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Home , Distichlis spicata, Juncus roemerianus

Gulf Research Reports

Volume 7 | Issue 4

January 1984 Autecology of the Black Needlerush roemerianus Lionel N. Eleuterius Gulf Coast Research Laboratory

DOI: 10.18785/grr.0704.05 Follow this and additional works at: http://aquila.usm.edu/gcr Part of the Marine Biology Commons

Recommended Citation Eleuterius, L. N. 1984. Autecology of the Black Needlerush . Gulf Research Reports 7 (4): 339-350. Retrieved from http://aquila.usm.edu/gcr/vol7/iss4/5

This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Gulf and Caribbean Research by an authorized editor of The Aquila Digital Community. For more information, please contact [email protected]. Gulf Research Reports, Vol. 7, No. 4, 339-350, 1984

AUTECOLOGY OF THE BLACK NEEDLERUSH JUNCUS ROEMERIANUS

LIONEL N. ELEUTERIUS Botany Section, Gulf Coast Research Laboratory, Ocean Springs, 39564

ABSTRACT Juncus roemerianus generully occupies the upper half of the intertidal plane and covers about 92% or 25 ,000 hectares of marsh in Mississippi. The vegetative canopy is best described as a series of disjunct and intergrading populations. Considerable phenotypic variation and differences in standing crop exist between populations. J. roemerianus has very wide environmental tolerances in comparison to all other tidal marsh angiosperms. Soil types inhabitedby the rush range from very sandy to highly organic muds and peats, which may vary in the concentration of nutrient elements (nitrogen, phosphorus and potassium). Neither soil type, nutrient concentration, water content, pH nor elevation can be used to dis- tinguish the habitat ofJ. roemerianas, because similar conditions are found in areas occupiedby pure or almost pure mono- typic stands of other species. Soil water salinity is cyclic in all populations of l. roemerianas examined and salinity appears to be the major edaphic factor affecting growth and distribution of the rush. The greatest concentration and fluc- tuation of salt content occurs in the near-surface soil layer and the lowest concentration of salt and most stable soil water regime occurs at increasingly lower depths. Experimental evidence indicates that the rush grows best in fresh water, with- out competition, and cannot tolerate continuous salinities greater than 30 ppt. Soil organisms which detrimentally affect the are major factors limiting distribution of the rush into freshwater areas. Salt concentrations in the soil solu- growing appar- tion of 35 -360 ppt occurs frequently in some near-surface marsh soil layers. "I. roemerianus on "salt flats" ently survives near-surface hypersaline soil water (90-360 ppt) because of deeply penetrating, specialized roots. About five billion seeds of J. roemerianas are produced annually in Mississippi tidal marshes, but few rush seedlings are found. Ger- mination requires light,and seedling establishment is the vulnerable stage in the life cycle of the species. Vigorous mature stands are maintained by growth and the frequent removal of dead-standing leaves by physical factors such as storms, heavy rains, tides, and currents.

INTRODUCTION pied by Juncus roemerianus and (2) to evaluate how they Juncus roemerianus Scheele dominates about 25,000 are related to the rush aad to areas inhabitated by other hectares or 92Vo of tidal marsh in Mississippi (Eleuterius marsh . From this general examination, (3) identify 1972) and about 320,000 hectares or 25% of tidal marsh and (4) provide experimental data on those exceptional fac- throughout North America (Eleuterius 1976a). Daubenmire tors affecting the growthand distribution of J. roemerianus. (1947) stated that autecological studies were impoftant be- This approach rapidly eliminates those minor factors, cause the factors affecting the most important plants of a either limiting or favorable, which can not be strongly re- community, including various stages in their life cycle, must lated to the distribution of the rush or account for varia- be understood before the ecology of the community can be tions in growth between populations. understood. Autecological studies upon angiosperms inhab- MATERIALS AND METHODS itating aquatic habitats are seriously lacking, but essential in understanding the peculiar adaptation of various species Twenty-six populations of luncus roemerianus werc (Davis and Heywood 1963, Alexander 1971). Baker (1959) sampled in the tidal marshes along the coast of Mississippi stated that discovering crucial environmental factors that af- (Figure 1). Standing crop was determined by counting and fect the plant may provide valuable information concerning clipping shoots from four or more rectangular (0.5 X 2.0 m) the evolution of the taxa. Furthermore, basic autecological frames and square (0.25rn2) frames in seven populations. information provides a foundation from which taxonomic Clipped samples were subsequently separated into living studies, genetic studies, population biology, studies on the and dead components and the number of leaves counted. breeding system, and other more specific studies on ecologi- Seventy-five of the longest living leaves in each population cal relationships can be initiated. An adequate understand- were selected randomly and measured for stand height ing of adaptation and the factors regulating important spe- (average maximum leaf length attained). Standing crop of cies over large tracts of would also provide the erect shoots was obtained by drying to constant weight in a most valuable information to expediently assess and man- forced air oven at 50oC for 24 hours and then weighing. age these complex and valuable ecosystems in view of con- Soil water salinity was determined from soil cores about tinuous loss, pollution, and the increased pressure of human 50 cm in length, obtained by using thin-walled stainless population growth on coastal areas. steel tubes with an inside diameter of 72 mm. Three cores The objectives of the present study are (l) to examine were taken seasonally from each habitat. Slices of the core the general characteristics of the intertidal habitats occu- about 2 cm thick were taken from the top or surface layer and at positions equivalent to 30 and 45 cm depths. Soil

Manuscript received June 25, 1 984; accepted September 10, 1 984. water was extracted from these slices by vacuum filtration.

