BIOL 4120: Principles of Ecology
Lecture 20: Nutrient
Regeneration in Terrestrial
and Aquatic Ecosystems
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Lodgepole pine
Death of trees in 1960s
Pinyou pine
Acidified precipitation was caused by air
pollution from power plants and fossil fuel
burning
Nitrous oxide (N2O)
Nitric acid (HNO3)
Sulfur dioxide (SO2)
Sulfuric acid (H2SO4)
pH of
rainwater
fall to as
low as 4
Clear Air Act significantly reduced SO2 and
N2O
In 1970,
Clean Air Act
passed
to reduce
emissions of SO2
and particulate
matter from
factories and
power plants.
But forests did
not show sign of
recovery.
Hubbard Brook study held several
important lessons for forest ecologists.
pH=4
pH=5
First, trees die not
because of direct
effects of high
hydrogen ion
concentrations, but
because of long- term
leaching of nutrients
from the soil.
Second, the natural
recovery of forests
growing on nutrientpoor soils will require
restoration of soil
nutrients through the
slow process of
weathering.
Outline
(Chapter 24)
20.1 Weathering makes nutrients available in terrestrial
ecosystems
20.2 Nutrient regeneration in terrestrial ecosystems occurs
in the soil
20.3 Nutrient regeneration can follow many paths
20.4 Mycorrhizal associations of fungi and plant roots
promote nutrient uptake
20.5 Climate affects pathways and rates of nutrient
regeneration
20.6 In aquatic ecosystems, nutrients are regenerated
slowly in deep water and sediments
20.7 Stratification hinders nutrient cycling in aquatic
ecosystems • Oxygen depletion facilitates regeneration
of nutrients in deep waters
20.8 Nutrient inputs control production in freshwater and
shallow- water marine ecosystems
20.9 Nutrients limit production in the oceans
Most essential nutrients are recycled within
ecosystem
Internal cycling
Retranslocation
or reabsorption
Nitrogen fixation
(N2) from
atmosphere
Fertilization
Weathering from
rocks and
sediments
Harvest
Leaching to
groundwater and
stream runoff
20.1 Weathering makes nutrients available in
terrestrial ecosystems
Weathering is the physical breakdown and chemical
alteration of rocks and minerals near the earth’s surface.
Important nutrients, such as nitrogen, phosphorus, and
sulfur, are typically scarce in parent material.
Igneous rocks such as granite and basalt contain no
nitrogen, only 0.3% phosphate, and only 0.1% sulfate
by mass. Most sedimentary rocks contain little more.
Hence, weathering adds little of these nutrients to soil.
Time: Initial differentiation can be within 30 years.
Formation of true soil, 2000 to 20000 years
BIOL 4120: Principles of Ecology
Lecture 20: Nutrient
Regeneration in Terrestrial
and Aquatic Ecosystems
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
Element budget in a
watershed
Stream gauges are used to measure
nutrient outputs.
Rain gauges are used to measure
nutrient inputs.
20.2 Nutrient regeneration in terrestrial ecosystems
occurs in the soil
Many organisms are involved in decomposition
Decomposition is the
breakdown of chemical bonds
formed during the
construction of plant and
animal tissues.
Processes: leaching,
fragmentation, changes in
physical and chemical
structure, ingestion and
excretion of waste products.
Microbial decomposers:
Bacteria are dominant
decomposer (to animal)
Fungi (to plant)
Aided by detritivores
4 major groups
Microfauna, mesofauna,
macrofauna, and megafauna
Breakdown of leaf litter occurs in four ways
1. Leaching of soluble
minerals
2. Consumption by
detritivores
3. Breakdown by fungi
4. Breakdown by bacteria
Proteins and soluble C are
decomposed very fast,
then the cellulose and
hemicellulose, lignin is
very difficult to
decompose
Proteins etc. 15%
Cellulose etc. 60%
Lignin: 20%
Decomposition rate measurement
Litterbag method
Mesh bag (12mm)
Mass of remaining
in the bag
includes both
original plant
matter as well as
bacteria and fungi
that have
colonized and
grown on the
plant litter.
