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2009 SOUTHEASTERN NATURALIST 8(1):141–156
Microstegium vimineum Invasion Changes Soil Chemistry
and Microarthropod Communities in Cumberland Plateau
Deborah A. McGrath1,* and Meagan A. Binkley1
Abstract - Microstegium vimineum (Japanese Stiltgrass) is an exotic shade-tolerant
C4 grass that invades open and forested habitats throughout the southeastern United
States. Studies suggest that invasive plants can alter ecosystem biogeochemistry by
changing soil chemistry and biota. The objective of our study was to determine if
M. vimineum invasion induces soil chemical changes that alter litter microarthropod
communities in acidic, nutrient-poor upland forests of the Cumberland Plateau. In
a greenhouse experiment comparing forest soil in tubs seeded with M. vimineum
to those left unseeded over 1 year, we found that after 6 months, soil pH under M.
vimineum was significantly higher than that in the unseeded tubs. We compared
A-horizon chemistry, litter nutrients, and microarthropod community diversity in 3
forested sites with and without M. vimineum. We found higher pH, phosphorus (P),
and base cations, and lower aluminum (Al) in soil under dense M. vimineum growth
compared to soil under surrounding uninvaded understory. M. vimineum litter was
more P-rich and had a higher abundance of mites than the surrounding forest fl oor
over 3 sampling periods. However, microarthropod community evenness was lower
in M. vimineum litter, indicating a decrease in diversity. These results suggest that
a rapid rise in soil pH and P availability following M. vimineum colonization may
reduce litter microarthropod community diversity by favoring mites.
The upland forests of Tennessee’s southern Cumberland Plateau are
among the most diverse plant communities in the southeastern United
States (Ricketts et al. 1999). The acidic sandstone-derived soils of the
upland ridges support drought-resistant mixed oak-hickory forests that are
increasingly undergoing conversion and fragmentation with surrounding
land use change (McGrath et al. 2004), often resulting in the influx of nonnative
plant opportunists. The invasion of Microstegium vimineum (Trin.)
A. Camus (Japanese Stiltgrass) is of particular concern because of its
traits as a “super generalist” that allow this C4 grass to invade a variety of
habitats, including forest understories where it utilizes sunflecks (Cheplick
2005, Horton and Neufeld 1998, Leicht et al. 2005). Consequently, dense
stands of M. vimineum are found in fields and along roadsides, as well as in
forests across the region.
Studies show that introduced plants can change soil processes by using or
obtaining resources differently than native plants, often altering rhizosphere
or litter chemistry, biomass accumulation, water relations, or microclimate
1Department of Biology, University of the South, 735 University Avenue, Sewanee,
TN 37383-1000. *Corresponding author - firstname.lastname@example.org.
142 Southeastern Naturalist Vol. 8, No. 1
(Ehrenfeld 2003, Vitousek 1990). By altering both habitat and substrate, soil
and litter changes following plant invasion can infl uence the composition
of soil biota, which in turn may affect soil food webs, litter decomposition
rates, mineralization, and biogeochemical cycling within the system (Belnap
and Phillips 2001, Scott et al. 2001, Yeates and Williams 2001). Researchers
report higher soil pH and extractable N under M. vimineum, as well as rhizosphere
microbial communities that differ from those under adjacent native
plants (Ehrenfeld et al. 2001, Kourtev et al. 2002).
As microbial grazers and saprophages, soil microarthropods such as
mites (Acari) and collembolans (Collembola) significantly contribute to
the decomposition and biogeochemical cycling of forest-floor habitats.
Microarthropod populations are sensitive to disturbance and land-cover
change, and a few studies demonstrate that community diversity decreases
with monotypic leaf litter (Coleman et al. 2004, Hansen 2000, Migge et al.
1998). The nutrient status, physical structure, and pattern of litter decay
also influences microarthropod habitat, regardless of whether the litter is
comprised of one or many species (Hansen 2000). Thus, invasion-induced
changes in plant communities may have a profound effect on litter microarthropod
communities. While there is ample evidence that plant invasions
change soil chemistry, the impact of such changes on soil microarthropods
is less studied.
The objective of our study was to determine if M. vimineum invasion
rapidly changes soil chemistry and litter microarthropod communities,
potentially altering biogeochemical processes in acidic nutrient-poor upland
soils of the Cumberland Plateau. First, we conducted a greenhouse
experiment to determine how M. vimineum invasion changed upland forest
soil chemistry in a single growing season. We then studied mineral soil
and litter chemistry with and without M. vimineum on three upland sites,
each under a different forest type (mature and early successional hardwood,
and a pine plantation). We hypothesized that upland soils with dense M.
vimineum growth would have higher soil pH and greater cation availability
than surrounding soils not colonized by M. vimineum, which might induce
other changes, including differences in litter nutrients. We compared microarthropod
abundance, order richness, and community diversity between M.
vimineum litter and that of surrounding forest without M. vimineum on the
same site. Because M. vimineum produces dense mats of monotypic litter,
we predicted that M. vimineum-invaded patches would host less diverse microarthropod
communities than those in the surrounding forest fl oor.
A native to East Asia, M. vimineum is recognized as a common
invasive plant in 25 states from New Jersey to Texas (Barden 1987,
Morrison et al. 2007). M. vimineum is a sprawling annual grass with
branching stems that root from nodes, facilitating the establishment of
2009 D.A. McGrath and M.A. Binkley 143
thick, widespread infestations that are evident as dense litter mats after
the plant dies. The species flowers in early fall and produces a large seed
bank that remains viable for 5–7 years (Gibson et al. 2002). The small
seed is dispersed easily by water and animals, facilitating invasion in disturbed
locations such as floodplains, road banks, and hiking trails (Hunt
and Zaremba 1992, Redman 1995).
