Evaluation of Soil Microbial Communities Between Black Locust (Robinia pseudoacacia) and Tulip Poplar (Liriodendron tulipifera) in a Pennsylvania Forest
Cramer, Sherry A.* and Karl W. Kleiner, Department of Biological Sciences, York College of Pennsylvania, York, PA 17405.
Our hypothesis was: Since black locust trees add
nitrogen back into the soil, there should be a lower
microbial diversity around the nitrogen-fixing black locust
trees when compared to the non-nitrogen fixing tulip
poplar (Liriodendron tulipifera) species.
1. Nitrate nitrogen amounts were quantified using the
Cadmium Reduction analysis with the HACH water
testing kit.
2. Functional richness and functional evenness were
calculated. Functional diversity was calculated using the
Shannon Diversity Index. (Cox 1996).
Phenolics
(absorbance @ 720 nm)
TP 4m
BL 8m
The effect of tree species and distance were analyzed using a
two-way ANOVA (SPSS).
0.25
BL 4m
TP 4m
BL 8m
TP 8m
Figure 5. Mean ( s.e.) soil phenolics for black locust
(N=11) and tulip poplar (N=11) at two distances.
Species effect (p=0.661), distance effect (p=0.708),
distance x species(p=0.477).
DISCUSSION
Our hypothesis that there would be lower soil microbial
diversity around the nitrogen-fixing black locust trees was
not supported. Trends were lower in functional richness and
evenness in the soil surrounding black locust, but diversity,
nitrogen, or phenolics did not differ.
The lack of a difference in the microbial communities may be due
to one or more of these possibilities:
15
0.75
0.50
0.25
Black Locust (
)
Tulip Poplar (-------)
10
5
0
0.0
0.00
BL 4m
TP 4m
BL 8m
TP 8m
Figure 2. Mean ( s.e.) functional eveness for black
locust (N=11) and tulip poplar (N=11) at two distances.
Species effect (p=0.911), distance effect (p=0.165),
distance x species (p=0.687).
0.1
0.2
0.3
0.4
0.5
0.6
0.7
NO3-N (mg/g soil)
Figure 6. Relationship between soil nitrate nitrogen and
functional diversity for black locust (N=11) and tulip
poplar (N=11). Black locust: r 2=0.01553, p=0.5806,
tulip poplar: r 2=0.00162, p=0.859.
1. As expected, the trend of lower functional richness and
functional evenness are present in black locust, but not
significant. This may be due to a small sample size.
2. In August 2002, our time of sampling, Pennsylvania had 1.5
inches of rain in a seven week period and had an annual deficit
of 10.7 inches (Horst 2002). The control of microbial
community structure primarily comes from the amount of soil
moisture (Schimel et al. 1999) and may have minimized
differences between the species.
3. Our soil sample was a heterogeneous mix of mineral soil and
organic matter, which may have contributed to high variation
among the samples.
LITERATURE CITED
3
2
1
0
BL 4m
TP 4m
BL 8m
TP 8m
Figure 3. Mean ( s.e.) functional diversity for black
locust (N=11) and tulip poplar (N=11) at two distances.
Species effect (p=0.919), distance effect (p=0.114),
distance x species (p=0.453).
Black Locust (
)
Tulip Poplar (-------)
15
Cowan, Marjorie Murphy. 1999. Plant Products as Antimicrobial Agents. Clinical
Microbiology Review 12(4):564-582.
5
Cox, George W. 1996. Measurement of Species Diversity. Pages 190-192. Lab
Manual of General Ecology. Wm. C. Brown Publishers, Dubuque, IA.
0.5
1.0
1.5
2.0
2.5
Phenolics
(absorbance @ 720 nm)
Figure 7. Relationship between soil phenolics and functional
diversity for black locust (N=11) and tulip poplar (N=11).
Black locust: r2=0.01324, p=0.6102, tulip poplar: r 2=0.1488,
p=0.0763.
0.3
RESULTS
0.2
1. As expected, functional richness (Figure 1) and
functional evenness (Figure 2) were lower in black
locust compared to tulip poplar, but the trends were not
significant.
0.1
BL 4m
TP 4m
BL 8m
TP 8m
Figure 4. Mean ( s.e.) soil nitrogen for black locust
(N=11) and tulip poplar (N=11) at two distances.
Species effect (p=0.664), distance effect (p=0.892),
distance x species (p=0.182).
Bever, James, D. 1994. Feedback between plants and their soil communities in an
old field community. Ecology 75(7):1956-1977.
Bever, James D., Kristi M. Westover, and Janis Antonovics. 1997. Incorporating
the soil community into plant population dynamics: the utility of the feedback
approach. Journal of Ecology 85:561-573.
