Transcript Chapter 6: Primary Producers

Stream Ecology (NR 280)
Topic 6 – Primary Production
What is production?
Who contributes to primary production?
Pros and cons of being an autotroph
Taxonomy of autotrophs
Regulation of primary production
Fate of primary production
Production
The creation of new, living biomass from
other sources of carbon and nutrients
• Primary production: creation of biomass from
inorganic carbon (CO2) and some energy source.
• Secondary production: creation of biomass from
organic sources of carbon (e.g., heterotrophy,
herbivory, predation)
northlandjournal.com
Photosynthesis is the most common
form of primary production
Energy
Photosynthesis
𝑥𝐶𝑂2 + 𝑥𝐻2 𝑂
𝐶𝑥 𝐻2∗𝑥 𝑂𝑥 + 𝑥𝑂2
Respiration
Energy
Note that photosynthesis creates new biomass.
Respiration utilizes biomass as a resource for activity, growth, and reproduction.
Primary production is
accomplished by autotrophs
• Energy source defines classes of autotrophs
– Photosynthesis (photoautotrophs): light
– Chemosynthesis (chemoautotrophs): chemicals
• Consider
– Does primary production in aquatic ecosystems
differ from primary production in terrestrial systems?
– Do autotrophs in aquatic systems differ from
autotrophs in terrestrial systems?
Types of autotrophs in streams
• Phytoplankton (aka Potamoplankton)
– Mostly microscopic algae growing
suspended in streams
• Periphyton (benthic algae)
– Microscope to macroscopic algae growing
on the stream bottom, attached to
various substrate
– Most abundant and diverse autotrophic
group in streams
• Macrophytes
– Macroscopic, mostly vascular
plants in flowing waters
– Includes mosses and liverworts
(called bryophytes)
Phytoplankton
• Floating, unattached algae
• Can be important in streams with long water
residence times due to:
– Large volume
– Slow flow
• Important in large rivers
– Mississippi and Nile
• Algal growth must exceed downstream
transport
Phylogeny & adaptations
• Species are adapted to staying in suspension
• Adaptations include:
– Small sizes
– Increased surface area and unique shapes
– Flagella, to move
– Vacuoles for flotation
and storage
starcentral.mbl.edu
microscopy-uk.org.uk
Periphyton often reside within
a surface biofilm (aufwuchs)
• Complex community of bacteria, protozoa, small
invertebrates (meiobenthos), algae, fungi
– Structural protection
– Enzymatic activity
– Nutrient acquisition & storage
• Polysaccharide (Slimy!)
matrix of organisms
Advantages of the periphytic life
• Consider two points of view in a field of flow
– Eularian: viewer is fixed, flow moves past viewer
– Lagrangian: viewer floats and moves with the flow
• Imagine yourself to be an aquatic autotroph
– Periphyton live in a Eularian world
– Phytoplankton live in a Lagrangian world
• Why is this important?
– Both groups can be equally productive
– Resources in the periphytic environment
are continuously replenished
– Resources in the planktonic environment
can be easily depleted
Some challenges for the periphytic life
• It’s necessary to expend resources to produce some way
to remain attached to the substrate (glues, basal strands)
that penetrate cracks to anchor
• Remaining close to the stream bottom places you in the
boundary layer where resource renewal can be slower.
• There is competition for resources (e.g., nutrients, space)
similar to terrestrial systems.
• You can’t escape difficult conditions (e.g., high light, high
temperature, low water
Nevertheless, benthic autotrophs typically contribute the
greatest amount of primary production on an areal basis.
Periphyton by substrate habitat
• Epilithon/epilithic
On rocks
• Epiphyton/epiphytic
On plants
• Epipelon/epipelic
On sediment
• Epipsammon/epipsammic
On sand
• Epidendron/epidendric
On wood
• Epizoon/epizooic
On animals
Examples
Epiphytic Chamaesiphon spp.
algae on Hygrohypnum moss.