Field data were collected from 2005–2007 on upland sites near Sewanee,
TN, on the southern tip of the Cumberland Plateau (35º18'N
and 86º06'W). Derived from Pennsylvanian sandstone, upland soils are
typically acidic, nutrient poor, and drought-prone (McGrath et al. 2004).
These upland soils support oak-hickory forests dominated by Quercus
prinus L. (Chestnut Oak) and Q. velutina Lam. (Black Oak), with Acer
rubrum L. (Red Maple), (Nyssa sylvatica Marsh. (Black Gum), Sassafras
albidum (Nutt.) Nees (Sassafras), Oxydendron arboreum (L.) DC. (Sourwood),
and Vaccinium spp. (blueberry) in the middle and lower canopy.
We chose 3 sites representing different forest types, all located along
the same upland ridge within 10 km of each other. Originally all native
oak-hickory forest, two sites had been converted to different land covers.
Thus, the study included a >10-ha tract of mature (60+ years) oak-hickory
forest, a 40-year old 5-ha Pinus strobus L. (White Pine) plantation, and a
5-ha agricultural homestead abandoned 15 years ago and undergoing succession
(early successional forest). Although structurally different, the
mature and early successional forests were comprised of species typical
of the region’s upland oak-hickory complex.
Greenhouse and field soil chemistry
Prior to conducting our field studies, we used a greenhouse experiment
to determine if the growth of M. vimineum changed forest soil chemistry in
one season. Ten rectangular (36 x 30 x 14 cm) plastic basins were perforated
on the bottom for drainage and filled with a 5-cm layer of sterilized sand and
gravel, followed by a 15-cm layer of sieved and homogenized mineral soil
collected and composited from the top 10 cm of 5 uninvaded mature oakhickory
forests located within 10 km of the field sites. In June 2005, 1.0 g
M. vimineum seed, harvested from wild plants during the previous season,
was broadcast evenly over a 20- x 12.5-cm area (250 cm2) in 5 of the 10
basins and covered lightly with soil. Five basins were left unseeded, and all
10 basins were randomly assigned a position in the greenhouse and sprinkled
daily with water using an automated system. The M. vimineum treatment germinated,
densely covering the seeded area, and grew throughout the summer,
ending its lifecycle after fl owering in late November. Prior to sowing the M.
vimineum, a composite soil sample comprised of 5 cores extracted from the
top 5 cm was collected from each basin and analyzed for pH (in a 2:1 slurry
of deionized water using a pH meter), concentrations of Melich-III extractable
P, K, Mg, Ca, Al, and organic matter (%), and cation exchange capacity
144 Southeastern Naturalist Vol. 8, No. 1
(barium chloride method) by A&L Analytical Laboratories (Memphis, TN).
-), analyzed by cadmium reduction of air-dried samples, was
used as an index of N availability. Soil from both the unseeded basins and
beneath the M. vimineum was re-sampled and analyzed chemically twice at
6-month intervals (December 2005 and July 2006).
To determine the effect of M. vimineum and time on soil chemical
properties, the data were analyzed statistically using a repeated measures
ANOVA with a between subject factor of treatment (seeded vs. unseeded)
and a within subject factor of sampling interval (pre-seeding, and 6 and
12 months post-seeding) performed in SPSS 16.0 (SPSS, Inc., 2007). We
conducted post hoc multiple comparisons using two sample t-tests to detect
significant differences in mean soil properties between treatments within a
In August 2006, we compared chemical properties between soils with and
without dense (>90%) M. vimineum growth on 3 forested sites. In the understories
of the pine, and mature and early successional oak-hickory sites, we
collected 5 composite A-horizon soil samples (10 cores each, 0–5 cm depth)
beneath areas covered with dense, live M. vimineum and under surrounding
uninvaded forest vegetation. We realize these 5 samples do not represent
a true site replication, but we were looking for initial site differences that
could be explored in greater detail later. The sampled areas of M. vimineum
growth were well established, varied from 4–36 m2 in size, and were located
intermittently as densely colonized patches in the understory of each forest
site. Uninvaded surrounding forest soil samples were collected within 3
m around the edge of each patch colonized by M. vimineum. The air-dried
soil samples were sieved through a 2-mm mesh and analyzed for the same
properties described for the greenhouse experiment. To compare chemical
properties between soils dominated by patches of dense M. vimineum
growth and surrounding uninvaded overstory, the data were analyzed using
a multivariate ANOVA with factors of site (pine, mature, and early successional)
and understory (invaded vs uninvaded), and their interaction (site x
understory), performed in SPSS 16.0 (SPSS, Inc., 2007). Probability plots
performed in SPSS confirmed that the data met the ANOVA normality assumption.
Overall soil differences among the 3 sites were identified using a
Bonferroni multiple comparison procedure.
Litter nutrients and microarthropods
In August 2005 and February 2006, we compared microarthropod abundance
and diversity between oak-hickory and M. vimineum litters at the
early successional forest site because it had the heaviest coverage of both
litter types in close proximity. We collected seven 0.25-m2 samples of litter
from patches dominated by M. vimineum and under surrounding uninvaded
forest vegetation, and extracted microarthropods from 5000-cm3 subsamples
over 24 hours using the Tullgren funnel method (Crossley and Blair
1991). Microarthropods dropping from the drying litter were collected in
jars beneath the funnels, preserved in 70% ethanol, and examined under
2009 D.A. McGrath and M.A. Binkley 145
a dissecting (10x) microscope. The microarthropods were counted and
identified by order using descriptions published by Meyer (1994). Litter
dry mass was used to calculate abundance as number of microarthropods/
100 g litter. Community diversity was calculated using the Shannon-Weiner
Index: H' = -Σpi ln pi, where pi is the proportion of the total number of individuals
for order i. The Shannon-Weiner index integrates both abundance
and richness to provide an indicator of community evenness (Schmitz
2007). In July 2007, we repeated the study on all three forested sites
(pine, early successional, and mature oak-hickory). Mean microarthropod
abundance, order richness, and community diversity (H') were compared
between M. vimineum and early successional oak-hickory (n = 7) litters, as
well as across all three forested sites (n = 21), using a multivariate repeated
measures ANOVA with a between-subject factor of litter type, a within subject
factor of time (August 2005, March 2006, July 2007 sampling periods)
and litter x time interaction. Post hoc t-tests identified differences between
litter types within a sampling period.