339 340 ELEUTERIUS

Mt S S lS S I t p, SOUND Upstream Limit of Tidal Marsh

0 3mi l-----rJ 0 3km

studied are indicated by Figure l. Map of the study area on the Mississippi coast. The location of populations of luncus roemerianus numbers.

fluorescent lamps at A1l samples were subjected to uniform vacuum extraction perature and placed under Gro-lux pistil- (60 cm of mercury). Soil water salinity was determined :SZS tu* (360 foot candles). Seeds from perfect and a population in the Davis with an American Optical refractometer, Model 10402 with late flowers were collected from tested' a direct-read-out scale in ppt, and compared to determina- Bay area. Approximately 1200 seeds were about 8400 seeds tions made with a Martex salinometer and a conductivity To test the general viability of seed, components of bridge. Soil water was also extracted by the method de' representing hermaphroditic and female solidified agar in petri scribed by Eleuterius (1980a) and compared to the vacuum seven populations were sown on were also filtration method. No significant differences were found be- plates and placed under Gro-lux lamps. Seeds under continuous tween the three methods used to determine salinity. Hydro- floated on saline solutions and placed on germina- gen ion concentration (pH) was determined in the field light for 6 weeks to test the effect of salinity weekly' with a Corning model 6 portable meter and compared to tion. Counts of germinated seed were made prepare saline solu- wet soil samples determined with an Orion meter in the Artificial sea mix (Rila) was used to the effect of salin- laboratory. A total of 234 soil samples were taken. The tions of different concentrations to test plant types and to de- same soil cores were used for determinations of salinity, or- ity on germination of seed from both growth of ganic matter content, nitrogen, phosphorus, and potas- termine the effect of salinity on vegetative randomly in each of sium from the 26 populations of Juncus roemerianus , lusir,g mature plants. Plants were selected grown a mixture of standard methods described by Black (1965). Similar soil several different populations and in potting soil' Then the samples were also gathered and analyzed from populations ll2 sand and l12 commercial organic plants and soil mixture of Spartina altemiflora, spicata, Scirpus olneyi, porous clay pots containing the were placed in large plastic buckets containing salt solutions and C ladium i amaic e n s e. were adjusted 3 cm Elevations in the marsh were determined using a survey' of different concentrations' Water levels Four replications of each or's transit and stadia rod in reference to a bench mark lo- below the soil surface in each pot. were grown in untreated tap cated in the sea wall on East Beach, Ocean Springs, Missis- treatment were used. Controls evaporation and transpiration was sippi, described in detail in Eleuterius and Eleuterius (1979). water. Water lost through to the surface of the soil To determine if light was required for germination, seeds replaced by adding distilled water 20-20'20 soluble fertilizer (Robert of Juncus roemerianus were collected, placed on solidified mixture. A solution of as a complete nutrient source agar in petri dishes in light and dark boxes at room tem' Peters Co., Inc.) was used AUTECoLoGY oF JUNjUS RoEMERIANUS 34r

TABLE 1 Estimates of living shoot density (LSD), living leaf density (LLD), average maximum length of living leaves (LLL), living standing crop (LSC) and dead standing crop (DSC) and total standing leaf crops (fSC) m-2, for seven different populations of luncus Roemerianus. Comparison of these data shows that some populations are structurally similar while others are very different, See the map in Figure I for location of stations.

Population Location Station Number m-2 g dry wt. m-2 TSC @escriptive) Number LSD LLD LLL LSC DSC (LSC + DSC)

Bluff Creek 1 492 !'13 886 t 240 210 !30 1664 !210 416 X'.|2 2080 !282 Upper Pascagoula River 2 572 !82 1258 !211 200 ! 41 2638 t20t 465 ! 62 3t04 ! 263 Lower Pascagoula River 5 782 !25 1715 !57 150 t 10 3844 t 150 430 + 43 427 5 ! 193 Grand Bayou 17 931 !21 2793 t44 180 t 12 4225 X 18'.1 4'10 t 32 4696 ! 18'7 Near salt flats 18 1680 145 4032 X97 80 18 1531 I 120 10s8 t 127 2s90 ! 247 On salt flats 19 170 ! t2 340 + 20 30 16 52t3 14 !1 66 !4 Belle Fontaine 20 768 + l7 1955 t 31 215 I 15 4196 i 90 1632 t 30 57 30 + 121 throughout the experiment. About 50 ml of a 5% solution stream and laterally in all local estuaries. The reverse is also was applied to the soil solution every 3 weeks. Plants were true with an increase in stem and leaf number (per unit of observed weekly and leaf length measured for 3 months. marsh surface) occurring with decreased salinity. This trend Al1 statistical comparisons used in this study are based appears to be the same in the riverine populations. In a pre- upon analysis of variance (ANOVA). vious study, Eleuterius and Caldwell (1981) showed that the patterns and rates of growth and longevity of J. roe- RESULTS merianus varied considerably between different populations.

