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Department of Biology, The College of Staten Island, City University of New York, Staten Island, New York 10314
Received for publication February 23, 1998. Accepted for publication September 22, 1998.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: annual dunegrass • coastal ecosystems • disturbed beaches • Poaceae • salt spray • sand burial • Staten Island • Triplasis purpurea.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Boyce, 1954
; Barbour, 1978
; Cartica and Quinn, 1980
; Sykes and Wilson, 1988
; Hesp, 1991
) and sand deposition (van der Valk, 1974
; Barbour, DeJong, and Pavlik, 1985
; Sykes and Wilson, 1990
; Maun, 1994
). Along the California coast, Barbour (1978)
documented ecologically significant gradients in salt spray that correlated closely with distance from shoreline and the distribution of beach plants. In an experimental investigation of 29 species in New Zealand, species most often associated with the coastal habitat were best able to tolerate salt spray (Sykes and Wilson, 1988
), suggesting that some species (and populations) have evolved adaptations to airborne salt (other examples in Oosting, 1945
; Hannon and Bradshaw, 1968
; Crawford, 1989
; Hesp, 1991
; Maun, 1994
; Greipsson, Ahokas, and Vähämiko, 1997
).
Pioneer coastal plants occur in an area where sand movement and deposition are common (Woodhouse, 1982
; Barbour, DeJong, and Pavlik, 1985
; Hesp, 1991
). Only species able to tolerate partial burial by sand may be able to maintain populations (Sykes and Wilson, 1990
; Maun, 1994
), and the distribution of coastal plant communities can be related to this ability (Moreno-Casasola, 1986
). A number of perennial species have been shown to be not only tolerant of, but stimulated by, sand deposition (Disraeli, 1984
; Maun and Baye, 1989
; Zhang and Maun, 1990
; Maze and Whalley, 1992
; Seliskar, 1994
). Although annual species can be abundant along disturbed coastal beaches, they might not be as tolerant of sand burial (Sykes and Wilson, 1990
); however, Cheplick and Grandstaff (1997)
reported that a pioneer annual dunegrass, Triplasis purpurea (Walt.) Chapm., showed stimulation of growth and seed production after seedlings were partially buried.
Despite their potential importance to coastal plant populations, the interactive role of saltwater spray and sand deposition in determining growth and reproduction has not been documented for most native coastal species. The present study extends the previous work of Cheplick and Grandstaff (1997)
by considering the interactive effects of both sand burial and saltwater spray on the growth and reproduction of the native dunegrass Triplasis purpurea (Walt.) Chapm. The specific objectives were to (1) determine natural levels of salt deposition and sand movement in relation to distance from shoreline and (2) experimentally quantify the impact of both saltwater spray and partial sand burial of seedlings on plant growth and seed production.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Duncan and Duncan, 1987
). Most cleistogamous (CL) spikelets form on panicles that are enclosed within leaf sheaths along culm internodes (Chase, 1918
; Cheplick, 1996
, 1998
). After spring germination in late April to early May, seedlings develop tillers over summer and CL seeds form from August until plants senese in late September. Terminal panicles may be formed at the tips of tillers of large individuals bearing chasmogamous spikelets from late August to early September (Cheplick, 1996
). Along the eastern shore of Staten Island, New York, T. purpurea typically inhabits highly disturbed, sandy beaches. It can be found as close as 25 m from the shoreline. For the present research, the population examined was at Midland Beach, Staten Island (40°34'4'' N, 74°5'30'' W). The substrate is predominantly composed of fine sand and is well drained and nutrient poor. The most common co-occurring species at that site are Ammophila breviligulata and Cenchrus tribuloides (G. P. Cheplick and H. Demetri, unpublished data).
Salt deposition at the field site
To determine natural levels of salt deposition and its relation to distance from shoreline, 72 flowering plants of T. purpurea were sampled from Midland Beach on 20 August 1996 and 23 September 1997. Twelve plants were randomly collected along each of six transects drawn parallel to shoreline and spaced at 9-m intervals. In 1996, plants were collected from transects at 45, 54, 63, 72, 81, and 90 m from shoreline; in 1997, plants were located closer to the shore and transects were therefore at distances of 30, 39, 48, 57, 66, and 75 m.
