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2U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Blvd., Lafayette, Louisiana 70506; and 3Wetlands Biogeochemistry Institute, Louisiana State University, Baton Rouge, Louisiana 70803
Received for publication February 13, 1998. Accepted for publication October 30, 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: coastal marsh • Louisiana • plant growth • salinity stress • stress tolerance • wetlands
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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listed four hypotheses to describe processes that could lead to this variation: physiological specialization to different environmental conditions along the gradient, differential dispersal, variation in interspecific competitive ability, and changes in predation pressure along the gradient. In coastal marsh habitats, salinity is an environmental factor that varies with distance from the source of salt water as well as over elevational gradients. Salinity regimes in coastal habitats can also fluctuate, regularly with daily tides and irregularly because of factors such as storms and hydrologic alterations (e.g., canal construction, marsh management practices). Increased salinity can affect plant growth by (1) the imposition of water stress through increased osmotic potential of the rooting medium (Levitt, 1972
; Yeo, 1983
; Wainwright, 1984
; Hale and Orcutt, 1987
), (2) the accumulation of ions or other possible plant toxins in the soil (Wainwright, 1984
; Hale and Orcutt, 1987
), and (3) the accumulation of ions in plant tissue (Yeo, 1983
; Flowers, 1985
; Munns, 1993
). Researchers have identified within-species ecotypic variation in salt tolerance (Ahmad and Wainwright, 1977
; Wainwright, 1984
; Blits and Gallagher, 1991
; Hester, McKee, and Mendelssohn, 1996
, 1998
), and variation among different life history stages (Zedler, Pauling, and McComb, 1990
).
Because plant zonation along a salinity gradient is recognized as a major feature of temperate coastal marshes (Odum, 1988
; Mitsch and Gosselink, 1993
), interest has focused on how plant communities respond to changes in salinity regimes. Coastal oligohaline wetlands may be subjected to sudden influxes of high salinity water that inundate an area for relatively short periods. Such events, often related to severe weather, may not permanently alter the physical or chemical characteristics of a site. They could, however, alter community structure and composition depending on the responses of individual plant species to the stressors and on species interactions (Valentine, 1977
; McKee and Mendelssohn, 1989
). Brewer and Grace (1990)
hypothesized that zonation of plant communities in a tidally influenced oligohaline marsh was regulated by the interaction of biotic factors and occasional pulses of higher salinity lake water during storm events.
Despite potential impacts on primary productivity, the effects of short-term changes in salinity regime on oligohaline marsh plant community dynamics are not clear. Our objective in this study was to quantify the impact of salinity change, including components of maximum salinity reached, rate of salinity increase, and duration of exposure, on growth of selected oligohaline marsh macrophytes in a single growing season. This paper is unique in that, to our knowledge, the effects of salinity influx rate and duration of exposure have not been previously evaluated. A companion paper examines the ability of the selected species to recover after salinity stress is removed (Howard and Mendelssohn, 1999
).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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), Panicum hemitomon J. A. Schultes, Sagittaria lancifolia L., and Scirpus americanus Pers. (synonymous with S. olneyi Gray; Kartesz, 1994
). These species display a range of leaf and stem morphologies, factors that may influence salinity tolerance in freshwater wetland species (Haller, Sutton, and Barlowe, 1974
). Relative distributions of the last three species across marsh types in coastal Louisiana were provided by Chabreck (1972)
.
We collected plant material from low salinity (average less than 2 g/L) sites in the Barataria and Lake Pontchartrain Basins of southeast Louisiana in April 1990. Tides in Louisiana are diurnal, average 
30 cm at the coast, and attenuate in an inland direction. Salinity and water depth at the collection sites are strongly influenced by prevailing wind patterns. Plants were transported to a greenhouse facility at Louisiana State University in Baton Rouge (30°30' N, 91°15' W), sorted, planted in small containers of Mississippi River silt, and allowed to acclimate to the greenhouse for 6 wk in fiberglass tanks (625 L) filled to pot-surface level with fresh tapwater. After the acclimation period, we selected plants of similar size within each species and standardized rhizome lengths (i.e., cut to same length) in Eleocharis, Panicum, and Scirpus. We did not attempt to standardize Sagittaria rhizomes because of their large size; variation in rhizome diameter may have influenced the effect cutting had on growth or survival. The plants were washed to remove soil from the roots, weighed, and repotted in plastic containers (15 cm diameter x 15 cm deep) filled with a soil mixture (two parts by volume Jiffy Mix Plus [a commercial potting soil containing N and P fertilizer] and one part Mississippi River silt); a drain hole was placed near the base of each pot. Each pot contained a single plant. Additional plants of each species were weighed and then dried at 75°C to obtain data for wet mass/dry mass conversion. Treatments were initiated after an additional 9–11 d acclimation period in June 1990.