(Stream Bryophyte Group 1999)
Epipsammon and epipelon on a
mudflat. (biomareweb.org)
Epilithic green algae on a cobble.
(M. Flinn photo)
Classification of Aquatic Primary Producers
Cyanobacteria
Divisions
2 of 3 Kingdoms, 2 of 5 Domains
Evolution
http://www.mun.ca/biology/scarr/Five_Kingdoms_Three_Domains.html
Next Lecture
Algae are a diverse group
Classification and identification are specialist disciplines
•
•
•
•
Habitat (latitude, temperature, pH, conductivity)
External structures (flagella, sheathes)
Internal organization (nucleus, cytoplasmic structures)
Color/pigments
– Chlorophylls a,b,c
– Carotenoids
– Phycobilins
•
•
•
•
•
Growth form (solitary, colonial)
Reproduction
Cell wall chemistry
Nutrition
DNA and genetics
5 most common divisions (of 10)
•
•
•
•
•
Division
Abundance
Bacillariophyta (diatoms)
dominant
Chlorophyta (green algae)
*intermediate
Cyanobacteria (blue-green algae) *intermediate
Chrysophyta (yellow-brown algae)
low
Rhodophyta (red algae)
low
*May dominate in eutrophic streams
Different algal groups can be indicators of trophic
status
Good web resource: common freshwater algae
Bacillariophyta (Diatoms)
• Unicellular
• Cell wall: silica
• Construction:
– 2 half valves (frustule)
– A pair of slits in the valve (raphe)
• Most diverse and common in
pristine systems
Chlorophyta (green algae)
• Form fuzzy mats that
appear to be green
• Mostly filamentous
• Dominate eutrophic systems
are bright
Cyanobacteria (blue-green algae)
• Absence of chloroplasts
– Pigments are distributed through cell protoplasm
– Wide range of pigments produce a range of colors
• Mostly filamentous, often have gelatinous sheathes
• Produce a musty smell
• Form mats of blue green, olive or brown color
www.prenhall.com
Chrysophyta (yellow-brown algae)
•
•
•
•
•
Mostly motile cells with flagella
Includes some filamentous and sheet-like forms
More commonly found in lakes than streams
Contains the pigment fucoxanthin
Derived from a non-photosynthesizing ancestor
Hyalobryon
Rhodophyta (red algae)
•
•
•
•
Multicelllular
“Red” comes from phycoerythrin pigment
Most are marine species
Indicators of clean systems in freshwater
Lemanea
Macrophytes – mostly vascular plants
• Emergent
– Stand out of water
– Water Willow; Pickerelweed (Pontedaria)
• Floating-leaved
– Leaves float
– e.g. Lilly pads
• Floating plants
– Whole plant floats
– Duckweeds
• Submerged
– Underwater except for flowers
– Pondweeds (Potamogeton)
Macrophytes
include
Bryophytes
• Non-vascular
• Reproduce via spores
• Mosses, liverworts,
hornworts
• Adapted to high flow
environments
• Attached to rocks
• Found in cool,
headwater reaches
M. Kendrick
L. Koenig
Methods – Phytoplankton
& Periphyton
• Water column
– Pass defined volume through
a filter
– Extract CHLa in defined
volume (EtOH, acetone)
– Read on spectrophotometer
or fluorometer
• Whole-rock scrubs
– Scrub a defined area of rock
and remove material
– Filter scrubate
– Process as for phytoplankton
Analytical tools
Spectrophotometer
Beer’s Law of absorption
Fluorometer
Auto- fluoresence of substances
Methods - Macrophytes
Point or Clipped Quadrats
Stream Ecology (NR 280)
Topic 6 – Primary Production
What is production?
Who contributes to primary production?
