Search

Coastal ecosystems provide critical storm and flood protection but are rapidly degrading worldwide, making their restoration urgent. We evaluated whether successional facilitation, where pioneers facilitate climax species, could be leveraged to accelerate coastal dune revegetation. A survey spanning 270 km of Southeast U.S. coastline revealed that Panicum amarum (bitter panicum) supported higher plant richness than Uniola paniculata (sea oats) and that sea oat cover was 230% greater on mature dunes than disturbed dunes, suggesting bitter panicum functions as a pioneer and sea oats as a climax species. A reciprocal transplant experiment confirmed this interpretation: bitter panicum stem production and height fell by 37% and >20 cm, respectively, when planted proximate to sea oats versus in isolation, whereas sea oats produced 38% more and >12 cm taller stems when planted proximate to bitter panicum versus in isolation. A second experiment evaluating the density‐dependence of this facilitative interaction revealed that sea oats transplanted into low densities of bitter panicum grew >15% taller than isolated and high‐density treatments. However, within 7 months, wave inundation eliminated over 60% of propagules in both experiments. To explore foredune inundation frequency and its implications for dune revegetation, we applied empirical wave runup models at 101 locations throughout Volusia County, Florida. While disturbance frequency varied seasonally and annually, sites with low dune crests and steep beach slopes experienced frequent inundation (>50 events/year). Given the interactions between geomorphology and vegetation success, we present a decision matrix to guide managers in determining optimal revegetation methods tailored to project goals and site conditions. [ABSTRACT FROM AUTHOR]

Restoration of degraded dunes through revegetation of native dune building species is critical to preserve multiple ecosystem services (i.e., coastal protection, habitat). As dunes exhibit high levels of abiotic stress, it is likely that facilitative interactions among plants occur, reducing stress caused by harsh abiotic conditions, and benefiting restoration efforts. The research was to determine how plant spatial arrangement (clumped vs. dispersed) at the dune slope affects the growth of two dominant dune grasses along the United States Atlantic coast, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). We determined the local distribution and density of each species through field surveys to inform a manipulative study of planting arrangement and to assess plant growth and survival under different spatial arrangements. Planting arrangement did not influence the survival of U. paniculata, but dispersed plantings had a positive effect on growth parameters (height, stem number, ramet number), compared to the clumped arrangement. No plantings of A. breviligulata survived by the end of the second season, regardless of planting arrangement. Clumped arrangements did not improve growth of U. paniculata or growth and survival of A. breviligulata over the two growing seasons studied; thus, creating clumped arrangements may not be necessary for revegetation efforts. However, observing natural spatial patterns and using this information to guide restoration planting may be beneficial as climate change may impact revegetation results due to increased abiotic stress. Further research focusing on biotic interactions and density of plantings at multiple locations along dunes will contribute to dune restoration planning. [ABSTRACT FROM AUTHOR]

Coastal foredunes form via biophysical feedbacks between sand accretion and burial‐tolerant vegetation and can protect coastlines from hazards such as extreme storms and sea level rise. Predicting how coastal dunes, and the services they provide, will change in the future requires an understanding of the relative roles of the physical and ecological processes that shape their structure and function. Here we assess the relative roles of sand supply, beach morphology, and vegetation in determining foredune morphology, and its change, along a 300‐km stretch of the US Central Atlantic coast. In particular, we used the spatial variability inherent in beaches and dunes of this region to determine the relative importance of shoreline change rate (SCR; a proxy for sand supply to the beach), beach morphology, and grass density of four widespread dune grasses (Uniola paniculata, Ammophila breviligulata, Panicum amarum, and Spartina patens) to foredune morphology metrics (height, width, and aspect ratio) along the North Carolina Outer Banks barrier islands. Foredune morphology and change metrics are correlated with three main factors: multidecadal SCR (1997–2016), beach slope, and dune grass density and species identity. Multidecadal SCR and beach width explained the most variation in, and were positively correlated with, foredune height and width, and were negatively correlated with foredune aspect ratio (height divided by width). In addition, grass density and changes in grass density contributed significantly to foredune morphology change. We found a positive relationship between change in A. breviligulata density and foredune width, which aligns with previous studies on the US Atlantic and Pacific Northwest coasts. Our results demonstrate the interactive roles of beach sand supply and dune grass functional morphology in dune building processes on highly vulnerable coastlines. [ABSTRACT FROM AUTHOR]

