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Inventory and Ventilation Efficiency of Nonnative and Native Phragmites australis (Common Reed) in Tidal Wetlands of the Chesapeake Bay


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Nonnative Phragmites is among the most invasive plants in the U.S. Atlantic coast tidal wetlands, whereas the native Phragmites has declined. Native and nonnative patches growing side by side provided an ideal setting for studying mechanisms that enable nonnative Phragmites to be a successful invader. We conducted an inventory followed by genetic analysis and compared differences in growth patterns and ventilation efficiency between adjacent native and nonnative Phragmites stands. Genetic analysis of 212 patches revealed that only 14 were native suggesting that very few native Phragmites populations existed in the study area. Shoot density decreased towards the periphery of native patches, but not in nonnative patches. Ventilation efficiency was 300 % higher per unit area for nonnative than native Phragmites, likely resulting in increased oxidation of the rhizosphere and invasive behavior of nonnative Phragmites. Management of nonnative Phragmites stands should include mechanisms that inhibit pressurized ventilation of shoots.
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Inventory and Ventilation Efficiency of Nonnative
and Native Phragmites australis (Common Reed) in Tidal
Wetlands of the Chesapeake Bay
Mirela G. Tulbure &Dana M. Ghioca-Robrecht &
Carol A. Johnston &Dennis F. Whigham
Received: 19 July 2011 / Revised: 5 June 2012 / Accepted: 14 June 2012
#Coastal and Estuarine Research Federation 2012
Abstract Nonnative Phragmites is among the most in-
vasive plants in the U.S. Atlantic coast tidal wetlands,
whereas the native Phragmites has declined. Native and
nonnative patches growing side by side provided an
ideal setting for studying mechanisms that enable non-
native Phragmites to be a successful invader. We con-
ducted an inventory followed by genetic analysis and
compared differences in growth patterns and ventilation
efficiency between adjacent native and nonnative Phrag-
mites stands. Genetic analysis of 212 patches revealed
that only 14 were native suggesting that very few native
Phragmites populations existed in the study area. Shoot
densit y decreas ed toward s the periphe ry of nativ e
patches, but not in nonnative patches. Ventilation effi-
ciency was 300 % higher per unit area for nonnative
than native Phragmites, likely resulting in increased
oxidation of the rhizosphere and invasive behavior of
nonnative Phragmites. Management of nonnative Phragmites
stands should include mechanisms that inhibit pressurized
ventilation of shoots.
Keywords Patch inventory .Intragenic physiological
differences .Intrapatch biomass allocation .Pressurized
ventilation .Ventilation efficiency .Invasive wetland plants .
Phragmites .Chesapeake Bay
Phragmites australis (Cav.) Trin. ex Steud. is a perennial
grass found on every continent with the exception of
Antarctica (Tucker 1990). Phragmites can grow in a variety
of freshwater and brackish wetlands, but it can also colonize
and expand in drier conditions (Global Invasive Species
Database; Paleological evidence sug-
gests that Phragmites is native to North America (Niering et
al. 1977; Orson 1999) but was historically a minor constit-
uent of the U.S. wetlands (Chambers et al. 1999). Molecular
studies conducted by Saltonstall (2002) have shown that there
are three distinct lineages of Phragmites currently occurring in
North America: the native subspecies (Saltonstall et al. 2004),
the lineage introduced from Eurasia (hereafter nonnative
Phragmites), and the Gulf Coast lineage (Lambertini et al.
2012; Saltonstall 2002,2003). In recent years, the nonnative
Phragmites has proliferated in brackish and tidal freshwater
wetlands on the Atlantic coast (McCormick et al. 2010),
whereas the native Phragmites has declined in the same region
(Saltonstall 2003; Vasquez et al. 2005).
The recent expansion of Phragmites into brackish tidal
wetlands on the US East Coast has been attributed to the
introduction of the nonnative lineage, but factors such as
disturbance (Bart and Hartman 2000,2003; Minchinton and
Bertness 2003) and anthropogenic modifications within
wetlands (Johnston et al. 2008; Maheu-Giroux and de Blois
2007; McNabb and Batterson 1991) or on adjacent upland
areas (King et al. 2007; Minchinton and Bertness 2003;
M. G. Tulbure :D. M. Ghioca-Robrecht :C. A. Johnston
Department of Biology and Microbiology, South Dakota State
Brookings, SD 57007, USA
D. F. Whigham
Smithsonian Environmental Research Center,
Edgewater, MD 21037, USA
M. G. Tulbure (*)
Australian Wetlands, Rivers and Landscapes Centre,
School of Biological, Earth and Environmental Sciences,
University of New South Wales,
Sydney NSW 2052, Australia
Estuaries and Coasts
DOI 10.1007/s12237-012-9529-4
Tulbure 2008; Tulbure and Johnston 2010) facilitate Phrag-
mites invasion. Once established, nonnative Phragmites forms
large stands, with shoots up to 34 m tall. Nonnative Phrag-
mites has high biomass (Meyerson et al. 2000), displaces native
vegetation, and changes ecosystem processes (Chambers et al.
1999; Ehrenfeld 2003).
Situations where patches of native and nonnative Phrag-
mites grow side by side in the field represent a unique oppor-
tunity to study intraspecific differences because comparative
studies can provide important information on the invasive
behavior of introduced populations (Daehler and Strong
1996; Seliskar and Gallagher 2000; Seliskar et al. 2002).
Despite the potential benefits of understanding mechanisms
that impart invasiveness in Phragmites when conducting
studies comparing native and nonnative Phragmites, to our
knowledge, only a limited number of studies have been con-
ducted in the U.S.A., of which the majority were greenhouse
studies. These studies showed that nonnative Phragmites
emerges from rhizomes earlier in the season, grows taller,
and has greater biomass (Holdredge et al. 2010; League et
al. 2006; Meadows and Saltonstall 2007; Mozdzer et al.
2010), can tolerate higher salinity levels (Vasquez et al.
2005), and has higher rates of photosynthesis than native
Phragmites (Mozdzer and Zieman 2010).
