Author Institution: Department of Botany, Ohio UniversityField investigations were carried out to determine growth and survival rates of Salicornia europaea L. in a saline environment at Rittman, Ohio. Collected data indicated that from 62% to 100% of the seedlings within the 'A saline zones investigated did not survive to maturity. Seedling mortality was statistically correlated at P<0.01 to rising soil salinity stress during late spring and summer. Plant growth was minimal between April and June, increasing sharply during late summer and fall

McGraw, David C.

Ungar, Irwin A.

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Copyright © 1081. Ohio Acad. Sci. 0030 00.-)0/81 /0003-0109 $2.00/0GROWTH AND SURVIVAL OF THE HALOPHYTE SALICORNIAEUROPAEA L. UNDER SALINE FIELD CONDITIONS1DAVID C. McGRAW and IRWIN A. UNGAR, Department of Botany, Ohio University, Athens,OH 43701A bstrad. Field investigations were carried out to determine growth and survivalrates of Salicornia europaea L. in a saline environment at Rittman, Ohio. Collecteddata indicated that from 02% to 100% of the seedlings within the 'A saline zonesinvestigated did not survive to maturity. Seedling mortality was statistically cor-related at P<().()1 to rising soil salinity stress during late spring and summer. Plantgrowth was minimal between April and June, increasing sharply during late summerand fall.OHIO J. SCI. 81(8): 109, 1981, Salicornia europaea L. is an annualhalophyte, in the family Chenopodiaceae,with succulent erect photosyntheticshoots (5-40 cm). The species is widelydistributed and is known to inhabitinland and coastal salt marshes of NorthAmerica, Europe, and Africa (Fernald1950).Germination, mortality, and growthof halophytic species are often controlledin nature by the interaction of twoenvironmental factors: soil moisture andsoil salinity, which are codeterminantsof soil water potential (Waisel 1972).Seed germination in many halophyticspecies occurs early in the growingseason when moisture is plentiful andthe soil salinity concentrations arereduced (Barbour 1970, Macke andUngar 1971). Retardation of seed germi-nation has been attributed to an osmot-ically induced salinity stress that isreversible (Rivers and Weber 1971,Ungar 1978).Increased salinity stress due todroughts and to a higher rate of evapora-tion during summer months may causerapid changes in the density and diversityof species in halophyte communities(Ungar 1974). Seasonal precipitationpatterns are often a major factor deter-mining soil water potentials. This factorin turn affects establishment of seedlings,'Manuscript received 10 January 1080 and in; revised form 2 May 1080 (#80-2). "often increasing the rate of mortalityduring drought periods (Ungar 1973).The optimum salinity for growth ofsome species of halophytes is oftenbetween 1% and 2% NaCl (Webb 1966,Langlois 1967, Tiku 1976, Ungar 1978);however, all halophytes exhibit reducedgrowth when salt concentrations exceedtheir limits of tolerance (Williams andUngar 1972, Hansen et al (1976). Popu-lation dynamics, particularly of inlandsalt marsh communities, are likely to begreatly affected by the seasonal distribu-tion of precipitation peculiar to eachgeographic location (Weaver 1918, Ungar1974). For example, in a salt marsh onthe property at Rittman, Ohio, Ungar(1973) related the death of Salicorniaeuropaea seedlings to below normalprecipitation during the summer months.The purpose of our investigation wasto determine how plant growth andmortality are related to changing fieldsoil salinities during the 1976 growingseason.METHODS AND MATERIALSLocation. The study area is located in asaline marsh formed due to mining operationsof the Morton Salt Company plant located inRittman, Ohio. A shallow salt pan (approxi-mately 10 m x 40 m) was located in the centerof the site where we collected field data. Thestudy area as characterized by 4 major vegeta-tion zones: a Meadow zone, a Hordeum jubatumzone, an Atriplex triangularis zone, and a Sali-cornia europaea zone.Dynamics of Populations. Monthly visitswere made to the study site during the 1976100110 D. C. McGRAW AND I. A. UNGAR Vol. 81growing season, from 12 April to 26 October.Groups of twenty-five 100 cm2 quadrats wereestablished in each of 3 separate regions of thezone dominated by Salicornia europaea. Onegroup was situated in the standing water (5 cm20 cm deep) of the pan, another was placed in atransitional zone at the water's edge (edge zone),while a third was located near the