Coastal dunes are important protective features against sea level rise and coastal storms. Interactions between dune plant aboveground structures and sediment trapping that allow for dune building and maintenance are well established. More recently, studies documenting belowground biomass for promoting erosion resistance in dominant dune species have been conducted, yet a knowledge gap remains regarding species‐specific characterization of whole plants, specifically with respect to roots, rhizomes, and belowground stems. Our objective was to quantify above‐ and belowground traits of four dominant dune grasses to document the potential for species‐specific effects on dune growth, maintenance, and erosion resistance. We examined above‐ and belowground traits among four prominent dune grasses of the Atlantic and Gulf Coasts of North America: Ammophila breviligulata, Panicum amarum, Spartina patens, and Uniola paniculata. Whole plant samples of each species were collected from the foredune at the US Army Engineer Research and Development Center's Field Research Facility in Duck, North Carolina, USA, and quantified for several above‐ and belowground traits (e.g., stem height, rhizome number and length, root surface area by diameter class, root tensile strength, and mycorrhizal percent infection). Belowground factors known to impact important dune processes, such as rhizome length, mycorrhizal percent infection, and root traits, differed substantially among species. When visualized in multivariate space, all species significantly differed in suites of above‐ and belowground traits. When considering belowground only, Ammophila and Spartina were similar, despite differences in biomass allocation. Species separated along axes related to mycorrhizal association, biomass allocation, and root construction. The four co‐occurring dune grass species were dissimilar in suites of plant traits. Belowground trait differences were driven by those describing root construction, biomass allocation, and mycorrhizal infection. Dissimilarity in above‐ and belowground suites of traits may demonstrate different approaches for surviving the dune environment. Incorporating belowground traits into modeling will enhance predictions of dune response to climate change through interactions between vegetation and dune dynamics that facilitate coastal resistance and resilience. [ABSTRACT FROM AUTHOR]

Coastal foredunes provide the first line of defense against rising sea levels and storm surge and for this reason there is increasing interest in understanding and modeling foredune formation and post‐storm recovery. However, there is limited observational data available to provide empirical guidance for the development of model parameterizations. To provide guidance for improved representation of dune grass growth in models, we conducted a two‐year multi‐species transplant experiment on Hog Island, VA, U.S.A. and measured the dependence of plant growth on elevation and distance from the shoreline, as well as the relationship between plant growth and sand accumulation. We tracked total leaf growth (length) and aboveground leaf length and found that Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats) grew more than Spartina patens (saltmeadow cordgrass) by a factor of 15% (though not statistically significant) and 45%, respectively. Our results also suggest a range of basal/frontal area ratios (an important model parameter) from 0.5‐1 and a strong correlation between transplant growth and total sand deposition for all species at the scale of two years, but not over shorter temporal scales. Distance from the shoreline and elevation had no effect on transplant growth rate but did have an effect on survival. Based on transplant survival, the seaward limit of vegetation at the end of the experiment was approximately 30 m from the MHWL and at an elevation of 1.43 m, corresponding to inundation less than 7.5% of the time according to total water level calculations. Results from this experiment provide evidence for the dune‐building capacity of all three species, suggesting S. patens is not a maintainer species, as previously thought, but rather a moderate dune builder even though its growth is less stimulated by sand deposition than A. breviligulata and U. paniculata. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Previous work on the US Atlantic coast has generally shown that coastal foredunes are dominated by two dune grass species, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). From Virginia northward, A. breviligulata dominates, while U. paniculata is the dominant grass south of Virginia. Previous work suggests that these grasses influence the shape of coastal foredunes in species-specific ways, and that they respond differently to environmental stressors; thus, it is important to know which species dominates a given dune system. The range boundaries of these two species remains unclear given the lack of comprehensive surveys. In an attempt to determine these boundaries, we conducted a literature survey of 98 studies that either stated the range limits and/or included field-based studies/observations of the two grass species. We then produced an interactive map that summarizes the locations of the surveyed papers and books. The literature review suggests that the current southern range limit for A. breviligulata is Cape Fear, NC, and the northern range limit for U. paniculata is Assateague Island, on the Maryland and Virginia border. Our data suggest a northward expansion of U. paniculata, possibly associated with warming trends observed near the northern range limit in Painter, VA. In contrast, the data regarding a range shift for A. breviligulata remain inconclusive. We also compare our literature-based map with geolocated records from the Global Biodiversity Information Facility and iNaturalist research grade crowd-sourced observations. We intend for our literature-based map to aid coastal researchers who are interested in the dynamics of these two species and the potential for their ranges to shift as a result of climate change.

