Does Biological Diversity Control Does Biological Diversity Control Ecosystem Function?Ecosystem Function?

Donald R. ZakDonald R. ZakSchool of Natural Resources & EnvironmentSchool of Natural Resources & Environment

University of MichiganUniversity of Michigan

Clearing and Fragmentation of Tropical Forests

Human Activity and the Loss of Human Activity and the Loss of Biological DiversityBiological Diversity

Human Activity and the Loss of Human Activity and the Loss of Biological DiversityBiological Diversity

Fire Suppression in Temperate GrasslandsFire Suppression in Temperate Grasslands

Human Activity and the Loss of Human Activity and the Loss of Biological DiversityBiological Diversity

Introduction of Exotic PredatorsIntroduction of Exotic Predators

Brown Tree SnakeBrown Tree Snake

Brown RatBrown Rat

Common Common MongooseMongoose

Red FoxRed Fox

Biological Diversity & Ecosystem FunctionBiological Diversity & Ecosystem Function

What happens to ecosystem function when the abundance of particular species or groups of species are reduced?

Biological Diversity & Ecosystem FunctionBiological Diversity & Ecosystem Function

Does biological diversity influence rates of ecosystem processes?

Is the relationship positive or negative?

What mathematical expression describes thisrelationship?

Research into the influence of biological diversity on ecosystem function has been motivated by three basic questions:

What are the Mechanisms Linking Plant Diversity What are the Mechanisms Linking Plant Diversity to Ecosystem Function?to Ecosystem Function?

Lack of specific mechanisms linking plant diversity & ecosystem function, especially for the influence of plant diversity on higher trophic levels.

Organic SubstratesOrganic SubstratesProduction & BiochemistryProduction & Biochemistry

Plant Diversity, Microbial Communities & Ecosystem Function:Plant Diversity, Microbial Communities & Ecosystem Function:Are There Any Links? Are There Any Links?

Soil Microbial CommunitiesSoil Microbial CommunitiesComposition & FunctionComposition & Function

Soil EnvironmentSoil EnvironmentTemperature & Water PotentialTemperature & Water Potential

Plant Community Plant Community Composition & Composition &

DiversityDiversity

Soil Microbial Community Composition Soil Microbial Community Composition & Function& Function

Substrate AvailabilitySubstrate AvailabilityAmount & BiochemicalAmount & Biochemical

CompositionComposition

Ecosystem ProcessesEcosystem ProcessesSoil C & N CyclingSoil C & N Cycling

Litter ProductionLitter ProductionAbove- & BelowgroundAbove- & Belowground

Plant Diversity & Microbial Communities Plant Diversity & Microbial Communities Conceptual ModelConceptual Model

+

+

+

+

Because plant species differ in their Because plant species differ in their biochemical composition, changes in diversity biochemical composition, changes in diversity should alter the production as well as range of should alter the production as well as range of compounds in detritus that limit, and thus compounds in detritus that limit, and thus control, the composition and function of control, the composition and function of heterotrophic microbial communities. heterotrophic microbial communities.

Changes in microbial community composition Changes in microbial community composition & function will alter ecosystem C and N & function will alter ecosystem C and N cycling.cycling.

Hypotheses:Hypotheses:

Cedar Creek Natural History AreaCedar Creek Natural History AreaBiodiversity ExperimentBiodiversity Experiment

Cedar Creek Natural History AreaCedar Creek Natural History AreaBiodiversity ExperimentBiodiversity Experiment

Experimental Plant Diversity Treatments - 169 mExperimental Plant Diversity Treatments - 169 m22 Plots Plots

•Random Draw of 18 Native Grasses, Random Draw of 18 Native Grasses, Forbs, and Woody PlantsForbs, and Woody Plants

•Species Richness TreatmentsSpecies Richness Treatments1, 2, 4, 8, 16 Species1, 2, 4, 8, 16 Species

•30 Replications of Each Species 30 Replications of Each Species Richness TreatmentRichness Treatment

Cedar Creek Natural History AreaCedar Creek Natural History AreaBiodiversity ExperimentBiodiversity Experiment