Experimental design and data collection
Initial conditions for the experiment were 0 g/L salinity and water depth 1 cm above the soil surface. Each species was exposed to the following five treatments, numbered in perceived order of increasing level of stress: (1) 0 g/L salinity, (2) final salinity of 6 g/L salinity reached in 3 wk, (3) final salinity of 6 g/L reached in 3 d, (4) final salinity of 12 g/L reached in 3 wk, and (5) final salinity of 12 g/L reached in 3 d. The 3-d influx rate was selected to simulate a severe storm event (e.g., a hurricane). The 3-wk influx rate simulated a more gradual salinity change, such as that associated with frontal events or canal construction. Final salinities were selected to encompass the 10 g/L salinity increase reported in a Louisiana wetland following passage of a mid-1980s hurricane (Meeder, 1987). The artificial salt source was Forty Fathoms Marine Mix (Marine Enterprise International Inc., Baltimore, Maryland). Although storm events will often have an associated change in water depth, we held flooding depth at 1 cm in this experiment to avoid introducing a fourth factor (i.e., to simplify interpretation of the results). Treatments were maintained for a period of 1, 2, or 3 mo (referred to as duration of exposure).
We randomly assigned treatments to one of five 625-L fiberglass tanks within each of three experimental blocks (zones of greenhouse). Low replication (N = 3) was necessary because of greenhouse space limitations. Within a block, six pots of each species were randomly assigned to each of the five treatments and were also assigned to a harvest or recovery category (Fig. 1). We used a total of 360 pots. To increase salinity, salt was added to treatment tank water in equal doses (by mass); the salt was first dissolved in 4 L of water removed from each tank and then distributed across the tank water surface. Five salt applications were made at 12-h intervals in the 3-d influx treatments, and 11 applications were made at 2-d intervals in the 3-wk influx treatments. Submersed pumps slowly circulated water within the treatment tanks and maintained salts in solution.
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Initially, tank water salinity and depth were monitored daily and adjusted as necessary until conditions became stable; tanks were thereafter monitored every other day. We measured stem (or leaf, for Sagittaria) density, total stem/leaf height (i.e., the sum of all individual stem/leaf heights per pot), and mean stem/leaf height every 2 wk; any mortality (defined as complete death of aboveground tissue) was noted. Harvested plants were divided into aboveground and belowground portions, and aboveground material was further separated into live and dead. It was not possible to distinguish live from dead in the belowground material, so reported values for this component included both. Plant tissue was dried at 75°C to a constant mass for biomass determination.
Statistical analyses
Data were analyzed separately by species. All analyses were performed using SAS/STAT software (SAS, 1989). Linear regression analysis was applied to data collected from the additional plant material collected at the start of the experiment to define a relationship between wet and dry biomasses. Our initial analyses regarded treatment as a main effect and were performed for each of the three durations of exposure. Univariate analysis of variance (ANOVA) was used with aboveground live biomass, belowground biomass, stem/leaf density, total stem/leaf height, and mean stem/leaf height as separate dependent variables. Initial dry biomass was included as a covariate for biomass analyses, and initial measurements of stem/leaf density, total stem/leaf height, and mean stem/leaf height were used as covariates with their corresponding response measures. The interaction between treatment and covariate was tested, and analysis of covariance continued in cases of nonsignificance. The covariate was dropped from analyses when not significant. We used a priori linear contrasts (Table 1) to determine effects of final salinity level and influx rate at each exposure duration.
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; Potvin, Lechowicz, and Tardif, 1990
). The Huynh-Feldt corrected significance level was used with the univariate approach when the sphericity criterion was not met (Potvin, Lechowicz, and Tardif, 1990
).
