Flashcards in Lecture 22 - Primary Productivity Deck (21)
What is an ecosystem?
A system that includes all living organisms in an area as well as the physical environment functioning together as a unit.
Where does an ecosystem start and end?
User-defined. It could be in a tree hole or a continent-wide forest. Edges are sometimes difficult to define
Define Ecosystem ecology
Study of how energy and nutrients move around inside an ecosystem
What's the difference between energy and nutrients in an ecosystem.
Energy flows but nutrients cycles.
Law of thermodynamics: Lost of energy. No conversion 100% efficient
Producers are ____, or "self-feeding" organisms that make their own organic molecules from _____.
______ use light energy to build sugars out of carbon dioxide.
All the consumers are ____, or “other-feeding” organisms, rely on the ecosystem's ____ for energy.
Define Gross primary production
Gross primary production = energy (or carbon) fixed via photosynthesis per unit time
Define net primary production
Net primary prod = gross primary prod - energy (or carbon) lost via respiration per unit time.
(the energetic costs of maintenance)
Primary Productivity (or production)
What is it?
(net) primary productivity = the rate at which energy is converted to plant biomass
Productivity can be expressed as the rate of biomass formation per unit time and space eg. biomass/m^2/yr
Or the rate of energy capture per unit time and space e.g. kcal/m^2/yr, or Watts/m^2
Primary Productivity (or production)
How to measure it? (3 methods)
1. Gas exchange:
Put a dark and light bags on the field
For aquatic life, light bottle, dark bottle. Measure the exchange (diff in O2) over-time.
2. Harvest method: biomass change between time1 and time2
Net primary prod = ∆B+L+G ,
∆B = biomass change
G = biomass grazed.
L = biomass lost
3. By satellite: Chlorophyll concentration can be estimated by spectral reflectance and spectral absorbance
How does it vary?
High in tropics, low in poles & deserts
High in northern waters, low in south/middle
What are the 4 factors that limit productivity.
• Every day, Earth is bombarded by approximately 1023 joules of solar radiation.
• Intensity varies with latitude
• Most radiation is scattered, absorbed, or reflected by the atmosphere.
• Only a small fraction actually strikes algae, photosynthetic prokaryotes, or plants, and only some of this is of wavelengths suitable for photosynthesis.
• Of the visible light that reaches photosynthetic organisms, only about 1% is converted to chemical energy.
• The first meter of water absorbs more than half of the solar radiation. (although not the primary limiting factor for photosynthesis in lakes and oceans)
• Colder water holds better nutrients because less volatile.
• Important to photosynthesis
• Materials for growth are required to do photosynthesis, and to store carbon as biomass
• Often limiting nutrients are:
• • Nitrogen: needed for chlorophyll and amino acids
• • Phosphorus: crucial for photosynthesis, and built into DNA and membranes
• • Micronutrients: e.g. Iron (in the ocean). Required for the synthesis of chlorophyll, several photosynthetic electron transport proteins
• Increases rate of photosynthesis
What's the relationship between phosphorus content and phytoplankton biomass.
What confirms that Marine ecosystem are nitrogen limited?
In experiment, phosphate and nitrogen are both added to water.
• Appears that nitrate pollution is taken up immediately, while phosphate is in excess
• Algae really grew when ammonium was added, confirms that they are nitrate limited.
Some parts of the ocean have plenty of N and P, but still low biomass, why?
Maybe productivity is high (lots of predation)
Or top down control in forms of grazers
What was added to southern ocean to increase chlorophyll concentration?
What do we know about the soil fertility or terrestrial ecosystems?
Nitrogen is the primary limiting nutrient and phosphorous becomes limiting when nitrogen is in excess.
Experiment where N added, P added (no big difference), N+P added (better)
What nutrients are often limiting in all habitat types?
N or P are often limiting in all habitat types
Net primary production (NPP) if terrestrial vegetation depends on ___, ___ and ___.
solar radiation, temperature and sand moisture.