Phosphorus addition reduces invasion of a longleaf pine savanna (Southeastern USA) by a non-indigenous grass (Imperata cylindrica)

Imperata cylindrica is an invasive C₄ grass, native to Asia and increasing in frequency throughout the tropics, subtropics, and southeastern USA. Such increases are associated with reduced biodiversity, altered fire regimes, and a more intense competitive environment for commercially important species. We measured rates of clonal spread by I. cylindrica from a roadside edge into the interior of two longleaf pine savannas. In addition, we measured the effects of fertilization with nitrogen and phosphorus on clonal invasion of one of these sites. Clonal invasion occurred at both sites and at similar rates. Older portions of an I. cylindrica sward contained fewer species of native pine-savanna plants. Clonal growth rates and aboveground mass of I. cylindrica were reduced by the addition of phosphorus relative to controls by the second growing season at one site. As a group, native species were not affected much by P-addition, although the height of legumes was increased by P addition, and the percent cover of legumes relative to native non-legumes decreased with increasing expected P limitation (i.e., going from P-fertilized to controls to N-fertilized treatments). Clonal invasion was negatively correlated with the relative abundance of legumes in control plots but not in P-fertilized plots. Species richness and percent cover of native plants (both legumes and non-legumes) were dramatically lower in N-fertilized plots than in controls or P-fertilized plots. Species richness of native plants was negatively correlated with final aboveground mass of I. cylindrica in control and P-fertilized plots, but not in N-fertilized plots. The results suggest that I. cylindrica is a better competitor for phosphorus than are native pine-savanna plants, especially legumes, and that short-lived, high-level pulses of phosphorus addition reduce this competitive advantage without negatively affecting native plant diversity. Ratios of soil P to N or native legume to non-legume plant species may provide indicators of the resistance of pristine pine savannas to clonal invasion by I. cylindrica.     

Role of species identity in plant invasions: experimental test using Imperata cylindrica

The role of species richness, functional diversity and species identity of native Florida sandhill understory species were tested with Imperata cylindrica, an exotic rhizomatous grass, in mesocosms. I. cylindrica was introduced 1 year after the following treatments were established: a control with no native species, five monocultures, a grass mix treatment, a forb mix treatment, and a 3-species treatment and a 5-species treatment. Monthly cover, final biomass, root length, root length density (RLD) and specific root length (SRL) of all species were determined for one full growing season. There was a significant negative linear relationship between the cover of native species and I. cylindrica (r ² = 0.59, P = 0.01) and a negative logarithmic relationship between the biomass of native species and I. cylindrica (r ² = 0.70, P = 0.003). There was no diversity–invasibility relationship. Grasses proved to be the most resistant functional group providing resistance alone and in mixed functional communities. Repeated measures analysis demonstrated that treatments including Andropogon virginicus were the most resistant to invasion over time (P < 0.001). Significantly greater root length (P = 0.002), RLD (P = 0.011) and SRL (P < 0.001) than all of the native species and I. cylindrica in monocultures and in mixed communities made A. virginicus successful. The root morphology characteristics allowed it to be a great competitor belowground where I. cylindrica was most aggressive. The results suggest that species identity could be more important than species or functional richness in determining community resistance to invasion.     

Effects of longleaf pine planting density and other factors on stand structure and associated wildlife habitat

The primary objective of many longleaf pine (Pinus palustris) restoration programs is to enhance or restore habitat for wildlife dependent on herbaceous plant communities. Because herbaceous cover is inversely related to canopy cover, restoration programs often place restrictions on longleaf pine planting density. However, the influence of planting density on understory plant communities has been inadequately evaluated. Therefore, we initiated a study to examine the relative influences of planting density and other factors on overall understory composition and forage availability for white‐tailed deer (Odocoileus virginianus) and northern bobwhite (Colinus virginianus) in nine longleaf pine stands throughout the Coastal Plain of Alabama during 2017–2018. We found that coverage of herbaceous plants decreased 3.5%, coverage of woody plants decreased 2.4%, and coverage of northern bobwhite forage plants decreased 1.9% for each 1 m²/ha increase in longleaf pine basal area. However, planting density was not a significant predictor of current basal area, nor coverage of any functional group of plants we examined, likely because current longleaf pine density averaged only 46% (range = 30–64%) of seedling planting density. We did not detect an effect of prescribed fire on stand condition or understory plant communities, likely due to variability in fire timing and frequency. Our findings related to planting density were likely a function of low longleaf pine survival, which is not uncommon. Because of this and the inherent variability in growth rates for young longleaf pine stands, restoration programs should consider placing greater emphasis on post‐planting monitoring and management than planting density.     

