1. Does Biological Diversity Control Ecosystem Function?
Donald R. Zak
School of Natural Resources & Environment
University of Michigan

2. Human Activity and the Loss of Biological Diversity
Clearing and Fragmentation of Tropical Forests

3. Human Activity and the Loss of Biological Diversity
Fire Suppression in Temperate Grasslands

4. Human Activity and the Loss of Biological Diversity
Introduction of Exotic Predators
Red Fox
Brown Rat
Common
Mongoose
Brown Tree Snake

5. Biological Diversity & Ecosystem Function
What happens to ecosystem function when the abundance of particular species or groups of species are reduced?

6. Biological Diversity & Ecosystem Function
Research into the influence of biological diversity on ecosystem function has been motivated by three basic questions:
Does biological diversity influence rates of
ecosystem processes?
Is the relationship positive or negative?
What mathematical expression describes this
relationship?

7. What are the Mechanisms Linking Plant Diversity to Ecosystem Function?
Lack of specific mechanisms linking plant diversity & ecosystem function, especially for the influence of plant diversity on higher trophic levels.

8. Plant Diversity, Microbial Communities & Ecosystem Function: Are There Any Links?
Organic Substrates
Production & Biochemistry
Nevertheless, our results and those summarized from the literature suggest that the rising atmospheric CO2 concentration will not initially slow rates of C and N cycling in the plant-soil system.
Thank you.
Soil Environment
Temperature & Water Potential
Soil Microbial Communities
Composition & Function

9. Plant Diversity & Microbial Communities Conceptual Model
Plant Community Composition & Diversity +
Litter Production
Above- & Belowground +
Substrate Availability
Amount & Biochemical
Composition +
Soil Microbial Community Composition & Function +
Ecosystem Processes
Soil C & N Cycling

10. Hypotheses:
Because plant species differ in their biochemical composition, changes in diversity should alter the production as well as range of compounds in detritus that limit, and thus control, the composition and function of heterotrophic microbial communities.
Changes in microbial community composition & function will alter ecosystem C and N cycling.

11. Cedar Creek Natural History Area Biodiversity Experiment

12. Cedar Creek Natural History Area Biodiversity Experiment
Experimental Plant Diversity Treatments m2 Plots
Random Draw of 18 Native Grasses, Forbs, and Woody Plants
Species Richness Treatments
1, 2, 4, 8, 16 Species
30 Replications of Each Species Richness Treatment

13. Cedar Creek Natural History Area Biodiversity Experiment
C4 Grasses
Andropogon gerardi
Buchloe dactyloides
Panicum virgatum
Schizachyrium scoparium
Sorghastum nutans
Sporobolus cryptandrus
C3 Grasses
Agropyron smithii
Elymus canadensis
Koeleria cristata
Poa pretensis
Legumes
Amorpha canescens Astragalus canadensis Lespedeza capatata
Lupinus perennis
Petalosetmum purpureum
Woody
Quercus ellipsoidalis
Quercus macrocarpa
Forb
Monarda fistulosa

14. Cedar Creek Natural History Area Biodiversity Experiment
After 7 Years of Plant Growth in the Experimental Treatments, We Measured:
Microbial Community Composition
- Phospholipid Fatty Acid Analysis
Microbial Community Function
- Microbial Respiration
- Gross Rates of Soil Nitrogen Cycling

15. Composition of Microbial Communities
Lipid Analysis
Phospholipid Fatty Acid
Fatty Acids
H H H H H H H H H H H H H H O
| | | | | | | | | | | | | | ||
Palmitic acid
i16:0
H-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 O
Linoleic acid
18:2w6
| | | | | | | | | | | | | ||
H-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 H

16. Plant and Microbial Biomass
Cedar Creek Old-Field Chronosequence
Zak, D.R., et al Biogeochemistry 11: 30 20
Microbial Biomass
g C/m-2 10
100
300
500
700
900
Total Plant Biomass
g/m2

17. Plant Species Richness
and
Total Plant Biomass
1500
Analysis of Covariance - Adjust Means for Differences in Total Plant Biomass Among Diversity Treatments.
R2 = 0.968
P < 0.001
1000
Total Plant Biomass
g/m-2
Assumption: Total Plant Biomass is a Surrogate for Detritus Production in Plant Communities that are Rapidly Accumulating Biomass.
500 5 10 15 20
Number of Plant Species

18. Plant Species Richness and Microbial Community Biomass
19000
18000
R2 = 0.983
P < 0.001
Microbial Biomass
pmol PLFA/g
17000
16000
15000
14000 5 10 15 20
Number of Plant Species

