Primary Production in Streams

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Primary Production

• Primary production is the storage of energy in chemical bonds by reducing carbon dioxide to carbohydrate in the presence of light

• 6 CO2 + 6 H20 ⇔ C6H12O6 + 6 O2

Primary Production• Gross primary production is the total elaboration

of organic matter through photosynthesis (GPP)• Autotrophic respiration is the metabolism of

organic matter by plants• Heterotrophic respiration is the metabolism of

organic matter by bacteria, fungi, and animals• Community respiration is the metabolism of

organic matter by both autotrophs and heterotrophs

Primary Production

• GPP - CR = NCPP

• GPP – (AR + HR) = NCPP

• GPP – AR = NPP

Autotrophic and Heterotrophic

• Autotrophic organisms are able to store energy (create their own food) through photosynthesis

• Heterotrophic organisms must consume organic matter produced by other organisms

• Autotrophic systems produce more organic matter through photosynthesis than they consume through respiration

• Heterotrophic systems consume more organic matter through respiration than they produce through photosynthesis

Autotrophic and Heterotrophic

• If systems are continuously heterotrophic, they require an external supply of organic matter (allochthonous organic matter)

Autotrophic and Heterotrophic

P/R Ratio

• A common measure of the trophic status of a system is the ratio of gross primary production to community respiration

• If P/R ratio is >1, the system is autotrophic

• If P/R ratio is <1, the system is heterotrophic

P/R Ratio

• Without additional information, you cannot determine the relative inputs of allochthonous and autochthonous sources by the P/R ratio

P/R ratio

• For example, a system with 8 units of energy from primary production that consumes 10 units of energy from community respiration would have a P/R ratio of 0.8

• The allochthonous inputs would be 2 units of energy

• Autochthonous inputs would be 4X the allochthonous inputs

Photosynthetic Pigments

• Photosynthetic pigments capture the energy in a photon of light and transfer it to photosynthetic reactions (Calvin cycle)

• Chlorophyll a is required by all plants for photosynthesis

• Accessory pigments capture the energy of photons in different wavelengths of light and transfer the energy to chlorophyll a

• Chlorophyll b, c, d• Carotenes and xanthophylls• Phycobiloproteins (phycoeryhtrin and

phycocyanin)

Photosynthetic Pigments

Photosynthetic Pigments

• Pigment abundance (mg chlorophyll/m2) is an approximate index of plant abundance at best

• Cellular pigment concentration is influenced by:

LightProductivitySenescence (age of cells)

• Biomass/chlorophyll ratios range from 50-400

• Ratios are higher under high light intensity, high productivity, and older cell age

• For example, biomass/chlorophyll ratios in a stream in an old-growth forest were 60 and ratios in an adjacent clearcut were 120.

Photosynthetic Pigments

Accrural of Pigment

• Pigment or biomass accumulation are poor estimates of production

• Accrural is influenced by:Production ratesHerbivoryScouring

Buoyancy• Buoyancy is increased by increasing the

surface-to-volume ratio– A few phytoplankton can change their morphology

through successive generations - cyclomorphosis– Long spines and projections increase the surface-

to-volume ratio• Buoyancy in increased by addition of

mucilage– Density of the mucilage is less than that of the cell,

therefore overall density decreases– Mucilage increases the surface to volume ratio

Buoyancy

• Buoyancy is increased by the presence of gas vacuoles– Blue-green algae are major forms of

phytoplankton that possess vacuoles• Buoyancy is increased by the

accumulation of fats

Influence of Light

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Influence of Light

• Light limited phase

• Photosynthetic saturation

• Photoinhibition

Influence of Light and Nutrients

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Nutrient Limitation

• Liebig’s law of the minimum --- production of an organism is limited by that substance that is in least supply relative to the demands of the organism

• Limitation of primary production by nitrogen or phosphorus is determined by the Redfield ratio

Nutrient Limitation

• Plant cells have N/P atomic ratios of 15-17 (molar concentrations)

• N is usually nitrate and ammonium and P is soluble reactive phosphorus

• If the N/P ratio of dissolved N and P is < 15, primary production is limited by the supply of N

• If the N/P ratio of dissolved N and P is > 15, primary production is limited by the supply of P

Low Nutrient Conditions• Small cell size

– Surface-to-volume ratio is increased and nutrients are taken up across the cell membrane

– Settling rates are reduced at increased surface-to-volume ratios

• Motility– Motility reduces the boundary layer effect

• In oligotrophic lakes, phytoplankton tend to be small and motile

Algae as a Food Resource

• Labile material is consumed or metabolized rapidly

• Refractory material is consumed or metabolized slowly

• Food quality is influenced by C/N ratios• Animals require C/N ratios of 17• C/N ratios of algae range from 3 to 15

Seasonal Patterns of Abundance• Maximum phytoplankton biomass in spring

and minimum in winter– Nutrient depletion leads to a reduction in biomass

in summer– Nitrogen-fixers, especially blue-green algae, may

"bloom" under depleted nutrient conditions of mid-summer

– In some lakes, particularly oligotrophic lakes, there may be another maximum in early fall at turnover

– Grazing by herbivores may be a factor in patterns of phytoplankton biomass and taxonomic composition in some lakes

Seasonal Patterns in Species

• Though patterns of taxonomic composition vary greatly a general pattern of taxonomic dominance can be described– Small dinoflagellates are often present in winter– Diatoms are a dominant form of phytoplankton in

spring– Green algae are dominant in early summer– Blue-green algae may be dominant in late summer

Vertical Distribution

• As fertility increases, primary productivity increases

• Effects of self-shading increase as primary productivity increases

Oligotrophic Mesotrophic

HypereutrophicEutrophic