Resource competition and fire‐regulated nutrient demand in carnivorous plants of wet pine savannas

Question: What are the mechanisms by which fire reduces competition for both a short‐lived and a long‐lived species in old‐growth ground‐cover plant communities of wet pine savannas (originally Pinus palustris, replaced by P. elliottii)? Location: Outer coastal plain of southeastern Mississippi, USA. Methods: I reviewed previous competition experiments and proposed a new hypothesis to explain the relationship between fire, competition, and species co‐existence in wet longleaf pine savannas. The first study is about growth and seedling emergence responses of a short‐lived carnivorous plant, Drosera capillaris, to reduction in below‐ground competition and above‐ plus below‐ground competition. The second study deals with growth and survival responses of a long‐lived perennial carnivorous plant, Sarracenia alata, to neighbour removal and prey‐exclusion to determine if a reduction in nutrient supply increased the intensity of competition in this nutrient‐poor system. Results: Fire increased seedling emergence of the short‐lived species by reducing above‐ground competition through the destruction of above‐ground parts of plants and the combustion of associated litter. Prey exclusion did not increase competitive effects of neighbours on the long‐lived species. However, because the experiment was conducted in a year without fire, shade reduced nutrient demand, which may have obviated competition for soil nutrients between Sarracenia alata and its neighbours. Conclusion: Repeated fires likely interact with interspecific differences in nutrient uptake to simultaneously reduce both above‐ground competition and competition for nutrients in old‐growth ground cover communities in pine savannas. Restoration practitioners should consider the possibility that the composition of the plant community is just as important as fire in ensuring that frequent fires maintain species diversity.     

Native Alternatives for Non-Native Turfgrasses in Central Florida: Germination and Responses to Cultural Treatments

Little information exists about the establishment of native longleaf pine flatwoods species for use in restoration efforts and as buffers around natural areas in the southeastern United States. Composition of groundcover in these systems is dominated by perennial graminoid species. Vegetation in current buffers is generally non‐native turfgrass that can escape into natural areas, often reducing establishment and survival of native species. Where management objectives involve actively restoring native groundcover or reducing the probability of invasion by these non‐native turfgrasses, identification of native species and restoration methods is needed. We investigated seed germination and establishment of four species native to longleaf pine flatwoods in central Florida and one species native to the adjacent wetland communities. Paspalum setaceum, Panicum anceps, Eustachys petraea, and Eragrostis refracta were directly seeded, and P. distichum was planted as sprigs into three former P. notatum pastures. Irrigation, fertilization, weed control, and mowing treatments were assessed in terms of cover development of the sown species. Paspalum distichum developed the highest percent cover—over 80% in wet areas after 1 year. Mowing had mixed impacts depending on the species, and fertilization never significantly increased cover. Directly seeded species developed sparse cover (0–40%), probably as a result of drought conditions. However, E. petraea and E. refracta appeared more promising for use on rights‐of‐way when using high sowing rates. A second experiment conducted on a roadside included these two species and sprigged P. distichum. Both E. petraea and P. distichum developed more than 45% cover on the roadside. Establishment of these natives from seed or sprigs was significantly enhanced when site preparation effectively reduced the seedbank of other species present in the soil.     

Introduced deer reduce native plant cover and facilitate invasion of non-native tree species: evidence for invasional meltdown

Invasive species are a major threat to native communities and ecosystems worldwide. One factor frequently invoked to explain the invasiveness of exotic species is their release in the new habitat from control by natural enemies (enemy-release hypothesis). More recently, interactions between exotic species have been proposed as a potential mechanism to facilitate invasions (invasional meltdown hypothesis). We studied the effects of introduced deer on native plant communities and exotic plant species on an island in Patagonia, Argentina using five 400 m² exclosures paired with control areas in an Austrocedrus chilensis native forest stand. We hypothesized that introduced deer modify native understory composition and abundance and facilitate invasion of introduced tree species that have been widely planted in the region. After 4 years of deer exclusion, native Austrocedrus and exotic Pseudotsuga menziesii tree sapling abundances are not different inside and outside exclosures. However, deer browsing has strongly inhibited growth of native tree saplings (relative height growth is 77% lower with deer present), while exotic tree sapling growth is less affected (relative height growth is 3.3% lower). Deer significantly change abundance and composition of native understory plants. Cover of native plants in exclosures increased while cover in controls remained constant. Understory composition in exclosures after only 4 years differs greatly from that in controls, mainly owing to the abundance of highly-browsed native species. This study shows that introduced deer can aid the invasion of non-native tree species through negatively affecting native plant species.     