Precipitation records from a weather station operated by the local newspaper (Staten Island Advance) revealed that the last major rainfall was 7 d prior to plant sampling in 1996 (16.5 mm on 13 August) and 6 d prior to plant sampling in 1997 (17.0 mm on 17 September). For the time periods up to and including the day of plant collection, average wind speeds ranged from 10.6 to 21.3 km/h in 1996 (N = 8 d) and from 23.8 to 33.0 km/h in 1997 (N = 7 d). Additional wind "gusts" of 55.5 km/h (=15.4 m/s, a "moderate gale"; Beer, 1997
) that were reported on 20–21 September 1997 resulted in bay waves of 76 cm, 45 cm higher than usual. Wind direction was highly variable, but winds came from the south, southeast, or southwest on about half of the days in both years.
After collection, plants were bagged and immediately returned to the laboratory. Each plant was immersed and agitated in 150 mL of distilled water to remove external salts from the shoot. The conductivity of the water was then measured with a conductivity meter (YSI-Model 30, YSI Incorporated, Yellow Springs, Ohio). The increase in conductivity above that of distilled water (negligible at 2 µS) was used as a measure of the quantity of salt present on the shoot of each plant.
The relationship between conductivity and salt quantity was developed using 50 samples of NaCl (ranging from 0.4 to 30 mg). Although there are other ions in seawater besides sodium and chloride, together these two ions account for over 86% of the dissolved material (Millero, 1974
; Judson, Kauffman, and Leet, 1987
). Thus, for most purposes, NaCl is considered the primary determinant of ocean salinity, and conductivity is useful as an estimate of salinity when the predominant ions are Na and Cl (Maze and Whalley, 1992
; Jones and Reynolds, 1996
; Beer, 1997
). Each NaCl sample was dissolved in 150 mL of distilled water, and the conductivity of the resulting solution was recorded. The regression of salt mass on conductivity was linear and highly significant (r2 = 0.9892, P < 0.001). The equation for the relationship is: salt mass (in mg) = 0.0786 (conductivity)- 0.1756. From this equation, the absolute quantity of salt deposited onto field-collected plants was determined for the two years of study.
After removal of superficial salts in both years, T. purpurea shoots were dried to a constant mass in a 60°C drying oven and weighed. This allowed the determination of salt deposition per unit shoot mass. However, in 1997, shoot areas were also determined prior to drying with a leaf area meter (LI-COR LI-3100, LI-COR, Lincoln, Nebraska) so that salt deposition could be more meaningfully expressed per unit shoot surface area. The relationship between shoot surface area and shoot dry mass was linear and highly significant (r2 = 0.9371, P < 0.001). The equation is: shoot area (in cm2) = 0.0357 (shoot mass) + 1.8653.
Sand deposition at the field site
Observations made at Midland Beach and other sites along the eastern shore of Staten Island indicate the potential for sand burial of seedlings, especially after summer storms. For example, field excavations of seedlings have revealed that plants sometimes emerge from seeds buried to 4 cm (Cheplick and Grandstaff, 1997
). Observations made at Fort Wadsworth, Staten Island, after one late summer storm in 1997 revealed that T. purpurea adult tillers were buried to 3–4 cm by freshly deposited sand (G. P. Cheplick, unpublished field notes, 12 September 1997).
In a preliminary attempt to assess patterns of sand movement at Midland Beach, on 3 July 1996, wooden stakes (25 cm long, 2 cm wide) were inserted into the sand along transects at the six distances from the shoreline used for salt deposition studies in 1996. Ten stakes were used per transect distance, each stake separated by 9 m. Thus, there was a total 60 stakes installed (ten replicates x six distances). A line drawn onto the stake 5 cm below the top indicated ground level; the remaining 20 cm of the stake were inserted into the sand. Because of moderately heavy human traffic at this site, it was hoped that stakes protruding only 5 cm above ground would not be noticed; however, some stakes were disturbed or removed. On 8 August 1996, 28 undisturbed stakes were relocated, and the depth to which sand had accumulated was recorded.
Records from the local newspaper show that for the time period of this study, average wind speed ranged from 14.3 to 28.6 km/h (N = 35 d). Winds were from the south, southwest, or southeast on 66% of the days; on the remainder of the days, wind direction was northwest or west.
Greenhouse experiment
This study used an experimental approach to document the impact of saltwater spray and partial sand burial on growth and reproduction. On 4 June 1996, hundreds of seedlings were randomly collected at Midland Beach and returned to the greenhouse at the College of Staten Island, CUNY. That same day, they were planted into square plastic pots (8 cm2 by 7.4 cm depth) containing a 2:1 mixture of fine sterile sand and topsoil. Because of late germination that year (mid-May), seedlings were only 1 cm tall at this time.
