matthew d. wallenstein natural resource ecology laboratory colorado state university
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Matthew D. WallensteinMatthew D. Wallenstein
Natural Resource Ecology Natural Resource Ecology LaboratoryLaboratory
Colorado State UniversityColorado State University
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The state of microbial The state of microbial ecology, ecology, circa circa 20092009
To date, most of our attention has been on describing patterns in community structure.
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Is it time to focus Is it time to focus on function?on function?
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Do different communities Do different communities function differently?function differently?
Traditional focus: functionTraditional focus: function• Potential rates under optimal Potential rates under optimal conditionsconditions
• Actual net rates under one set of Actual net rates under one set of field conditionsfield conditions
Traditional focus: communitiesTraditional focus: communities• DNA based assessment of total DNA based assessment of total community compositioncommunity composition
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Do different communities Do different communities function differently?function differently?
Traditional focusTraditional focus• Potential rates at optimal conditionsPotential rates at optimal conditions
r2=0.439; F2,19=7.44; p=0.004 Example: Denitrifier community structure relates to potential denitrification rates in urban streams.
Wang, S., J. Wright, E. Bernhardt, and M. Wallenstein, unpublished data.
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Microbes in current Microbes in current terrestrial ecosystem terrestrial ecosystem
modelsmodels
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Do different communities Do different communities function differently?function differently?
Emerging focus: functionEmerging focus: function• The range of conditions under which a The range of conditions under which a particular function can occur (functional particular function can occur (functional plasticity).plasticity).
• The persistence of function in the face of The persistence of function in the face of stress or disturbance.stress or disturbance.
Emerging focus: community compositionEmerging focus: community composition• Assessing the Assessing the ACTIVE ACTIVE microbes under microbes under different conditions with RNA or other different conditions with RNA or other novel molecular approaches (Stable Isotope novel molecular approaches (Stable Isotope Probing, BrdU)Probing, BrdU)
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In terms of niche In terms of niche theory…theory…
Abiotic condition(e.g. pH, temperature, moisture availability)
Activity Rate
(e.g. denitrification, respiration)
Community physiological response curve (PRC)
Species-specific PRC
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Under optimal conditions, no Under optimal conditions, no effect of community composition effect of community composition
on activity rate.on activity rate.
Activity Rate
temperature temperature
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Under in-situ conditions, Under in-situ conditions, direct effect of community direct effect of community
composition on activity rate.composition on activity rate.
Activity Rate
temperature temperature
Microbial composition affects the range of conditions under which microbial functions can persist.
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Soil Temperature @ 5 cm 2004-2005Toolik Lake, Alaska
-15
-10
-5
0
5
10
15
20
25
M J J A S O N D J F M A M J J A S O N
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Bacterial community composition
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Shrub Mineral Post-thaw
Shrub Mineral Pre-Freeze
Shrub organic Post-thaw
Shrub organic Pre-Freeze
Intertussock Post-thaw
Intertussock Pre-Freeze
Tussock Post-thaw
Tussock Pre-Freeze
Acidobacteria
Alphaproteobacteria
Betaproteobacteria
Deltaproteobacteria
Gammaproteobacteria
Firmicutes
Bacteroidetes
Actinobacteria
Verrucomicrobia
Other
Acidobacteria
Proteobacteria
Wallenstein et al 2007 FEMS Micro Ecol
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The ACTIVE microbial community appears to be more seasonally dynamic.
McMahon, Wallenstein, and Schimel. In prep.
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B-glucosidaseB-glucosidase (Lignocellulose)(Lignocellulose)
Lignocellulose degrading enzymes peak in late winter.Wallenstein, McMahon, and Schimel. 2009, Global Change Biology.
En
zym
e a
ctiv
ity
Month of year (2005)
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Seasonal changes in enzyme Seasonal changes in enzyme temperature sensitivitytemperature sensitivity
•Winter enzymes are more sensitive to temperature than summer enzymes!
•Suggests that different organisms are producing different iso-enzymes at different times of the year.
B-glucosidase
Wallenstein, McMahon, and Schimel. 2009, Global Change Biology.
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Modeled in-situ enzyme Modeled in-situ enzyme activitiesactivities
Wallenstein, McMahon, and Schimel. 2009, Global Change Biology.
Tussock
Shrub
Soil Temperature
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WinterWinter
Temperature
Mic
robi
al A
ctiv
ity
Fungi and Gram (-) bacteriaDegrading Lignocellulose
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Early SummerEarly Summer
Temperature
Mic
robi
al A
ctiv
ity
Diverse microbial communityDegrading chitin, protein, hemi-cellulose
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The challenge…The challenge…
SStudy the physiology of microbial tudy the physiology of microbial communities under a range of communities under a range of abiotic conditions to abiotic conditions to improve our improve our ability to predict ecosystem ability to predict ecosystem function in the face of function in the face of environmental change.environmental change.
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Emerging goals for Emerging goals for microbial ecologists microbial ecologists
(2010-2020)(2010-2020)1.1. Identify which microbes are active under Identify which microbes are active under
different in situ conditions.different in situ conditions.
2.2. Understand the physiology and ecological Understand the physiology and ecological roles of different microbial taxa.roles of different microbial taxa.
3.3. Measure and model how microbial Measure and model how microbial physiology affects the dynamic response physiology affects the dynamic response of ecosystem function to changing of ecosystem function to changing environments.environments.
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FunctionFunction