Reduced soil compaction enhances establishment of non-native plant species

Many studies have shown that soil disturbance facilitates establishment of invasive, non-native plant species, and a number of mechanisms have been isolated that contribute to the process. To our knowledge no studies have isolated the role of altered soil compaction, a likely correlate of many types of soil disturbance, in facilitating invasion. To address this, we measured the response of seeded non-native and native plant species to four levels of soil compaction in mesocosms placed in an abandoned agricultural field in the Methow Valley, Washington, USA. Soil compaction levels reflected the range of resistance to penetration (0.1–3.0 kg cm⁻²) measured on disturbed soils throughout the study system prior to the experiment. Percent cover of non-native species, namely Bromus tectorum and Centaurea diffusa, decreased by 34% from the least to the most compacted treatments, whereas percent cover of native species, mostly Pseudoroegneria spicata and Lupinus spp., did not respond to compaction treatments. Experimental results were supported by a survey of soil penetration resistance and percent cover by species in 18 abandoned agricultural fields. Percent cover of B. tectorum was negatively related to soil compaction levels, whereas none of the native species showed any response to soil compaction. These results highlight a potentially important, though overlooked, aspect of soil disturbance that may contribute to subsequent non-native plant establishment.     

Non-native grass invasion alters native plant composition in experimental communities

Invasions of non-native species are considered to have significant impacts on native species, but few studies have quantified the direct effects of invasions on native community structure and composition. Many studies on the effects of invasions fail to distinguish between (1) differential responses of native and non-native species to environmental conditions, and (2) direct impacts of invasions on native communities. In particular, invasions may alter community assembly following disturbance and prevent recolonization of native species. To determine if invasions directly impact native communities, we established 32 experimental plots (27.5 m²) and seeded them with 12 native species. Then, we added seed of a non-native invasive grass (Microstegium vimineum) to half of the plots and compared native plant community responses between control and invaded plots. Invasion reduced native biomass by 46, 64, and 58%, respectively, over three growing seasons. After the second year of the experiment, invaded plots had 43% lower species richness and 38% lower diversity as calculated from the Shannon index. Nonmetric multidimensional scaling ordination showed a significant divergence in composition between invaded and control plots. Further, there was a strong negative relationship between invader and native plant biomass, signifying that native plants are more strongly suppressed in densely invaded areas. Our results show that a non-native invasive plant inhibits native species establishment and growth following disturbance and that native species do not gain competitive dominance after multiple growing seasons. Thus, plant invaders can alter the structure of native plant communities and reduce the success of restoration efforts.     

Scaling species dynamics in Pinus palustris communities: Effects of pine straw raking

Abstract. In the southeastern USA, harvest of pine straw sometimes involves mechanical raking of natural Pinus palustris (longleaf pine) communities. Little is known about the effects of raking nor how these effects may vary in time and space. In a two yr experiment, we examined the effects of mechanized raking on Pinus palustris dominated communities (scrub oak, dry savanna, and mesic savanna) by monitoring vegetation at seven spatial scales (0.01–100 m²). We measured floristic similarity and the proportion of species initially present that were gained (i.e. new species) or lost during four sampling periods. Relationships between spatial scale and these community attributes were analyzed using a repeated measures approach and functional response curves. Spatial scale clearly affected observed rates of species loss and floristic similarity; losses declined and floristic similarity increased as scale increased. We relate these patterns to expanding population sizes with scale and our inability to detect species reductions in large populations. Scale had little influence on species gains. The effects of raking did not differ across scales, but raking caused greater mean losses of species and greater mean changes in floristic similarity when mean values were calculated over all scales. Raking also increased the mean rate of species gains in the mesic savanna during one period. Otherwise, interaction effects of community and raking were largely absent from both mean values and response curves. Despite significant short‐term effects of raking, changes in species richness were minor.     

Native plant diversity increases herbivory to non-natives

There is often an inverse relationship between the diversity of a plant community and the invasibility of that community by non-native plants. Native herbivores that colonize novel plants may contribute to diversity–invasibility relationships by limiting the relative success of non-native plants. Here, we show that, in large collections of non-native oak trees at sites across the USA, non-native oaks introduced to regions with greater oak species richness accumulated greater leaf damage than in regions with low oak richness. Underlying this trend was the ability of herbivores to exploit non-native plants that were close relatives to their native host. In diverse oak communities, non-native trees were on average more closely related to native trees and received greater leaf damage than those in depauperate oak communities. Because insect herbivores colonize non-native plants that are similar to their native hosts, in communities with greater native plant diversity, non-natives experience greater herbivory.     