19. Plant Species Richness and Microbial Community Biomass
Least Square Means Adjusted for Differences in Plant Biomass Among Diversity Treatments
18000
17000
Leaset Square Mean
Microbial Biomass
pmol PLFA/g
16000
15000
14000 5 10 15 20
Number of Plant Species

20. Plant Species Richness and Microbial Community Composition
0.240
0.226
R2 = 0.932
P < 0.001
0.212
Fungal PLFA:Bacterial PLFA
0.198
0.184 5 10 15 20
Number of Plant Species

21. Number of Plant Species
Plant Species Richness
and
Microbial Community Composition
Bacteria
Actinomycetes
Fungi
Astericks are Least Square Means Adjusted for Plant Biomass
1.0
2.0
3.4
3.8
4.2 1 2 4 8 16
16:15c *
br 15:0
2.5
i17:1
i17:0 * * *
0.8 *
1.9 * * * *
2.3 * * * * * * *
1.8
2.1
0.6
Mole Percent
1.7
1.9
0.4 1 2 4 8 16 1 2 4 8 16 1 2 4 8 16
17:0
10Me16:0
1.8
1.9
2.0
2.1 1 2 4 8 16
10Me18:0 * *
18:19c
0.58
4.8
7.6 *
4.6 * * * *
0.54 * * * * * *
4.4 *
7.2 * *
4.2
0.50
6.8
4.0 1 2 4 8 16 1 2 4 8 16 1 2 4 8 16
2.85
9.0
a17:0
cy19:0 *
a10Me16:0
18:26 * *
6.4 *
0.40 * * * * * *
7.0 *
2.75 *
6.0 * * * * * * * *
0.36
5.0
2.65
5.6
3.0
2.55
5.2
0.32
1.0 1 2 4 8 16 1 2 4 8 16 1 2 4 8 16 1 2 4 8 16
Number of Plant Species

22. Number of Plant Species
Plant Species Richness
and
Microbial Respiration
2.5
Number of Plant Species 5 10 15 20
1.5
1.6
1.7
1.8
1.9
2.0
2.1
Microbial Respiration
Least Square Mean
mol CO2 • g-1 • d-1
R2 = 0.953
P < 0.001
2.0
Microbial Respiration
mol CO2 • g-1 • d-1
1.5
1.0 5 10 15 20
Number of Plant Species

23. Plant Species Richness and Microbial Nitrogen Transformations
1.5
1.5
1.3
1.3
R2 = 0.799
P < 0.001
Gross N Mineralization
g N • g-1 • d-1
Gross N Immobilization
g N • g-1 • d-1
1.1
1.1
0.9
0.9
0.7
0.7 5 10 15 20 5 10 15 20
Number of Plant Species
Number of Plant Species
Gross mineralization was not greater in plots with legumes, compared to plots without legumes

24. Gross N Mineralization Gross N Mineralization
Plant Species Richness
and
Gross Nitrogen Mineralization
Adjusted for Differences in Plant Biomass & Soil Organic Matter Content
1.2
300
1.1
250
Gross N Mineralization
Least Square Means
g N • g-1 • d-1
Gross N Mineralization
mg N • g C -1 • d-1
R2 = 0.320
P < 0.001
R2 = 0.668
P < 0.001
1.0
200
0.9
150 5 10 15 20 5 10 15 20
Number of Plant Species
Number of Plant Species

25. Plant Species Richness and the Nitrogen Content of Plant Biomass15
R2 = 0.967
P < 0.001 10
Total Plant Nitrogen
g N m-2 5 5 10 15 20
Number of Plant Species

26. Plant Diversity, Microbial Communities & Ecosystem Function: Are There Any Links?
Conclusions
Plant Species Richness Indirectly Influenced Microbial Community Biomass, Fungal Abundance, and Respiration by Fostering Higher Plant Productivity and Detritus Inputs to Soil.
Plant Species Richness Directly Increased Gross N Mineralization and N Supply to Plants, Which Fed Forward to Further Enhance Plant Productivity.
Mechanisms for This Direct Effect?

27. Research Products from McIntire-Stennis Support
Publications
Zak, D.R., W.E. Holmes, D.C. White, A. Peacock & D. Tilman Plant diversity, soil microbial communities and ecosystem function: are there any links? Ecology in press.
Grant Submissions
Zak, D.R. Plant diversity and ecosystem function are linked by soil microbial communities. Submitted to USDA Soils & Soil Biology Program - October 23, 2002.