Since treatment effects were fixed, the models were assumed to be robust for the normality assumption (Montgomery, 1991
). Data were transformed when residual plots indicated failure to meet the assumption of variance homogeneity; specific transformations applied are indicated in tables presenting results of analyses. A significance level of 0.05 was used for all ANOVA and ANOVAR tests.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Salt concentration
Aboveground biomass of all species was significantly reduced in 12 g/L salinity (influx rates combined) compared to 0 g/L (Table 2, Fig. 2). The point when this reduction became apparent, however, varied with species. Both Panicum and Sagittaria responded negatively at 1-mo exposure, while Eleocharis and Scirpus remained unaffected until 2 mo (Fig. 2). Sagittaria was the first species to show visible signs of stress, with browning and curling of leaf edges apparent in treatment 5 (12 g/L, 3-d influx) on day 8 of the experiment. Response, as measured by mean stem height, was similar to aboveground biomass response (data not shown). Total stem height effects (Table 2) were a reduction in the 12 g/L treatments for all species at all durations. Stem density, which was unaffected in Scirpus at 12 g/L compared to 0 g/L (Table 2), was reduced in the other species, beginning at 1-mo exposure in Panicum and Sagittaria and at 2 mo in Eleocharis. Significant belowground biomass effects (Table 2) were reduction at 12 g/L compared to 0 g/L for all species; this effect, however, was delayed until 2 mo in Eleocharis and Panicum and 3 mo in Scirpus.
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Salinity influx rate
Within the 6 g/L salinity level, Eleocharis mean stem height, Panicum total stem height, and Sagittaria belowground biomass were all reduced in the 3-d influx compared to the 3-wk influx 1 mo into the experiment (Table 3). These effects, however, were temporary and disappeared with longer exposure. Within 12 g/L, the adverse effects of the rapid influx rate on growth of these species was apparent in the 2nd mo as well, and in the case of Sagittaria the effect on mean leaf height persisted at 3 mo (Table 3). In a deviation from the overall trend of reduced growth with increasing stress, belowground biomass in Sagittaria was actually higher at 2 mo in the 3-d compared to 3-wk influx rate (5.16 ± 1.53 vs. 3.37 ± 0.41, mean ± 1 SE). Scirpus did not respond to differential influx rate at either final salinity (Table 3).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). In another study, this species was tolerant of salinity up to 9.4 g/L for 1 mo growing in a mixed-species assemblage with natural substrate in greenhouse conditions; rapid exposure to 15 g/L in the field, however, led to total mortality in a few days (McKee and Mendelssohn, 1989
). In our study, growth of Panicum appeared unaffected at 6 g/L for the first 6–8 wk of exposure. While growth reductions began to appear at week 8 in 6 g/L treatments, dramatic adverse reactions to the 12 g/L treatments were seen by week 6, leading to the high mortality rates observed (i.e., 84% at 3 mo). No resprouting of dead stems was noted.
The results of our study also augment previous research on salinity tolerance in Sagittaria lancifolia. In a greenhouse experiment that included flooding stress, S. lancifolia had reduced photosynthetic capacity after 40 d of exposure to 2.9 g/L salinity; biomass effects were not described (Pezeshki, DeLaune, and Patrick, 1987b
). McKee and Mendelssohn (1989)
found tissue damage in this species after 35 d of exposure to 4.8 g/L in the greenhouse and complete mortality when the plants were exposed to a rapid increase to 15 g/L in the field. In our study, Sagittaria, while exhibiting tissue damage 8 d into the experiment in the 12 g/L, 3-d influx treatment, initially produced new leaves to replace damaged leaves (i.e., total leaf number did not increase). Leaf necrosis was also apparent in 6 g/L treatments after 4 wk, but complete death of aboveground tissue occurred only in the 12 g/L treatments with mortality rates relatively low at 17% after 2 mo of exposure and rising to 33% after 3 mo. The ability of this species to form new leaves using rhizome nutrient reserves would not be apparent in experiments lasting just a few days or weeks. The rapid expression of visual stress indicators in Sagittaria and the delayed response of Panicum (i.e., reduced growth compared to controls was not expressed until stress exposure exceeded 4 wk) would explain the conclusion reached by McKee and Mendelssohn (1989)
of lower salt tolerance in Sagittaria compared to Panicum. Their study was conducted over 35 d.
