Borrichia Frutescens Research Articles

Bottom‐up effects shift top‐down community structure of the parasitoid guild that attacks Asphondylia borrichiae (Diptera: Cecidomyiidae) on Borrichia frutescens (Asteraceae)

Abstract Asphondylia borrichiae induces galls at the apical meristems of its host plant, Borrichia frutescens, and the larvae develop and pupate within the gall. During development, immature stages of the midge are attacked by four species of parasitic wasps; two of these parasitoids, Galeopsomyia haemon and Torymus umbilicatus, are the most common members of the guild, and both are hyperparasitic. In the current study, plots of B. frutescens were randomly assigned to control (unmanipulated), salted or fertilised in a long‐term press experiment. Although plots initially exhibited no differences in stem length, gall and flower densities, after 3 months, they began to exhibit significant differences, suggesting stress (salted plots) and vigour (fertilised plots). Galls produced on plants from fertilised plots were approximately 20% and 31% larger than those from control and salted plots, respectively. Larger gall diameter in fertilised plots resulted in a shift of the parasitoid community towards the largest parasitoid, T. umgbilicatus, whereas smaller galls produced in salted plots became biased towards the smallest, but gregarious, G. haemon; interestingly, this pattern held for T. umbilicatus across treatments, and the effect for G. haemon was not significant when all treatments were combined. This study suggests that abiotic factors that alter host plant characteristics, such as gall diameter, affect the composition of the parasitoid guild that attacks A. borrichiae, which has implications for the acquisition of enemy‐free space during host range expansion of the midge.

Isolating and Characterizing Phosphorus Solubilizing Bacteria From Rhizospheres of Native Plants Grown in Calcareous Soils

Many soils including urban soils have high legacy soil phosphorus (P) due to repeated applications of P fertilizers, but a large portion legacy soil P is fixed by calcium in the calcareous soils. Phosphorus solubilizing bacteria (PSB) have the ability to transfer fixed (non-labile) soil P into bioavailable P. The aim of this study was to isolate P solubilizing bacteria from the rhizospheres of four local native plants [broomsedge bluestem (Andropogon virginicus), giant sword ferns (Nephrolepis biserrata), sawgrass (Cladium jamaicense), and sea ox-eye daisy (Borrichia frutescens)] grown in low bioavailable P calcareous soils and to determine their ability to solubilize P. A total of 44 strains of PSB were isolated with 15 of them being identified by sequencing the 16S rRNA genes as Bacillus flexus, Beijerinckia fluminensis, Enterobacter ludwigii, Enterobacter sp., and Pantoea cypripedii. After a 7-day incubation, these strains reduced pH to <4.27 and increased water-soluble P up to 588 mg L−1. Enterobacter ludwigii showed superior P solubilizing ability amount PSB isolated. Therefore, the isolated strains from the local native environment have the potential to thrive in local calcareous soils and possess strong ability to transform non-labile P into bioavailable forms for plants to uptake.

Pollinator-attracting Companion Plantings Increase Crop Yield of Cucumbers and Habanero Peppers

Cucumber (Cucumis sativus L.) and habanero pepper (Capsicum chinense Jacq.) growers have observed increased crop yield by placing bees in close proximity to these vegetable crops. However, adding managed bees typically may not be feasible for small-scale farmers or homeowners. Limited studies have demonstrated the potential of pollinator-attracting plants to be used as a lure to enhance the visitation of pollinators to adjacent food crops. This study evaluated the potential of adding pollinator-attracting plants in close proximity to cucumber and habanero plants to improve yields by either establishing permanent perennial companion plantings adjacent to the crops or interplanting annual companion plants within the row anew with each crop. The perennial treatment group consisted of Phyla nodiflora (L.) Greene, Borrichia frutescens (L.) DC., Salvia farinacea Benth. ‘Henry Duelberg’, and Eysenhardtia texana Scheele. The annual treatment group consisted of Cosmos bipinnatus Cav., Zinnia ×marylandica D.M. Spooner, Stimart, & T. Boyle, Borago officinalis L., and Ocimum basilicum L. Multiple cropping cycles were initiated using both spring and fall seasons, and yield was assessed for three successive cropping cycles. Fruit quality was unaffected by pollinator-attracting companion plantings; however total and marketable yields were impacted. Cucumber yields were significantly (P < 0.05) greater during fall harvests with annual companion plantings and with the second fall harvest in perennial companion plant plots. Perennial companion plots initially yielded less than control plots or annual companion plots due to the space allocated to the companion plantings and the fewer pollinators initially attracted to the plots compared with the annual companion plantings. When the perennial plots became more established, they resulted in similar yields as the annual companion planting plots. Although habanero yields were increased by annual companion plantings in spring and fall, cucumbers were unaffected by companion plantings in spring. This suggests a potential seasonality for the efficacy of some pollinator-attracting companion plantings for a given crop that could offer an opportunity to tailor companion plantings to attract specific pollinators at different times of the year.