Following the July 2007 microarthropod collection, the litter samples
were removed from the Tullgren funnels, oven dried for 24 hours, weighed,
ashed in a muffl e furnace, and analyzed for nutrient concentrations using
ICAP spectroscopy by A & L Analytical Laboratories (Memphis, TN). Mean
elemental concentrations in litters dominated by M. vimineum and surrounding
uninvaded understory vegetation (pine, mature and early successional
oak-hickory) were compared statistically using a multivariate ANOVA with
factors of site and litter type (M. vimineum vs uninvaded understory), and
their interaction (site x litter) performed in SPSS 16.0 (SPSS, Inc., 2007).
Overall differences in litter nutrients among sites were identified using post
hoc Bonferroni multiple comparisons.
Greenhouse and field soil chemistry
The greenhouse seeding study revealed significant effects of M. vimineum
growth, as well as time, on soil properties (Table 1). Soil pH, and extractable
-, P, Ca, and Mg all demonstrated significant treatment x time interactions
(Figs. 1a–d). Prior to seeding M. vimineum, the greenhouse soils did
not differ chemically; however, 6 and 12 months later, pH was significantly
higher in soil under M. vimineum than in the unseeded basins (Fig 1a). The
rise in soil pH appeared to reduce Al solubility, as indicated by lower extractable
Al under M. vimineum than the unseeded soil (Fig 1b). Soil NO3
- and P
concentrations in the M. vimineum treatment remained lower than those in
the unseeded soils, which rose significantly after 6 and 12 months, presumably
due to net N and P mineralization in the unseeded soils (Figs. 1c and
d). Soil NO3
- concentrations under M. vimineum remained the same after 12
months, while P was significantly higher compared to pre-seeding concentrations,
which was attributable to either lower uptake or greater solubility
induced at a higher pH (Fig. 1d). Ca also had a higher mean concentration
146 Southeastern Naturalist Vol. 8, No. 1
Table 1. The effects of treatment (seeded with M. vimineum vs. bare unseeded soil), time (pre-seeding, 6 and 12 months post-seeding) and treatment x time
interaction on greenhouse soil chemical properties. Data are means ± one SE; (n = 5. Significant (P < 0.05) differences between treatments within a sampling
period were determined using post hoc t-tests and are indicated by *.
Pre-seeding 6 months 12 months Repeated measures ANOVA P-values
Soil property M. vimineum Unseeded M. vimineum Unseeded M. vimineum Unseeded Treatment Time Treatment x time
pH 4.28 ± 0.02 4.29 ± 0.02 4.94 ± 0.11 4.24 ± 0.10* 4.9 ± 0.03 4.5 ± 0.1* 0.001 0.001 0.002
- 3.3 ± 0.2 2.9 ± 0.2 1.6 ± 0.3 20.8 ± 0.5* 3.4 ± 0.3 8.2 ± 2.9 0.001 0.01 0.002
P (mg/kg) 7.8 ± 0.3 7.7 ± 0.3 11.4 ± 1.1 21.4 ± 1.7* 20 ± 2 33 ± 2* 0.003 0.001 0.001
K (mg/kg) 94 ± 1 91 ± 2 62 ± 3 63 ± 4 56 ± 5 56 ± 1 0.80 0.001 0.62
Ca (mg/kg) 210 ± 8 201 ± 8 271 ± 22 273 ± 12 415 ± 28 597 ± 57* 0.05 0.002 0.02
Mg (mg/kg) 48 ± 1 45 ± 1 40 ± 5 43 ± 1 47 ± 1 39 ± 1* 0.78 0.01 0.07
Org mat (%) 6.0 ± 0.02 6.1 ± 0.02 6.0 ± 0.2 5.7 ± 0.2 4.4 ± 0.5 5.2 ± 0.5 0.81 0.07 0.73
CEC 9.0 ± 0.6 9.6 ± 0.5 7.0 ± 0.2 7.1 ± 0.2 7.4 ± 0.3 8.7 ± 0.3* 0.05 0.05 0.47
Al (mg/kg) No data: analysis not done 860 ± 18 948 ± 12* 838 ± 6 985 ± 10* 0.001 0.54 0.03
Table 2. A comparison of soil properties underlying dense patches of live M. vimineum and surrounding uninvaded forest vegetation across 3 sites (mature and
early successional oak-hickory and a 40-year-old White Pine stand) on the Cumberland Plateau. Data are means ± one SE (n = 5 samples per site). Significant
(P < 0.05) overall soil differences among sites were determined using a Bonferroni post hoc multiple comparison procedure and are indicated by *.
