Primary production
the fixation of inorganic carbon into organic matter by autotrophs
Autotrophs come in two forms:
Chemoautotrophs perform
chemosynthesis.
Chemosynthesis uses chemical energy to fix carbon
from CO2 into organic molecules.
Photoautotrophs perform
photosynthesis.
Photosynthesis uses light energy to fix carbon
from CO2 into organic molecules.
The first photosynthetic bacteria (Cyanobacteria)
contributed molecular oxygen (O2 ) to the atmosphere.
•
Responsible for the “great oxidation event” from 2.4 - 2.0 BYA when
atmosphere began changing from reducing to oxidizing.
• Found in
Stromatolites, bacterial mats along coastline
banded iron formations
Increased oxygen in atmosphere caused iron rich sediments on sea
floor to rust
(iron oxide = rust)
Primary production from photosynthesis depends on several abiotic and biotic factors:
Abiotic
Light intensity (more intense light allows more GPP)
• Water
availability (sufficient availability is critical)
• Temperature
(Photosynthesis does not occur below 0
Biotic
Celsius and shuts down at very high
temperature).
• Leaf area index (LAI) (leaf area per unit of
ground area
Leaf area index (LAI)
dividing the total leaf area of all trees and plants by the area of the ground they cover.
Gross primary production (GPP)
is the total amount of carbon fixed by primary producers
Net primary production (NPP)
gross primary production less respiration by primary producers
What is the significance of Net Primary Productivity (NPP)
NPP = GPP – Producer respiration
• chemical energy left
over for plant growth and reproduction.
• biomass gained by
plants over time
• the carbon pulled out of the atmosphere and
stored as plant biomass
Early successional stages
lower NPP
limited diversity of plants, lower leaf area index
Mid- successional stages
higher NPP
high diversity of plants, high nutrient levels, high
leaf area index, many opportunities for growth
Late successional stages
lower NPP
growth slows, and photosynthetic tissue and leaf area index both decrease
Stressors that drive changes in NPP:
Abiotic change (drought, extreme temperatures, pollution)
•
Biotic change (pathogens, parasites, invasives
Changes in NPP (and total size of the carbon pool) affect atmospheric CO2 , which is a greenhouse gas
Lower NPP = lower uptake of CO2 from atmosphere.
• Declining
carbon pool = net ecosystem exchange (NEE) is negative
Methods for measuring NPP
- Direct measurement of change in biomass
- Satellite remote-sensing of chlorophyll pigments
- Eddie Covariance method (direct measurements of atmospheric CO2 throughout ecosystem).
Net Ecosystem Exchange (NEE)
the net change in carbon stored within the ecosystem
Ex. Change in total biomass
Factors that limit global primary production:
Climate(Rainfall)
Climate (Temperature)
Nutrient Availability
Great Atlantic sargassum belt
- largest algal bloom
- caused by excess fertilizer and raw sewage flowing from Amazon and West Africa
Secondary production
energy derived from the consumption of organic compounds produced by other organisms.
Organisms that obtain energy in this manner are called heterotrophs.
Heterotrophic life forms include all animals and
fungi; some archaea and
bacteria
Decomposers
Detritivores ingest non-living organic matter,
obtaining organic nutrients by internal digestion (e.g., vultures,
earth worms, dung beetles).
Saprotrophs live in
or on non-living organic matter, secreting digestive enzymes and
absorbing digestive products (e.g., fungi and bacteria).
Case Study: Chemoautotrophs inhabit some of the most extreme
environments
on earth.
Riftia pachyptila
Giant tube worms form
symbiotic relationships with chemosynthetic bacteria
at
hydrothermal vents along the Galapagos Rift, 8,000 feet below
the ocean's
surface
Succession in hydrothermal vent communities
Bacteria colonize vents, followed by tube worms and other
fauna.
After 20-200 years, hot springs eventually stop emitting
water and sulfides, causing death of the hydrothermal vent community
Colonization and development of new vent communities is higher when new vents are closer to existing vent communities