C4 GrassesC4 Grasses Andropogon gerardiAndropogon gerardi Buchloe dactyloidesBuchloe dactyloides Panicum virgatumPanicum virgatum Schizachyrium scopariumSchizachyrium scoparium Sorghastum nutansSorghastum nutans Sporobolus cryptandrus Sporobolus cryptandrus

C3 GrassesC3 GrassesAgropyron smithiiAgropyron smithiiElymus canadensisElymus canadensisKoeleria cristataKoeleria cristataPoa pretensisPoa pretensis

LegumesLegumesAmorpha canescens Astragalus canadensis Lespedeza capatataLupinus perennisPetalosetmum purpureum

ForbForbMonarda fistulosaMonarda fistulosa

WoodyWoodyQuercus ellipsoidalisQuercus ellipsoidalisQuercus macrocarpaQuercus macrocarpa

Cedar Creek Natural History AreaCedar Creek Natural History AreaBiodiversity ExperimentBiodiversity Experiment

Microbial Community CompositionMicrobial Community Composition- Phospholipid Fatty Acid Analysis- Phospholipid Fatty Acid Analysis

Microbial Community FunctionMicrobial Community Function- Microbial Respiration- Microbial Respiration- Gross Rates of Soil Nitrogen Cycling- Gross Rates of Soil Nitrogen Cycling

After 7 Years of Plant Growth in the Experimental Treatments, We Measured:

H-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-OHH-C-C-C-C-C-C-C-C-C-C-C-C-C-C-C-OH

H H H H H H H H H H H H H H H H H H H H H H H H H H H H

H H H H H H H H H H H H H H OH H H H H H H H H H H H H H O

| | | | | | | | | | | | | | | | | | | | | | | | | | | |

| | | | | | | | | | | | | || | | | | | | | | | | | | | ||||

H-C-C-C-C-C-C=C-C-C=C-C-C-C-C-C-C-C-C-OHH-C-C-C-C-C-C=C-C-C=C-C-C-C-C-C-C-C-C-OH

H H H H H H H H H H H H H H H H HH H H H H H H H H H H H H H H H H

H H H H H H H H H H H H H OH H H H H H H H H H H H H O

| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

| | | | | | | | | | | | || | | | | | | | | | | | | || ||

Composition of Microbial Composition of Microbial Communities Communities Lipid AnalysisLipid Analysis

Palmitic acidPalmitic acidi16:0i16:0

Linoleic acidLinoleic acid18:218:266

Fatty AcidsFatty AcidsPhospholipid Fatty AcidPhospholipid Fatty Acid

Plant and Microbial BiomassPlant and Microbial Biomass

100 300 500 700 900

10

20

30

Total Plant BiomassTotal Plant Biomassg/mg/m22

Mic

rob

ial B

iom

ass

Mic

rob

ial B

iom

ass

g C

/mg

C/m

-2-2Cedar Creek Old-Field ChronosequenceCedar Creek Old-Field Chronosequence

Zak, D.R., Zak, D.R., et al. et al. 1990. Biogeochemistry 11:111-1191990. Biogeochemistry 11:111-119

Plant Species Richness Plant Species Richness and and

Total Plant BiomassTotal Plant Biomass

0 5 10 15 20

500

1000

1500

Number of Plant SpeciesNumber of Plant Species

Tot

al P

lan

t B

iom

ass

Tot

al P

lan

t B

iom

ass

g/m

g/m

-2-2RR22 = 0.968 = 0.968P < 0.001P < 0.001

Analysis of Covariance - Adjust Means for Differences in Total Plant Biomass Among Diversity Treatments.

Assumption: Total Plant Biomass is a Surrogate for Detritus Production in Plant Communities that are Rapidly Accumulating Biomass.