After establishing for 2 wk, height from the soil surface to the tip of the tallest leaf was recorded for each seedling on 18 June to account for possible variation in size at the start of the experiment. A 3 x 3 factorial design was used, with three levels of seedling burial and three levels of saltwater sprays. Fifteen seedlings were allocated to each treatment combination for a total of 135 plants.
To standardize seedling size at the time of burial, plants were partially buried with sand only when height was 
30 mm. Seedlings were (1) unburied, (2) buried to 50% height, or (3) buried to 75% height, beginning 18 June and continuing over the next 3 wk as more seedlings reached the minimum height. The mean ± SD height of the 45 plants buried to 50% at the time of burial was 34.8 ± 9.7 mm; height of the 45 plants buried to 75% was 34.1 ± 8.9 mm. The burial depths were chosen based on previous results with T. purpurea that showed high survival at 50% burial, but very poor survival at complete burial (100%) (Cheplick and Grandstaff, 1997
).
Saltwater sprays were initiated on 9 July. Seawater collected off the shore at Midland Beach on a single day in late June was used to subject plants to (1) no spray, (2) two sprays/wk (one spray on each of two days), or (3) six sprays/wk (three sprays on each of two days). The seawater sample was stored in a 3.8-L plastic jug in a 4°C refrigerator and used for the duration of the experiment. This seawater sample from along the shore had a salinity of 24.3 ppt at 17°C. This is lower than the salinity of the open ocean, which can range from 30 to 38 ppt (Judson, Kauffman, and Leet, 1987
), but slightly brackish waters are not uncommon along bays in areas where "rainfall or drainage patterns produce an excess of fresh water increment over evaporation" (Hedgpeth, 1983
). The influence of the East River and Hudson River on lower New York Bay could impact the salinity of the water surrounding Staten Island. Thus, although the collected seawater had lower salinity than the open ocean, it is ecologically meaningful to use the seashore water, the source of the airborne salts along the south shore of Staten Island.
Seawater was applied as a fine mist from a spray bottle held 20 cm from the side of each shoot. Because of tiny hairs on the shoots, minute beads of water could be seen adhering to each shoot after misting. Boyce (1954)
reported that such "beading" of seawater droplets typically occurs on the leaf surfaces of coastal grasses, including T. purpurea. Saltwater sprays were continued every week of the summer until 20 September, when plants were beginning to senesce.
Plants in all treatments were randomly located onto a single greenhouse bench and randomly repositioned after each saltwater treatment (twice weekly). During summer 1996, average (± SD) maximum and minimum greenhouse temperatures were 29.1° ± 2.0° and 20.6° ± 1.4°C, respectively (N = 31 randomly selected dates). Plants were watered from the top of the soil surface at the base of the plants as needed (about once per week) to flush out any salts that may have been deposited onto the soil during misting. This basal method of watering did not remove the salts deposited onto the shoots during the application of salt sprays.
Levels of salt deposition onto shoots for the two saltwater spray treatments were estimated as follows. Twenty T. purpurea plants not used in the experiment, but grown in the same greenhouse, were subjected to the same levels of saltwater spray as the experimental plants. First, the shoot was thoroughly rinsed and then placed into 150 mL of distilled water prior to being misted with saltwater. The conductivity of the water was measured as previously described. The same shoot was then sprayed once with seawater, immersed into 150 mL of distilled water, and the conductivity increase (over the unsprayed control) was recorded. The same shoot was sprayed three times with seawater, and the conductivity increase (over the unsprayed control) was recorded. This was repeated for all 20 plants. By using the equations described earlier, salt deposition could be estimated per square centimetre of shoot surface for each of the two saltwater spray treatments at each application.
As a nondestructive measure of size midway through the experiment, on 5 August, tiller number and total summed tiller length were recorded. During the growth period, survival and the number of plants with emergent terminal panicles were noted. All plants were harvested on 10–11 October 1996 by which time they had completely senesced. The few seeds that matured on terminal panicles were collected before they dropped. The intact plants containing sheath-enclosed seeds on axillary panicles were then dried at 60°C to constant mass. Variables recorded were the number and mass of axillary seeds from CL spikelets ("CL seeds") and the mass of shoots and roots. Derived variables were mean seed mass (mass of all CL seeds/number of CL seeds) and percentage allocation to seeds ([mass of CL seeds/total plant mass] x 100), to shoots ([mass of shoots/total plant mass] x 100), and to roots ([mass of roots/total plant mass] x 100).