10
0
0.0
0.0
3. Phenolics were analyzed using a colorimetric Prussian
Blue Assay (Price and Butler 1977). Phenolics are known
to have antimicrobial and antifungal properties.
0.50
TP 8m
Figure 1. Mean ( s.e.) functional richness for black
locust (N=11) and tulip poplar (N=11) at two distances.
Species effect (p=0.521), distance effect (p=0.190),
distance x species (p=0.656).
NO3-N (mg/g soil)
Average well color development was measured using Biolog
microtiter plates (Garland and Mills 1991). Absorbance was
read using the Wallac Victor2 Microtiter Plate reader.
0.75
0.00
BL 4m
METHODS
Soil was collected at two distances (4 m and 8 m) from around
11 black locust and 11 tulip poplar trees (N = 5 for each
distance) located in a York County, Pennsylvania forest. All five
samples from one distance were pooled together to create one
sample. Yellow poplar trees stood at least 10 meters away from
a black locust tree.
25
Functional Diversity
Traditionally, abiotic factors and competition have been
responsible for influencing plant growth (Westover et al. 1997;
Bever 1994). Interactions between soil microbes and plants
have been shown to reciprocally influence their community
structure. Plants can change the soil microbial community and
soil microbes can affect the growth rate of a plant population
(Bever et al. 1997). In a given community, positive and
negative feedback can be present. Negative feedback occurs
when a plant species decreases its own growth rate due to the
soil microbial community it supports. This feedback, although
negative, is essential for encouraging community diversity and
stability (Bever 1994). Black locust (Robinia pseudoacacia)
hosts a nitrogen fixing bacteria that returns significant amounts
of nitrogen back in the soil (Kleiner et al. 2002). Nitrogen has
also been shown to decrease the amount of plants around the
tree and among the plant community (Redding 2001).
50
Funtional Diversity
INTRODUCTION
1.00
0
Functional Diversity
Soil microbial communities are strongly linked with the diversity in
plant communities. However, there can be species-specific plant
effects on soil microbe populations. We compared the diversity
of microbial communities from the soil around tulip poplar
(Liriodendron tulipifera) and black locust (Robinia pseudoacacia)
trees in a mid-successional forest in York County, Pennsylvania.
Black locust is a nitrogen-fixing tree species that is known to
contribute substantial amounts of nitrogen to the soil. We
hypothesized that there would be lower microbial diversity
around the nitrogen-fixing black locust tree when compared to
tulip poplar. We evaluated the functional diversity of microbial
communities using Biolog EcoPlates. There was no difference in
functional evenness, functional richness, and functional diversity.
Functional Evenness
ABSTRACT
Functional Richness
75
2. There was no significant difference between the
species in abiotic factors, nitrogen (Figure 4) and
phenolics (Figure 5).
3. There was no relationship between either nitrogen
(Figure 6) or phenolics (Figure 7) and functional
diversity in black locust or tulip poplar.
Garland, Jay and Aaron Mills. 1991. Classification and Characterization of
Heterotrophic Microbial Communities on the Basis of Patterns of CommunityLevel Sole-Carbon-Source Utilization. Applied and Environmental Microbiology
57(8):2351-2359.
Horst, E.J. 2002. MUWIC Weather Newsletter. September 3, 2002.
Kleiner, K.W., J. M. Mann, and W.D. Eaton. 2000. Does it matter who your
neighbor is? The effect of black locust (Robinia pseudoacacia) on the growth
of neighboring trees. Journal of the Pennsylvania Academy of Science 73:162
(abstract).
Price, M.L. and L.G. Butler. 1977. Rapid visual estimation and spectrophotometric
determination of tannin content of sorghum grain. Journal of Agricultural Food
Chemistry 25:1263-1273.
Redding, Mike. 2001. The Effect of a Nitrogen-Fixing Tree (Robinia pseudoacacia)
on the Productivity and Diversity of the Understory Shrub Communities.
Journal of the Pennsylvania Academy of Science 74:146 (abstract)
Schimel, Joshua P., Jay M. Gulledge, Joy S. Clein-Curley, Jon E. Lindstrom, and
Joan F. Braddock. 1999. Moisture effects on microbial activity and community
structure in decomposing birch litter in the Alaskan taiga. Soil Biology and
Chemistry 31: 831-838.
Westover, Kristi M., Ann C. Kennedy, and Steven E. Kelley. 1997. Patterns of
rhizophere microbial community structure associated with co-occurring plant
species. Journal of Ecology 85:863-873.
ACKNOWLEDGEMENTS
Thanks to Mike Quigley for his many hours helping me clean up soil in
the lab.