Although all species responded negatively to increased final salinity level to varying degrees, the effect of influx rate within a given salinity was less compelling. Observed species differences in response to influx rate may be related to morphology. While succulence in halophytes is recognized as an adaptation that functions to dilute tissue ion content, this does not hold true for glycophytes. Leaves of Sagittaria are somewhat fleshy compared to the other species studied and have relatively high water content (percentage moisture [mean ± 1 SE, N = 10]: Eleocharis, 82.22 ± 0.94%; Panicum, 74.91 ± 0.96%; Sagittaria, 87.66 ± 1.01%; and Scirpus, 86.46 ± 1.24%). Osmotic stress in the fast influx to 12 g/L treatment was apparent first in Sagittaria (Table 3, Figs. 4, 5). Responses, however, were mostly short term, with differences because of influx rate disappearing at longer exposures of 2 and 3 mo. Plants subjected to the slow influx rate appeared to be suppressed to the same degree as those in the fast influx rate as exposure time increased.
Phenological patterns in peak standing crop may also have influenced growth responses to salinity stress. Sagittaria reached peak standing crop mid-experiment (Fig. 3). Maximum total leaf height at 0 g/L was reached for Sagittaria at 6 wk, and maximum total stem height in Panicum was attained at 10 wk; Eleocharis and Scirpus, however, had not yet reached the senescence phase of the typical growth curve 3 mo into the experiment (Fig. 5). The adverse effects of the stressor may have been magnified as plants approached the senescent phase of their annual growth cycle.
The effect of exposure duration was difficult to quantify in this experiment since it is confounded with plant age; in the 0 g/L treatment, plants accumulated biomass until the onset of seasonal senescence. All species, however, displayed trends of increasing differences between biomass of plants at 0 g/L and those subjected to raised salinity levels as exposure increased. Eleocharis and Scirpus either continued to acquire biomass at a reduced rate in salinity treatments or simply maintained biomass over time (Figs. 3, 4). In contrast, biomass of Panicum and Sagittaria in salinity treatments was reduced as exposure time increased, to a greater extent in the 12 g/L treatments than in the 6 g/L treatments. Llewellyn and Shaffer (1993)
found similar results for the freshwater marsh species Justicia lanceolata; growth of this species continued for 6 mo at salinity levels of 0 and 3 g/L but was eliminated after 9 wk of exposure to 6 g/L.
Although we did not collect data on causative factors for growth reduction due to salinity stress, Sagittaria growth patterns are consistent with a biphasic model of plant response to salinity proposed by Munns and Termaat (1986)
. In the first phase of this model, leaf expansion over the short term (days) is regulated by hormones or growth regulators produced in roots and translocated to shoots. In the second phase, leaf expansion over the long term (weeks to months) is related to the plant's ability to tolerate high salt concentrations in mature leaves and to the rate new leaves are produced; as older leaves start to die, the photosynthetic area of the plant will eventually decline to a low level at which carbohydrate production cannot support continued growth (Munns and Termaat, 1986
). In the present study, Sagittaria exposed to 12 g/L salinity moved through a sequence of leaf mortality, leaf regeneration, and eventual plant death. We did not collect data that could provide evidence of the first phase of the Munns and Termaat (1986)
model (i.e., an inhibitory signal from the roots). The second ion-dominated phase, however, was apparent in the visible injury, or "salt burning," that first occurred in the older leaves of Sagittaria. Munns (1993)
noted that leaf death under high salinity conditions is caused by a rapid rise in salt concentrations in cell walls or cytoplasm when the vacuoles can no longer compartmentalize the salts. The second phase of the Munns and Termaat (1986)
model hypothesizes that the rate of leaf death will eventually exceed the rate at which new leaves can be produced. New leaves produced by Sagittaria after more than 2 mo exposure to 12 g/L salinity survived only a few days, and complete aboveground tissue mortality soon followed.
Relative salinity tolerance
Panicum was the least tolerant of salinity stress based on the extent of aboveground tissue necrosis. Sagittaria did exhibit visual signs of stress before Panicum, but it experienced a lower mortality rate and, in contrast to Panicum, was able to produce new leaves to replace damaged ones for some time. No death of Eleocharis or Scirpus resulted from experimental conditions, but differences in relative tolerance can be identified. Overall, Scirpus displayed few significant responses to salinity increases, and where significant growth suppression did occur, the magnitude of growth suppression in salinity treatments compared to the freshwater treatment was less than that of Eleocharis. The relative tolerance of the species to experimental conditions of salinity stress, in order from least to most tolerant, was therefore Panicum hemitomon < Sagittaria lancifolia < Eleocharis palustris < Scirpus americanus. This corresponds to their distribution along a salinity gradient in coastal marshes of the northern Gulf of Mexico. Panicum hemitomon, which is restricted to the upper, near-freshwater end of the continuum, grades into mixed communities of Sagittaria lancifolia and Eleocharis palustris as salinity increases. Scirpus americanus is most common at the lower end of the oligohaline marsh zone and extends into brackish marshes.