Previous work on the US Atlantic coast has generally shown that coastal foredunes are dominated by two dune grass species, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). From Virginia northward, A. breviligulata dominates, while U. paniculata is the dominant grass south of Virginia. Previous work suggests that these grasses influence the shape of coastal foredunes in species-specific ways, and that they respond differently to environmental stressors; thus, it is important to know which species dominates a given dune system. The range boundaries of these two species remains unclear given the lack of comprehensive surveys. In an attempt to determine these boundaries, we conducted a literature survey of 98 studies that either stated the range limits and/or included field-based studies/observations of the two grass species.We then produced an interactive map that summarizes the locations of the surveyed papers and books. The literature review suggests that the current southern range limit for A. breviligulata is Cape Fear, NC, and the northern range limit for U. paniculata is Assateague Island, on the Maryland and Virginia border. Our data suggest a northward expansion of U. paniculata, possibly associated with warming trends observed near the northern range limit in Painter, VA. In contrast, the data regarding a range shift for A. breviligulata remain inconclusive. We also compare our literature-based map with geolocated records from the Global Biodiversity Information Facility and iNaturalist research grade crowd-sourced observations. We intend for our literature-based map to aid coastal researchers who are interested in the dynamics of these two species and the potential for their ranges to shift as a result of climate change. [ABSTRACT FROM AUTHOR]

Sand dunes are important geomorphic formations of coastal ecosystems that are critical in protecting human populations that live in coastal areas. Dune formation is driven by ecomorphodynamic interactions between vegetation and sediment deposition. While there has been extensive research on responses of dune grasses to sand burial, there is a knowledge gap in understanding mechanisms of acclimation between similar, coexistent, dune-building grasses such as Ammophila breviligulata (C3), Spartina patens (C4), and Uniola paniculata (C4). Our goal was to determine how physiological mechanisms of acclimation to sand burial vary between species. We hypothesize that (1) in the presence of burial, resource allocation will be predicated on photosynthetic pathway and that we will be able to characterize the C3 species as a root allocator and the C4 species as leaf allocators. We also hypothesize that (2) despite similarities between these species in habitat, growth form, and life history, leaf, root, and whole plant traits will vary between species when burial is not present. Furthermore, when burial is present, the existing variability in physiological strategy will drive species-specific mechanisms of survival. In a greenhouse experiment, we exposed three dune grass species to different burial treatments: 0 cm (control) and a one-time 25-cm burial to mimic sediment deposition during a storm. At the conclusion of our study, we collected a suite of physiological and morphological functional traits. Results showed that Ammophila decreased allocation to aboveground biomass to maintain root biomass, preserving photosynthesis by allocating nitrogen (N) into light-exposed leaves. Conversely, Uniola and Spartina decreased allocation to belowground production to increase elongation and maintain aboveground biomass. Interestingly, we found that species were functionally distinct when burial was absent; however, all species became more similar when treated with burial. In the presence of burial, species utilized functional traits of rapid growth strategy, although mechanisms of change were interspecifically variable. [ABSTRACT FROM AUTHOR]

Barrier islands are at the forefront of storms and sea-level rise. High disturbance regimes and sediment mobility make these systems sensitive and dynamic. Island foredunes are protective structures against storm-induced overwash that are integrally tied to dune grasses via biogeomorphic feedbacks. Shifts in dune grass dominance could influence dune morphology and susceptibility to overwash, altering island stability. In a glasshouse study, two dune grasses, Ammophila breviligulata and Uniola paniculata, were planted together and subjected to a 20 cm burial to quantify morphological and physiological responses. Burial had positive effects on both plants as indicated by increased electron transport rate and total biomass. Ammophila breviligulata performance declined when planted with U. paniculata. Uniola paniculata was not affected when planted with A. breviligulata but did have higher water use efficiency and nitrogen use efficiency. Planted in mixture, differential reallocation of biomass occurred between species potentially altering resource acquisition further. As U. paniculata migrates into A. breviligulata dominated habitat and A. breviligulata performance diminishes, biotic interactions between these and other species may affect dune formation and community structure. Our study emphasizes the importance of studying biotic interactions alongside naturally occurring abiotic drivers. [ABSTRACT FROM AUTHOR]