Variation in Growth and Form Yertical Distribution, Tidal Range and Evaluation

There is considerable variation in the vegetative growth Another feature csf Juncus roemerianus is its ability to and form of luncus roemerianus. Generally, specific char- grow over a relatively wide elevational range. Although vary- acteristics of growth'can be associated with specific popu- ing from place to place, the plant species seems to be re- lations. Therefore, distinct populations of J. roemerianus stricted to the upper half of the intertidal plane. The gen- can often be delineated on form, but not always. For ex- eral elevational range of J. roemerianus,ir relation to ranges ample, there is a gradual change in leaf length, leaf density, for other important marsh species, is shown in Figure 2. and corresponding leaf production over a 9-mile stretch in Considerable overlap in ranges between these four major salt the Pascagoula River marsh. However, if one samples the marsh species was found to occur. The comparative eleva- plant populations at intervals from the river mouth to the tions shown for J. roemerianus and almost pure stands of inland limit of marsh, differences in growth are obvious. , Spartina alterniflora, and Scirpus olneyi Leaf length also increases near upland borders in most indicates that unknown factors related to tidal inundation marshes. Kruczynski et al. (1978) states that both living aird exposure are responsible for the dominance of these and dead leaves, measured along a transect from the open species at their respective elevations. Furthermore, many water to the upland, increase away from the water. They other plant species can occupy the same elevations also also found that leaf length decreased towards the uplands. occupied by J. roemerianus, attested by the greater inter- This situation also occurs in Mississippi, but it is found less mixture of species in brackish and very low-salinity marshes. often than the reverse relationship previously described. On areas that gradually slope from pine-dominated uplands to Edaphic Factors in General tidal marsh, the condition described by Kruczynski is gen- Juncus roemerianus occurs in a wide variety of intertidal erally found. However, where the elevation of the marsh is soil types. The soils range from almost pure sand to fine silt relatively low near the upland and abruptly changes to up- and clay mixtures and highly organic soils, including par- land, the leaves of J. roemerianus are longer than those tially decomposed peat. Soils may be homogeneous, watery, found seaward. In disjunct populations, separated by up- unconsolidated materials (characteristic of the riverine land land masses and open bodies of water, more striking marshes) or the more consolidated soils composed of differences can be seen. Comparative data for seven differ- loosely or densely compacted sand, clay, and organic mate- ent populations are shown in Table 1. These locations are rial characteristic of coastal bay and bayou marshes. Some represented by the numbered stations as shown in Figure 1. soils may be layered or zoned especially in marshes located The plants of J. roemerianus tefld to have longer leaves and immediately adjacent to the coast and underlying island fewer stems and leaves m-2 with decreasing salinity both up- marshes. An intensely blue clay layer often underlies these 342 ELEUTERIUS

tions in many habitats were not detectable; however, in those areas where determinations were obtained, the con- 1.8 centrations never exceeded 3 ppm. Soil pH ranged from 4'5 1.7 to 7 with most soils having a pH of 5.8. Differences in soil composition, structure, elevation, and soil water salinity 1.6 prevented any meaningful correlation between concentra- SHRUE I tions the major plant nutrients in the soil and plant r.5 . t'NE of growth. Soil pH could not be correlated to plant growth for 1.4 the same reasons. Furthermore, comparison of the major nutrients (NPK) found in marshes occupied by Juncus r.3 roemerianus with those covered by Spartina alterniflora, spicata, Cladium and Scirpus olneyi 1.2 Distichlis iamaicense, showed that the nutrient concentrations of the latter fell I.I within the range for J. roemerianus. A11 of the plant hab- itats examined had wide variation within and between hab- 1.0 itats. Variability in soil structure and elevation also pre- tn o< ,9 vented any meaningful correlation between concentrations t-ttJ of the major plant nutrients in the'soil. Soil pH could not tJ-J : 8 be correlated for the same reason. Other factors such as seasonality, soil structure, organic matter, and soil water .7 content also influence spatial variation. Because of the wide .6 variation between habitats, statistically significant differ- ences in soil nutrients or pH could be found only between .5 some populations of J. roemerianus. The wide variation found within each habitat indicates a gradient between .4 them and renders any differences in nutrient concentrations .J meaningless. These findings indicate that J. roemerianus is capable of inhabiting a wide variety of soil types with .2 variable concentrations of nutrients.

