Transcript Announcements

Announcements
•
Handouts
• Wagener et al. article “Rivers and Soils…”
• Questions: written assignment due in your
section this week (Oct. 7th or 8th)
• Writing guidelines will help you with the
assignment
• You can get all of these online:
www.es.ucsb.edu/classes/envs100/
•
Lecture notes online
Summary from Friday…
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Biology controls the flow of energy
between organisms
Plant and animal allocation of energy
Endotherms vs. ectotherms and the
energy available in a food chain
Limits on Primary Productivity
• Light
• Temperature
• Nutrients
Two-minute Quiz
Imagine that you are a limnologist. (What is
a limnologist?)
Two-minute Quiz
Imagine that you are a limnologist. (What is
a limnologist?) You are doing your research
at Zaca Lake in Santa Barbara County.
Two-minute Quiz
Imagine that you are a limnologist. (What is
a limnologist?) You are doing your research
at Zaca Lake in Santa Barbara County.
You make measurements of phytoplankton
and macrophyte biomass over the course of
the year as part of a calculation of the net
uptake of CO2 by the lake.
Which of the following occurrences could
influence plant biomass in the lake? How?
1.
2.
3.
4.
5.
The watershed surrounding Zaca Lake
burns.
El Niño weather patterns cause a drop in
the mean air temperatures in Santa
Barbara County during the winter
months.
Mount Saint Helens erupts.
A dirt road surrounding the lake is
paved.
A group of anglers successfully lobby to
stock the lake with more fish.
Global Nitrogen Cycle
N deposition
Human
activities
Fixation by
lightning
Denitrification
Denitrification
Biological
fixation
Biological
fixation
Internal
cycling
Long-term
burial
Internal
cycling
Global Nitrogen Cycle
N deposition
Human
activities
Fixation by
lightning
Denitrification
Denitrification
Biological
fixation
Biological
fixation
Internal
cycling
Human activity:
More fixation, more N emissions
Cycle becomes more “open”
Long-term
burial
Internal
cycling
Plant-Microbe Mutualisms
•
Rhizobium
• Nitrogen fixation
• N2  NH4+
•
Mycorrhizal fungi
• Fungal hyphae take up
nutrients  used by plant
• Photosynthate from plants
 used by fungi
Mycorrhizal Fungi
•
Increase volume of soil exploited by plants
• Absorbing length increased by 2-3 orders of magnitude
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80% of angiosperms, all gymnosperms, some
ferns
4-20% of GPP from plant goes to fungus
Can enhance both N and P uptake
Mining of P only  induces N limitation
Orchids depend on mycorrhizae for carbon as
well as nutrients
What controls nutrient availability
to plants?
•
Decomposition
organic N
NH4+
NO3-
Decomposition
The physical and chemical breakdown of
dead organic matter
•
Decomposition is crucial because it:
• Provides energy for microbial growth
• Releases nutrients for plant uptake
• Influences ecosystem carbon storage and
therefore climate
Fungi
•
Most decomposition in aerobic environments
• 60-90% of microbial biomass in forests
• 50% of microbial biomass in grasslands
•
Broad enzymatic capability
• Cell walls (lignin, cellulose, hemicellulose)
• Cell contents (proteins, sugars, lipids)
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Can transport metabolites through hyphae
• Surface litter (import nitrogen from soil)
• Wood degraders (import nitrogen from soil)
• Mycorrhizae (trade carbohydrates for nutrients)
A fungus among us:
Laetiporus gilbertsonii
“chicken of the woods”
Often grows on
eucalyptus stumps
• Massive fruiting at the
end of the dry season
•
Announcements
•
Handouts
• Wagener et al. article “Rivers and Soils…”
• Questions: written assignment due in your
section this week (Oct. 7th or 8th)
• Writing guidelines will help you with the
assignment
• You can get all of these online:
www.es.ucsb.edu/classes/envs100/
•
Lecture notes online
Summary from Monday
•
Global Nitrogen Cycle
• Without humans, cycling within a system dominates
• Human impacts make a system more “open”
Summary from Monday
•
Global Nitrogen Cycle
• Without humans, cycling within a system dominates
• Human impacts make a system more “open”
•
Plant-microbe Mutualisms
• Mycorrhizae: very common, fungus gives nutrients to
plant in exchange for carbon
• Nitrogen-fixers: plant roots make nodules, bacteria
give N to plant in exchange for carbon
Summary from Monday
•
Global Nitrogen Cycle
• Without humans, cycling within a system dominates
• Human impacts make a system more “open”
•
Plant-microbe Mutualisms
• Mycorrhizae: very common, fungus gives nutrients to
plant in exchange for carbon
• Nitrogen-fixers: plant roots make nodules, bacteria
give N to plant in exchange for carbon
•
Decomposition: breakdown of organic matter
• Who does it? Macrofauna, mesofauna, microfauna
• Fungus
Two-minute Quiz
•
You are hunting for truffles (the yummy
underground fruiting body of a fungus) in
the forest with your trusty pig. Where are
you most likely to find them and why?
a) In a forest gap where there
is a grassy meadow
b) Near the base of a tree
c) Near a rocky outcrop where
the soils are thin and there is
not much vegetation
Can fungi photosynthesize?