point oftransition with the zone dominated by Atriplextriangularis (field zone). We made monthlycounts of plants for each quadrat and deter-mined values for mean and standard error of themean densities for each of the three regions.Analysis of Dry Weights. On 12 April, 9May, 6 June, and 14 August, we collectedSalicornia europaea from the edge and field loca-tions for dry weight comparison. Soil contain-ing numerous rooted specimens was collectedfrom the region adjacent to the Atriplex zoneand from the region near the edge of the panwater. We took the collections to the laboratorywhere 100 plants from each group were used forthe determination of plant dry weight. Sepa-rate root and shoot dry weights were determinedon 12 April, 6 June and 14 August 1976. Theplants were dried to constant weight at 105 °Cin a forced draft drying oven, and the specimenswere weighed in groups of 10 to the nearest0.1 mg with a Mettler (H15) balance.Field Soil Solution Conductivity. A series of13 conductivity sensors were implanted in theroot zone of the plants approximately 10 cmbeneath the soil surface. These were placedalong a transect at regular intervals betweenthe meadow and the center of the pan. Wemade monthly measurements of in situ soil solu-tion conductivity using a Soil Moisture Equip-ment Corp. #5500 salinity bridge. Samples ofpan water were collected and taken to thelaboratory for measurements of conductivitywith a Radiometer (CDM2d) conductivitymeter.RESULTSSoil Solution Conductivity. The soilsolution conductivity data indicates thepresence of a soil salinity gradient. High-est values were recorded from conducti-vity sensors located in the central area ofthe pan, and lowest conductivity was mea-sured at sensors located in the meadow(fig 1). The amplitude of the gradientdisplayed seasonal variability. On 12April, it ranged from 1.1 mmhos/cm inthe meadow to 48.0 mmhos/cm on thepan, while on 14 August, this range hadincreased from 2.4 mmhos/cm in themeadow to 142.8 mmhos/cm on the pan.A seasonal fluctuation of soil solutionconductivity was apparent at all loca-tions. The sensors located in the meadowzone had the earliest peak of soil solutionconductivity, occurring on 6 June. Sen-sors located in the Salicornia zone regis-JUNE JULYFIGURE 1. Monthly measurements of soilsolution conductivity (mmho/cm at 25 °C)made with in situ conductivity sensors.tered a peak in conductivity at the timeof the 5 July readings. The remainingsensors displayed their highest values on14 August. After this mid-summer con-ductivity peak was attained, a decreasein soil solution conductivity occurred inSeptember and October to levels foundearlier in the growing season (fig. 1).Samples of standing water in the pancollected at each visit to the research sitedisplayed a pattern of seasonal con-ductivity changes independent from thatestablished for the soil solution. Forexample, April, July, and October soilsolution conductivity values were 29.4,109.9 and 39.5 mmhos/cm, while stand-ing water on the pan at these locationshad conductivities of 64, 48, and 23mmhos/cm over the same time period.Soil moisture levels in all zones wereabove 50%, ranging from 50.9%to 61.4%over the growing season. These dataindicate that these soils did not have asignificant soil matric water stress duringthe period of active growth.Seedling Density and Mortality. Inthe Salicornia population, bordering theAtriplex zone (field), on 12 April 1976,the mean density was 276 plants per 100cm2 quadrat (fig. 2). The density of 51.europaea reached a peak of 362 on 9 May,followed by the greatest mortality re-corded for any region during the entiregrowing season, the reduction in plantdensity reaching 77% by 6 June. Thehigh mortality early in the growing sea-son resulted in a gradual decrease in plantnumber stabilized by 14 August, when theCONDUCTIVITY(MMHO/CM AT 25'CIOhio J. Sci. GROWTH AND SURVIVAL OF SALICORNIA 111mean density was 56 plants per 100 cm2quadrat. The decrease in density in thefield zone from 9 May to 26 October was85%, and in 24% of the plots fewer than5 plants survived (table 1).