Coastal dunes are valuable components of barrier shorelines, but establishing the appropriate vegetation to facilitate the growth and maintenance of this important habitat is difficult due to the presence of consistent stressors, including nutrient, water limitation, and salt spray. We examined whether the amendment of dune soils with postharvest sugarcane residue and broadcast fertilizer would enhance the establishment and growth of two key dune grass species, bitter panicum (Panicum amarum) and sea oats (Uniola paniculata), in natural and created sand dunes in coastal Louisiana in a short-term field study. The benefit of broadcast fertilizer addition to the growth of both species was evident, as was a tendency for greater establishment and growth of bitter panicum than sea oats. The created dune environment was significantly less favorable than the natural dune system in terms of soil characteristics and plant growth responses. Interestingly, postharvest sugarcane residue, which we hypothesized would improve dune grass establishment and growth by increasing soil organic matter and thereby soil moisture retention, failed to enhance dune grass growth. We conclude that dune restoration efforts in coastal Louisiana would benefit from the inclusion of a broadcast fertilizer regime, particularly in terms of accelerating bitter panicum growth and establishment. However, application of postharvest sugarcane residue does not appear to provide the same benefits to dune grass establishment and expansion as has been shown with other organic amendments. [ABSTRACT FROM AUTHOR]

In September 2003, Hurricane Isabel created an inlet over 500 m wide and 10 m deep that connected the Atlantic Ocean and Pamlico Sound. This breach was subsequently filled with sediments dredged from the adjacent sound. The purpose of this study was to determine if the barrier island terrestrial plant communities were naturally re-establishing through primary succession. In 2006-2008, we compared plant communities, soil carbon and nitrogen, and Aeolian transport of sediments in undisturbed back-dunes, undisturbed shrub thickets, putative back-dunes, and putative shrub thickets. We found that species richness and evenness were low on the filled area relative to adjacent plant communities that had persisted through the storm. Plants on the filled area were almost entirely limited to a band of primarily Spartina patens found at the margin of the sound and there were no signs of establishing the typical zonation of back dune grasses, shrubs, and salt marsh. Evaluation of soil quality suggests that nutrients and organic material are not limiting recovery. Aeolian transport, however, was demonstrably higher across the filled area, where no dense stands of taller plants buffered the airflow. Plant re-establishment is suppressed by wind erosion inhibiting deposition of seeds. Recovery of the site will likely depend on the rhizomatous spread of S. patens from the sound shore. S. patens can then potentially facilitate the colonization of other species by buffering the wind and trapping seeds of other plants. Ironically, this slow recovery may benefit federally threatened bird species that require sparse vegetation for nesting success. [ABSTRACT FROM AUTHOR]

Understanding the underlying causes of phenotypic trait variation among populations is important for informing conservation decisions. This knowledge can be used to determine whether locality matters when sourcing populations for habitat restoration. Uniola paniculata is a federally protected coastal dune grass native to the southeastern Atlantic and the Gulf coasts of the USA that is often used to stabilize restored dune habitats. This study uses neutral genetic markers (allozymes) and a greenhouse common garden study to determine the relative contributions of neutral evolutionary processes and natural selection to patterns of phenotypic variation among natural populations of U. paniculata. Seeds were sourced from foredune and backdune populations spanning shoreline-to-landward environmental gradients on each of four Georgia barrier islands. Based on previous work, we expected to find evidence of divergent selection among populations located on the shoreline-to-landward environmental gradient. However, differences among islands, rather than intra-island habitat differences, drive divergent selection on aboveground and total biomass. The lack of evidence for divergent selection across the shoreline-to-landward gradient suggests that previously documented intra-island trait variation is likely due to phenotypic plasticity. Our findings have implications for conservation and restoration efforts involving U. paniculata, as there is evidence for divergent selection among populations located on neighboring islands. [ABSTRACT FROM AUTHOR]

