•Leaves: anatomically similar to terrestrial

bottom of leaves have stomatacuticle 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 absentlack of rigidity prevents mechanical

damage

•Leaf texturetough and leathery - withstand wind, rain, hailwaxy 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 absentlack 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. 1993. Introduction to Freshwater Vegetation, Krieger Publ. Co. p. 106.

Myriophyllum humile

AA

BB

Part IIIMacrophytes 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 30-95 % Floating Leaved 30-70 % 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 onlyOxidizin

gConditions

ReducingConditions

Water Quality Changes

•pH and alkalinity

•DO

•humic acids

Dense stands of Ceratophyllum

pH

alkalinity

Water Quality Changes

•Nutrient cycling - 108 mg P/m2/day from sediment pore water, 45 to plant and 62 excreted to water. •(Eelgrass, McRoy, et al. 1972)

water20 ug/L 2000 ug/L

leavesroots &rhizomes

interstitialwater

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 releasedto 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