Microbial communities and global change

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Microbial communities and global change
David Lipson, Ph.D Professor, Department of
Biology San Diego State University dlipson_at_science
s.sdsu.edu
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The 3-Domain System
Based on ribosomal RNA gene sequences
Almost all life is microbial! The diversity of
microorganisms is vast
crown group of Eukaryotes, includes animals,
plants and multicellular algae
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Microbial Communities
Control Global Biogeochemistry
diverse, mostly uncultured
Not well understood
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Elevated atmospheric CO2
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Possible Microbial feedbacks in global change
Plant community change
?
Nutrient mineralization
Plant growth
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Warming
Microbial trace gas production


CO2 increase
Microbial Respiration
Red positive feedback (destabilizing) Green
negative feedback (stabilizing) Purple uncertain
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Methane (CH4)
About 1.7 ppm in atmosphere Strong greenhouse
gas Important in ozone chemistry
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Atmospheric methane is increasing in the
industrial age
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But why?
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(aerobic)
(anaerobic)
CO2
respiration
C fixation
Organic C
methanogenesis
Methanotrophy (methane oxidation)
CH4 (methane)
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Methanogens (Archaea)
Methanopyrus sp.
Methanococcus jannaschii
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Trichonympha, symbiotic protist in termite gut,
with its own symbiotic methanogens
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Agriculture and Methane production
Rice paddies Projected to increase by 70 in
next 25 years Anaerobic, rich in organic C
leads to methane production Some oxidiation
occurs due to O2 conducted by rice plants into
rhizosphere
Effect of N fertilization Stimulate plant and
methanogen growth Inhibit methane oxidation (in
most studies of upland rice and other
ecosystems)
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Competitive inhibition of methane oxidation by
ammonium
H
H
C
H
N
H
H
H
H
H
Ammonium
Methane
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However, in one recent study
In rice paddy soils, ammonium additions
stimulated CH4 oxidation methanotrophs were N
limited
Bodelier et al. 2000
Depends on CH4 and N availability lots of CH4
in rice paddy, overcomes competitive inhibition
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Nitrous oxide (N2O)
About 300 ppb in atmosphere Strong greenhouse
gas 200X worse than CO2. lifetime150 years.
Contributes to stratospheric ozone depletion
(after conversion to NO, nitric oxide)
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NOx in fossil fuel emissions
Clean air act
However, N2O concentration still increasing by
0.3 /year
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Global N cycle
(Units are 1012g/year)
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Rough global N2O budget
Oceans 2.0 Soils Tropical
3.7 Others 2.0 Fertilized agriculture
0.7 Land use change 0.7 Biomass burning
2.2 Total sources 11.3 Reaction with
O3 10.5 Atmospheric increase 3.0 Total
sinks 13.5
(1012 g N/yr)
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Simplified N cycle
anaerobic
N fixation
N2
NH4
(by-products of nitrification)
N2O
(N2O, NO)
Organic N
denitrification
ammonia oxidation (nitrification)
NO2-
NO3-
nitrite oxidation (nitrification)
aerobic
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nitrifiers
Nitrosococcus
Nitrosolobus
Nitrospina
Nitrosospira
Nitrosomonas
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Agriculture and Nitrous oxide
N2O
NO3-
NH3
N2O
leaky pipe model
More N fertilization leads to more NOx emissions
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Hall and Matson 1999
N additions stimulate NOx emissions in P-limited
tropical forest
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N saturation vs. N limitation
Most temperate ecosystems N limited, but
tropical forests often P limited Tropical
forests biggest natural source of N2O Globally,
2.2 Tg N/year deposited from fossil fuel
burning. Eventually, systems become saturated,
start leaking N
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Eutrophication
Nutrients lead to bloom, algae decompose, use up
oxygen
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Effect of fertilizer runoff on denitrification in
coastal areas
Off coast of India during monsoon season N in
runoff causes eutrophication of coastal
waters Lower oxygen leads to increased
denitrification
(Naqvi et al. 2000)
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Altabet et al. 2002
Over the last 60,000 years in the Arabian Sea,
temperature, CO2 and denitrification are
correlated
(Isotope data 15N related to denitrification)
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Hypothesized denitrification control over global
climate after last glacial maximum (22,000 ya)
High denitrification rates in ocean
Lower NO3- in ocean
Lower production rates in ocean
Slower CO2 removal by ocean
Climate warms
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Coccolithophores (Haptophyta)
Emiliana huxleyi
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Nutrient limitation in Oceans
Nutrient limitations depend on community
algae, cyanobacteria, diatoms
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Dinoflagellates
N limited in oceans
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Cyanobacteria
N2 fixers
Iron (or P) limited in oceans
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Diatoms
Silica limited
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Most Fe, P, and Si in ocean comes from land
Arroyo formed during huricane Nora
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The Iron hypothesis
Increased iron transport from land (more dust)
led to increased ocean productivity, lowered
atmospheric CO2 in last glacial maximum (18,000
years ago)
Lets dump iron into the ocean and save the
world! John Martin (1935-1993) Give me half a
tanker full of iron and Ill give you the next
ice age
Arguments against Silica has slower half-life,
limits diatom production, fits data better (8000
y lag after dust decreased) Evidence that P
controls N fixation in oceans Much spatial
variability, limitations depend on conditions and
community