Plant Species Richness Plant Species Richness and and

Microbial Community BiomassMicrobial Community Biomass

Mic

rob

ial B

iom

ass

Mic

rob

ial B

iom

ass

pm

ol P

LF

A/g

pm

ol P

LF

A/g

Number of Plant SpeciesNumber of Plant Species

1400014000

1500015000

1600016000

1700017000

1800018000

1900019000

00 55 1010 1515 2020

RR22 = 0.983 = 0.983P < 0.001P < 0.001

Lea

set

Sq

uar

e M

ean

Lea

set

Sq

uar

e M

ean

Mic

rob

ial B

iom

ass

Mic

rob

ial B

iom

ass

pm

ol P

LF

A/g

pm

ol P

LF

A/g

Number of Plant SpeciesNumber of Plant Species

1400014000

1500015000

1600016000

1700017000

1800018000

00 55 1010 1515 2020

Plant Species Richness Plant Species Richness and and

Microbial Community BiomassMicrobial Community Biomass

Least Square Means Adjusted for Differences in Plant Least Square Means Adjusted for Differences in Plant Biomass Among Diversity TreatmentsBiomass Among Diversity Treatments

00 55 1010 1515 2020

0.1840.184

0.1980.198

0.2120.212

0.2260.226

0.2400.240

Fun

gal P

LF

A:B

acte

rial

PL

FA

Fun

gal P

LF

A:B

acte

rial

PL

FA

Number of Plant SpeciesNumber of Plant Species

RR22 = 0.932 = 0.932P < 0.001P < 0.001

Plant Species Richness Plant Species Richness and and

Microbial Community CompositionMicrobial Community Composition

Number of Plant SpeciesNumber of Plant Species

Mol

e P

erce

nt

Mol

e P

erce

nt

BacteriaBacteria ActinomycetesActinomycetes FungiFungi

0.320.32

0.360.36

0.400.40a10Me16:0a10Me16:0

11 22 44 88 1616

**

**

** **

**

1.91.9

2.12.1

2.32.3

2.52.5

11 22 44 88 1616

i17:0i17:0

** ****

** **

17:017:0

0.500.50

0.540.54

0.580.58

11 22 44 88 1616 11 22 44 88 1616

a17:0a17:0

2.552.55

2.652.65

2.752.75

2.852.85

11 22 44 88 1616

cy19:0cy19:0

5.25.2

5.65.6

6.06.0

6.46.4

11 22 44 88 1616

i17:1i17:1

1.71.7

1.81.8

1.91.9

2.02.0

11 22 44 88 1616

br 15:0br 15:0

0.40.4

0.60.6

0.80.8

1.01.0

11 22 44 88 1616

**** ** ** **

**** ** ** **

10Me16:010Me16:0

4.04.0

4.24.2

4.44.4

4.64.6**

**

**4.84.8

****

****

****

**

** ** ** ** **

****

**

** **

1616

6.86.8

7.27.2

7.67.6

11 22 44 88

18:118:19c9c

1.01.0

3.03.0

5.05.0

7.07.0

9.09.0

11 22 44 88 1616

18:218:266

3.43.4

3.83.8

4.24.2

11 22 44 88 1616

16:116:15c5c

** ** ****

**

**

**

****

**

****

****

**

1.81.8

1.91.9

2.02.0

2.12.1

11 22 44 88 1616

10Me18:010Me18:0

** ** ** ** **

Plant Species Richness Plant Species Richness and and

Microbial Community CompositionMicrobial Community Composition

Astericks are Least Square Means Adjusted for Plant BiomassAstericks are Least Square Means Adjusted for Plant Biomass