Mature oak-hickory Successional oak-hickory 40-year old pine ANOVA P-values
Soil property M. vimineum Uninvaded M. vimineum Uninvaded M. vimineum Uninvaded Treatment Site Treat x site
pH 5.3 ± 0.1 4.5 ± 0.2 6.0 ± 0.2 5.3 ± 0.2* 5.5 ± 0.1 4.9 ± 0.1 0.001 0.001 0.76
- 4.0 ± 1.0 3.0 ± 0.1 7.4 ± 0.4 7.2 ± 0.5* 3.6 ± 0.4 4.0 ± 0.1 0.53 0.001 0.40
P (mg/kg) 19 ± 1 17 ± 1 37 ± 8 19 ± 1* 15 ± 2 12 ± 1 0.01 0.002 0.08
K (mg/kg) 71 ± 4 73 ± 6* 63 ± 2 61 ± 3 70 ± 3 56 ± 4 0.13 0.02 0.09
Ca (mg/kg) 854 ± 38 790 ± 79 1642 ± 236 946 ± 196* 1259 ± 74 892 ± 28 0.002 0.01 0.08
Mg (mg/kg) 70 ± 5 45 ± 5 56 ± 6 51 ± 3 94 ± 7 58 ± 3 0.001 0.001 0.02
CEC (cmol+/kg) 9.3 ± 0.6 10.3 ± 0.5 11.2 ± 1.1 8.8 ± 0.8 11.1 ± 0.6 9.4 ± 0.3 0.08 0.82 0.05
Al (mg/kg) 825 ± 60 1127 ± 43 535 ± 17 563 ± 25* 928 ± 76 984 ±67 0.04 0.001 0.02
Ca/Al 1.1 ± 0.1 0.70 ± 0.1 3.1 ± 0.5 1.7 ± 0.4* 1.4 ± 0.2 0.9 ± 0.04 0.003 0.001 0.15
Organuc matter (%) 5 ± 0.6 5 ± 0.3 3.6 ± 0.2 3.4 ± 0.2* 4.4 ± 0.1 4.3 ± 0.1 0.49 0.001 0.99
2009 D.A. McGrath and M.A. Binkley 147
under unseeded soil at 12 months, likely contributing to a slight rise in CEC
in unseeded soils sampled at that time (Table 1).
The field soil sampling showed that across the 3 forested sites, soils under
dense M. vimineum had significantly higher pH, extractable P, Ca, and
Mg, as well as lower extractable Al, compared to surrounding uninvaded soil
on the same site without M. vimineum growth (Table 2). Subsequently, Ca
and Al ratios (Ca/Al) were higher in soils under dense M. vimineum. Among
the 3 sites, soil pH under M. vimineum was highest in the early successional
oak-hickory forest, which corresponded with the highest P and Ca availability
and Ca/Al. Uninvaded soil in.surrounding mature oak-hickory forest
had the lowest pH, along with a mean Al concentration twice as high as that
under the early successional site (Table 2). Neither NO3
- nor percent organic
matter differed between soils with and without M. vimineum.
Litter nutrients and microarthropods
Across the 3 forest sites, P concentrations were significantly higher in
M. vimineum litter than in surrounding forest fl oor, which corresponded to
Figure 1. Greenhouse soil properties demonstrating significant (P < 0.05) treatment
(seeded with M. vimineum vs. unseeded bare soil) x time (pre-seeding, and 6 and
12 months post-seeding) interactions. Extractable aluminum analyses were not performed
on soils prior to seeding. For all other chemical properties, the soils showed
no statistical differences prior to seeding.
148 Southeastern Naturalist Vol. 8, No. 1
Table 4. The effects of litter type (M. vimineum vs. surrounding uninvaded forest fl oor), sampling year (Aug 2005, Feb 2006, July 2007), and litter by year
interaction on litter microarthropod abundance, diversity (H'), and richness were determined using a repeated measures multivariate ANOVA. In Aug 2005 and
Feb 2006, litter samples were compared only on the early succesional oak-hickory site (n = 7). In July 2007, litter microarthropods were compared across the 3
sites (mature, early successional, and pine; n = 21). Significant (P < 0.05) differences between litter types within a sampling period were determined using post
hoc t-tests denoted by *.
Aug 2005 (n = 7) Feb 2006 (n = 7) July 2007 (n = 21) ANOVA P-values
Uninvaded Uninvaded Uninvaded Litter type Year Treatment
Soil property forest M. vimineum forest M. vimineum forest M. vimineum (treatment) (time) x time
Abundance (arthropods/100 g) 547 ± 70 1144 ± 290* 172 ± 50 431 ± 183 100 ± 18 566 ± 133* 0.001 0.01 0.46
Diversity (H') 1.04 ± 0.11 0.50 ± 0.35* 0.41 ± 0.09 0.34 ± 0.06 0.61 ± 0.07 0.42 ± 0.05* 0.003 0.001 0.001
Richness (orders/sample) 8.3 ± 0.7 7.6 ± 0.6 3.2 ± 0.6 4.3 ± 0.8 3.4 ± 0.3 4.1 ± 0.4 0.55 0.003 0.29
Table 3. A comparison of elemental concentrations in M. vimineum litter and surrounding uninvaded forest fl oor across 3 sites (mature and early successional
oak-hickory and a 40-year-old White Pine stand) on the Cumberland Plateau. Data are means ± one SE (n = 7 samples per forest site). Significant (P < 0.05)
differences among sites across both litter types were determined using a Bonferroni post hoc multiple comparison procedure and are indicated by *.
