Productivity is the rate of carbon fixed, typically expressed in grams of carbon fixed per square meter per year (g C fixed/m^2/yr).
Atmospheric CO_2 is the source of all carbon in organisms.
It is fixed via photosynthesis.
Carbon flows through the food chain.
It is released back into the atmosphere via respiration, decomposition, and combustion.
Carbon Cycling Inputs and Outputs
Inputs:
Photosynthesis
Diffusion/transport (aquatic)
Outputs:
Respiration
Decomposition
Combustion (terrestrial)
Diffusion (aquatic)
Energy Capture
The amount of energy captured by green plants through photosynthesis and fixed into carbon, measured at the ecosystem scale.
Daily Variations in Carbon Cycling
Carbon dioxide concentration fluctuates throughout the day.
From Dawn to Dusk: XXX
From Dusk to Dawn: XXX
Seasonal Variations in Carbon Cycling
The production and use of carbon dioxide fluctuate with the seasons.
The fluctuations are greater in the Northern Hemisphere.
Gross Primary Productivity (GPP)
GPP – plant respiration (Respplant).
GPP is the total energy fixed and does not account for respiration.
Estimated as the rate of biomass accumulation over time.
Highest where conditions are optimal for plant growth.
Foundation for all processes in an ecosystem.
The physiological mechanism that produces merchantable yield.
Base of the food web.
A key part in determining ecosystem structure and function.
Components of Net Primary Productivity (NPP)
New plant biomass: 40-70% of NPP
Leaves and reproductive parts (fine litterfall): 10-30% of NPP
Apical stem growth: 0-10% of NPP
Secondary stem growth: 0-30% of NPP
New roots: 30-40% of NPP
Root secretions: 20-40% of NPP
Root exudates: 10-30% of NPP
Root transfers to mycorrhizae: 10-30% of NPP
Losses to herbivores and mortality: 1-40% of NPP
Volatile emissions: 0-5% of NPP
It is rare for all components to have been measured in a single study.
Global Patterns of Net Primary Productivity
Data taken from: IBIS Simulation (Kucharik, et al. 2000) (Foley, et al. 1996)
Net Primary Productivity is measured in kg-C/m^2/year
Data from Atlas of the Biosphere, Center for Sustainability and the Global Environment, University of Wisconsin-Madison
NPP and Environmental Factors
NPP is shown in g C m^{-2} yr^{-1}.
Radiation-limited conditions.
Water-limited conditions.
Gridded data from Global Primary Productivity Data Initiative (GPPDI).
Correlation of NPP with Temperature and Precipitation
NPP (in units of biomass) is greatest in warm, moist environments such as tropical forests, and lowest in cold or dry ecosystems such as tundra and deserts.
In tropical forests, NPP declines at extremely high precipitation (> 3m yr^{-1}), due to indirect effects of excess moisture, such as low soil oxygen and loss of nutrients through leaching.
Global Patterns of NPP - Ecosystem Specific
Open ocean:
Surface area: 65.0%
Average net primary production: 125 g/m^2/yr
Percentage of Earth's net primary production: 24.4%
Continental shelf:
Surface area: 5.2%
Average net primary production: 360 g/m^2/yr
Percentage of Earth's net primary production: 5.6%
Estuary:
Surface area: 0.3%
Average net primary production: 1,500 g/m^2/yr
Percentage of Earth's net primary production: 1.2%
Algal beds and reefs:
Surface area: 0.1%
Average net primary production: 2,500 g/m^2/yr
Percentage of Earth's net primary production: 0.9%
Upwelling zones:
Surface area: 0.1%
Average net primary production: 500 g/m^2/yr
Percentage of Earth's net primary production: 0.1%
Extreme desert, rock, sand, ice:
Surface area: 4.7%
Average net primary production: 90 g/m^2/yr
Percentage of Earth's net primary production: 0.9%
Desert and semidesert scrub:
Surface area: 3.0%
Average net primary production: 0.04 g/m^2/yr
Percentage of Earth's net primary production: 3.5%
Tropical rain forest:
Surface area: 3.3%
Average net primary production: 2,200 g/m^2/yr
Percentage of Earth's net primary production: 22%
Savanna:
Surface area: 2.9%
Average net primary production: 900 g/m^2/yr
Percentage of Earth's net primary production: 7.9%
Cultivated land:
Surface area: 2.7%
Average net primary production: 600 g/m^2/yr
Percentage of Earth's net primary production: 9.1%
Boreal forest (taiga):
Surface area: 2.4%
Average net primary production: 800 g/m^2/yr
Percentage of Earth's net primary production: 9.6%
Temperate grassland:
Surface area: 1.8%
Average net primary production: 600 g/m^2/yr
Percentage of Earth's net primary production: 5.4%
Woodland and shrubland:
Surface area: 1.7%
Average net primary production: 700 g/m^2/yr
Percentage of Earth's net primary production: 3.5%
Tundra:
Surface area: 1.6%
Average net primary production: 140 g/m^2/yr
Percentage of Earth's net primary production: 0.6%
Tropical seasonal forest:
Surface area: 1.5%
Average net primary production: 1,600 g/m^2/yr
Percentage of Earth's net primary production: 7.1%
Temperate deciduous forest:
Surface area: 1.3%
Average net primary production: 1,200 g/m^2/yr
Percentage of Earth's net primary production: 4.9%
Temperate evergreen forest:
Surface area: 1.0%
Average net primary production: 1,300 g/m^2/yr
Percentage of Earth's net primary production: 3.8%
Swamp and marsh:
Surface area: 0.4%
Average net primary production: 2,000 g/m^2/yr
Percentage of Earth's net primary production: 2.3%
Lake and stream:
Surface area: 0.4%
Average net primary production: 250 g/m^2/yr
Percentage of Earth's net primary production: 0.3%
Net Ecosystem Production (NEP)
NEP = GPP – Recosys ± Other transfers
Recosys = Respiration of plants, animals, and soil microbes, plus other C transfers from plants.
Other transfers include harvest, disturbance, leaching, and erosion.