Wetland Plant Identification Quiz 1

Hydrophyte

Plants adapted to living in water or saturated soil

3 types of hydrophytes

1.) Emergent

2.) Floating-leaf

3.) Submerged

Emergent

Extend above water surface

Floating leaf

Floating leafs, roots attached or floating

Submerged

Below water surface

What conditions/stressors do wetland plants need to deal with?

1.) Low or no oxygen

2.) Low light conditions in water

3.) High salt concentration

4.) Reproduction

Hypoxic

Low oxygen concentration

Anoxic

No oxygen present

Hypoxic or anoxic soils

Soil rapidly becomes anoxic when flooded

• Soil pore space fills with water

• Respiration uses remaining O2

• Water holds much less O2 than air

The problem with anoxic soils

Non-flooded soil

• Roots respire to metabolize sugars into energy (to survive)

• Respiration requires O2 from soil

Flooded soils: Non-adapted plants

• No O2 for root respiration

• Root cells (and plant) die (hours to days)

How do wetlands deal with anoxia?

Movement of gasses

1.) Passive diffusion of gases

2.) Aerenchyma tissue

3.) Pressurized gas flow

Stem adaptations

1.) Stem hypertrophy

Root adaptations

1.) Adventitious roots

2.) Pneumatophores

3.) Rhizosphere

4.) Shallow root systems

5.) Rapid shoot growth, stem elongation

Passive diffusion of gases

Primary mechanism of gas exchange

• Occurs in air & water (& oxic soil)

• Higher O2 concentration in air than water

• Passive diffusion slow in water

Aerenchyma Tissue

Tissue with large intercellular spaces

• Throughout the plant (leaves, stem, roots)

• Easy movement & exchange of gases

Pressurized gas flow

• Gas moves into internal gas spaces of young leaves

• Gas forced down through aerenchyma from stem to roots by slight pressure caused by the heating of the leaves

• Older leaves lose their capacity to support pressure gradients so gas from the roots returns out through the old leaves

Daily variation in solar energy, temperature

• Solar radiation peaks mid-day

• Air temp increases mid-day

• Leaf outer & inner temps increases

Pressure & gas flow within leaves

• Pressure builds within leaves/plant

• Gas flow in plant follows daily temperature fluctuations

Gas flow follows a 24 hour cycle

• Depends on time of year & light intensity

Stem hypertrophy

Swelling of the lower stem

• Increased cell size, number of cells unchanged

• Is not from aerenchyma tissue

• Increases gas exchange (increased surface area)

No hypertrophy

Hypertrophy

Adventitious Roots

Roots developed on the stem above the anaerobic zone

• Better obtain O2 for respiration

Pneumatophores

Root structure growing out of the water

• Gas exchange with atmosphere

Rhizosphere oxygenation

Release O2 from roots into soil to create oxic root zones

• Aerenchyma tissue provides O2 to roots

Rhizosphere

Narrow region of soil surrounding roots directly influenced by root secretions & root microbiome

Shallow root systems

Roots spread near soil surface to avoid anoxia in deeper soil

• Increased O2 near water column

Rapid shoot growth, stem elongation

Shoots get above water surface quickly to allow for gas exchange (& photosynthesis)

• Adjusts growth rate based on water levels

How do wetland plants adapt to low light levels in water?

1.) Increase leaf surface area

2.) Heterophylly

Increased leaf surface area

High surface area to volume ratio

• Maximizes photosynthesis & gas exchange

Heterophylly

• Different leaf shapes on the same plant

• Floating/emergent leaves

  • Maximize light exposure, gas exchange

• Submerged leave

  • Increased gas diffusion

  • Less resistance in water: waves, currents (less physical damage to plant)

High salt concentration: inland wetlands

Formed when groundwater collects salts from geologic deposits, then is forced to surface

Increased salinity from human actions

• Crop irrigation using saline groundwater

• Runoff from fertilized ag fields

• Road deicing salt runoff

High salt concentration stressor

Water availability

• Saline soils inhibit water uptake through osmosis

• Plants functionally in desert (despite flooding)

How do wetland plants adapt to high salt concentrations?

1.) Salt exclusion

2.) Salt secretion

Salt exclusion

1.) Prevent salts from entering or accumulating

• Higher K+ ions in root cells than Na+ in soil

  • Water enters roots through osmosis

2.) Allow salt to enter roots, but inhibit movement to stems & shoots (concentrated in roots)

Salt secretion

1.) Salt glands - actively move salt to outside of leaves

2.) Salt accumulates in older leaves

• Salt concentrates in older leaves

• Plants sheds these leaves once salt leaves are high enough

How do wetland plants reproduce?

• Produce buoyant seed

• Delay flowering when flooded and accelerate flowering when dry

• Large, persistent seed banks

• Germinate while on parent plant