>x^APRIL MAY JUNE JULY AUGUST SEPT. OCT.FIGURE 2. Monthly measurements of Sali-cornia europaea population densities (No./100 cm2) in the region adjacent to theA triplex triangularis zone (FIELD), theregion at the edge of the pan (EDGE), andthe region in the standing water of the pan(PAN). Bars represent standard error ofthe mean.A similar fluctuation of density wasnoted for 25 quadrats situated in theSalicornia zone at the water's edge (fig.2). The mean density in this region on12 April 1976 was 479 plants per quadrat,a number greater than the mean densityof the zone bordering A triplex. Fieldcounts on 9 May revealed a 19% reduc-tion in plant density. The highestmortality for the edge zone occurred be-tween 9 May and 6 June when a 62%reduction in the density of Salicorniawas observed. A gradual decrease indensity followed until 14 August, afterwhich the density of this population re-mained stable. A 90% decrease in plantdensity occurred between 12 April and26 October, and 8% of the quadrats hadno survivors (table 1).The population density of S. europaeafor the pan region displayed a high de-gree of variability between quadrats,ranging from 0 to 28 plants per quadrat.On 12 April, the highest density perquadrat was 28, while 70% of the quad-rats contained 0 to 4 plants. The meandensity per quadrat dropped from a highpoint of 4.3 plants per quadrat to 0.3 onTABLE 1Maximum and minimum survival levels forSalicornia europaea in 100 cm2quadrats in three marsh zones.Initial Plant Final PlantZone Number Number(12 April) (26 October)A triplex BorderPan ]PanMin.Max.EdgeMin.Max.Min.Max.2305601303921280*150*0*105*0*0**These values represent extremes and indi-cate the very high mortality. Differences inall plots significant at P<0.01.5 July. By 14 August, no S. europaeasurvived in the pan zone (fig. 2).Dry Weight Analysis. Plants growingin the field and edge zones were analyzedfor root and shoot dry weight on 12April, 6 June, and 14 August (fig. 3).Salicornia europaea plants collected on12 April and 6 June from soils within thefield zone had greater dry weights thanFIELD, ROOT| | FIELD,SHOOTo> 40E ESS? EDGE, ROOTED6E SHOOTZLAPRIL JUNE AUGUSTFIGURE 3. Seasonal pattern of root andshoot dry weight accumulation for Sali-cornia europaea plants growing in the regionadjacent to the A triplex triangularis zone(FIELD) and in the region at the edge ofthe pan (EDGE). Bars represent standarderror of the mean and are omitted for Apriland June data because SEM was less than±5mg.DRY WEIGHT (mg)112 D. C. McGRAW AND I. A. UNGAR Vol. 81plants from the edge zone. Collectionson 14 August and 12 September showedan apparent reversal of the early seasonpattern of growth. Shoot dry weightsfor S. europaea plants growing in theedge zone were 25% greater than forthose growing in the field zone on 14August, and by September, the disparitybetween the two regions increased to75%..The root:shoot ratio for Salicorniaeuropaea collected from the region ad-jacent to the A triplex zone decreasedfrom 0.60 on 6 June to 0.42 on 14 August.Salicornia europaea plants collected fromthe region at the edge of the pan showeda similar trend, with their root:shootratio decreasing from 0.75 on 6 June to0.34 on 14 August.DISCUSSIONA lower density was recorded forSalicornia europaea plants in April, May,and June 1976 for the field zone, borderingthe region dominated by Atriplex tri-angularis, than in the region at thewater's edge. The initially higher den-sity of S. europaea in the edge zonewas probably due to higher soil moisturelevels that facilitated seedling establish-ment. In August, September, andOctober, 61. europaea plants growing inthe field zone displayed up to 14% higheraverage densities than those inhabitingthe edge zone. The survival of 6".europaea in different regions of the sitewas low, ranging from 0 to 38% in anysingle quadrat. Plant death was sig-nificantly correlated at the P=.01 level(Field, r = 0.8887, Edge, r = 0.7628, Pan,r = 0.6311) with the increase in soilsalinity from May to August. A similarsituation was described by Weaver(1918), Ungar (1967), and McMahonand Ungar (1978) for populations ofSuaeda depressa and Atriplex triangularis,indicating that seedling mortality isclosely related to an increase in soilsalinity levels.Despite the presence of an abundanceof floating Salicornia europaea seedlingsin April and May in the pan zone, fewplants rooted in the submerged areas.In April, mean conductivity readings forthe pan water was 64 mmhos/cm, whilethe edge and field zones displayedsalinities of approximately 39.8 and 18.9mmhos/cm respectively. The very lowrate of S. europaea seedling establishmentobserved in the pan region was probablydue to the high salinity of the standingwater early in the growing season andthe high soil solution conductivities onthe pan, reaching a mean of 129 mmhos/cm by August.Seasonal changes in dry weightaccumulation observed in this investiga-tion