Effect of an invasive grass on ambient rates of decomposition and microbial community structure: a search for causality

In situ decomposition of above and belowground plant biomass of the native grass species Andropogon glomeratus (Walt.) B.S.P. and exotic Imperata cylindrica (L.) Beauv. (cogongrass) was investigated using litter bags over the course of a 12 month period. The above and belowground biomass of the invasive I. cylindrica always decomposed faster than that of the native A. glomeratus. Also, belowground biomass of both species decomposed at a consistently faster rate when placed within an invaded area consisting of a monotypic stand of I. cylindrica as opposed to within a native plant assemblage. However, there was no similar such trend observed in the aboveground plant material. The microbial communities associated with the invaded sites often differed from those found in the native vegetation and provide a possible causal mechanism by which to explain the observed differences in decomposition rates. The microbial communities differed not only compositionally, as indicated by ordination analyses, but also functionally with respect to enzymatic activity essential to the decomposition process. This study supports the growing consensus that invasive plant species alter normal ecological processes and highlights a possible mechanism (alteration of microbial assemblages) by which I. cylindrica may alter an ecosystem process (decomposition).     

Twenty years of vegetation change in five long-unburned Florida plant communities

Abstract. Rates and directions of change over a 20-yr interval in five long-unburned (> 60 yr) plant communities were studied using multivariate analyses and compositional vectors. The study sites were located in fire and summer-drought adapted, xerophytic vegetation with many endemics on acidic, nutrient-poor, sandy soils in south-central peninsular Florida. Sizes of individual stems from 72 sets of nested permanent quadrats were measured in 1969, 1979, and 1989. Patterns of vegetation change differed by community. Flatwood and bayhead quadrats showed rapid increases in densities and basal areas of Persea borbonia (red bay). In the southern ridge sandhill community, evergreen clonal Quercus species (oaks) and Pinus clausa (sand pine) increased in dominance and grasses declined. Oaks (especially Q. geminata) also increased in importance in scrubby flatwoods. Sand pine scrub was relatively stable in composition, but experienced marked structural changes due to substantial sand pine mortality (18% during 1969–1979, 39% during 1979–1989). Compositional changes in the absence of fire were greatest whereas structural changes were least in southern ridge sandhill and scrubby flatwoods, both communities which normally receive frequent, recurrent fire. Compositional changes were lowest in sand pine scrub, which is normally infrequently burned. Classic successional patterns such as species replacement, decreases in density, and increases in basal area were generally lacking. Tree densities increased in two of four community types (southern ridge sandhill, scrubby flatwoods); while basal area declined in the flatwoods/bayhead and sand pine scrub sites. Directions of compositional vectors included divergent, opposing, and complex patterns, suggesting vegetation change in the absence of fire has a strong stochastic component.     

Competitive effects of non-native plants are lowest in native plant communities that are most vulnerable to invasion

Despite widespread acknowledgment that disturbance favors invasion, a hypothesis that has received little attention is whether non-native invaders have greater competitive effects on native plants in undisturbed habitats than in disturbed habitats. This hypothesis derives from the assumption that competitive interactions are more persistent in habitats that have not been recently disturbed. Another hypothesis that has received little attention is whether the effects of non-native plants on native plants vary among habitats that differ in soil fertility. We documented habitat occurrences of 27 non-native plant species and 377 native plant species encountered in numerous study plots in a broad sample of ecosystems in MS (USA). We then reviewed experimental and regression-based field studies in the scientific literature that specifically examined potential competitive (or facilitative) effects of these non-native species on native species and characterized the habitats in which effects were the greatest. As expected, the non-native species examined here in general were more likely to be associated with severely disturbed habitats than were the native species as a group. In contrast, we found that non-native species with competitive effects on natives were more likely to be associated with undisturbed habitats than with disturbed habitats. When longer term studies involving more resident species were given more weight in the analysis, competitive effects appeared to be the greatest in undisturbed habitats with low soil fertility. These results reinforce the notion that invasion is not synonymous with impact. The environmental conditions that promote invasion may limit competitive effects of invaders on native plant communities following invasion.     