Plant Species Richness Plant Species Richness and and

Microbial RespirationMicrobial Respiration

Mic

rob

ial R

esp

irat

ion

Mic

rob

ial R

esp

irat

ion

mol

CO

mol

CO

22 • g

• g

-1

-1 •• dd

-1-1

1.01.0

1.51.5

2.02.0

2.52.5

00 55 1010 1515 2020

Number of Plant SpeciesNumber of Plant Species

RR22 = 0.953 = 0.953P < 0.001P < 0.001

Number of Plant Species0 5 10 15 20

1.5

1.6

1.7

1.8

1.9

2.0

2.1

Lea

st S

qu

are

Mea

nL

east

Sq

uar

e M

ean

Mic

rob

ial R

esp

irat

ion

Mic

rob

ial R

esp

irat

ion

mol

CO

mol

CO

22 • g

• g

-1

-1 •• dd

-1-1

Plant Species Richness Plant Species Richness and and

Microbial Nitrogen TransformationsMicrobial Nitrogen Transformations

Gro

ss N

Im

mob

iliza

tion

Gro

ss N

Im

mob

iliza

tion

g N

• g

g N

• g

-1-1 •

d •

d-1-1

00 55 1010 1515 20200.70.7

0.90.9

1.11.1

1.31.3

1.51.5

Gro

ss N

Min

eral

izat

ion

Gro

ss N

Min

eral

izat

ion

g N

• g

g N

• g

-1-1 •

d •

d-1-1

00 55 1010 1515 20200.70.7

0.90.9

1.11.1

1.31.3

1.51.5

RR22 = 0.799 = 0.799P < 0.001P < 0.001

Number of Plant Species Number of Plant Species

Gross mineralization was not greater in plots with legumes, compared to plots without legumes

Plant Species Richness Plant Species Richness and and

Gross Nitrogen MineralizationGross Nitrogen Mineralization

Adjusted for Differences in Plant Biomass & Soil Organic Matter ContentAdjusted for Differences in Plant Biomass & Soil Organic Matter Content

Gro

ss N

Min

eral

izat

ion

mg

N •

g C

-1 •

d-1

150

200

250

300

0 5 10 15 20Number of Plant Species

Lea

st S

qu

are

Mea

ns

Gro

ss N

Min

eral

izat

ion

g N

• g

-1 •

d-1

0.9

1.0

1.1

1.2

0 5 10 15 20

Number of Plant Species

RR22 = 0.320 = 0.320P < 0.001P < 0.001

RR22 = 0.668 = 0.668P < 0.001P < 0.001

00 55 1010 1515 2020

55

1010

1515

Tot

al P

lant

Nitr

ogen

Tot

al P

lant

Nitr

ogen

g N

mg

N m

-2-2

Number of Plant SpeciesNumber of Plant Species

RR22 = 0.967 = 0.967P < 0.001P < 0.001

Plant Species Richness Plant Species Richness and the and the

Nitrogen Content of Plant BiomassNitrogen Content of Plant Biomass

Plant Diversity, Microbial Communities & Ecosystem Function: Plant Diversity, Microbial Communities & Ecosystem Function: Are There Any Links? Are There Any Links?

ConclusionsConclusionsPlant Species Richness Indirectly Influenced Microbial Plant Species Richness Indirectly Influenced Microbial Community Biomass, Fungal Abundance, and Community Biomass, Fungal Abundance, and Respiration by Fostering Higher Plant Productivity and Respiration by Fostering Higher Plant Productivity and Detritus Inputs to Soil.Detritus Inputs to Soil.

Plant Species Richness Directly Increased Gross N Plant Species Richness Directly Increased Gross N Mineralization and N Supply to Plants, Which Fed Mineralization and N Supply to Plants, Which Fed Forward to Further Enhance Plant Productivity.Forward to Further Enhance Plant Productivity.

Mechanisms for This Direct Effect?Mechanisms for This Direct Effect?

Research Products from McIntire-Stennis SupportResearch Products from McIntire-Stennis Support

PublicationsPublications

Zak, D.R., W.E. Holmes, D.C. White, A. Peacock & D. Zak, D.R., W.E. Holmes, D.C. White, A. Peacock & D. Tilman. 2003. Plant diversity, soil microbial Tilman. 2003. Plant diversity, soil microbial

communities and ecosystem function: are there communities and ecosystem function: are there any any links? Ecology links? Ecology in press.in press.

Grant SubmissionsGrant Submissions

Zak, D.R. Plant diversity and ecosystem function are linked by Zak, D.R. Plant diversity and ecosystem function are linked by soil microbial communities. Submitted to USDA Soils soil microbial communities. Submitted to USDA Soils & Soil Biology Program - October 23, 2002.& Soil Biology Program - October 23, 2002.