We briefly outline the a priori theoretical and empirical
support for each of our goals and hypotheses which were to:
1. Identify native and nonnative Phragmites stands growing
side by side in the field: Finding stands of native and
nonnative Phragmites growing in close proximity was
not a trivial task as there are apparently few tidal wetlands
on the Mid-Atlantic Coast where native Phragmites occurs
(Saltonstall 2003; Vasquez et al. 2005). Because one of our
goals was to compare native and nonnative Phragmites
that occurred in the same wetlands, the first objective of
our study was to conduct a geographic survey and genetic
analysis of Phragmites in Chesapeake Bay to locate and
identify adjacent native and nonnative Phragmites stands.
2. Compare native and nonnative Phragmites patches that
were growing close to each other, a priori hypothesizing
(a) Nonnative Phragmites displays greater clonal growth
(i.e., produces more stems and biomass per unit area)
towards the edge of the clones: Phragmites can repro-
duce both sexually and vegetatively. Although the
ability to reproduce sexually increases the potential
for colonizing new sites, the shift in resource alloca-
tion towards clonal growth facilitates the establish-
ment and survival of populations (Sakai et al. 2001).
Plant species with clonal growth often exhibit greater
growth at the edge of patches (Lambrecht-McDowell
and Radosevich 2005; Parker 2000; Wikberg and
Svensson 2003), and rapid shoot initiation allows
ruderal species to spread (Grime 1977). Previous stud-
ies showed that nonnative Phragmites grows in denser
stands than does native Phragmites (Meadows and
Saltonstall 2007), but there have not been any studies
in which the shoot density between native and nonna-
tive stands has been compared at the leading edge of
the expansion of patches (i.e., density at the edge of a
patch versus density toward the center of the patch).
(b) Nonnative Phragmites has greater ventilation effi-
ciency per unit area than native Phragmites: The
mechanisms of internal pressurization and convec-
tive gas flow are important adaptations of wetland
plants to growth in anoxic substrates (Brix et al.
1992; Cronk and Fennessy 2001). Pressurized venti-
lation represents a bulk flow of oxygen and requires a
pressure gradient between two ends of a pathway
with an exit to the atmosphere (Colmer 2003). In
Phragmites, oxygen enters via the leaf sheath stoma-
ta of green stems, flows to the roots along the inter-
cellular spaces of the green shoots, and flows back
to the atmosphere via senesced culms (Armstrong
and Armstrong 1991; Colmer 2003; Rolletschek et
al. 1999). Therefore, high densities of pressurizing
living and dead culms play an important role in
delivering oxygen to belowground organs as well as
removing gases (e.g., carbon dioxide) associated with
belowground respiration. The convective flow-
through mechanism has been described for several
wetland species (Armstrong and Armstrong 1991;
Brix et al. 1992) and lower per stand ventilation
efficiency has been observed in declining Phragmites
stands in Europe (Ostendorp 1989). One factor be-
hind the recent expansion of nonnative Phragmites in
brackish tidal wetlands in the U.S.A. may be its
ability to more efficiently transport oxygen to roots.
The ability to efficiently deliver oxygen to roots
could be especially important in coastal wetlands that
are enriched by eutrophication and could result in a
decline in the native lineage for reasons similar to
those that have been responsible for the decline of
Phragmites in Europeas the substrate becomes
more reduced due to eutrophication, Phragmites is
unable to supply enough oxygen to the rhizosphere
(van der Putten 1997).
Native and Nonnative Phragmites Survey and Study Site
A field survey of 212 Phragmites stands was conducted in
eastern Maryland U.S.A. (Fig. 1) during summer 2006. Leaf
samples were collected from the 212 Phragmites patches and
Estuaries and Coasts
identified as native or nonnative lineage using the genetic
analysis described in Tulbure et al. (2007) that was based on
Saltonstalls (2002) protocol. The survey targeted suspected
locations of native Phragmites and was not intended to be
random or otherwise representative of the area.
We selected three pairs of native and introduced stands
identified during the survey that were located along Kings
Creek in Talbot County, Maryland (Fig. 1), northeast of the
town of Easton near the Nature Conservancys Kings Creek
Preserve site (The Nature Conservancy;
The site is a tidal freshwater wetland that drains into the
Choptank River, a subestuary of Chesapeake Bay. The pairs
of stands selected were within meters of each other and
close to the creek, with no standing water present but wa-
terlogged soils. A previous study at the wetland showed that
there were no differences in porewater ammonium and
phosphate, the primary limiting nutrients to Phragmites,
between native and nonnative stands (Mozdzer and Zieman
2010). Therefore, we assume that any differences between
native and nonnative Phragmites would be due to genetic
differences alone.
Clonal Study and Pressurized Ventilation
A northsouth transect was placed across each of the six
patches, and the transects were divided into three zones of
equal length. The zones are hereafter referred to as center,
intermediary, and edge. In August 2006, we harvested all
aboveground biomass in three 0.25-m
quadrats in each zone.
Biomass from each quadrat was divided into living (green)
and senesced (brown) shoots and then oven dried at 60 °C for
48 h. Gas flow parameters were measured on randomly cho-
sen stems (18 per lineage) in each stand following the meth-
odology described in Rolletschek et al. (1999). Pressurization
of the lacunal air in the shoots was measured with a digital
manometer (HM35, Revue Thommen AG, Switzerland) and
gas flow rate was measured with a flow meter (Gilmond
Instruments, Inc., USA). The static pressure differential of
the living culm (Pculm) and the cutoff at the base, the stubble
(Pstubble), was measured with a gas connection directly to the
manometer. The dynamic pressure differential (Pd) and the
gas flow rate (Fd) were measured with the culm connected to
the stubble with the manometer in parallel and the flow meter
in series (Rolletschek et al. 1999). Ventilation efficiency
(sensu Rolletschek et al. 1999) was determined as the effective
ventilation per unit area. The effective ventilation parameter,
Fd/(PdPstubble) represents the flow rate (Fd) standardized
by the effective pressure differential (PdPstubble). Shoot
height, circumference at the base of the stem, and number of
leaves per shoot were also recorded for the same stems used
in the ventilation study.
