Physiological and Ecological Adaptations of ... - Ehleringer net

John M. Zobitz, zobitz@math.utah.edu, UID: 00321217September 25, 2003Physiological and Ecological Adaptations of Halophytes in the Intermountain WestThe Great Salt Lake and surrounding salt flats are home to a particular type of vegetation calledhalophytes. Loosely speaking, halophytes are a type of plant that is adapted to live in highly saline soils.According to Lambers and others, three problems associated with living in such an environment are alow soil water potential (making it difficult to assimilate water into the plant), the uptake too manysodium ions (effectively poisoning the plant), and creation of ion imbalance between the inside of theplant and its environment (creating deficiencies). (Lambers et al; Eckert et al) While this list is notcomprehensive, these certainly are formidable challenges for plants in saline environments. Molarsaline concentrations as high as 595 g/L (converted from 1027 mM) have been found in some of theGreat Basin playas around Utah. (Gul and Weber) On the other hand, some non-halophytic plants canonly survive in soil salinities of less than 4 g/L. (Glenn et al) While many studies have focused onhalophytes’ adaptation through physiological adaptations (such as salt glands), current research hasshown that biotic and ecological factors also have a hand in forcing environmental adaptations. (Ungar)Examining physiological and ecological adaptations allows one to better understand halophytedistribution in Utah.Distribution and species present inthe Intermountain WestIn the Great Basin, the saltplayas occupy lower elevations inthe basins formed by LakeBonneville and Lahontan basin.(Wagner) At lower elevations freesalt (NaCl) is present along agradient whereas at higher elevationsthe soils are less saline but havehigher Na + ions. Lower diversity isfound in the lower elevation playas(usually iodine bush, pickleweed, orsalt grass), whereas the higherelevations have more perennials andPage 1 of 5Scientific Name Common Name Notes SourceFamily ChenopodiaceaeAllenrolfea occidentalis Iodine Bush Native shrub-found mainlyin NW UtahGul &Weber,GoodmanSalicornia europea Annual samphire Annual-found mainly nearGSLKhan, Gul,& WeberSarcobatus vermiculatus Greasewood Native shrub-foundthroughout UtahGoodmanSalsola ibericaRussian thistleweed,tumbleweedInvasive annual found indisturbed sites throughoutUtahAtriplex confertifolia Greasewood Native shrub foundthroughout UtahEurotia lanata aka White sageDominant Native shrubCertatoides lanatafound in variety ofelevations in UtahHalogeton glomeratusIntroduced annual indisturbed, very saline sitesSalicornia utahensis Utah samphire Found primarily aroundGreat Salt LakeFamily PoaceaeDistichlis spicata var.strictaDesert saltgrassNative perennial. Used forresting and food byshoveller, cinnamon teal,and food for Geese andground squirrells (Rawley)Family AsteraceaeArtemesia spinescens Bud sagebrush Native brush. Used forfood and cover bygrouse, rabbits, squirrels,gophers, antelope, and deer.Artemesia tridentada Sagebrush Native shrub dominantthrough Utah; found 1210-3030 m.Family BrassiceceaeLepidium perfoliatumClasping-leafpepperweedIntroduced annual found indisturbed sites.Table 1: Halophyte species present in UtahKhanUngarGoodmanGoodmanGul &WeberRawleyUngar,RawleyGoodmanGoodman

usually are in competition with other non-halophytic plants. (Wagner)From my literature search I came across many different and varied species of halophytes-bothinvasive and native species alike. By cross-referencing species found in literature (ones that werestudied and also just mentioned) with their corresponding entry in the Atlas of the Vascular Plants ofUtah by Albee and others, I feel that I have a comprehensive listing of the majority of halophytic speciesin Table 1.Physiological adaptationsThe physical structure of halophytes has evolved to cope with increased levels of salt. It wasfound that salt affects the hydraulic permeability, transpiration, and stunts plant growth. (Gale)Interestingly enough, no connection has been foundbetween increased salt levels and a decrease inphotosynthesis. (Gale) To offset these deleterious effectson the plant one of the many ways halophytes cope iswith salt hairs, salt glands (help to excrete salt), andincreased succulence (helps to lower salt concentrationsin a particular area). (Ungar) Figure 1 has a diagram of asalt gland for an Atriplex species. What thisaccomplishes for the halophyte is establishment of agradient between the physical environment and the plant,creating tolerable saline concentrations on the inside ofthe plant. Salt is pumped from the xylem into thevacuole, and then deposited on the leaf, giving it a whiteappearance. (Lambers et al) Other adaptations are earlier lignification (hardening) of plant tissue, andinhibition of tissue differentiation. (A. Poljakoff-Mayber) Intuitively these barriers make sense. If aplant has a lower saline concentration than its surrounding environment, ions will tend to diffuse into theplant to maintain chemical equilibrium. Thick, hardened tissue presents a greater barrier for diffusion ofsalts through the cellular membrane.Figure 1: Diagram of salt gland, fromLambers et alSeed germination/Timing of dispersalExperiments of germination and seed dispersal mechanisms for halophytic plants have been welldocumented in the literature. (Gul and Weber; Khan, Gul, and Weber) The traditional approach to suchstudies is to grow seeds of various halophytes in different saline conditions and count the number ofPage 2 of 5

