Community Metabolism: I) Primary Production

1.  Community Metabolism

           a. Autotrophs - energy sun & non-living sources

           b. Heterotrophs - energy & materials eating living matter

2.  Ecosystem-level

           a. Integration organisms & abiotic environment

           b. Metabolism - flow of energy or materials through foodweb

           c. Different units measured follow this energy flow:

                       i. Biomass - Rate of flow & input/output separate

                       ii. Chemical flow: Carbon (g)

                       iii. Energy flow: Community as energy transformer (joule)

3.  Primary production - 99.9% of life earth by weight is green plants fixing CO₂.

           a. Photosynthesis: solar energy to chemical energy and produce oxygen fix CO₂.

           b. Respiration: using energy for work & maintenance

           c. Compensation point

           d. Gross vs net primary production

           e. Terrestrial plants measure CO₂ changes time

           f. Marine plants measure O₂ change or radioactive carbon tracer

4. Global Patterns of Primary production:

           a. How do various communities differ in productivity?

                       i. Tropical rain forests high

                       ii. Open oceans high

5. What controls Primary production?

           Aquatic ecosystems

           a. Marine environment

                       i. Light - In aquatic systems >1/2 light abs. 1 m

                       ii. Nutrients also important factor

                       iii. N. Pacific Central gyre

                       iii. Vertical gradients show decrease photo. w/depth

                       iv. Nutrient limitation: primarily N marine env.

                       v. Sargasso sea; lg gyre low prod.; Fe limited

                       vi. Sequence of limiting nutrients

                       vii. Most open oceans low prod. rate exception upwelling areas

                       viii. Open ocean very large area therefore total carbon fixed high

           b. Freshwater environment

                       i. Nitrogen and Phosphorus additions increased phytoplankton biomass

                             ii. Causes eutrophication - shift in community of phytoplankton to bluegreen algae (lake scum) and increased respiration in response to nutrient loading

                       iii. Lake experiments shown correlation between chlorophyll & total P

           Terrestrial ecosystems

                       i. Monitored at large scale by satellites, similar ocean production monitoring

                       ii. Normalized Difference Vegetation Index: NDVI

                       iii. What limits terrestrial vegetation?

                                   Solar radiation

Temperature

Moisture

Nutrients also important

Nitrogen & Phosphorus

Micronutrients (Fe, Cu, Mo, etc.)

6. Summary

Communities (ecosystems) process energy & materials (C)

Community metabolism traces carbon through food web

Primary production amount carbon fixed per time

Utilize the energy from sun to sequester carbon (1% sun energy)

Global production varies split evenly aquatic & terrestrial env.

Oceans primarily N and Fe limited (some special cases P limited)

Freshwater systems primarily P limited

Terrestrial systems both N and P limited and micronutrients

Climatic factors > important in terrestrial systems

Satellites circle globe @ day important for productivity estimates

These data incorporated into climate change models – CO₂ etc.