Relationships of Salinity, Relative Humidity, Mud Flat Fiddler Crabs, Ants, and Sea Ox-Eye Daisy With Ixodid Distribution and Egg Survival on the South Texas Coastal Plains.

The South Texas coastal plains are mostly dominated by mesquite-thorn scrub from the Mexican border to cattle ranches extending north from Willacy Co. A wildlife corridor on the plains, composed of natural habitat, supports hosts of many ixodid species. Occasional wind (not lunar) tides and infrequent storm surges inundate coastal plain areas with hypersaline water from the Lower Laguna Madre, creating large areas of saline soil. Laboratory and field experiments and observations were used to identify relationships between salinity and other abiotic and biotic factors that influence ixodid distribution. Exposure of lone star tick, Amblyomma americanum (L.), and Rhipicephalus microplus (Canestrini) eggs to hypersaline water is lethal. Although intermittent hypersaline flooding kills ixodid eggs, saline soil was not particularly toxic. When relative humidity is relatively low, desiccation causes high egg mortality on dry soil, regardless of salinity. Substantial year-round populations of mud flat fiddler crabs, Uca rapax (Smith) (Decopoda: Ocypodidae), occur on saline soil and eliminated ≈80% of A. americanum egg masses overnight. On saline and low-salinity soils predatory formicids, including the red imported fire ant, Solenopsis invicta (Buren), were indifferent to the eggs. Saline soils were dominated by the sea ox-eye daisy, Borrichia frutescens (L.) DC, and its color allowed production of a GIS-based map. At least 24.4% of the wildlife corridor supports heavy stands of B. frutescens which is indicative of high U. rapax populations. Ixodid populations were negligible on heavy B. frutescens stands because of associated salt water toxicity, desiccation, and predation by U. rapax on eggs.

Modeling the effect of water level on the Nueces Delta marsh community

Water resource development has decreased water delivery to marshes in the Nueces Delta, Corpus Christi, Texas, USA by 45% since 1983, which has led to marsh degradation. Recent management actions will allow for partial hydrological restoration of the marsh, but there is a need to understand the dynamics and the interactive roles of climate and water cycle changes in order to predict changes in salt marshes in the future. In this study, a model of multi-species competition with respect to hydrological change was developed to perform modeling experiments of the effects of water elevation on development of marsh plant species. Nueces Delta plants were divided into two functional groups: (1) clonal stress tolerant plants (Batis maritima, Distichlis spicata, Monanthcloe littoralis, and Salicornia virginica), and (2) clonal dominants (Borrichia frutescens and Spartina alterniflora). Growth rates were calculated for three climate regimes (wet, moderate, and dry), and in three elevation locations (low, mid, and high marsh). The model predicts reductions in plant cover in both drought and moderate conditions. Marsh plant coverage increases only during wet conditions and when there is space available for plant expansion. It is concluded that changes in areal extent of the marsh largely depend on water flow and elevation, which in turn depends on the quantity of fresh water flowing into the marsh. However, under current climate and water management conditions, the marsh will degrade further.

Genetic and epigenetic differences associated with environmental gradients in replicate populations of two salt marsh perennials.