Carbon is lost to the atmosphere as CO2 in the process of respiration
Smith 2002
Based on the
data, the
decomposition
rate can be
calculated
Decomposition rate
calculated as k=0.0097
wk-1 and 0.0167 wk-1
for two tree species
Lignin contents influence litter decomposition
Terrestrial environment
Aquatic environment
20.3 Rates of Decomposition and
influencing factors


Rate at which nutrients are made
available to primary producers is
determined largely by rate of
decomposition.
influenced by:
• temperature,
• moisture,
• chemical compositions of leaves
• Decomposers
Physical conditions influence litter decomposition
O2 concentration
Decomposition of
Spartina litter is
more efficient in
aerobic than
anaerobic
conditions
Lack of fungi, which
require oxygen for
respiration, hinders
the decomposition
of lignin
component, slow
the decomposition
rate.
Litter bags on the marsh surface or buried 5-10
cm below surface
Valiela 1984
Changes in climate influence litter
decomposition
7.2oC, 621 mm
12.2oC, 720 mm
14.4oC, 806 mm
Decomposition of red maple litter at three sites (litter quality similar for
three sites). Warm and wet conditions, decompose fast (3 studies)
Temperature influence on decomposition
Diurnal changes in air temperature and decomposition in a temperature
deciduous forest (Whitkamp and Frank 1969)
20.4 Nutrient regeneration can
follow many paths
Monomers: monomeric subunit of large organic polymers such as
amino acids, nucleic acids.
Depolymerization is accomplished by microorganisms secreting
enzymes and other reactive substances.
Mineralization, immobilization and
net mineralization rate



Mineralization: a process that microbial
decomposers –bacterial and fungitransform nitrogen and other elements
contained in organic matter compounds
into inorganic (or mineral) forms.
• Organic N ammonia (waste product of
microbial metabolism)
Immobilization: uptake and assimilation of
mineral nitrogen by microbial decomposer.
• N used by microbes to grow
Net mineralization rate: different between
the rate of mineralization and
immobilization
Nitrogen remaining in the litter during
decomposition
Initial phase
(A) leaching
soluble N,
then
immobilized
by microbes,
then net N
release from
litter.
Chemical compositions of leaves in
response to nutrients



C:N ratio
• low C:N ratio – high protein level
• High C:N ratio – low in proteins, high in
lignin and secondary metabolites
Leaf C:N ratio is influenced by nutrients
availability in the environment
Leaf C:N ratio influences decomposition
rate and interactions with herbivores
• Nutrient requirements for compensatory
growth
N content
influence the
decomposition
Under high N,
the initial N can
exceed the rate
of
immobilization
from onset of
experiment, N
concentration
will not increase
Patterns of immobilization and mineralization of sulfur (S), calcium
(Ca), and manganese (Mn) in decomposing needles of Scots pine
Five year litterbag experiment
20.5 Mycorrhizal associations of fungi
and plant roots promote nutrient uptake
Symbiotic association of fungus and
root is called a Mycorrhiza:
Arbuscular Mycorrhizae ( AM)
penetrate cell walls in root tissue and
form vesicles or branched structures
in intimate contact with root cell
membranes.
Ectomychorrhizae ( EcM): form a
dense sheath around the outsides of
small roots and penetrate the spaces
between the cells of the root cortical
layer
Function: promote plant growth,
increase a plant’s uptake of minerals
by penetrating a greater volume of
soil than the roots.
Plant roots and mycorrhizal fungi
Fungi assist the plant with the uptake of nutrient
from the soil (extended water and nutrients
absorption)
Plant provides the fungi with carbon, a source of
energy.