To determine whether or not salts had accumulated in the soil in the saltwater spray treatments, 30-g samples of soil were collected at the end of the experiment from pots containing surviving plants for treatments of zero, two, and six salt sprays/wk (all unburied). All of the soil at all depths from each pot was thoroughly mixed before collecting the sample. Each sample was added to 150 mL of distilled water, agitated by shaking vigorously, and the conductivity increase (over distilled water) was recorded. Using the relationships described earlier, salt quantity could be expressed as micrograms of salts per gram of soil.
Data analyses
Analyses of variance (or covariance), with all factors treated as fixed, were most appropriate for the data collected (Potvin, 1993
; Underwood, 1997
). For the field salt deposition data, one-way ANOVAs were performed separately for 1996 and 1997 because the factor of interest (distance from shoreline) differed in the two years. Because many of the stakes used for the sand deposition study did not provide usable data at all six distances examined (see Methods), the distance categories were grouped into the three closest and the three farthest from shoreline and compared with a t test.
The greenhouse experiment had a 3 x 3 factorial design (three levels of sand burial and three levels of saltwater spray); an ANCOVA was used, with initial seedling height as the covariate. Log10 or arcsine square-root transformations were necessary for some variables to meet normality assumptions and to deal with heterogeneity of variances (Dowdy and Wearden, 1991
; Underwood, 1997
). The GLM procedure of the Statistical Analysis System (SAS Institute, Cary, North Carolina), Version 6.08, was used for all ANOVAs and ANCOVAs. The LSMEANS statement was used to generate least square means after ANCOVA and option PDIFF was used for multiple comparisons of the adjusted means (Dowdy and Wearden, 1991
). To compare mean salt deposition levels in both the field and the greenhouse after ANOVA, Scheffé's test was performed (Day and Quinn, 1989
).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Sand deposition at the field site
Because only 21 stakes provided estimates of sand deposition over one summer month, this study must be regarded as preliminary. Nevertheless, the data suggest that low, but measurable, levels of sand movement do occur at this site. To provide sufficient data for analysis, values were grouped for three distances closest to shore (45–63 m) and three farthest from shore (72–90 m). Closest to shore, the mean (± 1 SD) level of sand accumulation was 12.1 ± 11.3 mm (N = 8), which was significantly lower than the level farthest from shore (29.5 ± 18.7 mm, N = 13; t = 2.65, P < 0.05).
Greenhouse experiment
Initial height at the start of the experiment had a significant effect on both nondestructive measures of plant size taken at midseason: tiller number and total summed tiller length (Table 1). Plants that had been partially buried as seedlings showed a significantly greater tiller length, but not tiller number compared to unburied plants (Fig. 2A). Saltwater sprays had a significant effect on tiller number (Table 1), generally resulting in a decrease with increasing applications of salt (Fig. 2B).
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). Total CL seed production, a good measure of fitness in this annual species, was influenced by both saltwater and burial treatments (Table 1). Saltwater spray generally decreased seed output, while partial burial of seedlings enhanced adult seed output (Fig. 3). In fact, for plants that had been buried to 50 or 75% of their height as seedlings, the deleterious effect of six salt sprays/wk was less severe. For example, multiple comparisons among least square means revealed that significantly fewer seeds were produced by unburied plants sprayed with saltwater six times/wk compared to unburied, unsprayed plants (P = 0.02). However, the analogous comparison was not significantly different at 50% (P = 0.12) or 75% burial (P = 0.22).
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There were additional changes in mass allocation patterns due to sand deposition and salt sprays. Allocation to seeds was reduced at increasing levels of salt sprays, but this decrease was most pronounced for unburied plants as evidenced by a significant burial by salt interaction term (Table 1). The decline in percentage allocation to seeds from zero to six salt sprays/wk was 31% for unburied plants, but only 1.8 and 18.8% for plants buried to 50 and 75% of their height, respectively (Table 3). The decline in percentage allocation to seeds with salt application corresponded to an increase in percentage allocation to shoots. Allocation to roots was unaffected by treatment (Table 1) and only varied between 10 and 12% (Table 3).
