1. Ashley Popovich Jenn McQuade Alyssa Novarro Molly Stetz
Mycorrhizae Influence Plant Community Structure and Diversity in Tallgrass Prairie
Ashley Popovich
Jenn McQuade
Alyssa Novarro
Molly Stetz

2. Introduction
Arbuscular mycorrhizal (AM) fungi are ubiquitous in terrestrial plant communities, forming symbiotic associations with the roots of the majority of plant species.
The fungus spreads threadlike feeding structures called hyphae into the soil. This type of colonization allows the host plant to develop a much larger root system, sometimes 100 times in length with up to 2,000 times more surface area. 

3. Mutualism biological interaction that is beneficial to both parties.
Benefits—fungus
gains carbon source
Benefits—host
enhanced uptake and transport of poorly mobile soil nutrients.
improved water relations.
reduced pathogenic infections.
The increased root surface area provides more room for water and nutrients to be taken in. The fungus serves as a bridge between the host plant and available nutrients. The hyphae help to break down organic material thus helping to release nutrients to the plant.
**** under certain conditions fungi may result in no benefit or detrimental effects on the host.
****this raises the question if mycorrhizal associations are mutualistic or may vary along a symbiotic continuum from strong mutualism to antagonism.

4. Previous Studies
Involved growing plants individually in pots in the glasshouse or laboratory. OR
In monospecific stands
Field data relating plant performance to mycorrhizal symbiosis are inconsistent with these techniques.
Scientists h
ypothesize that mycorrhizas can regulate plant competitive relationships and the composition, species diversity, and successional dynamics of some plant communities, although the patterns and mechanisms remain the subject of debate.

5. Objective of Study

6. METHODS

7. Experimental Site
Conducted at the Konza Prairie Research Natural Area (KPRNA)
Vegetation dominated by perennial, warm season matrix grasses
Big Bluestem (Andropogen gerardii Vit.)
Little Bluestem (Andropogon scoparius Michx)
Indian grass (Sarghastrum nutans [L.] Nash)
Switchgrass (Panicum virgatum L.)
High diverse mixture of less abundant plant species of warm and cool season grasses, composites, legumes, other forbs, and woody species
Vascular flora of KPRNA includes over 500 species representing over 90 families

8. Experimental site (continued)
Temperatures range from -2.7°C to 26.6°C
Total annual precipitation of 835mm, 75% of which is during the growing season
Mean annual rainfall of 858mm during the study
Soils consist of Chase silt loams and silty clay loams
Spores of 13 species of mycorrhizal fungi were identified in the area
Dominant fungi were:
Glomus aggregatum
G. Constictum
G. Macrocarpun

9. Experiment Organization
KPRNA is divided into 60 watersheds units .55km2
Units are specifically prescribed unique burning regimes and grazing treatments
For this study, six ungrazed units are used
Two annually burned upland units
Two infrequently burned upland units
One annually burned lowland unit
One infrequently burned lowland unit
Within each unit:
20 replicate permanent 2 x 2m plots were created 2m apart from each other
10 plots are control plots, other 10 are experimental plots

10. Experimental plots Plot area is treated to suppress AM fungi
Treated with applications of fungicide benomyl
7.5 L of benomyl per plot
Applied every two weeks during the growing season as a soil drench
Benomyl has the fewest drawbacks out of all potential methods for suppressing AM fungi, and is most effective with no direct effects on a wide range of plants
KPRNA also evaluated the effectiveness of benomyl themselves
Control plots were given 7.5 L of water every two weeks during the growing season

11. Sampling
Samples were taken from the plots during the months of May and September from the years of 1991 to 1995
Measurements were taken using a modified point- frame method
Frames, containing m long parallel vertical pins arranged 10cm apart, were placed systematically over four locations 25cm apart in the central 1m2 of each plot
Every contact between the pins and above ground plant structure was recorded; this shows the change in plant growth over time
The goal of this method was to observe the affects of AM fungi on plant species richness, diversity, and evenness