Numerous sea oats ( Uniola paniculata L.) plants are transplanted to Northern Gulf of Mexico beaches each year to reduce coastal erosion. To adapt to environmental changes and effectively reduce coastal erosion, genetically diverse sea oats plants with demonstrated plant performance must be used. The objectives of this study were to: (i) identify improved sea oats lines; and (ii) determine the genetic diversity of improved sea oats lines. From 2003 to 2005, 2,000 sea oats lines were evaluated in unreplicated field trials at natural beach sites. In 2005, 75 sea oats lines were selected based upon phenotypic performance. The 75 selected lines and 3 plants of 'Caminada', the only commercially available sea oats line, were evaluated in replicated field trials in 2008 and 2010. In 2008, UP01LA-15 K-HB-3092, UP01LA-16S-GP-3138, UP01LA-31-GP-3103, UP01LA-33-GP-1303, and UP01NC-04-HB-3374 had higher ( p < 0.05) stem densities than Caminada. In 2010, variation was not detected for any trait measured; lack of significant differences was most likely due to plant stress caused by storm surge one week after transplant. Amplified Fragment Length Polymorphism detected 534 loci for the 75 selected lines and 3 Caminada plants. One hundred eighty one loci were polymorphic; the average polymorphism rate was 34% (range = 25-43%). Polymorphic information content values ranged from 0.15 to 0.41 and averaged 0.29 while Jaccard similarity coefficients ranged from 0.8243 to 0.9794. These findings demonstrate the application of plant breeding techniques to develop genetically different sea oats lines with improved performance for coastal restoration projects in the northern Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Coastal dunes are well known for plant species zonation but less is known about species-specific responses to underlying environmental gradients. We investigated variation in morphological traits and tissue nutrient concentration in Uniola paniculata, along a shoreline-to-landward gradient (transects spanning from the dunes directly behind the high tide mark to 40–100 m inland) in the southeast USA. Several environmental factors decreased with distance from the shoreline (soil B, K, Mg, Na; salinity, pH, and sand accretion), and differences were most pronounced between the 10 m closest to the shoreline and the remainder of the transect. In the 10 m closest to the shoreline, 94% more sand accumulated, which was 31% more saline. Additionally, plants here were taller, contained higher aboveground tissue N and K, and a higher percentage tended to flower. This contrasts with patterns found in salt marshes and saline desert dunes, where plant size is often negatively correlated with salinity. During the 2 years following the planned study, storms washed out ≤25 m of the transects. Resampling of the remaining sites demonstrated that even after erosion of the dune profile, a higher percentage of the plants in the 10 m closest to the shoreline plants tended to flower, relative to populations located further from the shore. Our findings suggested that the environment and plant response in the shoreward 10 m can re-establish relatively quickly. [ABSTRACT FROM AUTHOR]

Subtropical coastal sand dune ecosystems have been greatly altered by agricultural use, invasive exotic encroachment, urban development, and beach raking, rendering several plant species endangered or threatened. Restoration planning of this ecosystem will benefit from a comprehensive study on how environmental variables change across the coast- to-inland gradient of this ecosystem and it is therefore presented here. We also examined the relationship between the environmental characteristics and plant species composition across the gradient. We used the two largest extents of remaining dune ecosystem on the southeastern coast of Florida, where relatively intact populations of endangered species occur. Vegetation and environmental data were collected from 97 3 ×8 m plots in two sand dune parks along the coast-inland gradient. Soil moisture, most nutrients, cation exchange capacity, and organic matter accumulation increased with distance from the coast, whereas pH and salt spray decreased. The number of species per plot was higher at further distances from the coast at one site only, and higher woody cover was associated with less species diversity at the other site. Canonical correspondence analysis revealed the importance of P, Mg, Ca, pH, cation exchange capacity, organic matter, estimated nitrogen release, and salt spray in affecting vegetation zonation. We conclude that soil chemistry is the most determinant factor of community zonation in these subtropical dunes. Restoration planning should be site specific because of the differences in environmental factors between the two study sites. [ABSTRACT FROM AUTHOR]