Pros and cons of being an autotroph
Taxonomy of autotrophs
Regulation of primary production
Fate of primary production
Regulation of Primary Producers
• Environmental factors
–
–
–
–
Light
Temperature
Substrate
Current/ Storm events
• Chemical Factors
– Nutrients
– Pollutants
• Biological factors
– Herbivory
R1
T1
T2
Temperature (ToC)
Q10
𝑄10
𝑅@𝑇2
=
𝑅@𝑇1
10
𝑇2 −𝑇1
Pmax
α
Algal Growth (VS)
R2
Algal Growth (PI)
Algal Growth (RT)
Biophysical Relationships
Vmax
½ Vmax
km
Light (I)
Nutrients ([S])
Jassby-Platt
Photosynthesis/
Irradiance Curves
Michaelis-Menten
kinetics
𝛼∗𝐼
𝑃𝐼 = 𝑃𝑚𝑎𝑥 ∗ 𝑡𝑎𝑛ℎ
𝑃𝑚𝑎𝑥
𝑉𝑆 = 𝑉𝑚𝑎𝑥 ∗
[𝑆]
𝑘𝑚 + [𝑆]
Regulation: Algae & light 1
Light-adapted community
Shaded-adapted community
Allen (1994)
Algae & Light 2
Benthic
• Benthic algae has greater photosynthetic
potential than seston algae (phytoplankton)
• Open-canopy systems exhibit greater algal
biomass
Coarse-grained
Fine-grained
Water column
(seston)
Munn et al (2010)
Algae & Temperature
• Q10 = ~ 2 (Falkowski
& Raven 2007)
• Photosynthesis (and
growth) are sensitive
to high temperatures
Growth/Photosynthesis
• Growth rate
generally increases
with temperature
Optimal T°C = 20°C
for photosynthesis
(Konokpa & Brock 1978)
Temperature
Assessing nutrient limitation
• Liebig’s Law of the Minimum
– Growth is controlled by the scarcest resource
– the “limiting nutrient” – that which limits growth
• Macro-nutrients are required in large amounts
– C, H, N, O, P, N, Si
• Micro-nutrients required in lesser amounts
– S, Cl, K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Mo, B, Se, Co
• Enrich a whole-system or create a microcosm in
the lab with a potential limiting nutrient
– If biomass increases; the added nutrient is limiting
– If no response, something else is limiting
Interaction of light
and nutrients
(nutrient diffusing substrate)
In this case, the effect of lack of
light overwhelmed the effect of
added nutrients.
Other factors affecting
primary production
Algae & current
“Subsidy-stress” response
• Flow renews nutrients and gasses to algae
• But also exerts a shear stress causing cell
sloughing and death
(Allen 1994)
Algae & substrate
• Bedload movement
– Rolling rocks removes algae
– Sand scours
– Re-deposited sediment may bury periphyton
• Sediment size as stability
– Smaller particles are
more likely to move
– Boulders are most stable
followed by cobble & gravel
(Allan 2007)
Algae & grazers
• Losses to grazers
are substantial
when snails are
present
• When snails were
excluded,
– AFDM, biomass
and productivity
increased
Rosemond (1993)
Algae & grazers (& nutrients)
• Both grazers & nutrients influence algal growth

Trade-off between resistance to herbivory and
competitive ability
◦ Study showed that algal species most reduced by grazing were
those that increased most to nutrients
Fate of primary productivity?
• Phytoplankton
– Minor: Grazing by zooplankton
– Major: Export downstream
• Periphyton
– Major: Consumed by herbivores
• Usually high quality food
• Trophic efficiency is usually low (~10%)
– Major: Enters pool of particulate detritus
• Locally or after downstream transport
• Macrophytes
– Consumed by herbivores
– Creates considerable detritus
– Secretion of DOC and DON
Summary of Key Points
• Autotrophs are fundamental to the food
chains of all ecosystems
– 3 generic types of autotrophs
– Periphyton dominate streams
• Periphyton and biofilms contribute to the rich
diversity of streams
• Biophysical and physical factors regulate
autotrophic productivity
• Heterotrophs depend on autotrophs for their
energy and raw materials