Macrophytes: Ecology of Aquatic Plants

Macrophytes:
Ecology of Aquatic Plants

Macrophytes
 refers to large plant visible to the naked eye and having at
least their vegetative parts growing permanently or
periodically aquatic habitats
 Includes all aquatic vascular plants and bryophytes, together
with groups of algae
 an important component of the aquatic ecosystem and broad
 changes in the abundance of individual species and
community composition
a. Classification of Macrophytes
1. Floating :plants whose leaves float on the water’s surface
but their roots are anchored in the substrate
Water Lily Water Hyacinth

Nymphaea Eichhornia crassipes
2. Submergent: plants that are usually rooted in the bottom soil
with the vegetative parts predominantly submerged
Stonewort Bladderwort
Charales Utricularia
3. Emergent: plants that are rooted in shallow water
with vegetative parts emerging above the water surface
: most particularly productive of all aquatic
macrophytes since they make the best use of all three possible
states—with their roots in sediments beneath water and their
photosynthetic parts in the air (Westlake, 1963).
Cattail Wild Rice

Typha Zizania
b. Abiotic Parameters
 Water Transparency -The occurrence of macrophytes is
strongly governed by water transparency, itself determined
by the colour of the water (partly related to dissolved organic
matter), the concentration of suspended solids and the
concentration of plankton.
 The depth limit of macrophytes is when the water
transparency allows less than 1–4% light to reach the plants
(Sculthorpe, 1967)
 Water Nutrient Content -Carbon, nitrogen and phosphorous
are the main nutrients required for plant life, and their
availability therefore governs primary production in
freshwater ecosystems.
 Two groups of species can be distinguished, those that can
only use carbon dioxide (in air, water or in sediment) and
those that can use both carbon dioxide and HCO3.
 Plants with floating leaves are able to use carbon dioxide
from the air.
 Substrate Characteristics -Carbon, nitrogen and phosphorous
are the main nutrients required for plant life, and their
availability therefore governs primary production in
freshwater ecosystems.
 Two groups of species can be distinguished, those that can
only use carbon dioxide (in air, water or in sediment) and
those that can use both carbon dioxide and HCO3.
 Plants with floating leaves are able to use carbon dioxide
from the air.
 Among submerged species, some are restricted to carbon
dioxide (Maberly and Madsen, 1998).
c. Disturbances
 Floods -High frequency and/or intensity of scouring floods
lead to the breakage or uprooting of aquatic plants,and also
wash out fine sediment and seed banks. The recovery of
aquatic plant communities relies on the occurrence of refuges
along the banks of the scoured sites,and on dispersal of seeds
and plant fragments transported by the flood itself (Henry et
al., 1996).
 Biomass losses through breakage are low, but plants must
resist low light, anoxia and burial (Blom et al.,1994).
 The tallest plastic plants with large storage organs tolerate
better long-term submersion the best, as they can either
regenerate vegetative parts of the individuals destroyed by
long-term submersion, or elongate themselves to reach the
light.
c. Disturbances
 Floods -Long-term flooding has a rather different impact, such as
the long-term submergence (i.e. usually several weeks) of aquatic
plants under turbid water and sediment deposits that tend to slow
down plant growth.
 The recovery of aquatic plant communities relies on the
occurrence of refuges along the banks of the scoured sites,and on
dispersal of seeds and plant fragments transported by the flood
itself (Henry et al., 1996).
 Rooted submersed plants are disfavoured, due to the high
turbidity of the water and phytoplankton growth under eutrophic
situations. Species able to anchor themselves in sediment of low
cohesive strength (Handley and Davy, 2002), or those able to
produce adventitious roots or to spread laterally close tothe
surface of the newly deposited sediment or at thesurface of the
water should also be favoured (Bornette et al., 2008)
c. Disturbances
 Drawdowns - Rare drawdowns have contrasting effects on
plant communities, depending on the intrinsic ability of
species to tolerate dewatering.
 Some species are able to tolerate the drought event, with
plastic modifications of the plant growth form (e.g. leaf
plasticity, size decrease and tissue modifications; Goliber and