•
All fungi are heterotrophs
• they cannot photosynthesize and gather energy
from the sun
• they must take carbon from dead organic matter
•
Some fungi are green, but they do not
photosynthesize
Main Players in Decomposition
Macrofauna (greater than 2 mm):
ecosystem engineers, turn soil over
• earthworms
• termites
Mesofauna (0.1-2 mm):
fragment litter, injest litter covered with
microfauna
• collembola
Microfauna (less than 0.1 mm):
main decomposers, larger ones prey on bacteria
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•
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nematodes
amoebas
fungi
bacteria
How does it decomposition work?
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smaller molecules can get engulfed
completely (phagocytosis)
larger molecules must be broken down
outside of the decomposer’s body
• hyphae are small!
• bacteria are even smaller!!
•
bacteria and fungus produce exoenzymes
to break things down
Fungi
•
Why are there so many in forests?
• fungi specialize in breaking down wood
fruiting bodies
high C
N
C
high N
hyphae
Bacteria
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Grow rapidly
Specialize on labile substrates
Some bacteria function anaerobically
Dependent on diffusion
Spatial specialists
• Rhizosphere, macropores, interior of aggregates
• Biofilms on particle surfaces
•
Chemical specialists
• Different bacteria produce different enzymes
(consortia)
Why do Decomposers Decompose Stuff?
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Decomposition does release nutrients into
the soil, BUT…
Decomposers don’t care that they are
performing an “ecosystem process”
Decomposers need C and nutrients too!
They get energy (C) and nutrients from
breaking down organic matter
What controls decomposition?
•
Climate
Quantity of dead material
(also known as “substrate”)
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Quality of substrate
• Size
• Bond Strength
• Regularity
• Toxicity
• Nutrient Content
Substrate Quality
1. Size of molecule
• Large molecules must be broken down
outside of cells
• Exoenzymes
Substrate Quality
2. Bond Strength
• Peptide bonds compared to aromatic rings
• peptide bonds are easy to break
• aromatic rings have double bonds & are stronger
• The same amount of nitrogen:
• fresh litter is high in protein
• older organic matter in soil has aromatic rings
Substrate Quality
3. Regularity of structure
• Cellulose has a regular structure
• Lignin has an irregular structure
4. Toxicity
• Toxins protect plants from herbivory & pathogens
• May also affect decomposers
5. Nutrient content
• Nutrients are essential for microbial growth
Predictors of Decomposition Rate
•
C:N ratio
• Index of ratio of cytoplasm to cell walls
• Measure of nitrogen concentration
• Directly affects decomposition ONLY in
presence of labile C
•
Lignin:N ratio (this is a better predictor)
• Integrated measure of N concentration and
substrate size/complexity
Announcements
•
Office hours on Monday:
• Look for Kevin in my office (Girvetz 2307)
•
Online fun!
Summary from Wednesday
•
How decomposition occurs
• microbes exude exoenzymes that attack substrate
•
Bacteria
• small, grow quickly, spatial specialization
• chemical specialization
cellulose
1
more recalcitrant
cellulose 2
fragment
glucose
more labile
Summary from Wednesday
•
Why decomposition occurs
• microbes don’t care that they are performing an
“ecosystem service”, they just need energy and
nutrients
•
Controls on decomposition
• Climate
• Quantity of substrate
• Quality of substrate
• size of molecule
• bond strength
• regularity of structure
• toxicity
• nutrient content
Soils
•
"We know more about the movement of
celestial bodies than about the soil
underfoot."
- Leonardo Da Vinci, circa 1500's
Soils
•
"Be it deep or shallow, red or black, sand
or clay, the soil is the link between the
rock core of the earth and the living things
on its surface. It is the foothold for the
plants we grow. Therein lies the main
reason for our interest in soils."
- Roy W. Simonson, USDA Yearbook of
Agriculture, 1957
What is Soil?
Natural body comprised of solids, liquids, & gases
• On the surface of the land
• Has one or both of the following:
•
• horizons
• the ability to support rooted plants
•
Upper limit:
• boundary between soil and air, shallow water, live
plants, or plant materials that have not begun to
decompose
•
Lower limit:
• bedrock or 200m
additions
translocations
transformations
losses
Soil Formation Factors
Cl.O.R.P.T.H.
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Climate
Organisms
Relief
Parent material
Time
Human activity
Biome:
A large climatic region where plants
are similar to each other