Biomass, density, and ventilation efficiency data were
analyzed using Generalized Linear Mixed-Effects Models
to examine how lineage (native or nonnative Phragmites)
and location within a patch (edge, intermediary, or center)
affect total stem density as well as new and old culm density,
biomass, and ventilation efficiency. Lineage was treated as a
fixed effect, while stand was treated as a random effect
nested in lineage. When testing several a priori working
hypotheses, AIC is the method of choice over null hypoth-
esis testing (Anderson et al. 2001). We used an information
theoretic approach based on the second-order Akaikes In-
formation Criterion corrected for small sample size, AICc
(Burnham and Anderson 2002). Models were run using the
glmer function in the lme4 package in the software R (R
Development Core Team 2008).
Survey of Native and Nonnative Phragmites
PCR/RFLP genetic analysis of leaf samples revealed that only
14 Phragmites stands out of the 212 Chesapeake Bay stands
sampled were native. None of the samples collected from the
Fig. 1 Location of Phragmites stands sampled around Chesapeake
Bay. The three insets represent the areas where we identified native
Phragmites stands
Estuaries and Coasts
western shore of Chesapeake Bay (167) were native patches
(Fig. 1). Eleven native and 20 nonnative patches were
identified at the Kings Creek site and, as already described,
native and nonnative patches growing side by side were
identified. The other three native stands were from Tuckahoe
Creek (two stands) and Wicomico Creek (one stand). All
native patches identified as part of this study were located
on the eastern shore of Chesapeake Bay (Fig. 1).
Clonal Study and Pressurized Ventilation
The mean diameter of the nonnative stands was 30 % greater,
but the difference was not significant (Table 1). Shoot
circumference was 15 % greater for nonnative Phragmites,
the number of green leaves was 37 % greater, and the shoot
length was 16 % higher for nonnative than native Phragmites
(Table 1). Mean aboveground biomass was substantially
greater for nonnative than native Phragmites (Table 2), and
the difference was significant (F069.12, df 01, p-value0
0.01). Biomass per unit area decreased by 45 % from the
center towards the edge in patches of the native lineage and
differences between the three zones were significant (one-way
ANOVA F02.41, p-value00.1, df02; Table 2). There were
no significant biomass differences among zones within stands
of the nonnative lineage. The nonnative Phragmites always
had significantly greater biomass in each of the three
zones compared to the native lineage, and stem density was
significantly greater for the nonnative lineage (F09.75,
df 01, p-value 00.03) within each of the three zones
(Table 2). Nonnative Phragmites had almost twice as many
green stems as the native lineage (F06.16, df01, p-value0
0.06; Table 2). The standing dead density of stems was
appro ximately four times greater for the nonnative
lineage compared to the native Phragmites (F014.01,
df 01, p-value 00.02; Table 2). Information theoretic
model selection based on AICc revealed strong support
from the data for the influence of lineage (i.e., whether
Phragmites patches were native or nonnative) on biomass,
total stem density, new and old stem density, and ventilation
efficiency (Table 3). Ventilation efficiency was 300 % higher
for nonnative than native Phragmites (nonnative Phragmites,
1.85±0.5 mL min
; native Phragmites, 0.44 ±
0.4 mL min
), whereas effective ventilation of
single stems was approximately 200 % for nonnative than
native Phragmites (nonnative Phragmites, 0.016±0.004 mL/
min Pa
; native Phragmites, 0.007± 0.004 mL/min Pa
This study advances scientific knowledge about Phragmites
in several ways. This is the first study showing differences
in ventilation efficiency between native and nonnative
Phragmites. Also, we inventoried the lineage of Phragmites
stands on both shores of Chesapeake Bay, expanding upon
earlier work characterizing the eastern shore (Meadows
and Saltonstall 2007 ). Finally, our Phragmites stand
characterization is novel in comparing the allocation of stem
density and biomass in native versus introduced Phragmites
Once established, Phragmites can change environmental
conditions to create more favorable conditions for growth and
reproduction (Rudrappa et al. 2007). We found that nonnative
Phragmites had greater ventilation efficiency per unit area
than native stands. This was likely created by the fact that
introduced Phragmites had higher pressurized gas flow rates,
denser growth pattern, and greater number of old culms which
act as efflux culms. The flow rates measured were at the lower
range of values measu red for P hragmites i n Europe
(Rolletschek et al. 1999). Results of the pressurized ventilation
study demonstrated that nonnative Phragmites had the
potentialto oxidize the substrate more than native Phragmites.
While not measured in the field, one consequence of the
higher ventilation rates would be more efficient oxidation of
the substrate and a less reduced substrate in stands of
nonnative Phragmites, which in the long run would improve
sediment condition.
The convective flow-through pressurized ventilation
mechanism has been described for several wetland species
(Armstrong and Armstrong 1991), and Phragmites was
shown to have the highest flow rate when compared to 13
other wetland plants (Brix et al. 1992). This mechanism may
offer a competitive advantage over species relying exclusively
on diffusive gas transport (Brix et al. 1992). Higher
Table 1 Characteristics of
nonnative and native Phragmites
stands at King's Creek (MD)
measured in August 2006
(mean ± SE)
Nonnative Native F statistic df p-value Sample
size, n
Shoot length (cm) 300.58 ± 15.13 260.12 ± 14.52 3.72 1 0.12 18
Shoot circumference (cm) 2.71±0.11 2.30±0.11 6.31 1 0.06 18
Number of green leaves
per shoot
13.50± 1.43 8.48± 1.42 6.19 1 0.06 18
Diameter (m) of native
and nonnative stands
32.67± 8.83 23.13± 4.23 0.95 1 0.38 3
Estuaries and Coasts
ventilation efficiency can also benefit the nonnative
Phragmites by oxidizing potentially toxic compounds
in the rhizosphere (Armstrong and Armstrong 1991). Efficient
ventilation would oxidize sulfides, allowing Phragmites to
grow in brackish wetlands with higher sulfide concentrations
(Cronk and Fennessy 2001). Although nonnative Phragmites
can tolerate higher salinity levels than native Phragmites
(Vasquez et al. 2005), it cannot tolerate high sulfide
concentrations (Bart and Hartman 2003; Chambers et al.