This study examined geomorphologic changes, littoral processes and sediment budget along the west side of the Cape Lookout, North Carolina, cuspate foreland, where a prograding spit at right angles to an eroding barrier island forms prominent features. Progradation of the spit is of interest geologically because it occurs within a transgressive, sediment- starved coastal setting in which adjacent barrier island limbs are eroding and in which immediate sediment sources and transport mechanisms are not obvious. Results indicate that as the spit extends to the north, it also widens to the west through swash bar attachment, leaving a well-defined record of dune ridges that mark former shoreline positions. Although northerly longshore transport occurs only under SW wave conditions, the average rate, ∼0.18 x 106 m³/y, is considered high given the sheltered position of the spit within the cuspate foreland. Results of modeling and development patterns of a series of ridge and runnel systems along the spit indicate that sediments are derived from the eastern limb of the cape or, under certain conditions, from sediments stored in Cape Lookout Shoal by longshore currents. Because the spit forms the distal end of a terminal littoral cell, it has an important effect on the regional sediment budget. Shackleford Banks, oriented at right angles and located immediately downdrift of Power Squadron Spit, is sheltered by the spit at its eastern end but suffers high erosion rates in its central section from lack of sediment input from the updrift direction. This result suggests that change in the input sediment budget can be a major factor in controlling coastal geomorphologic change under uniform physical conditions. [ABSTRACT FROM AUTHOR]

Sea turtle nesting presents a potential pathway to subsidize nutrient-poor dune ecosystems, which provide the nesting habitat for sea turtles. To assess whether this positive feedback between dune plants and turtle nests exists, we measured N concentration and δ15N values in dune soils, leaves from a common dune plant (sea oats [Uniola paniculata]), and addled eggs of loggerhead (Caretta caretta) and green turtles (Chelonia mydas) across a nesting gradient (200-1050 nests/km) along a 40.5-kin stretch of beach in east central Florida, USA. The δ15N levels were higher in loggerhead than green turtle eggs, denoting the higher trophic level of loggerhead turtles. Soil N concentration and 8 N values were both positively correlated to turtle nest density. Sea oat leaf tissue δ15N was also positively correlated to nest density, indicating an increased use of augmented marine-based nutrient sources. Foliar N concentration was correlated with δ15N, suggesting that increased nutrient availability from this biogenic vector may enhance the vigor of dune vegetation, promoting dune stabilization and preserving sea turtle nesting habitat. [ABSTRACT FROM AUTHOR]

Uniola paniculata, commonly known as sea oats, is a C4 perennial grass capable of stabilizing sand dunes. It is most abundant along the Gulf of Mexico and southeastern Atlantic coastal regions of the United States. The species exhibits low seed set and low rates of germination and seedling emergence, and so extensive clonal reproduction is achieved through production of rhizomes, which may contribute to a decline in genetic diversity. To date, there has been no systematic assessment of genetic variability and population structure in naturally occurring stands in the USA. This study was conducted to assess the genetic relationship and diversity among nineteen U. paniculata accessions representing eight states: Texas, Louisiana, Mississippi, Alabama, Florida, South Carolina, North Carolina, and Virginia, using amplified fragment length polymorphism (AFLP). Twelve AFLP EcoRI+ MseI primer combinations generated a wide range of polymorphisms (42–81%) with a mean of 59%. Overall, the sea oats plants exhibited a low range of genetic similarity. Florida accessions, FL-33 and FL-39, were most genetically diverse and the accessions from both Carolinas and Virginia (NC-1, NC-11, SC-15, and VA-53) harbored less genetic variability. Cluster analysis using the UPGMA approach separated U. paniculata plants into four major clusters which were also confirmed by principal coordinate analysis (PCO). Further examination of the different components of genetic variation by analysis of molecular variance (AMOVA) indicated the largest proportion of variability at the state level (47.8%) followed by the variation due to the differences among the genotypes within an accession (34.4%), and the differences among the accessions within a state (17.8%). The relationship between genetic diversity and geographic source of sea oats populations of the United States as revealed through this comprehensive study will be helpful to resource managers and commercial nurseries in identifying suitable plant materials for restoration of new areas without compromising the adaptation and genetic diversity. [ABSTRACT FROM AUTHOR]