While traits and trait plasticity are partly genetically based, investigating epigenetic mechanisms may provide more nuanced understanding of the mechanisms underlying response to environment. Using AFLP and methylation-sensitive AFLP, we tested the hypothesis that differentiation to habitats along natural salt marsh environmental gradients occurs at epigenetic, but not genetic loci in two salt marsh perennials. We detected significant genetic and epigenetic structure among populations and among subpopulations, but we found multilocus patterns of differentiation to habitat type only in epigenetic variation for both species. In addition, more epigenetic than genetic loci were correlated with habitat in both species. When we analysed genetic and epigenetic variation simultaneously with partial Mantel, we found no correlation between genetic variation and habitat and a significant correlation between epigenetic variation and habitat in Spartina alterniflora. In Borrichia frutescens, we found significant correlations between epigenetic and/or genetic variation and habitat in four of five populations when populations were analysed individually, but there was no significant correlation between genetic or epigenetic variation and habitat when analysed jointly across the five populations. These analyses suggest that epigenetic mechanisms are involved in the response to salt marsh habitats, but also that the relationships among genetic and epigenetic variation and habitat vary by species. Site-specific conditions may also cloud our ability to detect response in replicate populations with similar environmental gradients. Future studies analysing sequence data and the correlation between genetic variation and DNA methylation will be powerful to identify the contributions of genetic and epigenetic response to environmental gradients.

Manner of Apical Meristem Destruction Affects Growth, Reproduction, and Survival of Sea Oxeye Daisy

Although herbivory may result in plant death, the mode and timing of damage may produce variable wounding responses in the attacked plant. In this study, effects of different types of apical meristem damage on growth and performance of sea oxeye daisy Borrichia frutescens (L.) DC were compared. Damage involved either clipping or galling of the apical meristem by the gall midge Asphondylia borrichiae Rossi and Strong. Apical dominance was relatively weak before flowering and stronger in short ramets that were shaded by taller neighbors later in the season. Clipped ramets delayed sprouting new stems, and galled ramets sprouted new stems quickly compared to intact ramets, but final stem counts were similar across treatments. Clipping significantly delayed flowering, reduced seed head ripening time, and resulted in fewer seed heads and seeds. Galling did not significantly impact reproduction compared to intact ramets. Nitrogen supplementation significantly increased stem count and seed count and lengthened seed ripening time. Borrichia frutescens responds differently to clipping versus galling by A. borrichiae and better tolerates galling in terms of nonreproductive performance and survival. Galling from A. borrichiae likely prevents Borrichia frutescens from flowering, which suggests resource regulation of meristems by the midge.

Growth and Flowering Responses of Sea Marigold to Daminozide, Paclobutrazol, or Uniconazole Applied as Drenches or Sprays

Borrichia frutescens (L.) DC., sea marigold, is a woody perennial shrub native to the Gulf and Atlantic coasts of North America and has potential as a landscape shrub or groundcover. This study assesses application rates of three commercially available plant growth regulators (PGRs) on B. frutescens during container production. In one experiment, plants were drenched with 0, 0.5, 1, 2, or 4 mg active ingredient (a.i.) pot−1 of uniconazole or 0, 5, 10, 20, or 40 mg a.i. pot−1 of paclobutrazol, and in a second experiment, plants were sprayed with solutions of either 0, 25, 50, 100, or 200 mg a.i. L−1 of uniconazole, 0, 50, 100, 200, or 400 mg a.i. L−1 of paclobutrazol, or 0, 2500, 5000, 10000, or 20000 mg a.i. L−1 of daminozide. Drench-applied paclobutrazol (40 mg a.i. pot−1) reduced shoot mass and root mass (52.9 and 48.5 %, respectively). Both paclobutrazol (40 mg a.i. pot−1) and uniconazole (2 mg a.i. pot−1) reduced leaf number by as much as 56.7 and 23.8 %, respectively. Height was reduced 54.9 % by paclobutrazol at 40 mg a.i. pot−1 and 34.9 % by uniconazole at 2 mg a.i. pot−1. Drench application of paclobutrazol and uniconazole reduced internode extension by 50.1 and 41.4 %, respectively. At the levels tested, daminozide, paclobutrazol, and uniconazole were generally ineffective at controlling growth when applied as a spray. Drench application of paclobutrazol or uniconazole can be used to control height during container production of B. frutescens, whereas spray application rates need to be tested at higher concentrations or multiple applications to achieve desired control.