1998; Wijte and Gallagher 1996). By supplying oxygen to
nitrifying bacteria, the nitrification of ammonium is
increased (Armstrong and Armstrong 1991), which could
benefit the plant, nitrate being mentioned as a primary cause
for increased introduced Phragmites abundance (Marks et al.
1994). Future studies should collect soil redox data and relate
them with ventilation efficiency and stand characteristics.
Our survey of Chesapeake Bay Phragmites stands revealed
that surprisingly few stands, all located on the eastern shore,
were of the native lineage (Fig. 1). Meadows and Saltonstall
(2007) reported that native Phragmites was much more
common on the Maryland eastern shore than in Delaware or
southern New Jersey, but they did not search for stands along
the western shore of Chesapeake Bay. Although subsequent
work by co-author Whigham and colleagues had identified a
stand of native Phragmites along Parkers Creek on the
western shore of Chesapeake Bay, it was in an area with very
little shoreline or upland development, atypical of the western
shore. Upland development and disturbance in wetlands have
been reported as factors contributing to the spread of nonnative
Phragmites (Bertness et al. 2002; King et al. 2007; Meadows
and Saltonstall 2007; Minchinton and Bertness 2003), often at
the expense of the native subspecies (Saltonstall 2003). We
cannot attribute causality to the low proportion of native
stands, but it is clear that the introduced lineage is far more
prevalent than the native lineage around Chesapeake Bay. The
rapid expansion of the nonnative Phragmites (McCormick et
al. 2010) potentially could result in the complete elimination
of the native haplotype when they co-occur.
Table 2 Differences in above ground biomass and stem density within the three zones of a stand (center, intermediary, and edge) for nonnative and
native Phragmites
Nonnative Native
Center Intermediary Edge Per stand Center Intermediary Edge Per stand
Biomass (mean ± SE)
as dry weight (g m
2,410.4± 69.7 2,868.8 ± 106.0 2,667.5 ±72.6 2,649±80.0 974.6 ± 45.0 708.0 ± 38.4 545.5± 26.1 742.7 ± 35.4
Density of new culms
(# stems m
96.9± 21.2 72.4 ± 10.2 83.6±10.7 84.3± 8.5 48.4 ± 6.5 37.3± 6 49.3± 12.5 45 ± 5
Density of old culms
(# stems m
31.6± 4.9 56.0± 14.7 37.3± 10.0 41.6 ± 6.3 9.3± 3.0 10.7± 2.2 8.0± 3.0 9.3± 1.6
Total stem density
(# stems m
128.4± 14.8 128.0±15.3 120.9± 16.3 126.0±31.3 57.8± 11.6 48.0±11.2 57.3± 9.0 54.4 ±20.2
Table 3 AICc-based model
selection for (1) total stem
density, (2) new culm density, (3)
old culm density, (4) biomass, and
(5) ventilation efficiency.
Generalized Linear Mixed-Effect
Models used site as a random
factor and included Lineage (Lin)
and Location within stand (L) as
fixed factors. We show the
number of predictor variables (K),
AICc differences (Δ) and Akaike
weights (ώ)
Model rank Model KAICc ώ
Total stem density (# stems m
) Lin + L 3 624.1 32.0 0.001
Lin 2 592.1 0.0 0.999
L 2 606.1 14.0 0.009
New culms (# new stems m
) Lin + L 3 624.1 32.0 0.001
Lin 2 592.1 0.0 0.999
L 2 606.1 14.0 0.009
Old culms (# old stems m
) Lin + L 3 575.2 29.3 0.004
N 2 545.9 0.0 0.996
L 2 557.2 11.3 0.003
Biomass Lin + L 3 962.8 32.6 0.008
Lin 2 930.2 0.0 0.999
L 2 944.8 14.6 0.006
Ventilation Efficiency (per m
) Lin + L 3 823.5 27.9 0.008
Lin 2 795.6 0.0 0.992
L 2 805.5 9.9 0.007
Estuaries and Coasts
The growth of the native and introduced stands within
meters of one another at Kings Creek made this site the ideal
setting for our study because edaphic conditions were similar,
therefore any differences observed could be attributed to
differences in lineage. Even though sampling nonnative and
native Phragmites pairs at different locations would have been
desirable, we could not locate other native and nonnative
Phragmites growing side by side at other sites besides Kings
Creek. As expected, nonnative Phragmites had greater
biomass and stem density per unit area than the native
Phragmites, similar to the findings of previous studies
(League et al. 2006; Meadows and Saltonstall 2007; Mozdzer
and Zieman 2010; Vasquez et al. 2005), which increase the
competitiveness and the ability of the nonnative Phragmites to
compete for resources such as light and space.
Rapid vegetative growth is one of the qualities of successful
weeds (Baker 1974; Sakai et al. 2001), allowing them to
maintain vigorous growth in their current habitat (Eriksson
1994). A greater growth rate towards the periphery of patches
has been shown to be inversely related to the time of stand
recruitment and clone density (Hartnett and Bazzaz 1985;
Parker 2000). We predicted that the stands of nonnative
Phragmites would exhibit greater clonal vigor (number of
stems and biomass) towards the edge of the clones. We
observed that biomass decreased toward the periphery of
native stands but not stands of the nonnative lineage, nor did
stem density per unit area change with increasing distance
from the center of stands (Table 2). However, Phragmites
stands sampled here have been established at Kings Creek
for several decades, very likely during the 1980s (Rice et
al. 2000), and lack of vigor could be related to patch age. To
further test our prediction that introduced stands would have
greater clonal vigor with increasing distance from the center of
the stand, future studies would either have to compare the
clonal growth in stands of Phragmites of different ages or use
newly established stands and measure parameters of clonal
vigor during several years immediately after establishment.