Geographic and fine-scale population genetic structures of Uniola paniculata, the dominant coastal dune grass in the southeastern USA, were examined. The linear, naturally fragmented distribution of this native perennial was hypothesized to lead to high genetic structure and lower genetic diversity at the margin of the species range. The extensive ramet production and low seed germination of this species were also expected to cause populations to be dominated by a few large clones. At 20 sites throughout the range of the species, leaf tissue was collected from 48 individuals. Clonal structure was examined using leaf tissue collected from an additional 60 individuals, each in four patches at two sites. Starch gel electrophoresis was used to resolve 27 allozyme loci. The results indicated that Uniola had greater genetic structure (GST = 0.304) than most other outcrossing species, indicating moderate barriers to gene flow. There was a weak but significant positive relationship between genetic distance and geographic distance, supporting an isolation-by- distance model of gene flow. There were no obvious disjunctions between regions. Genetic diversity (He) was relatively uniform throughout most of the range of the species but was lower in all western Gulf of Mexico populations. Clonal diversity varied both within and among sites, but clones were often small, suggesting that sexual reproduction and recruitment from seeds are important factors maintaining genetic diversity. [ABSTRACT FROM AUTHOR]

This study examined the water relations and growth responses of Uniola paniculata (sea oats) to (1) three watering regimes and (2) four controlled water-table depths. Uniola paniculata is frequently the dominant foredune grass along much of the southeastern Atlantic and Gulf coasts of the United States, but its distribution is limited in Louisiana. Throughout most of its range, U. paniculata tends to dominate and be well adapted to the most exposed areas of the dune where soil moisture is low. Dune elevations in Louisiana, however, rarely exceed 2 m, and as a result the depth to the water table is generally shallow. We hypothesized that if U. paniculata grows very near the water-table, as it may in Louisiana, it will display signs of water-logging stress. This study demonstrated that excessive soil moisture resulting from inundation or shallow water-table depth has a greater negative effect on plant growth than do low soil moisture conditions. Uniola paniculata's initial response to either drought or inundation was a reduction of leaf (stomatal) conductance and a concomitant decrease in leaf elongation. However, plants could recover from drought-induced leaf xylem pressures of less than-3.3 MPa, but prolonged inundation killed the plants. Waterlogging stress (manifested in significantly reduced leaf stomatal conductances and reduced biomass production) was observed in plants grown at 0.3 m above the water table. This stress was relieved, however, at an elevation of 0.9 m above the water table. As the elevation was increased from 0.9 to 2.7 m, there were no signs of drought stress nor a stimulation in growth due to lower soil moisture. We concluded that although U. paniculata's moisture-conserving traits adapt it well to the dune environment, this species can grow very well at an elevation of only 0.9 m above the water table. Field measurements of water-table depth in three Louisiana populations averaged about 1.3 m. Therefore, the observed limited distribution of U. paniculata along the Louisiana coast apparently cannot be explained by water-logging stress induced by the low dune elevations and the corresponding shallow water-table depth. [ABSTRACT FROM AUTHOR]

For efficient use of mycorrhizal inoculum the effectiveness of the isolate used and the rate of application required for maximum colonization must be known. The objectives of this research were to (1) define the lower limit of inoculum density required for maximum colonization of Uniola paniculata in a commercial nursery and (2) evaluate the performance of a selected native dune vesicular-arbuscular mycorrhizal (VAM) isolate versus a commercially available non-dune VAM (foreign) isolate on three diverse Florida beaches. An inoculum-dilution study was conducted in a commercial nursery with cutroot inoculum of a Glomus sp. that had been isolated from a Florida dune. Maximum colonization was achieved with approximately 1 propagule ml of growth medium. In a separate nursery study, 10 inoculation treatments (combinations of inoculum source and level) were established in the commercial nursery. Treatments included cut-root and sheared-root inoculum of the native dune isolate, and Nutri-Link, a commercial inoculum of G. intraradices. Colonized plants from selected treatments were transplanted to beach sites around Florida. At Miami Beach, after one growing season, the shoot mass of plants inoculated with the native isolate was approximately twice that of plants inoculated with the foreign isolate. At Katherine Abbey Hanna Park and Eglin Air Force Base there were no significant inoculum source effects on shoot mass or root length after one growing season. However, the native isolate produced a greater colonized root length than the foreign isolate in all plantings. The soil hyphal density was measured at Eglin Air Force Base, and the results showed that plants inoculated with the native isolate had more soil hyphae (4.33 mg) than plants inoculated with the foreign isolate (3.65 mg) or the non-inoculated plants (2.12 mg). Even where there were no obvious shoot growth responses, mycorrhizal inoculation may have an important effect on dune stabilization, as soil hyphae are known to bind sand grains and improve dune stability. [ABSTRACT FROM AUTHOR]