Freshwater inflow requirements for the Nueces Delta, Texas: Spartina alterniflora as an indicator of ecosystem condition

Estuarine wetlands and salt marshes are fundamentally driven by variations in freshwater inflow. However, many estuaries have been subject to a heavily modified hydrology due to flood protection engineering and the construction of upstream dams for municipal water supply. Assessment of the impacts of these activities on the health of estuarine wetlands has traditionally focused on tracking the abundance of economically important shellfish and finfish species. In this study, we examine fluctuations in the abundance of selected salt marsh plants and use this information to develop estimates of freshwater inflow needs. The impact of freshwater inflow events on 3 common emergent plants in the Nueces River Delta (Spartina alterniflora, Borrichia frutescens, Salicornia virginica) was determined from long-term monitoring of permanent census plots. Of the 3 species examined, Spartina alterniflora was determined to be the best indicator species because its abundance most closely tracked variations in freshwater inflow. For example, under low salinity conditions S. alterniflora cover approached 66%. However, when salinities exceeded 25‰, S. alterniflora cover declined rapidly. Our results provide clear evidence that the presence or absence of key plant indicator species (in this case S. alterniflora) is reflective of overall estuarine hydrological condition over time scales exceeding 6 months. Citation: Stachelek J, Dunton KH. 2013. Freshwater inflow requirements for the Nueces Delta, Texas: Spartina alterniflora as an indicator of ecosystem condition. Texas Water Journal. 4(2):62-73. Available from: https://doi.org/10.21423/twj.v4i2.6354.

Geographic and Host-Associated Size Variation in the Parasitoid WaspTorymus umbilicatus(Hymenoptera: Torymidae) in Florida: Implications for Host Survival and Community Structure

Acquisition of enemy-free-space has been suggested to reduce selective pressure against host range expansion in phytophagous insects. The gall midge, Asphondylia borrichiae Rossi and Strong (Diptera: Cecidomyiidae), which attacks the stem tips of its 3 host plants produces a spherical tumor-like growth (= gall). Juvenile stages (larvae and pupae) of A. borrichiae develop inside the gall; the midge spends approximately 95–98% of its life cycle embedded within the gall. During these juvenile stages, A. borrichiae are parasitized by 4 species of hymenopterans. Previous studies have found that one of the most common and the largest parasitoid, Torymus umbilicatus (Gahan), tends to dominate large galls owing to its significantly longer ovipositor, which enables it to penetrate the biggest galls and reach larvae and pupae that become unavailable to the other 3 parasitoids, which have much shorter ovipositors. Moreover, previous studies suggest that the gall midge is diverging both morphologically and genetically in sympatry. The current study is the first to provide morphological evidence that T. umbilicatus, which is a dominant member of the parasitoid guild that attacks A. borrichiae, may also be diverging in sympatry along with its host. Female T. umbilicatus from sea oxeye daisy (Borrichia frutescens [L.] DC) were significantly larger than those from alternative host plants of the gall midge, dune elder (Iva imbricata Walter) and marsh elder (I. frutescens L). Additionally, size of female T. umbilicatus collected from 2 geographically distant sites were significantly different and these differences were consistent with a latitudinal gradient in size between plant species. Although T. umbilicatus were larger from galls collected from B. frutescens compared to I. frutescens at both sites, gall diameter demonstrated a significant decline along a south-north latitudinal gradient. However, a significant interaction between plant species and site suggests that differences in T. umbilicatus size (and most likely their gall midge host) is caused either by phenotypic plasticity of the species at the 2 sites, or these insects (T umbilicatus and gall midges) tend to be smaller with increasing latitude. Moreover, galls on I, frutescens, owing to their smaller size and increased crowding, decline in size at a greater rate than those from B. frutescens which produces significantly larger and less crowded galls.

Effects of Relative Host Plant Abundance, Density and Inter-Patch Distance on Associational Resistance to a Coastal Gall-Making Midge,Asphondylia borrichiae(Diptera: Cecidomyiidae)