Studies documenting differences between native and
nonnative Phragmites are essential for a sound management
of Phragmites. This study explored one aspect of Phragmites
invasion, namely mechanisms employed by Phragmites to
sustain its invasion.
Once established, Phragmites is difficult to control as it
displaces native vegetation and changes wetland properties.
This study is the first one to show that nonnative Phragmites
has a higher ability to send oxygen to the rhizosphere than
native Phragmites, a physiological attribute that clearly bene-
fits nonnative Phragmites and provides a partial explanation
for its success. While testing with an experimental approach
should be conducted, our results suggest that once established,
along with other management practices (e.g., herbicide treat-
ment), measures targeted at inhibiting the pressurized ventila-
tion mechanism, such as completely removing the culms
which act as influx/efflux culms, followed by flooding for a
long period of time can reduce Phragmites success.
Acknowledgments We thank Dr. Doug Samson from The Nature Con-
servancy for providing information about the Kings Creek Preserve, Drs.
Joydeep Bhattacharjee and Neil Reese for help with choosing the instru-
ments, Jay ONeill for lab assistance, Dr. Kristin Saltonstall and Robert
Meadows for suggestions regarding native stand locations in Maryland,
Elaine Friebele for permission to sample Jug Bay wetlands, and Ned Gerber
for allowing us to use his farm during the field season. Funding came
through the Joseph F. Nelson scholarship to MGT. We thank the editors and
two anonymous reviewers for helpful comments on an earlier draft.
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... Importantly, the ventilation efficiency is 300% higher in non-native Phragmites, relative to the native taxa, due in large part to the differences in stem density between lineages (Tulbure et al. 2012). With fewer old, broken culms, the convective throughflow is slower in the native lineage (Tulbure et al. 2012), leading to probable differences in rhizosphere oxygen concentrations between lineages. ...
... Importantly, the ventilation efficiency is 300% higher in non-native Phragmites, relative to the native taxa, due in large part to the differences in stem density between lineages (Tulbure et al. 2012). With fewer old, broken culms, the convective throughflow is slower in the native lineage (Tulbure et al. 2012), leading to probable differences in rhizosphere oxygen concentrations between lineages. Because rates of nutrient cycling are faster in aerated soils, non-native Phragmites may benefit from increased rates of nutrient cycling in a more heavily aerated rhizosphere Lathrop 1999, Windham and. ...
... Given that ventilation efficiency differs dramatically between native and non-native Phragmites (Tulbure et al. 2012), one might expect to see differences in microbial communities based on respiratory mode. However, the discrepancies in ventilation did not appear to affect endophytic colonization. ...
The mechanisms driving biological invasions are important for predicting range expansion and developing effective invasive species management strategies but are often difficult to disentangle. One driver of plant invasions may be through differential interactions with belowground microbes, whereby invasive plants gain a disproportionate advantage over natives either through a relatively stronger interaction with mutualists or a weaker interaction with pathogens. I aimed to examine whether invasive Phragmites australis, a clonal wetland plant, gains a performance advantage over a related native lineage through interactions with belowground microbial communities. I explored bacterial, fungal, and oomycete communities associated with native and non-native Phragmites in the Great Lakes region and the impacts of those microbial communities on invasiveness. I used a combination of field surveys of natural populations and controlled environment experimental manipulations combined with next-generation sequencing to thoroughly examine whether invasiveness in Phragmites is facilitated by interactions wih belowground microbes and which microbial players are most influential. My results were very consistent among all chapters in this dissertation, finding no strong link between invasiveness and belowground microbial communities, and therefore suggesting that belowground microbes are not fostering invasion of Phragmites australis in the Great Lakes region. Field surveys provided evidence that belowground microbial communities did not differ between Phragmites lineages in roots or rhizospheres of natural populations. Root communities did differ in fungal colonization and in oomycete richness, but both of those differences were weak and inconsistent among different environmental conditions. In addition, the few differences that were found between lineages were consistently opposite of my expectation that non-native Phragmites would be associated with more mutualists and/or fewer pathogens than native. The rhizosphere largely followed the same patterns with one exception: the rhizosphere bacterial communities differed by lineage in large, dense patches of Phragmites, but not elsewhere. Given the small magnitude of the observed differences in bacterial communities, and the fact that they only existed in dense, mature patches of Phragmites, no differences in functional potential could be attributed to the community differences observed. Taken together, the evidence that I have obtained strongly suggests that any observed differences in soil microbial communities between Phragmites lineages may be a consequence rather than a driver of invasiveness. Consistent with results from natural populations, I also observed that experimentally-conditioned soils differed only slightly between lineages in bacterial community composition and even less so in fungal community composition. The plant response to those slightly different microbial communities was more significant, but again opposite of expectations if microbes were driving invasiveness. Non-native Phragmites was overall negatively impacted by the total soil microbiome, whereas native was unaffected by the total soil microbiome, regardless of which lineage conditioned the soil, with bacterial pathogens likely playing a significant role in the negative plant-soil interaction. These findings on lineage-specific plant responses are counter to our expectation that if microbial communities are driving invasiveness, non-native Phragmites should derive disproportionate benefits from microbial communities over native. Given the preponderance of data suggesting that belowground microbes are not drivers of invasiveness in Phragmites, it is reasonable to assume that the non-native’s invasiveness is primarily derived from other sources. However, importantly, differential response to similar microbes in native and non-native lineages suggests that microbial manipulation could be a reasonable tool for lineage-specific biocontrol.
... For instance, in waterlogged soils, oxygen diffusion into the soil could select for more aerobic organisms in the root zone. Importantly, native and non-native Phragmites differ vastly in their ability to aerate soils in the root zone, with the differences driven mostly by higher live stem density and a large number of senesced stems from previous years in invasive populations (Tulbure et al., 2012). Therefore, microbial community differences between Phragmites lineages may result from differences in soil oxygen concentrations and the strength of differences may depend on the stand age, density, and dominance of the patch. ...