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Soil salt levels at the end of the experiment were significantly greater for two sprays/wk (1222.4 µg/g [SD = 500.1]) and six sprays/wk (1358.9 µg/g [SD = 501.9]) compared to the soil under unsprayed plants (789.7 µg/g [SD = 247.3]; F2,36 = 6.55, P = 0.004). Multiple comparisons of means with Scheffé's test revealed that the two salt spray treatments did not differ significantly in soil salt levels (P > 0.05).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Salt deposition and its effects
In the field, the level of salts found on shoots at any one time is influenced by topography, wind speed (which impacts surf activity), the timing of rainfall events, and distance from shore (Oosting and Billings, 1942
; Boyce, 1954
; Edwards and Claxton, 1964
; Barbour, 1978
; Sykes and Wilson, 1988
; Hesp, 1991
). Within the same population, the level of salt deposition was different on the two occasions in the two years when T. purpurea was collected, but did show the expected decline with increasing distance from shore (see also Maze and Whalley, 1992
). It is difficult to compare values obtained here with results in the literature, especially when salt traps are used instead of living plants (as used here) and the time period over which salt is deposited is variable. Nevertheless, Barbour (1978)
used data from salt traps along the California coast to "extrapolate" down to plant leaf surfaces and reported average daily salt spray loads from 186 µg/cm2 (converted from his units of milligrams per decimeter squared) for Atriplex leucophylla down to 75 µg/cm2 for Camissonia cheiranthifolia. These values are considerably greater than the salt loads on T. purpurea from 6 to 7 d after no rainfall (e.g., 29 µg·cm-2·d-1 at 39 m in 1997). Along the coast of North Carolina, daily salt deposition averaged 144 µg/cm2 at 45 m from shore and 72 µg/cm2 at 95 m under low wind (3 m/s) (Boyce, 1954
). Although absolute levels were much lower, the 1997 data in the present study suggest a similar gradient (Fig. 1). The greater wind speeds and wave heights reported prior to the 1997 plant collection probably contributed to the higher salt loads found in that year.
The relatively lower salt deposition found along the shore of Staten Island compared to California or North Carolina may be due to reduced wave action within the lower New York Bay bordered by Brooklyn and Staten Island. The energy of incoming waves along an irregular shoreline tends to be least along the bays (Strahler and Strahler, 1978
; Judson, Kauffman, and Leet, 1987
). Thus, the relatively minor surf activity at Midland Beach, Staten Island, might not result in as much airborne salt compared to unprotected coastlines exposed to a heavier surf.
In the greenhouse experiment, a single spray of saltwater resulted in salt accumulation similar to that found on field plants in 1997 at 57 m from shore. Three sprays of saltwater in the greenhouse resulted in salt levels that were considerably higher than mean salt accumulation onto plants at any distance from shore on the two occasions when it was measured. The greenhouse data reveal extensive variation among plants in salt deposition after both one and three sprays, reflecting the difficulty of experimentally controlling salt deposition levels. At two salt sprays/wk, experimental plants were experiencing average salt levels found relatively close to shore, whereas at three sprays/wk, plants were mostly experiencing salt levels that were typically greater than that detected in the field on the two dates T. purpurea plants were collected. However, field salt deposition levels also varied greatly; for example, a few values above 300 µg/cm2 were detected in 1997 at 39 m from shore, indicating that some plants in the field may, at times, experience much higher salt deposition than average levels.
The intermediate level of salt sprays (two sprays/wk) applied to greenhouse plants significantly reduced their early growth and final dry mass, especially when seedlings were not partially buried with sand. At the highest level of salt sprays (six sprays/wk), these growth measures as well as seed production and the mass of individual seeds, were even more negatively impacted. The effect of salt sprays on mean seed mass may have significant ecological implications, given that seed mass can be positively linked to establishment success and competitive ability in the dune environment (Symonides, 1978
; Barbour, De Jong, and Pavlik, 1985
; Rees, 1995
; Cheplick and Grandstaff, 1997
).
Although salt levels in the soil were higher in the two salt spray treatments relative to unsprayed controls, evidence suggests that it did not have an effect on growth or reproduction. If the salt applications were having their effects via the soil, then there should be no differences in plants in the two and six sprays/wk treatments because the levels of salt in the greenhouse soil did not differ significantly between these two treatments. However, for dry mass and seed production, six sprays/wk had a much greater impact than did three sprays/wk, suggesting that the relative level of airborne salt deposited onto the shoots was the primary cause of reduced growth and reproduction in the greenhouse experiment.