.l Soil Woter Salinity MLW Soil water availability and soil water salinity are related to tidal inundation and exposure of the marsh surface. -.1 River outflow often interrupts the general tidal patterns -2 over riverine marshes. However, in the Pascagoula River marshes soil water salinity is cyclic and variable with season, -.3 soil depth, and location in the estuary, as shown in Figure 3A, and B. Small differences occur between surface and sub- -.4 surface determinations and between seasons, reflecting the prevails in these inland -.5 general low-salinity condition which marshes as shown in Figure 3A. The most inland location Figure 2. Elevational ranges and relationship of luncus roemer'unus consistently sampled (Station 2) is least influenced by the (JR) to Distichlis spicata (DS), Scirpus olneyi {SO), Spartina alterni- tides and shows a low concentration and correspondingly (SA) low (MLW). Ilora and mean water low fluctuation in soil water salinity, while the location sandy or organic surface soils. Sometimes sand is washed near the mouth of the Pascagoula River shows relatively over organic soils in coastal and insular marshes forming high and low concentrations of salt at various times in the Iayen in this fashion. J. roemerianus occupies a $eater var- annual cycle and correspondingly wide fluctuations (Sta- iety of soil types than any other marsh plant observed on tion 5 as shown in Figure 3B). The soil water salinity pat- the Mississippi Coast. tern for a station in a coastal bayou marsh (Davis Bayou, Soil nutrients varied considerably within and between Station 15), which is strongly influenced by tidal waters, is the 26 widely separated habitats. Phosphorus (P) concen- shown in Figure 3C. This pattern is similar to that found tration ranged from 3 to 122 ppm, but averaged about 35 near the mouth of the Pascagoula River, but characterized ppm in most habitats. Relatively large amounts of potas- by greater concentrations and fluctuations in salinity. Rela- sium (K) ranging from 3 1o245 ppm were found, averaging tively large differences were found between surface and about 170 ppm for most habitats. Nitrogen (N) concentra- subsurface determinations and se asonal determinations AL TECoLoGY o F -/1..\-CLT S Ro EME RIANU S 343 indicating (Figure 3C) that considerable fluctuation occurs in this marsh (Station 15). The greatest soil water salinity occurs on sandy "salt A flats." Salinities here (Station 19) were much greater than 3 those found in other marsh locations, but the pattern of F z fluctuation between surface and subsurface determinations ) and the general seasonal changes were similar. The wet sandy "salt flats" are apparently an amplification of salinity cycles and processes which take place throughout local tidal marshes. The soil water salinity pattern for Juncus roemer- ianus marsh areas along the edge of these "salt flats" is shown in Figure 3D. Three important facts are evident: (1) Soil water salinity varies seasonally and is cyclic in all populations; (2) the soil water salinities of the lowest depths remain the most constant; and (3) the surface layer B of soil has the greatest fluctuation. The most crucial period ? of survival for J. roemerianus occvrs during the summer and s fall months when soil water salinity is extremely high be- tz cause ofevaporation and plant transpiration, especially dur- ) ing periods of tidal exposure in daylight hours (Eleuterius, in preparation, a). Eleuterius and Eleuterius (1979) found that the zone of Spartina altemiflora in Mississippi, over an annual period, is flooded 139 times more frequently than the adjacent zone ocr of Juncus roemerianus and that the duration of flooding in S. alterniflora was l l times as long as that of ,L roemerianus. Frequent tidal flooding prevents concentration of salts in the soil water, because it dilutes the soil water solution. c Long periods of exposure may result in high concentration s of salt, often exceeding sea stren$h. In many instances soil ts water salinity in the marsh may exceed that of the adjacent 2 open water (bayou, bay, river, or sound). Tidal flooding = also contributes to soil water salinity in those marshes under the strongest tidal influence, and when flooded by highly saline water these marshes often develop hypersaline soil water concentrations when they become exposed for long periods during summer.

Salinity, Tolerance and the Effect on Plant Growth and Form The gradient series composed of a freshwater control (0 ppt) and seven different concentrations of salt (10-70 D ppt) indicate that adaptation has occurred in plants com- posing some populations in the tidal marshes of Mississippi. The salt tolerance of plants from different populations and the effect of salt on the growth of the rush can 3 ts be seen by comparison of the increase in leaf length of z J immature plants grown in soil solutions of different salt

Figure 3. A. Soil water salinity as determined from soil cores from the Pascagoula River marsh near the inland limit of distribution of Juncus roemerianz,r (Station 2). B. Soil water salinity of a dense slznd of funcus roemerianus near the mouth of the Pascagoula River (Station 5). C. Soil water salinity of a dense stand of funcw roemer- ianus on Marsh Point south of Davis Bay (Station 15). D. Soil water salinity of a population of funcus roemerionus located on a "salt flat" on Deer Island (Station 19). 344 ELE,ute RIus

30 tinuous. Therefore, J. roemerianus is able to survive these A S,, cE relatively "brief' periods ofintense salt concentration. The I I second process concerns a peculiar biological attribute of ots z generally produced dzo 5 J. roemerianus. Two kinds of roots are {rs fi by J. roemerianus (Eleuterius I976b). In hypersaline z marshes, specialized, deeply penetrating roots (6 to 8 feet) may allow the plants to draw less saline water which occurs ?r0 3 () 5 at lower depths. The absence of fibrous, absorbing roots z produced on plant shoots near the soil surface may indicate that high concentrations of salt in the upper soil layers in-

SAIiNIIY (ppt) SAIINITY (ppt) hibits their formation. However, J. roemerianus appears to have a much greater tolerance to salt than most plants in- or saline marshes. 30 habiting brackish