Endomycorrhizae
(a)
Ectomycorrhizae
(b)
Mycorrhizal
fungi work
well under
poor nutrient
conditions
20.6 Key ecosystem processes
influence the rate of nutrient cycling



Primary productivity determines rate
of nutrient transform from inorganic
form to organic form (nutrient
uptake)
Decomposition determines the rate
of transformation of organic to
inorganic form (N mineralization)
Rates of these two determine the
internal cycling
Feedback
between nutrient
availability, NPP
and N release
20.7 Climate affects pathways and rate
of nutrient retention
Climate affects weathering, soil properties, and rate of decomposition of
detritus.
Tropical soils:
Deeply weathered, less clay (can’t hold nutrients)
Leach out if not uptake by plants, nutrient-poor soils
Why productivity is high?
1) rapid decomposition of detritus under warm, humid conditions;
2) rapid uptake by plants and other organisms from upper-most layer
of soils
3) effective retention of nutrients by plants and mycorrhizal fungal
associations
Litter on the forest floor constitutes only 1-2% of total biomass of
vegetation and detritus; <25% of carbon stored in soils
Temperate forests:
1) Litter on the forest floor constitutes 20% in needle-leaved forests,
5% in hardwood forests.
2) 50% carbon stored in soils and litter.
Tropical forest
ecosystems hold
most of their
nutrients in living
vegetation
In an ash-oak
forest in Belgium,
most of the P and N
stored in the soil as
detritus,
decomposed
organic or inorganic
nutrients.
But in a tropical
deciduous forest in
Ghana,
soil:biomass ratios
are much lower.
Eutrophic and oligotrophic soils
Two type of soils in tropics
Eutrophic soil: well-nourished soils.
developed in geological active areas where erosion is high
and soils are relative young.
bedrock closer to soil surface, weathering adds nutrients
more rapidly and soil retain nutrients more effectively
Occur: Neotropics -- Andes, Center America, West Indies
Oligotrophic soil: nutrient-poor soil
develop in old, geologocally stable areas, intense
weathering over long periods removes clay and reduce the capacity
of soils to retain nutrients.
Occur: Amazon Basin
In oligotrophic tropical soils, plants retain nutrients by keeping
leaves for long periods and by withdrawing nutrients from them
before they are dropped.
Dense mats of root (and fungi) to help nutrient uptake.
Recap
Nutrient regeneration in terrestrial ecosystems occurs in the
soil:
Litter and soil organic carbon decomposition
Influence factors on litter decomposition
Nutrient regeneration can follow many paths
Mineralization, immbilization and net minerlization
Mycorrhizal associations of fungi and plant roots promote
nutrient uptake
Function of AM and ECM
Climate affects pathways and rate of nutrient retention
Tropic
Habitat conversion and soil nutrient
Habitat conversion changes
soil nutrient conditions
Deforestation (cutting) and
burning
Habitat conversion and soil nutrient
Deforestration and convert from forests to crops in the tropics
1. Cutting and burning loss nutrients directly
2. Without plants, nutrients leach out quickly
3. Upward movement of water draws ion and Al3+ to the surface
and form laterite (bricklike substance), as soil dries out
4. Surface runoff without plants will cause soil erosion.
A study compared soil nutrient changes in three places
Canada prairie site
C: 8.8 kg/m2; after 65 yrs, reduced by 51%, 1% per year
Brazil Forest site
C: 3.4 kg/m2; after 6 yrs, decreased by 40%, 9% per year
Venezuelan rain forest
C: 5.1 kg/m2; after 3 yrs, decreased by 29%, 11% per year
Global warming and boreal forest
Boreal forests hold 200-500 Gt of C,
80% of total C in the atmosphere
Annual change from a loss of 0.7
metric Ton C to a gain of 0.1 T per
ha over four years. Four year
total, a slightly loss
20.6 In aquatic ecosystems, nutrients are
regenerated slowly in deep water and sediments
In terrestrial ecosystem (shallow water), plants bridge the physical
separation between the zones. In deep ocean, there is no direct link.