... Given the mixed evidence for distinction in rhizosphere microbial communities between Phragmites lineages, we sought to examine whether soil communities surrounding each lineage differed or, as with the root communities of the Great Lakes, were similar. Despite no differences found in roots , rhizosphere communities may be driven by a separate set of factors such as differences in oxygen diffusion sensu Tulbure et al. (2012). Accordingly, stand density and dominance may play an important role in the strength of differentiation in microbial communities between lineages. ...
... F I G U R E 5 Relative abundance of dominant fungal functional groups found in the rhizosphere. Results of a two-way ANOVA with Type III sum of squares verified that no comparisons between sites, lineages, or their interactions were significant at α = 0.05 of Phragmites stems in non-native stands (Tulbure et al., 2012). In anoxic wetland soils, an increase in the soil oxygen concentration could plausibly change the composition of bacterial communities, such that more aerobic microbes are present. ...
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Microorganisms surrounding plant roots may benefit invasive species through enhanced mutualism or decreased antagonism, when compared to surrounding native species. We surveyed the rhizosphere soil microbiome of a prominent invasive plant, Phragmites australis, and its co-occurring native subspecies for evidence of microbial drivers of invasiveness. If the rhizosphere microbial community is important in driving plant invasions, we hypothesized that non-native Phragmites would cultivate a different microbiome from native Phragmites, containing fewer pathogens, more mutualists, or both. We surveyed populations of native and non-native Phragmites across Michigan and Ohio USA, and we described rhizosphere microbial communities using culture-independent next-generation sequencing. We found little evidence that native and non-native Phragmites cultivate distinct bacterial, fungal, or oomycete rhizosphere communities. Microbial community differences in our Michigan survey were not associated with plant lineage but were mainly driven by environmental factors, such as soil saturation and nutrient concentrations. Intensive sampling along transects consisting of dense monocultures of each lineage and mixed zones revealed bacterial community differences between lineages in dense monoculture, but not in mixture. We found no evidence of functional differences in the microbial communities surrounding each lineage. We extrapolate that the invasiveness of non-native Phragmites, when compared to its native congener, does not result from the differential cultivation of beneficial or antagonistic rhizosphere microorganisms.
... Phragmites australis is generally considered to be tolerant of high water levels because it can aerate flooded tissues by transporting oxygen through the aerenchyma, creating an extensive network of internal airspaces (Armstrong and Armstrong 1991;Jackson and Armstrong 1999;Eller et al. 2017). To date, there is limited information regarding whether P. australis genotypes or lineages vary in their gas transport efficiencies or response to high water or flooding (but see Engloner and Major 2011;Tulbure et al. 2012). In our study, the high-water treatment maintained water depth at 40 cm, well within the level found in the MRD where water depths can range from 0 cm to at least 150 cm (J. ...
... The highly efficient gas transport system of the EU lineage (Tulbure et al. 2012) likely predisposes it to being able to thrive in flooded/high-water environments. Currently, nothing is known about gas and nutrient transport in the Delta and Gulf lineages but they appear to be adapted to different environments. ...
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In 2016, widespread dieback of Phragmites australis was reported in the Mississippi River Delta (MRD), Louisiana. We conducted two common-garden experiments to investigate several potentially important factors associated with this dieback: scale insects, water depth, fertilization and P. australis genetics (three lineages: Gulf, Delta and invasive EU). Predictions tested were scale abundance is lower in high water, at low fertilization, and for EU; plant biomass is negatively impacted by scales, high water and high fertilization; and EU suffers the least damage from the three potential stressors. Scale abundance was 41% lower in high water and decreased 2.7 fold as fertilization increased. Also, EU had 1.5–2.6 times fewer scales than Gulf, but had similar scale abundance to Delta. Impacts of scales, water depth and fertilizer on plant biomass depended strongly on lineage. Scales reduced biomass of Delta, EU and Gulf by 38%, 32% and 10%, respectively. In comparison, biomass was 30% higher for EU, 46% lower for Gulf and unchanged for Delta in high versus low water. Finally, at high fertilization levels, Gulf produced 57% more biomass than EU. Owing to its greater tolerance to scales and high water, EU may be most suitable for use in restoration of the MRD.
... could not survive through winter on native Phragmites because they oviposit beneath leaf sheaths, which typically abscise in autumn, whereas leaf sheaths of non-native Phragmites tend to persist through winter and thus offer greater protection. In fact, loose leaf sheaths are a typical but variable trait of native Phragmites, which is why using it as an identifying characteristic has given way to genetic analysis in cases where lineage needs to be determined unequivocally (Saltonstall 2003c;Tulbure et al. 2012;Guo et al. 2014). Some native populations retain leaf sheaths to a greater degree than others and Allen et al. (2017a, b) and Swearingen and Saltonstall (2012) have cautioned that morphological and phenological traits are subtle, sometimes subjective, and variable across the North American range of Phragmites. ...
... Native Phragmites, or other robust native graminoids such as Spartina alterniflora or Typha L., might replace some of the biologicallycontrolled non-native Phragmites. However, at least in some situations, non-native Phragmites has been shown to exceed native Phragmites in rhizosphere oxygenation, photosynthetic rate, photosynthetic canopy, specific leaf area, nitrogen content, length of growing season, sexual reproduction, shoot density and height, biomass, and relative growth rate (Mozdzer and Zieman 2010; Kettenring and Mock 2012;Tulbure et al. 2012;Mozdzer et al. 2013), but it is not known how these traits might drive differences in ecosystem services overall. Also, as explained above, native Phragmites may be adversely affected by biocontrol of non-native Phragmites. ...