12. RESULTS

13. Significant decrease in abundance of dominant warm-season grass species with benomyl application.
EXCEPTION: Switchgrass (Panicum virgatum)
Warm-season and cool-season grasses increased significantly in percent cover with AM fungal suppression
Fungal suppression = ↑ in relative abundances of several tallgrass prairie forbs and ↑diversity.
Benomyl applications resulted in a significan decrease in the percent cover of the dominant warm-season grasses. The only exception to this pattern among the warm-season tallgrasses was switchgrass, which showed no significant difference between control and fungicide-treated plots in any year.
Conversely, several subdominant warm-season and cool-season grasses increased significanly in percent cover over the same period with AM fungal suppression. The cool-season C3 plants showed the largest responses increasing in cover to greater than 150% than that of the control plants by Two subdominant warm-season C4 grasses of side oats grama and prairie dropseed increased significantly with mycorrhizal suppression to about 50% greater than the controls by 1993.
Heath aster, aromatic aster, pitcher’s sage, false bonset, and prairie goldenrod all increased significanly in relative abundances with fungal suppression than the control plots. The net result of these different species responses was a significant increase in components of plant species diversity with suppression of AM fungi of the 5-yr. period.

14. Results
Benomyl-treated plots increases species richness and plant species diversity.
1991
1993 and 1995
Species Richness:
No initial differences between fungicide-treated and control plots
6.0 species/m2 (CONTROL)
7.1 species/m2 (Benomyl)
Species Diversity:
No initial difference between fungicide-treated and control plots
1993: 14% greater than control
1995: 42% higher than control
Plant species richness showed no initial differences between fungicide-treated and control plots in 1991, but was significantly greater in fungicide-treated compared to control plots in both spring and fall of 1993 and In both 1993 and 1995, mean plant species richness was 6.0 species/m2 in control plots and 7.1 species/m2 in benomyl-treated plots. This showed similar patterns with relative species abundances in that there was no initial differences in 1991 and significantly greater evenness in the mycorrhizal-suppressed plots compared to controls.
Plant species diversity was significantly increased by suppression of AM fungi. For both the spring and fall vegetation sampling, the enhancement in plant species diversity with fungicide treatment was greater in 1995 than in In 1993 the mean diversity of benomyl-treated plots was 14% greater than mycorrhizal control plots. In 1995 the effect of benomyl treatment was enhanced even further and diversity of benomyl-treated plots was 42% higher than controls.

15. Results
Fungicide treatment resulted in NO change in total aboveground canopy density or biomass.
Despite such a shift in plant community composition and species diversity due to AM fungal suppression, the fungicide treatment resulted in no change in total aboveground canopy density or biomass. Total canopy density varied considerably between spring and fall sampling and among years, but was almost identical in control and fungicide-treated plants at all sample dates from 1991 to 1995.
Plant species richness, evenness, diversity, and canopy cover of control and Benomyl plots are represented in these graphs. Solid bars represent fungicide-treated plots, and open bars represent controls. Bars represent means of six transects (10 plots/transect) for each sampling date. An asterisk above a bar indicates that control plots are significantly different from fungicide plots as determined by least significant difference.
(Hartnett et al. 1999)

16. DISCUSSION

17. Changes in species composition
C4 grasses declined
Mycorrhizal dependency/responsiveness of >99%
Andropogon gerardii, Sorghastrum nutans, & A. scoparius
C3 grasses and forbs increased concomitantly
Subordinate species; less dependent on mycorrhizae
Aster ericoides (63%), Salvia azurea (87%), Dichanthelium oligosanthes (50%) & Kuhnia eupatroides (22%)

18. No effect on total aboveground biomass
Estimated by total number of pin-contacts per plot
Strong suppression of competitively dominant grasses
Equal increase in the subordinate species
Subordinate competitors experienced competitive release when mycorrhizae were suppressed

19. Mycorrhizae decreases floristic diversity in tallgrass prairies
“Different host plants species responses to colonization by mycorrhizal fungi result in changes in species diversity if the dominant competitors are significantly more strongly or more weakly mycotrophic than their neighbors”
The dominant C4 grasses were more strongly mycotrophic than their neighbors
Fungal suppression reduces their dominance, leading to an increase in species diversity

20. CONCLUSION
Mycorrhizal symbiosis has a large impact at the community level
-Key factor in explaining the dominance of C4 grasses and limiting plant species evenness and diversity
Alterations in belowground fungi and rhizosphere processes have large effects on aboveground floristic composition and diversity at Konza Prairie

21. Possible Future Studies
How are the results of this experiment affected by other factors
- Grazing, fire, water availability

22. Bibliography
Hartnett, David C., Gail W. T. Wilson. Mycorrhize Influence Plant Community Structure And Diversity In Tallgrass Prairie. Ecology 80, no, 4 (1999):