Associational resistance (AR) is an emergent property of ecological communities and may play an important role in their assembly and structuring. Gall densities of the midge Asphondylia borrichiae Rossi & Strong (Diptera: Cecidomyiidae) on the coastal plant Iva frutescens L. (Asteraceae) are reduced in the presence of a second host, Borrichia frutescens (L.) (Asteraceae). In this system associational resistance is mediated by parasitoid natural enemies that emerge from Borrichia galls and attack galls on Iva, thereby reducing gall densities on Iva. We quantified distances between patches of Iva and Borrichia and the relative abundances of both plant species and predicted that gall densities would be reduced and parasitism rates elevated on Iva closer to Borrichia compared with more distant patches and on Iva occurring with relatively greater Borrichia abundance in comparison to reduced ratios of Borrichia to Iva abundance. Although gall densities were elevated on Iva more distant from Borrichia, as compared with Iva adjacent to Borrichia, parasitism rates were unaffected by patch distance in this system. Increasing relative abundance of Borrichia was found to significantly reduce gall densities on Iva, though parasitism rates on Iva galls were unaffected by Borrichia abundance. These results suggest other factors, e.g., environmental quality, host plant genotype, etc., may swamp out the effects of parasitoid—mediated AR in this system as Iva becomes more distant from Borrichia or as the abundance of Borrichia relative to Iva is reduced.

Effects of large‐scale host plant addition and removal on parasitoid‐mediated associational resistance in the gall midge Asphondylia borrichiae

Abstract Associational resistance (AR) occurs when a plant species experiences less herbivory when growing in the presence of other plant species than when growing in monoculture. Densities of the gall midge Asphondylia borrichiae Rossi & Strong on the coastal plant Iva frutescens L. are depressed in the presence of a second coastal plant species, Borrichia frutescens (L.). Previous studies suggested that hymenopteran parasitoids from Borrichia galls spill over onto Iva galls and reduce gall densities. This study employs large‐scale addition or near‐complete removal of Borrichia from a series of spoil islands near the west central Florida coast. Densities of galls on Iva decreased where Borrichia was added, increased where Borrichia was removed and remained unchanged on islands where Borrichia abundance was not manipulated. Relative to unmanipulated islands, the total parasitism rate on Iva galls and parasitism rate by Torymus umbilicatus, the parasitoid hypothesised to be primarily responsible for AR in the system, declined on islands where Borrichia was removed and increased on islands where Borrichia was added, supporting the idea of parasitoid‐mediated AR.

Elevation and Plant Community Distribution in a Microtidal Salt Marsh of the Western Gulf of Mexico

The relationship between elevation and the natural occurrence of several species of emergent vascular plants was examined in a microtidal deltaic marsh system near Corpus Christi, on the southwestern Texas coast. Vegetation percent cover was estimated quarterly from November 2003 to November 2006 in 374 permanent plots located in 9 sites. Soil elevation was measured in each plot using sub-centimeter real-time kinematic GPS. Cluster analyses determined that there were two significantly (P < 0.05) different sets of co-occurring species, one comprising Borrichia frutescens, Salicornia virginica and Distichlis spicata and the other including Batis maritima, Salicornia bigelovii and Lycium carolinianum. Analysis of species groupings across an elevation gradient using non-metric multi-dimensional scaling and hierarchal cluster analysis indicated that these assemblages represent a low marsh assemblage (25–50 cm NAVD88) and a high marsh assemblage (50–65 cm NAVD88), respectively. The strong relationship between elevation and species distribution suggests that abiotic factors play a key role in determining plant distribution in this ecosystem, and indicate that even apparently small differences in elevation can be important in a microtidal system.

Relative Stability of Plant Communities in a South Carolina High Salt Marsh

ABSTRACT The high marsh in southeast Atlantic coast salt marshes forms a relatively small but ecologically important transition zone between low marsh and the terrestrial shoreline. However, long-term trend data from high marshes are limited to a few studies. Permanent plots established in a high marsh near Waties Island in northeast South Carolina were measured for plant coverage from 2002–2010. At the beginning and at the end of the study, four groups of plots were identified: mixed indicated by Borrichia frutescens, Distichlis spicata, and Fimbristylis castanea; Juncus indicated by Juncus roemerianus; Salicornia indicated by Salicornia virginica; and Spartina indicated by Spartina patens. Ordination of the 2010 plot data and soil analyses produced clear separation of the groups along a single dominant axis with Salicornia and Juncus groups at the high end of a salinity gradient and the Spartina group at the high end of soil organic matter gradient. Comparison of plots classified in 2002 to the same p...