Investigators have noted that the effects of airborne salt depend on species and population, ranging from increases in mortality and leaf damage and/or decreases in growth, to relatively little or no effect in species (or populations) that exhibit some level of salt "tolerance" (Oosting and Billings, 1942
; Oosting, 1945
; Cartica and Quinn, 1980
; Barbour, De Jong, and Pavlik, 1985
; Sykes and Wilson, 1988
; Greipsson, Ahokas, and Vähämiko, 1997
). Obviously, care must be taken to distinguish tolerance to airborne salt from that of soil salinity (e.g., Rozema et al., 1985
; Greipsson and Davy, 1996
; Hester, Mendelssohn, and McKee, 1996
; Wang and Redmann, 1996
). In contrast to plants of salt marshes, dune species are not plants of saline habitats and tolerance to salt exposure depends primarily on the prevention of salt accumulation in the shoot (Boyce, 1954
; Crawford, 1989
). Even though T. purpurea was adversely affected by salt sprays and showed a decline in seed output and percentage allocation to seeds at high external salt levels, plants still produced a substantial number of seeds within the enclosing leaf sheaths. In the field, T. purpurea can be found in close proximity to the shoreline (20 m) with species such as Salsola kali and Cakile edentula, which have obvious adaptations to salt (e.g., succulence; Rozema et al., 1985
; Duncan and Duncan, 1987
; Hesp, 1991
; Maun, 1994
).
In an investigation of 29 species from New Zealand sand dunes, Sykes and Wilson (1988)
stated that the grasses were "little affected by salt spray." Although T. purpurea showed a reduction in fitness and reproductive allocation at the highest salt spray levels in the greenhouse, it is unclear whether or not airborne salt directly reduces growth and reproduction along the shore. In fact, plants along the Staten Island shore do not appear to be adversely affected by natural levels of salt deposition and are often largest in close proximity to the water (G. P. Cheplick and H. Demetri, unpublished data), but this could be due to other factors unrelated to salt spray such as reduced intraspecific density or greater availability of moisture and soil nutrients from detritus deposited on the beach by waves. Boyce (1954)
presented evidence that the "beading" of seawater droplets on the surfaces of dune grass leaves, including T. purpurea, helps to reduce the "entrance of chlorides" into leaf tissues. He postulated that this was a major reason why many grasses were tolerant of salt spray and able to grow close to ocean shorelines.
Sand deposition and its effects
Sand accumulation at the field site was greatest at the farthest distances from shore (72–90 m), perhaps because the prevailing winds often came from offshore (south or southeast) and lifted sand away from the part of the beach closest to shore, depositing it farther inland. Indeed, during the final week of the study (1–7 August 1996), records in the local newspaper revealed all winds to have been from the south (with speeds from 11 to 22 km/h). Although the degree of sand accumulation estimated here appears minor compared to other coastal ecosystems (e.g., Barbour, De Jong, and Pavlik, 1985
; Greipsson and Davy, 1996
), windspeeds were relatively low during the study period, sample size was low, and sand movement was documented only over a single, limited time period in midsummer. However, at the scale of the seedling, partial burial during spring storms could benefit future growth and reproduction in T. purpurea.
Although annuals can comprise a significant fraction of the dune flora (Barbour, De Jong, and Pavlik, 1985
; Hesp, 1991
), their responses to sand burial have been little investigated. However, in perennial dune plants, increasing sand accumulation has been related to enhanced growth and vigor (Woodhouse, 1982
; Disraeli, 1984
; Maun and Baye, 1989
; Zhang and Maun, 1990
; Hesp, 1991
; Maze and Whalley, 1992
; Seliskar, 1994
; Greipsson and Davy, 1996
). Perennial graminoids often respond to sand burial by stem elongation (Disraeli, 1984
; Seliskar, 1990
; Sykes and Wilson, 1990
). A similar response was detected in T. purpurea. For this annual, greater tiller lengths and increased seed production may be due to longer internodes that can mature more seeds on longer axillary panicles (Cheplick and Sung, 1998
). This agrees with previous research that showed both an increase in tiller size and seed production for adults that had been partially or completely buried as seedlings (Cheplick and Grandstaff, 1997
).
For T. purpurea, the ability of seeds and seedlings to tolerate sand burial is ecologically important in coastal habitats. Stimulation of growth and reproduction in partially buried plants, if it occurs in nature, is presumably adaptive on sandy beaches. Furthermore, tolerance of moderate levels of airborne salt sprays and prolific seed production (Cheplick, 1996
) allows this species to maintain population densities well above that of many other annuals on disturbed beaches.
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FOOTNOTES |
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2 Author for correspondence (e-mail: gpcsi{at}cunyvm.cuny.edu
).
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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———, and A. J. Davy. 1996 Sand accretion and salinity as constraints on the establishment of Leymus arenarius for land reclamation in Iceland. Annals of Botany 78: 611–618.
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