Profile B t.. Dr-9 25 Diagrams I () The profiles shown in Figure 5 diagrammatically show 220 z 20 the elevation, edaphic characteristics, plants, and plant as- fl15 l5 semblages associated with Juncus roemerianus taken on z z midsummer at three different ql0 t0 three subsequent days during estuarine locations. These illustrations simultaneously sum- u5 z 5 marize several segments of new information. Relationships roemerianus ar,d adjacent ones occu- 0 between habitats of l. 0 to 203010 50 60 70 010203040506070 pied by other plant species, can be readily shown from these SAL,NIIY (pPt) SAIINIIY (ppt) profile diagrams by comparing plant zones, and distance Figure 4. Growth of. luncus roemerianus under different salinity and ecological, especially edaphic, data. Plant community regimes. composition and plant zonation of pure stands in low- and high-salinity regimes in the Davis Bay estuarine system are concentrations for a pedod of 3 months. The total leaf shown in Figure 5A and 58, respectively. Some differences length of the test seedlings was about 25 cm, based on meas- are found in available soil nitrogen, phosphorus, and potas- urements of a1l leaves present at the start of the experi- sium between zones or habitats at each location or between ment. Seedlings were selected with five leaves and leaves of locations. Statistically significant differences are found be- similar length. An increase in the number of new leaves pro- tween some zones while no differences are found between duced by each plant corresponds with a decrease in salinity. others. Substantial differences in soil water salinity were Transplants from the low-salinity area (Station 2) died in found between some zones. The soil water salinity of "salt the highest salinities at the end of 2 weeks (Figure 4A), flats" is significantly different from that ofall other vegeta- while others from Station 5 and Station 15 had a greater tional zones. Soil pH is significantly higher in the more tolerance and survived a longer period of time in the higher saline areas. The very sandy (0.1 to2.5% OM),barren "salt concentrations of salt. Dwarfed transplants from the hyper- flat" on Deer Island (Station 19) is flanked by habitats with saline salt flats (Station 19) exhibit the greatest tolerance higher ratios of organic matter to sand ranging from 0.4 to (Figure 4D). The growth of afl surviving transplants regard- 6.07o (Figure 5C). These insular habitats are often underlain less of marsh location is decreased with increasing salinity. at a depth of 2 m by a stratum of blue clay. The diagrams Survival of mature plants of J. roemerianizs in the marsh and corresponding ecological data show that./. roemerianus probably occurs through two processes. One process con- grows in a variety of habitats and occurs closely associated cerns the "duration" or the length of the period of time with several species known to be highly salt that the plants are exposed to high salt concentration. In tolerant (see associated species listed in Figure 5C). Based most populations of ,I. roemerianus, nearest the coast, rela- on edaphic data, the sites occupied by other species on tively high concentrations of salt in soil water is not con- Deer Island also appear to be suitable for the growth of

Figure 5. A, Profile diagram of an inland, relatively low-salinity marsh along Simmons Bayou (Station 9) showing the vegetation composi- tion and related edaphic conditions. Elevations are shown approximately and not to scale. Soluble nutrients (NPK) are expressed in ppm, and soil water (interstitial) salinities are shown as isohalines in ppt. B. Profile diagram of a relatively high salinity marsh, seaward of the loca- tion shown in Figure 5A, near the mouth of Simmons Bayou (Station 11), The vegetation composition and related edaphic conditions are shown. C. kofile diagram of salt marshes and related areas on the eastern portion of Deer Island (Station 19). Plant species composing the plant populatiom and .ornrnunities are shown with corresponding edaphic data. The "barren salt flat" is devoid of vegetation' Dwarf plants occur in zones immediately adjacent to the hypersaline barren zone. Soluble plant nutrients (NPK) are expressed in ppm, while soil salinities at different depths (isohalines) are shown as ppt. AUTECoLoGy oF JUNCUS R)EMERIANUS 345

*Cladium A tspartina iamaicen* cynosuroides Panicum virgatum Lilaeopsis carolinensis Fimbristylis spadicea lpomoea purpurea

I Myricr ccrifcra *Distichlis spicata *luncus roemerianus I Nys 5ylvrtic. \ ,un"rs roemerianus Boltonia asteroides / { lpomoea purpurea Panicum virgatum Eoltonia asteroides Distichlis spicata Pinus elliottii Panicum virgatum Cladium iamaicense Sium suave lpomoea purpurea 36.6m 54.9m 6.1m l.8m - 2goc l.2m - P 88 0 o/oo 290c 2s" c 25.264c N 5 Ooloo 0.6m - K 140 0 o/oo pH5 o/oo Simmon's Bayou P88 6oloo P 88 5 o/oo P8t O P Eo/oo o/oo N o/oo N5 O o/oo 5 o/oo I 5 5 5 5 5 o/oo .t* oloo N 5 6 12 o loo K 95 l0 o/oo K80 2 pH 4.9 't0 o/oo K1 6 pH 4.5 pH5 pH5 tH5.2

B llex glabra rSpartina alternif lora lruncus roemerianus Scirpu5 robustus

30.5m 1.8m - 1.2m - 21o c O.6m - 29C Simmon'5 Bayou l- I 1 5 o/oo o/oo 't6 o/oo o/oo pH5 P88 .4 :o P 120 P40 0 o/oo N5 12 oloo N6 14 o/oo N5 O .15 K 130 o/oo K r80 l6 o/oo x 105 0 o/oo pH 5.6 pH 5.6

C Panicum amarulum Batis maritima - Dwarf Plants lva frutescens , uncus roemerainus t Distichlis spicata Batis maritima I uncus roemerianu5 bigelovii roemerianus ( J uncus I uncus roemerianus Suaeda Unearis Distichlis spicata Spartina alterniflora Batis maritima , , Distichlit sPicata "Barren Zone" Salicornia bigelovii, ViSna repens robustut i Distichlis seicata ScirPus Suaeda linearis Cakile harperi Batis maritima No Vascular Plants PreEnl Panicum amarulum I -s Uniola paniculata 1 I o.Om a $'' 30.5m 61.0m 45.1n 45.1m lpomoea sagittata Soil Surface -C Surfa( 26"c water 29C 28oc 31 Waler 26C 2s"c Misi5sippi Biloxi Bay Sound