Genetic differentiation in natural populations of a Keystone Bunchgrass (<Emphasis Type="Italic">Aristida stricta</Emphasis>) across its native range

Aristida stricta Michx. (Poaceae) is a perennial bunchgrass native to the Southeastern Coastal Plain of North America where it is a keystone species in the longleaf pine savannas and slash pine flatwoods from southeastern North Carolina to Florida, and westward to the coast of Mississippi. We examined genetic relationships within and among ten populations of A. stricta by using eight inter-simple sequence repeat (ISSR) markers to generate band frequency data for 32 individuals from each sampled population. An analysis of molecular variance showed that 38% of the variation resided among populations while 62% was attributable to variation within populations. Grouping the populations by habitat or by geographic location did not show significant differentiation between the groups. Overall, pair-wise geographic and genetic distances were not correlated. Data indicate that while individuals within each population are genetically diverse, there seemingly are barriers to gene flow across populations leading to their divergence. Each population contains several exclusive loci suggesting that limited gene flow and/or genetic drift are likely leading to this pattern of localization. Our results, coupled with those of the previous studies that presented evidence for local adaptation and phenotypic differences among populations, suggest that there is sufficient differentiation among populations of this species to warrant: (1) maintenance of the existing genetic diversity at individual sites, and (2) use of local seed and plant sources for conservation projects.     

Influence of woody invader control methods and seed availability on native and invasive species establishment in a Hawaiian forest

When invasive woody plants become dominant, they present an extreme challenge for restoration of native plant communities. Invasive Morella faya (fire tree) forms extensive, nearly monospecific stands in wet and mesic forests on the Island of Hawai’i. We used logging, girdling, and selective girdling over time (incremental girdling) to kill stands of M. faya at different rates, with the objective of identifying a method that best promotes native forest re-establishment. We hypothesized that rapid canopy opening by logging would lead to establishment of fast-growing, non-native invaders, but that slower death of M. faya by girdling or incremental girdling would increase the establishment by native plants adapted to partial shade conditions. After applying the M. faya treatments, seed banks, seed rain, and plant recruitment were monitored over 3 years. Different plant communities developed in response to the treatments. Increased light and nitrogen availability in the logged treatment were associated with invasion by non-native species. Native species, including the dominant native forest tree, (Metrosideros polymorpha) and tree fern (Cibotium glaucum), established most frequently in the girdle and incremental girdle treatments, but short-lived non-native species were more abundant than native species. A diverse native forest is unlikely to develop following any of the treatments due to seed limitation for many native species, but girdling and incremental girdling promoted natural establishment of major components of native Hawaiian forest. Girdling may be an effective general strategy for reestablishing native vegetation in areas dominated by woody plant invaders.     

Ectomycorrhizal fungal communities of native and non-native Pinus and Quercus species in a common garden of 35-year-old trees

Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi.     

Inhibitory effects of Eucalyptus globulus on understorey plant growth and species richness are greater in non‐native regions

Aim

We studied the novel weapons hypothesis in the context of the broadly distributed tree species Eucalyptus globulus. We evaluated the hypothesis that this Australian species would produce stronger inhibitory effects on species from its non‐native range than on species from its native range.

Location

We worked in four countries where this species is exotic (U.S.A., Chile, India, Portugal) and one country where it is native (Australia).

Time period

2009–2012.

Major taxa studied

Plants.

Methods

We compared species composition, richness and height of plant communities in 20 paired plots underneath E. globulus individuals and open areas in two sites within its native range and each non‐native region. We also compared effects of litter leachates of E. globulus on root growth of seedlings in species from Australia, Chile, the U.S.A. and India.

Results

In all sites and countries, the plant community under E. globulus canopies had lower species richness than did the plant community in open areas. However, the reduction was much greater in the non‐native ranges: species richness declined by an average of 51% in the eight non‐native sites versus 8% in the two native Australian sites. The root growth of 15 out of 21 species from the non‐native range were highly suppressed by E. globulus litter leachates, whereas the effect of litter leachate varied from facilitation to suppression for six species native to Australia. The mean reduction in root growth for Australian plants was significantly lower than for plants from the U.S.A., Chile and India.

Main conclusions

Our results show biogeographical differences in the impact of an exotic species on understorey plant communities. Consistent with the novel weapons hypothesis, our findings suggest that different adaptations of species from the native and non‐native ranges to biochemical compounds produced by an exotic species may play a role in these biogeographical differences.     