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Classical biocontrol constitutes the importation of natural enemies from a native range to control a non-native pest. This is challenging when the target organism is phylogenetically close to a sympatric non-target form. Recent papers have proposed and recommended that two European moths (Archanara spp.) be introduced to North America to control non-native Phragmites australis australis, claiming they would not adversely affect native P. australis americanus. We assert that these papers overlooked research contradicting their conclusions and that the authors recommended release of the non-native moths despite results of their own studies indicating that attack on native Phragmites is possible after field release. Furthermore, their open-field, host-specificity tests were conducted in non-wetland fields in Switzerland using potted plants, reflecting considerably different conditions than those of North American wetlands. Also, native Phragmites in eastern North America has declined, increasing its potential vulnerability to any new stressors. Because all inadvertently introduced, established, Phragmites-specialist, herbivorous insects have done more harm to native than non-native Phragmites, native Phragmites may experience more intense herbivory than non-native Phragmites from the introduction of Archanara spp. due to demographic mechanisms (e.g., increase in density of the biocontrol agent and spillover onto alternate hosts) or because the herbivores may undergo genetic change. In addition to the risk to native Phragmites, significant biomass reduction of non-native Phragmites may decrease important ecosystem services, including soil accretion in wetlands affected by sea level rise. We strongly caution against the approval of Archanara spp. as biocontrol agents for non-native Phragmites in North America.
... Compared to a native American lineage Phragmites australis subsp. americanus, the invasive European lineage has greater phenotypic plasticity , nitrogen uptake capacity (Packett and Chambers, 2006;Mozdzer and Zieman, 2010), ventilation efficiency (Tulbure et al., 2012) and salt tolerance (Vasquez et al., 2005). These traits have allowed invasive Phragmites to become dominant in many wetland habitats, particularly in areas susceptible to disturbance and nutrient enrichment (Kettenring et al., 2015;Sciance et al., 2016) where it can gain a competitive advantage over native vegetation (Bertness et al., 2002;Holdredge et al., 2010). ...
Land use changes and greater nitrogen input into waterways have facilitated the spread of an invasive Eurasian lineage of Phragmites australis across North America. Its establishment has led to decreases in wetland plant diversity, and displacement of a native American Phragmites lineage considered to be a low-nutrient specialist. We hypothesized that carbon-rich amendments that reduced nitrogen availability would competitively favor the native lineage and nitrogen additions would favor the invasive lineage. In the greenhouse we assessed competitive interactions between native and invasive lineages following sawdust (low nitrogen) and urea (high nitrogen) additions by measuring total biomass, chlorophyll fluorescence and evaluating biomass allocation. Sawdust additions did not limit invasive Phragmites growth, while urea increased aboveground biomass of both lineages. Unexpectedly, mixtures of native and invasive Phragmites produced more above and belowground biomass than monocultures. Our findings suggest that at the level examined in this study, carbon additions would not be an effective management tool to control invasive Phragmites or restore the native North American lineage, but that facilitation between native and invasive lineages could promote their coexistence across a range of nutrient availability. Our results also provide limited evidence that displacement of native Phragmites could be due to other factors such as disturbance rather than competitive exclusion.
... Facultative anaerobes were affected by soil saturation level, but they made up a much smaller proportion of bacterial sequences (Appendix S1: Table S7, Fig. S6). Given that ventilation efficiency differs dramatically between native and non-native Phragmites (Tulbure et al. 2012), one might expect to see differences in microbial communities based on respiratory mode. However, the discrepancies in ventilation did not appear to affect endophytic colonization. ...
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Microbial interactions could play an important role in plant invasions. If invasive plants associate with relatively more mutualists or fewer pathogens than their native counterparts, then microbial communities could foster plant invasiveness. Studies examining the effects of microbes on invasive plants commonly focus on a single microbial group (e.g., bacteria) or measure only plant response to microbes, not documenting the specific taxa associating with invaders. We surveyed root microbial communities associated with co‐occurring native and non‐native lineages of Phragmites australis, across Michigan, USA. Our aim was to determine whether (1) plant lineage was a stronger predictor of root microbial community composition than environmental variables and (2) the non‐native lineage associated with more mutualistic and/or fewer pathogenic microbes than the native lineage. We used microscopy and culture‐independent molecular methods to examine fungal colonization rate and community composition in three major microbial groups (bacteria, fungi, and oomycetes) within roots. We also used microbial functional databases to assess putative functions of the observed microbial taxa. While fungal colonization of roots was significantly higher in non‐native Phragmites than the native lineage, we found no differences in root microbial community composition or potential function between the two Phragmites lineages. Community composition did differ significantly by site, with soil saturation playing a significant role in structuring communities in all three microbial groups. The relative abundance of some specific bacterial taxa did differ between Phragmites lineages at the phylum and genus level (e.g., Proteobacteria, Firmicutes). Purported function of root fungi and respiratory mode of root bacteria also did not differ between native and non‐native Phragmites. We found no evidence that native and non‐native Phragmites harbored distinct root microbial communities; nor did those communities differ functionally. Therefore, if the trends revealed at our sites are widespread, it is unlikely that total root microbial communities are driving invasion by non‐native Phragmites plants.
... australis, has a ventilation efficiency 300% greater than the North American P. australis subsp. americanus lineage (Tulbure et al. 2012). Plant radial oxygen leakage can also influence C cycling in cold peat bogs, as was demonstrated in Patagonia by comparing methane (CH 4 ) emissions and redox potential in Sphagnum systems with and without cushion plants (Astelia spp. ...
New soil organic matter (SOM) models highlight the role of microorganisms in plant litter decomposition and storage of microbial-derived carbon (C) molecules. Wetlands store more C per unit area than any other ecosystem, but SOM storage mechanisms such as aggregation and metal complexes are mostly untested in wetlands. This review discusses what is currently known about the role of microorganisms in SOM formation and C sequestrations, as well as, measures of microbial communities as they relate to wetland C cycling. Studies within the last decade have yielded new insights about microbial communities. For example, microbial communities appear to be adapted to short-term fluctuations in saturation and redox and researchers have observed synergistic pairings that in some cases run counter to thermodynamic theory. Significant knowledge gaps yet to be filled include: 1) What controls microbial access to and decomposition of plant litter and SOM? 2) How does microbial community structure shape C fate, across different wetland types? 3) What types of plant and microbial molecules contribute to SOM accumulation? Studies examining the active microbial community directly or that utilize multi-pronged approaches are shedding new light on microbial functional potential, however, and promise to improve wetland C models in the near future.
