Transcript ecology project[1]

Mycorrhizae Influence Plant
Community Structure and
Diversity in Tallgrass Prairie
Ashley Popovich
Jenn McQuade
Alyssa Novarro
Molly Stetz
Introduction
• Arbuscular mycorrhizal (AM) fungi are
ubiquitous in terrestrial plant communities,
forming symbiotic associations with the roots
of the majority of plant species.
Mutualism
• biological interaction that is beneficial
to both parties.
Benefits—fungus
o gains carbon source
Benefits—host
o enhanced uptake and transport of poorly mobile soil
nutrients.
o improved water relations.
o reduced pathogenic infections.
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.
Objective of Study
METHODS
Experimental Site
•
Conducted at the Konza Prairie Research Natural Area (KPRNA)
•
Vegetation dominated by perennial, warm season matrix grasses
o Big Bluestem (Andropogen gerardii Vit.)
o Little Bluestem (Andropogon scoparius Michx)
o Indian grass (Sarghastrum nutans [L.] Nash)
o 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
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
o 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:
o Glomus aggregatum
o G. Constictum
o G. Macrocarpun
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
o
o
o
o
Two annually burned upland units
Two infrequently burned upland units
One annually burned lowland unit
One infrequently burned lowland unit
• Within each unit:
o 20 replicate permanent 2 x 2m plots were created 2m apart from each
other
o 10 plots are control plots, other 10 are experimental plots
Experimental plots
• Plot area is treated to suppress AM fungi
• Treated with applications of fungicide benomyl
o 7.5 L of benomyl per plot
o 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
o KPRNA also evaluated the effectiveness of benomyl themselves
• Control plots were given 7.5 L of water every two weeks
during the growing season
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
o Frames, containing 10 - 1m long parallel vertical pins arranged 10cm
apart, were placed systematically over four locations 25cm apart in the
central 1m2 of each plot
o 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
RESULTS
• 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.
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
Species Richness:
6.0 species/m2 (CONTROL)
7.1 species/m2 (Benomyl)
Species Diversity:
No initial difference between
fungicide-treated and control plots
Species Diversity:
1993: 14% greater than control
1995: 42% higher than control
Results
• Fungicide treatment resulted in NO change in total
aboveground canopy density or biomass.
(Hartnett et al. 1999)
DISCUSSION
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%)
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
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
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
Possible Future Studies
• How are the results of this experiment affected by other
factors
- Grazing, fire, water availability
Bibliography
Hartnett, David C., Gail W. T. Wilson. Mycorrhize Influence
Plant Community Structure And Diversity In
Tallgrass
Prairie. Ecology 80, no, 4 (1999): 1187-1195.