BIOL 4120: Principles of Ecology
Lecture 20: Ecosystem
Ecology
Dafeng Hui
Room: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Outline (Chapter 22)
Biogeochemical cycles
Biogeochemical cycles:
Bio-living things; geo-rocks and soil; chemicalprocesses involved.
All nutrients (or elements) flow through from the
nonliving to the living and back to the nonliving
components of the ecosystem in a cyclic path
22.1 Two major types of
biogeochemical cycles


All nutrients follow biogeochemical cycles
Two types of cycle
• Gaseous


Major reservoirs are atmosphere and oceans
Global in nature, important gases
• Oxygen 21%
• Nitrogen 78%
• Carbon of carbon dioxide 0.03%
• Sedimentary



Major reservoirs are soil, rocks and minerals
Rock phase and salt solution phase
Salt solution is the available form
• Phosphorus
• Metals, eg Calcium, Magnesium, etc

Some cycles are hybrid
• Sulfur (S)
• Major pools in Earth’s crust and atmosphere
Two major types of biogeochemical
cycles

Common features:
• Involve biological and non-biological processes
• Driven by the flow of energy through
ecosystem
• Tied to water cycle (water is the important
medium; Without water cycle, biogeochemical
cycle would cease).

Share three basic components:
• inputs,
• internal cycling
• outputs.
22.2 Inputs and outputs

Nutrients enter the ecosystem via inputs
• Gaseous cycle from atmosphere (C,N)
• Sedimentary from rocks and minerals (P, Ca)

Wetfall and dryfall
• Precipitation -- wetfall
• Airborne particular and arsenal (rainfall on the
forest floor is nutrient rich than on the bare
soil) -- dayfall

Nutrient in aquatic ecosystem
• From surround lands in the form of drainage
water, detritus, sediment and precipitation.
Inputs and outputs

There are also outputs to the biogeochemical cycles
• Carbon to carbon dioxide, release back to atmosphere
• Nutrient to gaseous form (denitrification)
• Loss of organic matter from ecosystem by washout (from terrestrial to
aquatic)
• Herbivores between aquatic and terrestrial


Moose (feed on aquatic plants, deposit nutrient in terrestrial ecosystem in the
form of feces)
Hippopotamus (move organic matter from terrestrial to aquatic)
• Harvesting may be replaced by fertilization
• Loss of nutrient (e.g.Leaching) may be balanced by inputs (weathering of
rocks and minerals)
Internal cycling

Nutrients are recycled within the ecosystem
• Internal recycling important within ecosystem
• Some systems have large amount of short term
recycling

Lakes
• Other have most stored as biomass

Forests
• Long term storage in water systems is in the sediment

System dependent on primary production and
decomposition
• Without latter, everything will become locked up
A generalized
biogeochemical
cycle
Note
input,
internal
cycling,
and
output
Pools and fluxes
Three calcium pools:
Plants, dead OM and
soil
Pool size: 290, 140,
440 kg ha-1
Fluxes (kg ha-1 yr-1)
F1: uptake
F2: litterfall
F3:leaching from
plants?
F4:net mineralization
Turnover time: t=P/f steady-state
t_p=4.8, t_OM=2.3, t_s=7.3
22.3 Carbon cycle




Tightly linked
to energy flow
Difference
between
production and
loss
NPP=GPP-Ra
Net ecosystem
productivity
• NEP=GPPRa-Rh
• NEP=NPP-Rh

Note storage
• Carbonates


•
•
•
•
Coral reefs
Limestone
Coal
Oil
Gas
Peat
Carbon cycle varies daily and seasonally
High CO2
concentration on the
forest floor is caused
by microbial
respiration.
CO2 high in winter and
decline with onset of
photosynthesis (May to
June, in Alaska)
Global carbon cycle
Carbon budget
of Earth is
closely linked
to
atmosphere,
land and
ocean and
mass
movement
around planet.
Unit in gigatons (Gt= 10^9 metric ton=10^15 g)
Earth
contains
10^23 g of
C
Missing carbon

Atmospheric increase=
•
•
•
•


Emissions from fossil fuels
+Net emissions from changes in land use
-Oceanic uptake
-Missing carbon sink
3.2 (±0.2)=6.3 (±0.4)+2.2 (±0.8)2.4 (±0.7)-2.9 (±1.1)
http://www.whrc.org/carbon/index.htm
22.4 Nitrogen cycle

Nitrogen is essential to life

Starts with nitrogen
fixation from atmosphere

Plants can only utilize
nitrate or ammonia
• Atmospheric deposit

Dryfall+wetfall
• Nitrogen fixation
 High energy
(lightning, 0.5 kg N
ha-1)
 Biological
• Bacteria, 10 kg N
ha-1.
N fixation: N2 is converted into NH3 (NH4+ when ) by bacteria.
Ammonization: a process that organic N is converted to NH4+
Nitrification: a process that NH4 is oxidized to NO2- and to NO3Denitrification: under anaerobic condition, NO3- is reduced to N2O and
N2 and returned to atmosphere.
Global nitrogen cycle
Unit:
10^12
g N yr1
22.5 Phosphorus cycle has no atmospheric pool





No atmospheric reservoir (rock and natural phosphate
deposits)
Permanent loss of phosphorus to oceans
Input limited to weathering of rocks
Terrestrial systems can be limited by phosphorus
availability
Phosphorus is more abundant in marine and freshwater
systems
• Particular
• Dissolved organic phosphorus


Rapidly utilized by zooplankton
Secrete inorganic
• Dissolved inorganic phosphorus


Rapidly utilized by phytoplankton
Phosphorus can sink as particulate phosphorus and become
locked in bottom sediment
• Depletion of surface layers
Global phosphorus cycle
Unit 10^12 g P yr-1
22.6 Sulfur cycle is both sedimentary and
gaseous (hybrid)
Global sulfur cycle (poorly understood)
22.7 Oxygen cycle in largely under biological
control
Sources of O2
1. Breakup of
water
2.
Photosynthesis
Now in balance
Three pools
22.8 Various biogeochemical cycles are linked
All elements are components of living organisms
and constituents of organic matter
Thus all cycles are linked:
Chemically
Energetically
Biologically
Stoichimetry: quantitative relationship of
elements in combination.
Example: C:N ratio, 8 to 15 for microbes, 30 for
leaf, etc
C:N:P ratio
End