Mature oak-hickory Early successional oak-hickory 40-year old pine ANOVA P-values
M. vimineum Oak-hickory M. vimineum Oak-hickory M. vimineum White Pine Treatment
Element litter litter litter litter litter litter Treatment Site x site
N 1.3 ± 0.09 1.6 ± 0.6 1.3 ± 0.08 1.2 ± 0.07 1.2 ± 0.05 1.1 ± 0.06 0.74 0.52 0.69
S 0.14 ± 0.01 0.12 ± 0.003 0.14 ± 0.01 0.15 ± 0.004* 0.12 ± 0.004 0.11 ± 0.002 0.14 0.0001 0.05
P 0.08 ± 0.004 0.06 ± 0.004 0.15 ± 0.01 0.11 ± 0.005* 0.08 ± 003 0.05 ± 0.003 0.0001 0.0001 0.74
K 0.25 ± 0.06 0.16 ± 0.01 0.21 ± 0.05 0.21 ± 0.01 0.18 ± 0.02 0.14 ± 0.01 0.09 0.23 0.43
Mg 0.13 ± 0.003 0.12 ± 0.004 0.08 ± 0.003 0.11 ± 0.005 0.08 ± 0.003 0.07 ± 0.005* 0.03 0.0001 0.001
Ca 0.79 ± 0.08 1.0 ± 0.05 0.70 ± 0.03 1.5 ± 0.11 0.83 ± 0.04 0.70 ± 0.02* 0.001 0.0001 0.001
Al 1489 ± 545 913 ± 138 2249 ± 333 401 ± 69 1672 ± 340 567 ± 71 0.001 0.79 0.12
2009 D.A. McGrath and M.A. Binkley 149
higher soil availability of this element (Tables 2 and 3). In contrast, Ca was
lower in M. vimineum litter than in oak-hickory litter, despite higher soil
extractable Ca. Litter K concentrations appeared higher in M. vimineum on
2 sites. Surprisingly, Al in M. vimineum litter was higher than in surrounding
forest fl oor, even though soil Al concentrations were lower beneath the grass
Litter type significantly affected abundance and diversity of microarthropod
populations (Table 4). Microarthropod abundance was higher in the M.
vimineum litter than in uninvaded understory litter from the same site across
the sampling periods. Order richness did not differ between the 2 litter types,
perhaps because the taxon is too inclusive (Table 4). Mite abundance was
higher in M. vimineum litter and nearly 10 times greater than that of Collembola,
the next most abundant order (Figs. 2a and b). However, because mites
dominated M. vimineum litter, diversity (H') was higher in surrounding uninvaded
litter collected in 2005 and 2007, where microarthropod abundance
was spread more evenly across several orders (Table 4). Collembolan abundance
exhibited no pattern with respect to litter type (Fig. 2b). Colleoptera,
the third most abundant order, had equally low mean abundance in both M.
vimineum and surrounding forest litter for all three sampling periods (P ≥
0.30), ranging from a high of 11 (± 2 SE) per 100 g litter in Aug 2005 to 2
(± 0.7 SE) in the July 2007 sampling. A comparison among the sites showed
that H' was higher (marginally significant) in surrounding uninvaded litter
only in the 2 oak-hickory forests (Fig. 3a); however, mite abundance was
greater in M. vimineum litter on all 3 sites (Fig. 3b).
The repeated measures ANOVA demonstrated significant effects
of sampling date on microarthropod abundance, community diversity,
and order richness (Table 4). Microarthropod order richness, abundance,
Figure 2. A comparison over 3 sampling periods of mean (± one SE) abundance of (a)
mites and (b) collembolans between litters dominated by M. vimineum and surrounding
uninvaded forest vegetation on the same sites. In Aug 2005 and March 2006, n =
7 samples of each litter type collected from the early successional forest site. In July
2007, n = 21 (3 forest sites x 7 replications).
150 Southeastern Naturalist Vol. 8, No. 1
and community diversity (H') were significantly higher in surrounding
forest litter collected in August 2005 than that in the subsequent sampling
periods (Table 4). The more diverse August 2005 samples contained
representatives of over 10 other orders, including Diplura, Diptera, Hymenoptera,
Isoptera, Lepidoptera, and Protura. Only order richness in
M. vimineum litter differed significantly among the 3 sampling periods,
again with the August 2005 sampling exhibiting the greatest diversity.
Microarthropod abundance, order richness, and H' were similarly low in
the February 2006 and July 2007 samples (Table 4), likely due to a colder,
drier climate in February and a 100-year drought during the summer of
2007 (National Climate Data Center 2008).
Changes in soil chemistry
Although numerous studies have established the capacity of plants to
acidify soil, mainly through rhizosphere production of organic acids (Kelly
et al. 1998), it is less often reported that soil pH rises in response to a change
in plant species. Despite a small sample size, our greenhouse study demonstrated
a significant rise in soil pH that occurred within 6 months of M.
vimineum germination, and confirmed that the pH change was a result of
M. vimineum growth. Across the forest sites, the higher soil pH under M.
vimineum was accompanied by greater availability of P and base cations
Mg and Ca compared to soil under surrounding overstory vegetation. These
soil changes under M. vimineum are not surprising since pH has a major
role in controlling nutrient bioavailability (Kelly et al. 1998). Phosphate is
more labile in soils with a pH > 5 because it does not react with Al or Fe,
both of which are soluble at pH values 3–5 (Bohn et al. 2001). Base cation
Figure 3. A comparison over 3 sampling periods of mean (± one SE) (a) community
diversity (H') and (b) mite abundance between litters dominated by M. vimineum and
surrounding uninvaded forest vegetation on 3 sites (data collected in July 2007, n =
7 for each forest site).
2009 D.A. McGrath and M.A. Binkley 151
availability can be greater in higher pH soils because the exchange complex
is not dominated by hydrogen ions (H+) (Sposito 2008).