Sea-level rise implications
Relative global sea-level rise has been estimated at 2.4 ± 0.90 mm/yr (Peltier and Tushingham, 1989
), but in much of Louisiana high rates of subsidence contribute to an increase in the rate of relative sea-level rise to 1 cm/year (Penland and Ramsey, 1990
). Because diverse plant communities persist in tidally influenced oligohaline marshes, the species are necessarily adapted to temporally changing salinity regimes. Under a scenario of increasing rate of sea-level rise, however, it is likely that hydrologic regimes in oligohaline marshes will become more extreme (i.e., higher maximum salinities, more rapid rates of salinity increase, longer periods of anoxia due to flooding). For example, as sea level rises, coastal marshes will become more susceptible to impacts from inundation of high-salinity water associated with storm events and hurricanes. There is also concern that global climate change and the accompanying increase in sea surface temperatures may lead to an increase in the intensity and frequency of tropical cyclones (Raper, 1993
). Our results indicate that a sensitive species such as Panicum may succumb to salinity stress, allowing more tolerant species present to expand or opening the site to colonization by new species. Plant community response would depend on the characteristics of the salinity-change event itself and on biotic factors such as interspecific competitive relationships, composition of standing vegetation, and composition of the available seed bank (Baldwin, McKee, and Mendelssohn, 1996
; Wijte and Gallagher, 1996
). Community response may in turn influence the integrity of emergent marsh habitat through changes in plant root structure and autochthonous organic matter contribution to the substrate. Inadequate vertical accretion, which leads to submergence, has been attributed in some coastal marshes to inadequate organic matter accumulation resulting from decreased plant production (Nyman et al., 1993
). If more tolerant species are unable to colonize a stressed site, marsh loss and conversion to open water may occur. This scenario is of great concern in coastal Louisiana, where landward retreat of wetlands is limited by human populations and infrastructure, such as highways and levees.
This experiment described short-term growth responses to salinity stress in plants harvested immediately following stress treatments; for the first time, the effects of salinity influx rate and exposure duration were quantified. The ability of plants to recover after stress is alleviated is an equally important consideration when investigating salinity pulse effects. We address the recovery capabilities of these four marsh macrophytes in a companion paper (Howard and Mendelssohn, 1999
).
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FOOTNOTES |
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Baldwin, A. H., K. L. McKee, and I. A. Mendelssohn. 1996 The influence of vegetation, salinity, and inundation on the seed banks of oligohaline coastal marshes. American Journal of Botany 83: 470–479.[CrossRef][ISI]
Blits, K. C., and J. L. Gallagher. 1991 Morphological and physiological responses to increased salinity in marsh and dune ecotypes of Sporobolus virginicus (L.) Kunth. Oecologia 87: 330–335.[CrossRef][ISI]
Brewer, J. S., and J. B. Grace. 1990 Plant community structure in an oligohaline tidal marsh. Vegetatio 90: 93–107.[CrossRef][ISI]
Chabreck, R. H. 1972 Vegetation, water and soil characteristics of the Louisiana coastal zone. Louisiana Agricultural Experiment Station Bulletin 664. Baton Rouge, LA.
Flowers, T. J. 1985 Physiology of halophytes. Plant and Soil 89: 41–56.[CrossRef][ISI]
Hale, M. G., and D. M. Orcutt. 1987 The physiology of plants under stress. John Wiley & Sons, New York, NY.
Haller, W. T., D. L. Sutton, and W. C. Barlowe. 1974 Effect of salinity on growth of several aquatic macrophytes. Ecology 55: 891–894.[CrossRef][ISI]
Hester, M. W., I. A. Mendelssohn, and K. L. McKee. 1996 Intraspecific variation in salt tolerance and morphology in the coastal grass Spartina patens (Poaceae). American Journal of Botany 83: 1521–1527.[CrossRef][ISI]
———, ———, and ———. 1998 Intraspecific variation in salt tolerance and morphology in Panicum hemitomon and Spartina alterniflora (Poaceae). International Journal of Plant Science 159: 127–138.[CrossRef][ISI]
Howard, R. J., and I. A. Mendelssohn. 1999 Salinity as a constraint on growth of oligohaline marsh macrophytes. II. Salt pulses and recovery potential. American Journal of Botany 86: 795–806.