Molecular oxygen and carbon dioxide may be limited for aquatic plants, but they have various mechanisms for acquiring these gases from the atmosphere, soil, or metabolic processes. The most common adaptations of aquatic plants involve various aerenchymatic structures, which occur in various organs, and enable the throughflow of gases. These gases can be transferred in emergent plants by molecular diffusion, pressurized gas flow, and Venturi-induced convection. In submerged species, the direct exchange of gases between submerged above-ground tissues and water occurs, as well as the transfer of gases via aerenchyma. Photosynthetic O2 streams to the rhizosphere, while soil CO2 streams towards leaves where it may be used for photosynthesis. In floating-leaved plants anchored in the anoxic sediment, two strategies have developed. In water lilies, air enters through the stomata of young leaves, and streams through channels towards rhizomes and roots, and back through older leaves, while in lotus, two-way flow in separate air canals in the petioles occurs. In Nypa Steck palm, aeration takes place via leaf bases with lenticels. Mangroves solve the problem of oxygen shortage with root structures such as pneumatophores, knee roots, and stilt roots. Some grasses have layers of air on hydrophobic leaf surfaces, which can improve the exchange of gases during submergence. Air spaces in wetland species also facilitate the release of greenhouse gases, with CH4 and N2O released from anoxic soil, which has important implications for global warming.
Recently, coastal land reclamation through the use of embankments has increased worldwide, and its impacts on ecosystem processes and functionality have been widely reported. However, the ecosystem nitrogen (N) cycling turnover processes following the establishment of coastal embankments remain unknown. For this study, we investigated stocks of various types of N in soils, N storage in plant subsystems, the microbial immobilization and mineralization of N, as well as soil physiochemical properties in embanked and adjacent unembanked Spartina alterniflora, Suaeda salsa, and Phragmites australis saltmarshes in the coastal wetlands of China. Coastal embankments in a S. alterniflora saltmarsh significantly decreased the total plant N storage by 50.24%, concentrations of total soil organic N (SON) by 55.16%, ammonia nitrogen (NH4-N) by 32.33%, nitrite nitrogen (NO2-N) by 41.23%, nitrate nitrogen (NO3-N) by 13.38%, and the value of soil net ammonification (RA) by 83.49%. However, in P. australis saltmarshes they significantly increased the total plant N storage by 160.24%, concentrations of SON by 57.28%, NH4-N by 7.89%, NO2-N by 101.76%, NO3-N by 32.05%, and the value of RA by 392.95%. Nevertheless, there were no significant differences in N cycling following the establishment of coastal embankments in S. salsa saltmarshes. Significant changes in the organic and inorganic soil N pools of S. alterniflora and P. australis saltmarshes were driven by plant residue inputs, which were significantly affected by decreasing soil salinity in these coastal wetlands. Furthermore, our results indicated that coastal embankments altered the immobilization of soil N and mineralization of microorganisms by influencing the growth and activities of soil microbes, which were primarily associated with changes in soil organic and inorganic N pools following the development of coastal embankments. In summary, alterations in the organic N inputs of plants were initiated by the dramatically decreased soil salinity, which was the main determinant that drove N cycling in the soil subsystems of coastal wetlands subsequent to the establishment of coastal embankments.
(1) Populations of Solidago canadensis were studied on an abandoned agricultural field in east-central Illinois. The patterns of genet recruitment, the population dynamics of genets and ramets following colonization, and changes in genet diversity during succession were examined. (2) Invasion occurred mainly during the third, fourth and fifth years after the field was abandoned. There was no recruitment after the sixth year, but rapid clonal expansion of the established genets caused ramet densities to continue to increase for several years. (3) Both genet survivorship and clonal growth were inversely related to the time of recruitment, so that after a few years the populations were composed mainly of genets that had established during the first year of colonization. (4) The density of genets reached a maximum in the fifth year and then slowly declined. The density and composition of genets in an adjacent 15-year old field remained constant over 6 years suggesting that the number of genets may reach an equilibrium in older populations and a diversity of genets may be maintained. (5) The interdependence among ramets within clones and their ability to integrate environmental heterogeneity may buffer against localized `patch-specific' selective influences resulting in little differential mortality among genotypes. This may be one mechanism maintaining a diversity of genets in successional S. canadensis populations.
We give suggestions for the presentation of research results from frequentist, information-theoretic, and Bayesian analysis paradigms, followed by several general suggestions. The information-theoretic and Bayesian methods offer alternative approaches to data analysis and inference compared to traditionally used methods. Guidance is lacking on the presentation of results under these alternative procedures and on nontesting aspects of classical frequentist methods of statistical analysis. Null hypothesis testing has come under intense criticism. We recommend less reporting of the results of statistical tests of null hypotheses in cases where the null is surely false anyway, or where the null hypothesis is of little interest to science or management.
Gradients in oxygen availability and salinity are among the most important environmental parameters influencing zonation in salt marsh communities. The combined effects of oxygen and salinity on the germination of two salt marsh grasses, Spartina alterniflora and Phragmites australis, were studied in growth chamber experiments. Germination of both species was initiated by emergence of the shoot and completed by root emergence. Percentage S. alterniflora germination was reduced at high salinity (40 g NaCl/L) and in decreased oxygen (5 and 2.5%). In 0% oxygen shoots emerged, but roots did not. P. australis germination was reduced at a lower salinity (25 g NaCl/L) than S. alterniflora, and inhibited at 40 g NaCl/L and in anoxia. However, a combination of hypoxia (10 and 5% O2) and moderate salinity (5 and 10 g NaCl/L) increased P. australis germination. When bare areas in the salt marsh are colonized, the different germination responses of these two species to combinations of oxygen and salt concentrations are important in establishing their initial zonation. In high salinity wetlands S. alterniflora populates the lower marsh and P. australis occupies the high marsh at the upland boundary.