A higher soil pH under M. vimineum corresponded with a significant
rise in Ca/Al, due to a combination of lowered Al solubility and higher Ca
concentrations. In acid soils, Ca/Al can be an indicator of forest health, with
plants in soils with Ca/Al ≤ 1.0 at greater risk for Al stress, the effects of
which include impaired Ca and Mg uptake, as well as inhibition of cell division
and energy transfer (Borer et al. 2004, Cronon and Grigal 1995). Some
Al-resistant plants exclude the uptake of this element by raising rhizosphere
pH, and subsequently lowering the solubility of toxic Al (Degenhardt et al.
1998, Jansen et al. 2002). Grasses are often more sensitive to Al toxicity than
other angiosperms (Jansen et al. 2002), and studies suggest that Al exposure
could stimulate NO3
- uptake, raising rhizosphere pH through anti-port transport
- across the root cell membrane in exchange for a hydroxyl (OH-)
anion (Degenhardt et al. 1998).
Ehrenfeld et al. (2001) attributed an elevated soil pH under M. vimineum
to rapid NO3
- uptake stimulated by an increase in soil nitrification rates beneath
the shallow-rooted grass. We did not find an effect of M. vimineum
invasion on soil NO3
- concentrations, which were equally low in dense
patches of M. vimineum and surrounding overstory vegetation. However,
data from the greenhouse study suggest that M. vimineum may be very effective
at taking up mineralized N. After 6 months, greenhouse soil nitrate
concentrations were 7-fold higher in the unseeded soil, but remained the
same under M. vimineum, presumably due to uptake by the grass. In contrast,
not all bioavailable P was taken up by M. vimineum, as evidenced by a rise
in greenhouse soil P concentrations under the grass at 6 and 12 months.
Changes in litter nutrients and microarthropods
In all 3 forests, M. vimineum appeared to produce a more P-rich litter than
surrounding forest fl oor, but N concentrations did not differ from overstory
litter. Ehrenfeld et al. (2001) reported that M. vimineum had N-poor litter,
which decomposed more slowly and immobilized N, compared to native
forest litter. We observed that dead M. vimineum falls over and forms dense
litter mats which may persist over multiple seasons (as evidenced by layers
of hardwood litter above the M. vimineum mat), suggestive of slower decomposition
relative to oak-hickory litter. In addition, M. vimineum litter had a
higher Al concentration than surrounding overstory litter across the 3 sites,
and studies show that this element tends to adsorb to litter exchange sites
during prolonged periods of decomposition (Rustad 1994).
Numerous variables are reported as factors controlling litter microarthropod
community composition including nutrient availability (King
and Hutchinson 1980, Lindbert and Perrson 2004), soil properties (Huhta
and Ojala 2006, L’ubomir et al. 2001), plant diversity (Hansen 2000,
Migge et al. 1998), litter complexity (Hansen and Coleman 1998), and
disturbance (Bird et al. 2004, Reynolds et al 2007). We hypothesized that
there would be greater diversity and abundance of microarthropods in
152 Southeastern Naturalist Vol. 8, No. 1
the early successional oak-hickory forest floor than in M. vimineum litter
due to greater complexity of the mixed hardwood litter as a habitat.
We found that M. vimineum litter had a higher abundance, but an overall
lower evenness in order distribution of microarthropods than surrounding
hardwood litter, due to the dominance of mites in the former. Hansen
and Coleman (1998) attributed higher oribatid mite species richness and
abundance to complementary resource availability provided by more
complex litters with different leaf architectures, chemical characteristics,
and thus differing rates of decomposition and nutrient release. After expanding
our study to include the 3 forest sites, we found the same pattern
of higher mite abundance in M. vimineum litter compared to the surrounding
forest floor, even though oak-hickory and pine litter vary considerably
with respect to litter complexity and heterogeneity. Similar to Huhta and
Ojala (2006), we found no consistent effect of litter type on collembolan
populations, perhaps because these microarthropods are characterized as
opportunists or “r” strategists (Coleman et al. 2004), feeding upon both
fungi and decomposed plant litter.
Generally, mites comprise the majority of litter microarthropods, and
despite high variability among sampling years, we observed densities in
M. vimineum litter ≥500 mites/100 gm, at the upper end of reported values
for similar sampling methods (Coleman et al. 2004). Oribatid mites
are considered “K” strategists because they are long-lived fungal grazers,
with both low mobility and reproductive rates that are favored by stable
habitats (Coleman et al. 2004). Hansen (2000) hypothesized that oak litter,
which breaks down slowly initially but decomposes rapidly later in
the season, produces fl ushes and troughs of microbial growth, rendering
it an unstable habitat for mites. In contrast, Ehrenfeld et al. (2001) found
that dead M. vimineum blades broke down quickly, but the remaining grass
culms decomposed slowly. Therefore, we believe that the slowly decomposing
M. vimineum litter provides a more sustained supply of P for microbial
growth than surrounding forest fl oor, thereby creating a more stable habitat
for mites. Studies have shown an increase in microarthropod abundance in
response to fertilization, which raises both litter nutrient concentrations
and plant productivity (Bird et al. 2004, Lindbert and Persson 2003). King
and Hutchinson (1980) demonstrated a 4-fold increase in grassland mite
densities following superphosphate application, with litter P concentration
providing a better predictor of microarthropod abundance than N. Thus,
higher soil and litter P availability, induced by a rise in pH following M.
vimineum invasion may favor litter mite proliferation, perhaps at the expense
of overall microarthropod community evenness. Higher soil Ca availability
under M. vimineum may also contribute to their abundance, because oribatid
mites are known to sequester Ca (metabolized from fungi) in exoskeletons
(Coleman et al. 2004). In addition, the dense M. vimineum litter mat may
promote moisture retention (Ehrenfeld et al. 2001) or moderate temperature
extremes, either of which could increase habitat stability.