Feldman, 1989).
 For others, the aboveground biomass dies, and the species
survive through subterranean organs. Some also flower
during the water drop and die, constituting a dormant seed
bank that sprouts when the water level rises again (Casanova
and Brock, 2000).
c. Disturbances
 In temporary wetlands (annually dewatered), the
maintenance of aquatic plants relies mainly on their ability to
produce seeds able to tolerate drought.
 In wetlands characterized by alternating dry and wet periods,
a cyclical seasonal succession occurs, characterized by the
replacement of submerged species, by floating-leaf species,
and finally emergent ones.
 Some variations around this pattern can occur over the years
depending on the hydrological characteristics of the drawdown
event (Van der Valk, 2005). In such situations,
slow-growing species, whose maintenance relies mainly on
vegetative multiplication, are disfavoured.
d. Biotic Interactions
 Competition for Light –occurs both within macrophyte
communities and between macrophytes and microphytes.
 In terresteral habitat, the main parameter that determines
competitive ability for light is plant size, which is strongly
correlated with plant biomass (Tilman, 1982).
 In aquatic habitats, not related to plant size but their ability
to produce floating or emerged leaves.
 In addition, the size of plants is not simply related to their
biomass, since submerged organs (e.g. leaves) present lower
construction costs than floating ones (Titus and Sullivan,
2001).
 Competition for Light –occurs both within macrophyte
communities and between macrophytes and microphytes.
 In terresteral habitat, the main parameter that determines
competitive ability for light is plant size, which is strongly
correlated with plant biomass (Tilman, 1982).
 In aquatic habitats, not related to plant size but their ability to
produce floating or emerged leaves.
 In addition, the size of plants is not simply related to their
biomass, since submerged organs (e.g. leaves) present lower
construction costs than floating ones (Titus and Sullivan, 2001).
 As a consequence, species that present very contrasting growth
forms are considered as competitively dominant: free-floating
species and tall species with floating leaves (Bornette et al., 1994).
 Allelopathy–the production and release of chemical
substances that inhibit the growth of other macrophytes or
microphytes, has been demonstrated to occur among
macrophytes (Gross, 2003) even though many published
studies fail to demonstrate in an unfalsifiable way the
allelopathic mechanism, and the toxic compound involved in
the interaction (Ervin and Wetzel, 2003).
 These authors provide a review of the relevant papers that
identify allelopathic species, and show that allelopathic effects
of macrophytes occur in contrasting taxonomic groups such
as Najadaceae or Potamogetonaceae. In some situations,such
mechanisms impede microphyte growth and maintaina clear
water stage in lakes (Hilt and Gross, 2008).
 Herbivory
 Aquatic plants are consumed by many animals, such as
fishes, birds, mammals, molluscs and arthropods (insects,
crustaceae), and plant populations can also be significantly
affected by grazing (Gross et al., 2001).The sensibility of aquatic
plants to graze depends on taxonomic groups (Elger et al., 2004),
but also on the developmental stage, the submerged vs.
floating type of leaves (Sand-Jensen and Jacobsen, 2002),
and on the organ considered, some species grazing
specifically flowers, and seedlings being more susceptible
to graze than fully developed plants.
e. Threats to Macrophytes
 Eutrophication– is described to be the first and frequently
threat to freshwaters, leading to the decrease, and even the
disappearance of submerged species, to the benefit of free-
floating species, and ultimately microphytes.
 The process by which a body of water acquires a high
concentration of nutrients, especially phosphates and nitrates.
These typically promote excessive growth of algae. As the
algae die and decompose, high levels of organic matter and
the decomposing organisms deplete the water of available
oxygen, causing the death of other organisms, such as fish.
Eutrophication is a natural, slow-aging process for a water
body, but human activity greatly speeds up the process.” -
Art, 1993.
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Macrophytes:

Ecology of Aquatic Plants

Water Lily Water Hyacinth

Cattail Wild Rice

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