Environmental heterogeneity mediates a cross‐ecosystem trophic cascade

1. The flow of energy and nutrients across ecosystem boundaries can have significant community‐wide effects, but the role of productivity of the recipient habitat in mediating these effects remains unclear. This is especially true when organisms moving across ecosystem boundaries serve simultaneously as predators and prey.2. In this study, the effects of odonates, primarily Enallagma civile (Hagen), on a salt marsh system were examined. Cages were used to exclude odonate predators, but not other arthropods, from experimental plots of the sea oxeye daisy, Borrichia frutescens (L.) in high and low productivity areas. The effects were assessed on the in situ arthropod community and the host plant.3. There were strong direct effects of predation on the herbivores Pissonotus quadripustulatus Van Duzee and Asphondylia borrichiae Rossi and Strong, with higher densities where damselflies were excluded. Damselflies also served as prey for web‐building spiders. This resulted in lower spider densities inside cages, and a positive indirect effect on grasshopper densities.4. Direct and indirect effects of odonates were greater in the high productivity area, resulting in a trophic cascade, with greater damage and reduced flowering and density of the host plant inside cages.5. The results of this study support the subsidy hypothesis and show that theoretical models of trophic dynamics, which were developed to explain exchanges within ecosystems, may have predictive and explanatory value for exchanges across ecosystems as well.

Post-mortem ecosystem engineering by oysters creates habitat for a rare marsh plant

Oysters are ecosystem engineers in marine ecosystems, but the functions of oyster shell deposits in intertidal salt marshes are not well understood. The annual plant Suaeda linearis is associated with oyster shell deposits in Georgia salt marshes. We hypothesized that oyster shell deposits promoted the distribution of Suaeda linearis by engineering soil conditions unfavorable to dominant salt marsh plants of the region (the shrub Borrichia frutescens, the rush Juncus roemerianus, and the grass Spartina alterniflora). We tested this hypothesis using common garden pot experiments and field transplant experiments. Suaeda linearis thrived in Borrichia frutescens stands in the absence of neighbors, but was suppressed by Borrichia frutescens in the with-neighbor treatment, suggesting that Suaeda linearis was excluded from Borrichia frutescens stands by interspecific competition. Suaeda linearis plants all died in Juncus roemerianus and Spartina alterniflora stands, regardless of neighbor treatments, indicating that Suaeda linearis is excluded from these habitats by physical stress (likely water-logging). In contrast, Borrichia frutescens, Juncus roemerianus, and Spartina alterniflora all performed poorly in Suaeda linearis stands regardless of neighbor treatments, probably due to physical stresses such as low soil water content and low organic matter content. Thus, oyster shell deposits play an important ecosystem engineering role in influencing salt marsh plant communities by providing a unique niche for Suaeda linearis, which otherwise would be rare or absent in salt marshes in the southeastern US. Since the success of Suaeda linearis is linked to the success of oysters, efforts to protect and restore oyster reefs may also benefit salt marsh plant communities.

Diet mixing in a parasitic plant: adaptation or constraint?

Some herbivores deliberately consume a mixed diet, either to obtain a superior mix of nutrients or to avoid consuming too much of any one toxin. Few studies have examined diet mixing in parasitic plants, which typically have very broad host ranges. We offered the parasitic plant Cuscuta indecora (dodder), a range of mixtures of two hosts (Iva frutescens and Borrichia frutescens) in the greenhouse, and observed correlations between the host community and Cuscuta infection in the field. In the greenhouse, Cuscuta performed better on mixtures with a higher relative abundance of Iva. Cuscuta selectively foraged on whichever host was more abundant (diet switching), the exact opposite of the behavior that would be expected if diet mixing was advantageous. In the field, the intensity of Cuscuta infections was decreased by the presence of non-hosts (grasses), not strongly affected by the presence of intermediate hosts, and increased by the presence of Borrichia. We conclude that Cuscuta does not obtain nutritional benefits from a broad diet, but instead is constrained by its relative lack of mobility to attack hosts of intermediate value. In general, the lack of mobility of parasitic plants compared to herbivores probably selects for broad host ranges in parasitic plants.