Kartesz, J. T. 1994 A synonymized checklist of the vascular flora of the United States, Canada, and Greenland, 2d ed. Timber Press, Portland, OR.
Levitt, J. 1972 Salt and ion stresses. In J. Levitt [ed.], Responses of plants to environmental stresses, 489–532. Academic Press, New York, NY.
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Meeder, J. F. 1987 Variable effects of hurricanes on the coast and adjacent marshes: a problem for marsh managers. Proceedings of the Water Quality and Wetland Management Conference 4: 337–374.
Mitsch, W. J., and J. G. Gosselink. 1993 Wetlands, 2d ed. Van Nostrand Reinhold Company, New York, NY.
Montgomery, D. C. 1991 Design and analysis of experiments, 3rd ed. John Wiley & Sons, New York, NY.
Moser, E. B., A. M. Saxton, and S. R. Pezeshki. 1990 Repeated measures analysis of variance: application to tree research. Canadian Journal of Forest Research 20: 524–535.
Munns, R. 1993 Physiological processes limiting plant growth in saline soils: some dogmas and hypothesis. Plant, Cell and Environment 16: 15–24.
———, and A. Termaat. 1986 Whole-plant responses to salinity. Australian Journal of Plant Physiology 13: 143–160.[ISI]
Nyman, J. A., R. D. DeLaune, H. H. Roberts, and W. H. Patrick, Jr. 1993 Relationship between vegetation and soil formation in a rapidly submerging coastal marsh. Marine Ecology Progress Series 96: 269–279.[CrossRef][ISI]
Odum, W. E. 1988 Comparative ecology of tidal freshwater and salt marshes. Annual Review of Ecology and Systematics 19: 147–176.
Peltier, W. R., and A. M. Tushingham. 1989 Global sea level rise and the greenhouse effect: might they be connected? Science 244: 806–810.
Penland, S., and K. E. Ramsey. 1990 Relative sea-level rise in Louisiana and the Gulf of Mexico: 1908–1988. Journal of Coastal Research 6: 323–342.[ISI]
Pezeshki, S. R., R. D. DeLaune, and W. H. Patrick, Jr. 1987a Response of the freshwater marsh species, Panicum hemitomon Schult., to increased salinity. Freshwater Biology 17: 195–200.[CrossRef][ISI]
———, ———, and ———. 1987b Effects of flooding and salinity on photosynthesis of Sagittaria lancifolia. Marine Ecology Progress Series 41: 87–91.
Potvin, C., M. J. Lechowicz, and S. Tardif. 1990 The statistical analysis of ecophysiological response curves obtained from experiments involving repeated measures. Ecology 71: 1389–1400.[CrossRef][ISI]
Raper, S. C. B. 1993 Observational data on the relationships between climatic change and the frequency and magnitude of severe tropical storms. In R. A. Warick, E. M. Barrow, and T. M. L. Wigley [eds.], Climate and sea level change: observations, projections and implications, 192–212. Cambridge University Press, Cambridge.
SAS. 1989 SAS/STAT user's guide, version 6, 4th ed. SAS Institute, Cary, NC.
Valentine, J. M., Jr. 1977 Plant succession after saw-grass mortality in southwestern Louisiana. Annual Proceedings of the Southeast Association of Fish and Wildlife Agencies 30: 634–640.
Wainwright, S. J. 1984 Adaptations to flooding with salt water. In T. T. Kozlowski [ed.], Flooding and plant growth, 249–343. Academic Press, New York, NY.
Wijte, A. H. B. M., and J. L. Gallagher. 1996 Effect of oxygen availability and salinity on early life history stages of salt marsh plants. I. Different germination strategies of Spartina alterniflora and Phragmites australis (Poaceae). American Journal of Botany 83: 1337–1342.[CrossRef][ISI]
Yeo, A. R. 1983 Salinity resistance: physiology and prices. Physiologia Plantarum 58: 214–222.[CrossRef]
Zedler, J. B., E. Pauling, and A. McComb. 1990 Differential responses to salinity help explain the replacement of native Juncus krausii by Typha orientalis in western Australia salt marshes. Australian Journal of Ecology 15: 57–72.[CrossRef][ISI]
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