Emergents % Floating Leaved % Submersed 1-40 % Image from Whitley et al. Water Plants for Missouri Ponds

Litter Emergents tend to have more cellulose and more lignins and other refractory components than submersed plant tissues. Water transparency and pH is also affected by humic and fulvic DOC (dissolved organic carbon). Combined with higher biomass, greater contribution to the litter and peat accretion. Floating leaved tissues intermediate in refractory component.

Oxidized Rhizosphere Loss of oxygen from the roots varies with plant species Oxygen leakage is primarily from root tips, although some leak along whole length of root, others (e.g. water lilies) leak only from 1 cm apex Young root tissue release more oxygen than old (more cuticularized tissue) Fe

Oxidized Rhizosphere Oxygen leakage serves to oxidize and detoxify potentially harmful reducing substances in the rhizosphere (Fe, Mn, S). Species with convective through flow significantly increase the root length that can be aerated compared to diffusion only Oxidizing Condition s Reducing Conditions

Water Quality Changes pH and alkalinity DO humic acids Dense stands of Ceratophyllum pH alkalinity

Water Quality Changes Nutrient cycling mg P/m 2 /day from sediment pore water, 45 to plant and 62 excreted to water. (Eelgrass, McRoy, et al. 1972) water 20 ug/L 2000 ug/L leaves roots & rhizomes interstitial water

Effects on Nutrient Cycling On at least a seasonal basis, rooted macrophytes act as nutrient pumps, translocating nutrients from the sediments to the water column. Studies indicate that between 30 and 70% of nutrients taken up from the sediments are released to the water column during scenescence. The balance is tied up in DOM (detritus).

Water Quality Changes, cont. Aquatic macrophytes reduce bio-turbidity - through competition with phytoplankton Macrophytes reduce the action of current on waves against the sediment water interface, thereby reducing resuspension.

Water Quality Changes, cont. Aquatic macrophytes (living and dead) provide a surface area for growth of periphyton (bacteria, algae, fungi, invertebrates living attached or associated with surfaces). The primary producers in this biofilm obtain their nutrients from the water column.

Habitat Structure Effects on fish: protection from predation Effects on macroinvertebrates: higher biomass and species richness

Habitat Structure PERIPHYTON - usually primary source of fixed edible carbon Macrophytes - not heavily grazed, more nutritious as detritus (covered with bacteria and other decomposers: peanut butter)

Habitat Structure Effects on birds: more herbivorous species

Habitat Structure Effects on zooplankton: refugia, particularly during the day

Macrophytes : Conclusions Evolved a variety of adaptations to life in the water Have specialized tissue that transport and store oxygen Accessory pigments allow utilization of low light levels Rooted plants act as nutrient pumps, w/ moderate net sink Food web based on periphyton and detritus (with detritus contributing bulk of organic carbon) Macrophytes provide physical refugia and surface area