appear to be directly related tosoil salinity stress. The greatest increasein dry matter production occurredbetween the August and Septembersampling period when the soil salinitylevels began declining. Although seedsof S. europaea were found germinatingin March, little dry weight productionoccurred until the latter part of thegrowing season. Data collected duringthe 1977 growing season corroboratedthese findings, indicating that there isessentially no increase in dry matterproduction between early and mid-summer (Ungar, unpublished data). Inthe late summer between 7 August and16 September, dry weights increased tofour times the previous value, and thesevalues doubled again between 16 Septem-ber and 10 October. This rapid increasein biomass production late in the growingseason may be a mechanism that hasevolved in this species to avoid decreasingwater potentials and the accompanyingosmotic and ionic stress during theearly and mid-summer months. Thevery low increase in dry weight betweenMay and July indicates that the lowsoil water potentials at this time werelimiting to plant growth. This longterm cessation of plant growth duringthe middle of the growing season hasnot been previously reported for halo-phytes. The period of maximum growthoccurred just prior to the time of flowerand seed production. Waisel (1972) andChapman (1974) have reported thathalophytes often exhibit stunted growthwhen found under saline conditionsapproaching their tolerance limits, indi-cating that increased salinity stressduring the summer months could accountfor the decreased growth and highmortality found for these populations ofS. europaea.Ohio J. Sci. GROWTH AND SURVIVAL OF SALICORNIA 113Acknowledgments. This research was sup-ported in part by NSF grants BMS 74-19435and DEB 76-00444 and Ohio University Re-search Committee grant no. 578. We wish tothank the Morton Salt Company for allowingus to carry out this research project on theirproperty and Professor W. A. Wistendahl forhis comments on this manuscript.LITERATURE CITEDBarbour, M. G. 1970 Is any angiosperm anobligate halophyte? Amer. Midi. Nat. 84:105-120.Chapman, V. J. 1974 Salt marshes and saltdeserts of the world. Verlag von J. Cramer.Bremerhaven, Fed. Rep. Germany. 494 pp.Fernald, M. L. 1950 Gray's manual of Bot-any. D. Van Nostrand Co., New York.1632 pp.Hansen, D. J., P. Dayanandan, P. B. Kaufmanand J. D. Brotherson 1976 Ecological adap-tations of salt marsh grass Distichlis spicata(Gramineae), and environmental factors af-fecting its growth and distribution. Amer.J. Bot. 63: 635-650.Langlois, J. 1967 Cultures sans sol de Sali-cornia stricta Dumort. Rev. Gen. Bot. 74:176-196.McMahon, K. and I. A. Ungar 1978 Phenol-ogy, distribution and survival of A triplextriangularis Willd. in an Ohio salt pan. Amer.Midi. Nat. 100: 1-14.Macke, A. J. and I. A. Ungar 1971 The ef-fects of salinity on germination and earlygrowth of Puccinellia nuttalliana. CanadianJ. Bot. 49: 515-520.Rivers, W. G. and D. J. Weber 1971 The in-fluence of salinity and temperature on seedgermination in Salicornia bigelovii. Physiol.Plant. 24: 73-75.Tiku, B. L. 1976 Effect of salinity on thephotosynthesis of the halophyte Salicorniarubra and Distichlis stricta. Physiol. Plant.37:23-28.Ungar, I. A. 1967 Vegetation-soil relation-ships on saline soils in northern Kansas.Amer. Midi. Nat. 78: 98-120.1973 Salinity tolerance of inland halo-phytic vegetation of North America. Bull.Soc. Bot. (France) 120: 217-222.1974 Population dynamics of inlandhalophytic communities. Bull. Soc. Bot.(France) 121: 287-292.1978 The effects of salinity and hor-monal treatments on growth and ion uptakeof Salicornia europaea. Bull. Soc. Bot.(France) 125: 95-104.1978 Halophyte seed germination.Bot. Rev. 44: 233-264.Waisel, Y. 1972 Biology of halophytes. Aca-demic Press, New York. 395 pp.Weaver, T- E. 1918 The quadrat method inteaching ecology. Plant World 21: 267-283.Webb, K. L. 1966 NaCl effects on growthand transpiration of Salicornia bigelovii a saltmarsh halophyte. Plant Soil 24: 261-268.Williams, D. W. and I. A. Ungar 1972 Theeffect of environmental parameters on thegermination, growth, and development ofSuaeda depressa (Pursh) Wats. Amer. J.Bot. 59: 912-918.

Growth and Survival of the Halophyte Salicornia Europaera L. Under Saline Field Conditions

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Growth and Survival of the Halophyte Salicornia Europaera L. Under Saline Field Conditions

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