2009 D.A. McGrath and M.A. Binkley 153
Potential effects on biogeochemical cycling
The most consistent effect we found was that M. vimineum invasion
elevated soil pH and P availability, and lowered litter microarthropod community
diversity by significantly increasing the abundance of mites. It is
unclear how higher mite abundance in response to M. vimineum invasion
would affect biogeochemical cycling. Mites contribute to litter decomposition
by mobilizing nutrients and fragmenting litter as they graze upon
bacteria and fungi, but their direct effect on litter mass loss is minimal (Beare
et al. 1992). However, a higher mite abundance and lower microarthropod
order evenness would likely change soil food-web dynamics, as mites are
prey for many larger organisms such as beetles, ants, and salamanders (Coleman
et al. 2004).
The broader question of whether a change in soil pH is enough to
alter soil biogeochemistry deserves further examination. A comparison
among the 3 forest sites yields limited inferences without replication
of each forest type; however, it is likely that the effect of M. vimineum
invasion on soil chemistry depends upon the initial soil characteristics
and the plant community overlying it. For example, only soils under mature
oak-hickory forest had Ca/Al < 1, which rose to > 1 under adjacent
patches of M. vimineum (theoretically lowering the risk of Al-toxicity)
due to a pH-induced decrease in Al solubility. Moreover, the early successional
oak-hickory site, which had the highest soil pH among the sites
under both M. vimineum and surrounding overstory also had significantly
greater soil P and Ca concentration, the highest mite abundance, and the
lowest Al concentration. This observation, although requiring further
study, suggests that there may be a pH threshold at which a rise in soil
pH induced by M. vimineum invasion triggers large changes in soil chemistry
and biota. Another interesting question is whether a rise in pH and
other soil changes following M. vimineum invasion facilitates changes in
plant community composition by rendering soil more favorable for other
invaders, such as Lespedeza cuneata (Dum. -Cours.) G. Don (Chinese
Lespedeza), or Al-sensitive native species, such as Acer saccharum Marshall
(Sugar Maple). In summary, while we found clear and rapid effects
of M. vimineum invasion on soil pH, ecosystem P availability, and litter
mite abundance, how these changes alter biogeochemical cycling in upland
forests of the Cumberland Plateau merits further study.
This study was funded by grants from the DuPont and Lilly Foundations. We
thank Nick Hollingshead of the University of the South’s Landscape Analysis Lab
for statistical consult, Kara Allen for her assistance in data collection and analysis,
and Natasha Cowie for her work establishing the greenhouse experiment. We are
grateful for the helpful comments made by Cynthia D. Huebner and three anonymous
154 Southeastern Naturalist Vol. 8, No. 1
Barden, L.S. 1987. Invasion of Microstegium vimineum (Poaceae), an exotic, annual,
shade-tolerant, C4 grass, into a North Carolina fl oodplain. American Midland
Beare, M.H., R.W. Parmelee, P.F. Hendrix, and W. Cheng. 1992. Microbial and faunal
interactions and effects on litter nitrogen and decomposition in agroecosystems.
Ecological Monographs 62(4):569–591.
Belnap, J., and S.L. Phillips. 2001. Soil biota in an ungrazed grassland: Response
to annual grass (Bromus tectorum) invasion. Ecological Applications 11:1261–
Bird, S.B., R.N. Coulson, and R.F. Fisher. 2004. Changes in soil and litter arthropod
abundance following tree harvesting and site preparation in a Loblolly Pine (Pinus
taeda L.) plantation. Forest Ecology and Management 202(1–3):195–208.
Bohn, H.L., B.L. McNeal, and G.A. O’Connor. 2001. Acid Soils. Pp. 48–66, In Soil
Chemistry. Third Edition. John Wiley and Sons, New York, NY. 303 pp.
Borer, C.H., P.G. Schabert, D.H. DeHayes, and G.J. Hawley. 2004. Accretion, partitioning,
and sequestration of calcium and aluminum in Red Spruce foliate:
Implications for tree health. Tree Physiology 24:929–939.
Cheplick, G.P. 2005. Biomass partitioning and reproductive allocation in the invasive,
cleistogamous grass Microstegium vimineum: Infl uence of the light environment.
Journal of the Torrey Botanical Society 132(2):214–224.
Coleman, D.C., D.A. Crossley, and P.F. Hendrix. 2004. Microarthropods. Pp.
98–124, In Fundamentals of Soil Ecology. Second Edition. Elselvier Academic
Press, Burlington, MA. 375 pp.
Cronan, C.S., and D.F. Grigal. 1995. Use of Calcium/Aluminum ratios as indicators
of stress in forest ecosystems. Journal of Environmental Quality 24:209–226.
Crossley, D.A., Jr., and J.M. Blair. 1991. A high efficiency, “low-technology”
tullgren-type extractor for soil microarthropods. Agriculture, Ecosystems and
Degenhardt, J., P.B. Larsen, S.H. Howell, and L.V. Kochian. 1998. Aluminum resistance
in the Arabidopsis mutant alr-104 is caused by an aluminum-induced
increase in rhizosphere pH. Plant Physiology 117:19–27.
Ehrenfeld, J.G. 2003. Effects of exotic plant invasions on soil nutrient processes.
Ehrenfeld, J.G., P. Kourtev, and W. Huang. 2001. Changes in soil functions following
invasions of exotic understory plants in deciduous forests. Ecological Applications
Gibson, D.J., G.Spyreas, and J. Benedict. 2002. Life history of Microstegium vimineum
(Poaceae), an invasive grass in southern Illinois. Journal of the Torrey
Botanical Society 129(3):207–219.
Hansen, R.A. 2000. Effects of habitat complexity and composition on a diverse litter
microarthropod assemblage. Ecology 8(4):1120–1132.