Elton’s hypothesis revisited: an experimental test using cogongrass

In the 1950s Charles Elton hypothesized that more diverse communities should be less susceptible to invasion by exotic species (biodiversity–invasibility hypothesis). The biodiversity–invasibility hypothesis postulates that species-rich communities are less vulnerable to invasion because vacant niches are less common and the intensity of interspecific competition is more severe. Field studies were conducted at two sites, a logged site and an unlogged site in Santa Rosa County, Florida, U.S.A, to test Elton’s hypothesis using cogongrass (Imperata cylindrica), a non-indigenous grass invading large areas of the Southeastern United States. The logged site was under 17-year-old loblolly pine prior to clear cutting. The unlogged site, a longleaf pine forest, was at the Blackwater River State Forest. Both the logged site and unlogged site showed no significant relationship between the rate of cogongrass spread and native plant species richness, functional richness, and cover of the invaded community. Increased species or functional richness may increase the use of resources; however, the extensive rhizome/root network possessed by cogongrass and its ability to thrive under shade may allow for its persistence in a diverse community. The results from both the logged and unlogged sites do not support the general hypothesis of Elton that invasion resistance and compositional stability increase with diversity. Biodiversity does not appear to be an important factor for cogongrass invasion in the southern United States. Extrinsic factors in this study prevent the ability to draw a defined causal relationship between native plant diversity and invasibility. Underlying reasons for why no relationship was observed may be simply due to the tremendous competitive ability of cogongrass or the narrow range of species richness, functional richness and cover observed in our study.     

Genetic structure of <Emphasis Type="Italic">Aegilops cylindrica</Emphasis> Host in its native range and in the United States of America

Chloroplast and nuclear microsatellite markers were used to study genetic diversity and genetic structure of Aegilops cylindrica Host collected in its native range and in adventive sites in the USA. Our analysis suggests that Ae. cylindrica, an allotetraploid, arose from multiple hybridizations between Ae. markgrafii (Greuter) Hammer. and Ae. tauschii Coss. presumably along the Fertile Crescent, where the geographic distributions of its diploid progenitors overlap. However, the center of genetic diversity of this species now encompasses a larger area including northern Iraq, eastern Turkey, and Transcaucasia. Although the majority of accessions of Ae. cylindrica (87%) had D-type plastomes derived from Ae. tauschii, accessions with C-type plastomes (13%), derived from Ae. markgrafii, were also observed. This corroborates a previous study suggesting the dimaternal origin of Ae. cylindrica. Model-based and genetic distance-based clustering using both chloroplast and nuclear markers indicated that Ae. tauschii ssp. tauschii contributed one of its D-type plastomes and its D genome to Ae. cylindrica. Analysis of genetic structure using nuclear markers suggested that Ae. cylindrica accessions could be grouped into three subpopulations (arbitrarily named N-K1, N-K2, and N-K3). Members of the N-K1 subpopulation were the most numerous in its native range and members of the N-K2 subpopulation were the most common in the USA. Our analysis also indicated that Ae. cylindrica accessions in the USA were derived from a few founder genotypes. The frequency of Ae. cylindrica accessions with the C-type plastome in the USA (~24%) was substantially higher than in its native range of distribution (~3%) and all C-type Ae. cylindrica in the USA except one belonged to subpopulation N-K2. The high frequency of the C-type plastome in the USA may reflect a favorable nucleo-cytoplasmic combination.     

Large-scale manipulation of plant litter and fertilizer in a managed successional temperate grassland

Plant litter may play an important role in herbaceous plant communities by limiting primary production and influencing plant species richness. However, it is not known how the effect of litter interacts with fertilization. We tested for the role of litter and fertilization in a large-scale experiment to investigate effects on diversity and biomass of plant species, growth forms, native vs. non-native groups, and abiotic ecosystem components (e.g., soil moisture, PAR). We manipulated plant litter (removed vs. left in situ) and nutrient availability (NPK-fertilized vs. unfertilized) for 4 years in 314-m² plots, replicated six times, in an old-field grassland. While many of our species-level results supported previously published studies and theory, our plant group results generally did not. Specifically, grass species richness and forb biomass was not affected by either fertilization or plant litter. Moreover, plant litter removal significantly increased non-native plant species richness. Relative to native plant species, all of our experimental manipulations significantly increased both the biomass and the species richness of non-native plant species. Thus, this grassland system was sensitive to management treatments through the facilitation of non-native plant species. We coupled biotic and abiotic components within a nonmetric multidimensional scaling (NMS) analysis to investigate treatment effects, which revealed that specific treatments altered ecosystem development. These results suggest that fertilization and plant litter may have larger impacts on plant communities and on ecosystem properties than previously understood, underscoring the need for larger-scale and longer-term experiments.