Plasticity, Not Adaptation to Salt Level, Explains Variation Along a Salinity Gradient in a Salt Marsh Perennial

Evolutionary ecologists have long been intrigued by the fact that many plant species can inhabit a broad range of environmental conditions and that plants often exhibit dramatic differences in phenotype across environmental gradients. We investigated responses to salinity treatments in the salt marsh plant Borrichia frutescens to determine if the species is responding to variation in edaphic salt content through phenotypic plasticity or specialized trait response. We grew seedlings from fruits collected in high- and low-salt microhabitats, assigned seedlings to high- and low-salt treatments in a greenhouse, and measured traits related to salt tolerance. All traits were highly plastic in response to salinity. Plants from the two microhabitats did not differ in trait means or respond differently to the treatments. These results suggest that environmental differences between the two microhabitats are not creating genotypes adapted to high and low salt levels. In addition, despite evidence for variation in allozyme markers in this population, there was no significant genotypic variation (family effect) in any of the trait means measured across microhabitats. There was variation in plasticity for only leaf Na and leaf B concentration. The high degree of plasticity for all traits and the lack of differences among microhabitats across the salinity gradient suggest plasticity in many traits may be fixed for this species.

Effects of pulsed riverine versus non-pulsed wastewater inputs of freshwater on plant community structure in a semi-arid salt marsh

The use of treated wastewater to restore freshwater inputs to arid and semi-arid wetlands is a relatively new concept, and the long-term effects of such practices on plant community structure are largely unknown. We compared vegetation composition, pore water salinity, and soil moisture along permanent transects at a restoration site receiving wastewater effluent since October 1998 to three nearby downstream sites subjected only to freshwater inputs via precipitation and river flooding. Local climate during this period was highly variable and included two droughts and a wet period that began with a series of large floods. Significantly lower pore water salinities were observed at the wastewater site compared to downstream sites, particularly during droughts, when salinities were 20%.–40%. lower at the wastewater site. Between July 1997 and July 2002, cover of the clonal stress-tolerator, Salicornia virginica, decreased from 87% to 33% at the wastewater site, while cover of the clonal dominant, Borrichia frutescens, increased from 5% to 55%. In contrast, S. virginica cover increased at two downstream sites during the same period, while cover of B. frutescens remained relatively stable. Following large floods in summer 2002, which marked the beginning of a three year-wet period, B. frutescens cover increased at all sites. We concluded that constant wastewater additions and climate-driven wet periods affected plant community structure similarly by promoting expansion of the clonal dominant B. frutescens and inhibiting expansion of the stress-tolerant species S. virginica. We propose distinct management strategies for using wastewater to 1) increase plant cover, 2) promote endemic plant assemblages, and 3) maximize species richness.

Hyperspectral Reflectance Response of Freshwater Macrophytes to Salinity in a Brackish Subtropical Marsh

Coastal freshwater wetlands are threatened by increased salinity due to relative sea level rise and reduced freshwater inputs. Remote radiometric measurement of freshwater marsh canopies to detect small shifts in water column salinity would be useful for assessing salinity encroachment. We measured leaf hyperspectral (300-1100 nm) reflectance of freshwater macrophytes (cattail, Typha latifolia and sea oxeye, Borrichia frutescens) in a field study in a subtropical brackish (2.5-4.5 parts per thousand salinity, per thousand) marsh to determine salinity effects on visible and near-infrared spectral band reflectance and to identify reflectance indices sensitive to small (1 per thousand) changes in wetland salinity. For sea oxeye, floating-position water band index [fWBI = R(900)/minimum(R(930) - R(980)), where R(lambda) = reflectance at band lambda], normalized difference vegetation index [NDVI = (R(774) - R(681))/(R(774) + R(681))], and a proposed wetland salinity reflectance ratio (WSRR = R(990)/R(933)) were sensitive to salinity with R2 of 40, 35, and 65%, respectively (p < 0.01). For cattail, NDVI and photochemical reflectance index [PRI = (R(531) - R(570))/(R(570) + R(531))] were sensitive to salinity with R2 of 29 and 33%, respectively (p <or= 0.01). Higher salinity significantly reduced mean reflectance of sea oxeye in 328- to 527-nm and 600- to 700-nm wavebands (p < 0.05), which corresponded to chlorophyll bands. Reflectance of cattail was not significantly affected by the highest salinity, although the spectral band most affected was 670 nm (p < 0.10), which is a chlorophyll a band. Our findings indicate that hyperspectral radiometry can detect the response of emergent freshwater plants to changes in wetland salinity, which would help with monitoring salinity effects on coastal wetlands.