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Structural Support
Emergents
•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
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. 1993. Introduction to
Freshwater Vegetation, Krieger Publ. Co. p. 106.
A
Myriophyllum humile
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
30-95 %
30-70 %
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
Fe
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)
Oxidized Rhizosphere
Oxidizing
Condition
s
• 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
Reducing
Conditions
Water Quality Changes
Dense stands of Ceratophyllum
•pH and alkalinity
•DO
pH
•humic acids
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)
20water
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