Hansen, R.A., and D.C. Coleman. 1998. Litter complexity and composition are
determinants of the diversity and species composition of oribatid mites (Acari:
Oribatida) in litterbags. Applied Soil Ecology 9:17–23.
Horton, J.L., and H.S. Neufeld. 1998. Photosynthetic responses of Microstegium
vimineum (Trin.) A. Camus, a shade-tolerant, C4 grass, to variable light environments.
2009 D.A. McGrath and M.A. Binkley 155
Huhta, V., and R. Ojala. 2006. Collembolan communities in deciduous forests of different
origin in Finland. Applied Soil Ecology 31:83–90.
Hunt, D.M., and R.E. Zaremba. 1992. The northeastward spread of Microstegium
vimineum (Poaceae) into New York and adjacent states. Rhodora 94:167–170.
Jansen, S., M.R. Broadley, E. Robbrecht, and E. Smets. 2002. Aluminum hyperaccumulation
in Angiosperms: A review of its phylogenetic significance. The Botanical
Kelly, E.F., O.A. Chadwick, and T.E. Hilinski. 1998. The effect of plants on mineral
weathering. Biogeochemistry 42:21–53.
King, K.L., and K.J. Hutchinson. 1980. Effects of superphosphate and stocking
intensity on grassland microarthropods. The Journal of Applied Ecology 17(3):
Kourtev, P.S., J.G. Ehrenfeld, and M. Haggbloom. 2002. Exotic plant species alter the
microbial community structure and function in the soil. Ecology 83:3152–3166.
Leicht, S.A., J.A. Silander, Jr., and K. Greenwood. 2005. Assessing the competitive
ability of Japanese Stilt Grass, Microstegium vimineum (Trin.) A. Camus. Journal
of the Torrey Botanical Society 132 (4):573–580.
Lindbert, N., and T. Persson. 2003. Effects of long-term nutrient fertilization and
irrigation on the microarthropod community in a boreal Norway Spruce stand.
Forest Ecology and Management 188(1–3):125–135.
L’ubomir, K., P. Luptacik, D. Miklisova, and R. Mati. 2001. Soil oribatida and collembola
communities across a land depression in an arable field. European Journal
of Soil Biology 37(4):285–289.
McGrath, D.A., J.P. Evans, C.K. Smith, D.G. Haskell, N.W. Pelkey, R.R. Gottfried,
C.D. Brockett, M.D. Lane, and E.D. Williams. 2004. Mapping land-use change
and monitoring the impacts of hardwood-to-pine conversion on the southern
Cumberland Plateau in Tennessee. Earth Interactions 8(9):1–23.
Meyer, J.R. 1994. Kwik-Key to Soil-Dwelling Invertebrates. Department of Entomology.
North Carolina State University, Vision Press, Raleigh, NC. 43 pp.
Migge, S., M. Maraun, S. Scheu, and M. Schaefer. 1998. The oribatid mite community
(Acarina) of pure and mixed stands of beech (Fagus sylvatica) and spruce
(Picea abies) of different age. Applied Soil Ecology 9(1–3):115–121.
Morrison, J.A., H.A. Lubchansky, K.E. Mauck, K-M. McCartney, and B. Dunn,.
2007. Ecological comparison of two co-invasive species in eastern deciduous
forests: Alliaria petiolata and Microstegium vimineum. Journal of the Torrey
Botanical Society 134(1):1–17.
National Climate Data Center (NCDC). 2008. Climate of 2007—Tennessee Moist.
Status. Available online at http://lwf.ncdc.noaa.gov/oa/climate/research/prelim/
drought/st040dv00pcp.html. Accessed 06 February 2008.
Redman, D.E. 1995. Distribution and habitat types for Nepal Microstegium [Microstegium
vimineum (Trin.) Camus] in Maryland and the District of Columbia.
Reynolds, B.C., J. Hamel, J. Isbanloly, L. Klausman, and K.K. Moorhead. 2007.
From forest to fen: Microarthropod abundance and litter decomposition in a
southern Appalachian fl oodplain/fen complex. Pedobiologia 51(4):273–280.
Ricketts, T.H., E. Dinerstein, D. Olson, C.J. Loucks, W. Eichbaum, D. Della Sala, K.
Kavanagh, P. Hedao, P. Hurley, K. Carney, R. Abell, and S. Walters. 1999. Terrestrial
Ecoregions of North America: A Conservation Assessment. Island Press,
Washington, DC. 491 pp.
156 Southeastern Naturalist Vol. 8, No. 1
Rustad, L. 1994. Elemental dynamics along a decay continuum in Red Spruce ecosystem
in Maine, USA. Ecology 75(4):867–879.
Schmitz, O.J. 2007. Biodiversity and habitat fragmentation. Pp. 80–81, In Ecology
and Ecosystem Conservation. Island Press, Washington, DC. 159 pp.
Scott, N.A., S. Saggar, and P.D. McIntosh. 2001. Biogeochemical impact of Hieracium
invasion in New Zealand’s grazed tussock grasslands: Sustainability implications.
Ecological Applications 11(5):1311–1322.
Sposito, G. 2008. Exchangeable ions. Pp. 219–239, In The Chemistry of Soils, Second
Edition. Oxford University Press, New York, NY. 321 pp.
SPSS, Inc. 2007. SPSS 16.0 Statistical Analysis for Mac. Chicago, IL.
Vitousek, P.M. 1990. Biological invasions and ecosystem processes: Towards an
integration of population biology and ecosystem studies. Oikos 57:7–13
Yeates, G.W., and P.A. Williams. 2001. Infl uences of three invasive weeds and site
factors on soil microfauna in New Zealand. Pedobiologia 45:367–383.