2oo/oo \ 2O ol

TABLE 2 dense stand by vigorous rhizome growth. The rate of rhi- growth is Inhibition and germination of seeds in various concentrations of zome not rapid in comparison to many other tidal sea salt solutions at room temperature and under 360 foot marsh plants, but on new terrain and in the best developed candles of light. Approximately 100 seeds stands, the production of new rhizomes is prolific. Mature were placed on each plate. plants are steadfast, strong competitors, persistent in growth, and are therefore aggressive colonizers. Salt Percent Number of days Concenfuation Germination for germination DISCUSSION ppt to occur The availability of the major soluble nutrients, nitrogen

Distilled water t3 52 1 (N), phosphorus (P), and potassium (K) cannot be used to 1 67 4'.l 7 delineate the habitat of Juncus roemerianus from that of 2 58 36 7 Spartina alterniflora, Distichlis spicata, Scirpus olneyi, and 5 34 20 14 Cladium iamaicense. Furthermore, NPK concentrations 7 t7 11 21 could not be used to separate morphologically distinct pop- 10 6 2 30 15 0 0 ulations of l. roemerianus. The spatial variation of NPK 20 0 0 within and between J. roemerianus populations and hab- 25 0 0 itats of other plants indicates that nutrient availability is 30 0 0 influenced by soil water salinity, season, elevation, soil structure, organic matter content (Boyd 1970), and the fre- Many seed samples from perfect flowers were not viable. quency and duration of the tides. Relatively large amounts The seeds from plants with pistillate flowers are round in of K and P are readily available in all tidal marsh soils sam- cross section, full, robust, dark brown or reddish brown. pled and certainly do not seem to be a limiting factor. Avail- However, the seeds from plants with perfect flowers are of- able N was not detected in most soil samples. However. N ten flattened, thin, transparent, light brown, tan oryellow- transformation in wetland soils and the effect on the vege- ish in color. A few seeds in each capsule may be robust, but tation has been the subject of intensive research (Waring generally they are slightly smaller in size (Eleuterius 1975). and Bremner 1964,Ty\er 1967,Maye 1972, Ponnaperuma 1972, Engler and Patrick 1974, Delaune, et al. 1976). Se edling E s ta bl ishm e nt How "I. roemerianus and many other tidal marsh plants ob- A conspicuous aspect of all populatiots of luncus roe- tain a sufficient supply of N remains, at present, unknown. merianus is the absence of seedlings.Perhaps the dense vege- Researchers have recently shown that some aquatic plants tative canopy reduces light below the required intensity for are capable of nitrogen fixation @atriquin and Knowles germination, Furthermore, none have been found on 1972). However, it should be pointed out that the distribu- muddy or organic substrates, vegetated or barren, probably tion of other soil nutrients, such as sulfur, iron, cobalt, zinc, because the seeds are easily buried. Seedlings have been and magnesium, may differ significantly between popula- found on sand substratum. A sandy substratum probably tions of l. roemerianus and those of other marsh plants. I favors germination, because sufficient light penetrates conclude this section on soil nutrition by pointing out that through the thin layer of sand covering the seeds and the in the inland, low-salinity regions of tidal marshes in Missis- seeds are not easily covered by sand. On sandy shores and sippi, more than 50 species of plants occupy the same wet- sandy areas resulting from dredging operations, seedlings land terrain asJ. roemeianus (Eleuterius 1972, Eleuterius often become established, but few plants reach maturity. and McDaniel 1978, and Eleuterius 1980b). These species About 20 seedlings were observed on a sandy shore, near occur intermixed with J. roemerianus at the same elevation, the high tide lines (4 feet above MLW), several years ago. soil structure and nutrient concentration. Because of their About 75% were subsequently lost because of erosion from abundance, the major soil elements utilized as nutrients by heavy rains, storm waves, and currents. Most of the seed- J. roemerianus, do not seem to be a limiting factor for the lings were washed away, others were buried. Later, drought growth and distribution of the rush. The amount of water or salt concentrations in the soil probably caused the death composing a soil sample is a nebulous measurement because of the remaining seedlings. In other instances, I have seen a of the ebb and flood of the tide and fluctuation caused by few seedlings become established and develop into mature evaporation. However, the amount of water composing the stands, but always associated with great mortality of seed- solution is important in relation to the concentration of lings. The seedlings of f. roemerianus are obviously much soil nutrients. Thus, the concentration ofplant nutrients in more sensitive to environmental stress than mature plants. the soil solution is obviously in a constant state of fluctua- The vulnerable stages in the life cycle of Juncus roemer- tion. This may account for the difficulty in relating plant itnus are,therefore, germination and seedling establishment. growth to nutrient concefltrations in soil solutions in tidal Once seedlings reach maturity, the rush becomes an aggres- marshes. Ho (1971) found that seasonal changes occurred sive colonizer. Mature plants of "r. roemerianus maintain a in the water and sediment of an estuarv in Louisiana. The ELEUTERIUS 348 of competing flowering favorably m-erianus' one way is the removal soil data obtained in the present study compare roemerianus' plants, which are less salt tolerant that J' those of marshes found in Louisiana, , and growth with salt tolerant competitors favors the 1g72,Maye1g72,Stewart,era:. 