Need a transport system.
Primary productivity in aquatic ecosystems is
highest where nutrients regenerated in sediments
can reach the photic zone
20.7 Stratification hinders nutrient cycling in
aquatic ecosystems
Vertical mixing of
water
Energy input and wind
Turbulent mixing in
shallow water and
upwelling along coasts
Thermocline
Density and
temperature
Turnover of water and
nutrient link two zones
together
Change in T, light
and nutrient
influence NPP,
and
photosynthesis
also influences
nutrient
availability
Vertical mixing can stimulate productivity, and can also reduce
productivity, as mixing bring phytoplakton far below photic zone.
20.8 Oxygen depletion facilitates regeneration of
nutrients in deep waters
During prolonged periods of
stratification in freshwater lakes,
bacteria respiration in the carbonrich bottom sediments tend to
deplete O2 supply in the
hypolimnion.
Bacteria switch to sulfate as an
oxidizer and produce H2S
(hydrogen sulfide)
In O2 depleted environments,
bacteria have insufficient O2 to
nitrify NH4+;
Iron and Mg shift to reduced forms
(increase solubility). Thus,
nutrients accumulate under these
reducing conditions.
20.9 Nutrient inputs control production in
freshwater and shallow-water marine ecosystems
Productivity depends on external inputs from rainfall and streams
and regeneration of nutrients in the lake.
Phosphorus is critical
to the productivity of
freshwater lakes.
Two parts separated,
one side added
carbon and nitrogen
(near), another side
added C, N and P
(far).
P caused eutrophication in a Canadian Lake
experiment
With P,
photosynthesis
cyanobacteria were
developed within 2
months
Fertilization and eutrophication
Overfertilizaiton
Runoff
Eutrophication: overproduction of organic matter
within a lake or river
Consequences:
More food source for fish
But if too productivity, can lead to imbalance
when decomposers of this excess organic matter
consume O2 faster than it can regenerated by
photosynthesis.
 O2 depletion
Estuaries and salt marshes
High
productivity
Due to plentiful
supplies of
nutrients
Inputs from
rivers and tidal
flow and
regenerated
within
ecosystem.
Where does the primary production go?
Energy flow diagram shows energy flow in a Georgia salt marsh
Hypoxic zones in Estuaries and Shallow
Marine Ecosystems
Hypoxia: the depletion of O2 to the extent that acquatic organisms
can no longer survive
Defined as: <2 mg O2/liter of water (normal, >10)
Reason: high nutrient concentrations
20.10 Nutrients limit production in the oceans
Productivity in the
open ocean is
typically low
Lack of nutrients
(nitrogen and
phosphorus)
Ion and silicon are
important and in
shortage
Temperature and
climate factors also
influence
productivity
Does iron limit marine productivity?
Iron addition
Increased productivity
in the South patch
The Redfiled ratio and nutrient limitation in the
open ocean
Nutrient concentrations in the ocean need to match the
requirements of photosynthetic organisms; otherwise, production
would be reduced and abundant nutrients go unused.
Alfred Redfield
In phytoplankton, N:P is approximately 16:1 (Redfield ratio)
Phytoplankton incorporate 16 times as much as nitrogen as
phosphorus into their biomass and release the same ratio as they
decompose after death.
Adding C, C:N:P =106:16:1
Stoichiometry
20.10 Water flow influences nutrient cycling in
streams and rivers
Nutrient spiraling
Jack Webster (Virginia Tech)
Because nutrients are
continuously being transported
downstream, a spiral rather than
a cycle better represents the
cycling of nutrients.
One cycle in the spiral: uptake of
one nutrient atom, its passage
through food chain, and its return
to water, where it is available for
re-use.
The longer the distance required,
the more open the spiral.
Newbold et al. from ORNL
Phosphorus
at Walker Branch watershed
Phosphorus movement: 10.4 m per day
Cycled once every 18.4 days
One spiral: 190 m
The End