Matthew D. WallensteinMatthew D. Wallenstein

Natural Resource Ecology Natural Resource Ecology LaboratoryLaboratory

Colorado State UniversityColorado State University

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.

Is it time to focus Is it time to focus on function?on function?

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

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Wang, S., J. Wright, E. Bernhardt, and M. Wallenstein, unpublished data.

Microbes in current Microbes in current terrestrial ecosystem terrestrial ecosystem

modelsmodels

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)

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

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

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.

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

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

The ACTIVE microbial community appears to be more seasonally dynamic.

McMahon, Wallenstein, and Schimel. In prep.

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)

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.

Modeled in-situ enzyme Modeled in-situ enzyme activitiesactivities

Wallenstein, McMahon, and Schimel. 2009, Global Change Biology.

Tussock

Shrub

Soil Temperature

WinterWinter

Temperature

Mic

robi

al A

ctiv

ity

Fungi and Gram (-) bacteriaDegrading Lignocellulose

Early SummerEarly Summer

Temperature

Mic

robi

al A

ctiv

ity

Diverse microbial communityDegrading chitin, protein, hemi-cellulose

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.

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.

FunctionFunction