1g73, beath of less Georgia(chabreck roemerinnus by providing more space and et d.. rg75,and Steward and and spread of J. Burpbacher, er a7. rg73,vo1k, and light' Soil water sa- is capable reducing competition for nutrients ornes 1975). It is concrudeo irrat J. roemerianus october' obser- rinity reaches'annual peaks in August and of inhabitating a variety of soil types with different nutri entconcentrations.'yotsolltypeswrtrrurrvationsmadeoveranumberofyearsindicatethatthesummer rains' but August be modified by heavy is an important factor in the seaward distribu- ;;k -"y Elevation hu, consistently occurred locally without spartina alternifrora can toler- trre octouer p.ut rion of Juncus roemerianus. ior the past decade' Therefore' the greatest more tidal flooding in comparison to ,I. interruption ate considerably pt*ration andeffect of salt water in bayous and which is clearly shown in the present study upu"ut roemerianus o"tu" during October and early November of each and by previous research (Kurz and Wagner 1957, Adams of salt year''iue" This relatively brief period (3 to 6 weeks) 1963, Eleuterius andEleuterius Lg79).J.ror*nrirrurhu'u the modi inirusio" ulso benefiti J' toemerianus by range above mean low water, which means water wide vertical on the soil microorganisms. The introduction same erevation ur.nurv-o,rr., iiour fying.effect that it grows at the these otherwise freshwater-domi- marshes where of salt into the soils of marsh plants. In the lower regions of riverine the number nated tiiar marshes obviously kills or reduces tidal influence is greatest, J. roemerianus grows at the same b)' mi.roorgunirms ('Eleuterius, in preparation' almost pure stands of Distichlis spicata and. or n..iri elevation as delineates sart marshes on an areal elevations as Thus, tidal influence also scirpus olneyi,and in some places at the same the soil solu- by the direct introduction of sea salt into stands of spartina attrrnrftoio, spartina basis almost monotypic the tidal amplitude is relatively smal1 cynosuroidei, and Ctadiu* 1o*ifrrn,,. tion' In ft,itittippi' patens, Spartina between high and low tides' How- riverine regions, J. roemerinnus with an 1'8 fooi In the inland, 1ow-salinity 'ange lows may extend over a ever, the annual cycle of highs and above, at the same elevation u, iOi rp..l.s occurs, as stated feet or-more (Eleuterius and Eleuterius elevation, p;; ;;, can not vertical range of i of tidal marsh plants..Therefore, tides are important 1979). Theiefore, seasonal pattems of individual popurations or the overal haa,itat of J. delineate a complex relationship to plant distribution of many other plants. Eleuterius and und ,rpr.r.nt roemeianusfrom that toemerianus extends 10-15 miles that other factors are obviously (chapman lg76)' J' Eleuterius (jgIg)showed estuaries' A similar pattern is also roemetrianus from *runa the river involved in delineating a habitat of J. "r"rrg of associated fot-'nd in tJu*ut bayous' where the number alterniflora,but the factors were not defined. "I. the Spartina with decreased salinity' In Mississippi' to occupy the upper 40% of the species increases roemeianuswas shown or about 25'000 hectares of tidal marsh stroniy irnorr.rO rush.dominates 92% intertidal plane in an estuarine coverage also sug- marsh (Eleuterius r-g72)..This extensive bythetideatasinglerocationinMississippi. environmental toler- gests th)t the rush has relatively wide competition with other flowering prants is an important The leaves ances' factor in the distributi ot of Juncus roemerianus' on the growth' ur-tt. nrrrnu.r Soilwater salinityhaspronouncedeffects become longer, but shoot density decreases of Juncus roemer' in river- form, and the physiological adaptatiot of competitor plants in.r.rr., upstream and inland also also inirrbits germination. Phleglrer (1971) the upper ends of bayous strongly influ- ianus ine marshes and in .a.,d in sand curtures reduced the penfound o'N.ur found, that salt concentration enced by the tides. and Hathaway tigiai present study' where growth of Sp artina foliosa Trin' In the (lg4g),and Gillham (1957) reported ,ilnifur' Oi,t'itutionA container and entire root mass was included in the test errect'of competition is a reduction in the patterns. The overall of the soil water remained constant' the test rush. plants ,.pr.r.riirs ,t. the salinlty growth and production of the shown to have differ- wilh an ptunt, iro- different populations were [mit of inland distribution are arso in .o*p.iitio. group had definite ent tolerances to salt' but each test array of microfloraa not lounsfound lrlin theLrrs r,urmore saline down- of rimits to irreir ability to withstand high concentrations stream marshes. of These data indicate that different populations "I' plant in hypersaline areas appeal almost stabilized, salt' zones tolerances to salt' Furthermore years. Invasion of a roemerianus have different based on observations over a number of has oc- strongly suggest that physiological adaptation from an adjacent zone does not readily oc- they zone byplants populations studied' In nature' how- represent plant populations .,"'A i" ti-" aifit"nt cur. The plant zones appear to soil water salinity ever, soil water salinity fluctuates and the of balanced existence unique to tidar marshes. in a state depth- The hypersaline soil water factor affecting decreases with increasing Soil water salinity is the most important amplifica- Salinity ,tgi-t rouna on the tutt autt appears to be an the growth and distribut ion of Juncus roemerianus. takes place plant tion or un.ruggrrution of the same process that was also determined to be the major factor affecting habitats of J' roemeriaruts' ., by Reed (L947),Jackson 6gsz), in other zonation in tidal ,r,u.rt of the effects of salinity on germination Adams Soii water Co-pu'l'on Kurz and Wagner (1g57),and lfOO:). plants indicates that tolerance to of J. with torerances of mature sarinity operates in two ways to favor the gr"*rr, roe- AUTECoLoGY oF JUNCUS RoEMERIANUS t49 salt obviously increases with maturity. Absence of seedlings Soil water salinity appears to exert a selective pressure in vegetated tidal marshes may also result from the failure on luncus roemerianus, which has resulted in physiological of seed to germinate, because the seeds are quickly buried and perhaps genetic differentiation. Physiological and in muddy substratum, or they become coated with fine genetic variation may account, in part, for the phenotypic mud particles, where without the presence of light they can variation between different populations of J. roemerianus, not germinate, or they are simply swept out to sea. Paradoxically, the absence of seedlings in the marsh does Richards and Clapham (1941), Lazenby (1955), Tadmor, not provide the number of progeny of different genotypes et al. (1958), and Welch (L966,1967) found that other upon which a selective force, such as soilwater salinity, can species of Juncus required light for germination. Further- work. This conflict in operative mechanisms may be decep- more, the low ambient temperature of winter and more fre- tive since the selective process is a slow one which may have quent rainfalls indirectly result in lower soil water salinity occurred ages ago. Corroborative support for this possibility and reduce stresses on J. roemerianus. Low temperatures is the present maintenance of the mature stands of ,.I. reduce evaporation and transpiration. The low temperatures roemerianus by vigorous vegetative growth for long periods and low-salinity regimes of winter favor germination and of time. These results and interpretations have evolutionary seedling growth. implications and raise important questions regarding the Chapman (1942) presented data on the germination of future survival of J. roemerianus. Juncus maritimus after 23 days in tap water and various Other factors affecting the growth of Juncus roemer- concentrations of salt. Germination in tap water was 50%, ianus, descrlbed in this study, are of minor importance. 10 ppt-18%,20 ppt*S%, and 33 ppt-l%. He also showed However, I should point out in closing this discussion that that germination of an unidentified species of Salicomiu there looms on the horizon a greater threat to survival of ,I. reduced increased salinity, germination was with blt 12% roemerianus and all other components of tidal marshes, occurred in 100 ppt NaCl. Ungar (1962) indicated that the both plant and animal. Although both federal and state limiting factor for seed germination of Salicornia under agencies are charged with the responsibility to safeguard high salinities was chiefly osmotic. This appears to be true our estuaries and tidal marshes, domestic and other forms also for"I. roemeri.anus. Ayers (195 1) also reported a steady pollution unabated, and estuarine water quality drop rn Salicornia germinalion with increased salinity. Ungar of continue have (L962) reported an abrupt decrease in Salicornia germina- continues to decline. A continuation of this trend may tion when a 50 ppt salt concentration was reached. The a severe effect on the future of J. roemerianus atd other retardation and prevention of germination of .L roemerianus estuarine organisms well adapted to relatively pristine en- by high salinity in the present study is obviously caused by vironments. osmotic factors. Salinity is known to affect many aspects of the meta- ACKNOWLEDGMENTS bolism of plants and to induce changes in their anatomy and I thank the members of the Botany Section of GCRL for morphology (Uphof 1941, Bernstein and Hayward 1958, their assistance with many aspects of this work and my Nestler 1977). These changes are often considered to be summer students who helped to verify field data. I appre- adaptations which increase the chances of the plant to en- ciate the patience and excellent work of Mrs. Helen Gill and dure stress imposed by salinity (Waisel 1972, Poljakoff- Cynthia Dickens who prepared the typescript. I thank Mayber and Gale 1975). Numerous investigations into the Dr. Lloyd Knutson and members of his staff at the Insect constitution of various species ofplants from different eco- Identification Institute, Beltsville Agriculture Research logical groups showed that only a few phenotypical adapta- Center, U.S. Department of Agriculture, Beltsville, Mary- tions, such as ecads, actually exist. Most of the populations land, for their help in identifying the grasshopper species. investigated went through the action ofnatural selection to Special thanks are given to the reviewers of this paper: form genetically fixed ecotypes (Turesson 1922 , l93l , Steb- Dr. Sidney McDaniel, Department of Biological Science, bins 1950, Waisel 1959). Salt-resistant forms have evolved in Mississippi State University, Mississippi State, Mississippi, Typha angustifolia L. and T. latifulia L. in soil containing and Dr. William L. Kruczynski, Environmental Review Sec- high concentrations of salt (McMillan 1959, McNaughton tion, U.S. Environmental Protection Agency, Atlanta, 1966). Similar results were obtained for Phragmites com- Georgia. Their critical and helpful comments improved this munis Tin. (Waisel 1972).In order for evolutionary change paper. This work was supported, in part, by funds from the to occur, there must be a source of genetic variation and a U.S. Corps of Engineers, Mobile District under contract driving force (Grant 1971, Jones and Luchsinger L977). No. DACWOl-72-C-0001.

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