seedlings that germinate. As noted in Gul and Weber, halophyte seeds remain viable for long periodsand wait for environmental cues such as light and temperature to blossom. For the Great Basin, thiswould correspond to times of snowmelt that floods the lower areas, leading to a reduced salineconcentration in the soil. Usually such times occur during the spring-a time with increased light andwarmer temperatures. Almost counter intuitively, germination studies of S. iberica and A. occidentalisindicate that germination rates decreased with increasing salinity, suggesting that there is an upperbound on saline concentrations tolerable for halophyte survival. (Gul and Weber; Khan, Gul, andWeber)Competition factorsPage 3 of 5Competition with halophytic and non-halophytic plants determines species distribution andsurvival in the Great Basin. In a 1991 study by Kenkeland others, three different grasses (Poa pratensis,Hordeum jubatum, and Puccinelia nuttalliana) thatvaried in their level of salt tolerance were grown incontrolled conditions as a mixture at different salinities.P. nuttalliana was the most salt tolerant whereas H.jubatum was the least salt tolerant. P. pratensis is knownto be a halophytic plant. It resulted that the meanproportional aboveground biomass of P. nuttallianaincreased with increasing salinity, whereas the other twoplants decreased in biomass. This indicates that the moresalt-tolerant plant becomes a better competitor withincreasing salinity. (Kenkel et al) See Figure 2 for theresults reproduced from the original paper.Being a halophytic and an invasive species may also confer advantages over other native plants.In a controlled greenhouse study of invasive halophytic plants and native plants to the Colorado RiverDelta, Glenn and others found that mesic species such as Salix goodingii, Populus fremontii, andBaccharis salicifolia cannot be competitive above 4 g/l NaCl concentration, whereas an invasive such asTamarix ramosissima had a maximum growth rate at 8 g/L NaCl. These findings supportedobservations and soil measurements along the Colorado River where Tamarix was dominant (NaClconcentration of 6-8 g/L) and areas where soil salinity was much lower, native species dominated.(Glenn et al)Figure 2: Aboveground biomass of 3 plantsgrown in mixture at increasing salinity.Note how the biomass of the Puccinelliaincreases with increasing salinity.

Management issuesManagement of halophytes can be divided into two areas: keeping the existing native halophyticspecies intact and preventing more salt-tolerant species from displacing native flora. As noted above inthe competition section, research indicates a tradeoff between competitiveness and salt tolerance. If thedistribution of the salt playas shifts on the Great Salt Lake, perhaps decreasing the salinity of a moresaline area, then that environment would allow for more competitive, less salt-tolerant plants, to invade.Thus non-halophytic plants could expand their area and distribution in such a scenario.In general halophytes can germinate and grow better in less saline conditions, and rely on theseasonal melt of snow to begin germination. (Zedler et al; Gul & Weber) This should be of concernsince this climate change might lead to a change in vegetation and allow for more competitive invasivespecies to dominate the landscape, as has already been observed with saltcedar (Tamarix chinensis), aRussian invasive that has begun to dominate riparian areas. (Everitt)There has been a concerted effort in recent years to understand the ecology and the relationshipthat salt playas and halophytes have on other animals. The Great Salt Lake is not uniformly saline withthe north arm (Gunnison Bay) being more saline than the northeastern, eastern, and southeastern shores.(Great Salt Lake Planning Team) Yet these salt playas also tend to shift seasonally but are a criticalhabitat for snow plovers and foraging areas for avocets and stilts. (Great Salt Lake Planning Team)Future decisions about development or protection of the area surrounding the Great Salt Lake must takethe whole ecosystem into consideration.In regards to restoring halophytic plants to native habitats, one of the ways to accomplish this isby transplanting seedlings into less saline environments (such as a greenhouse) until germination andthen restore them to their habitat. (Zedler et al) Taking a more proactive stance, one way to combat theexpansion of halophytic invasive species from taking over riparian zones is to intentionally flood areas,allowing soil salinity to decrease so native flora can survive. (Glenn et al)Halophytes are unique plants that live in difficult conditions. Salt glands and hairs are a uniqueadaptation that allows them to survive where other plants cannot. As evidenced, halophytes can be boththe aggressor (as with the case of T. chinensis) as well as the victim (evidenced with plants on the saltplayas). It will take active planning and consideration to ensure 100 years from now these species are asmuch of a facet of the vegetation of the Intermountain West as they are today.Page 4 of 5

Works CitedAlbee, Beverly J., Leila M. Shultz, Sherel Goodrich. Atlas of the Vascular Plants of Utah. Salt LakeCity, UT: Utah Museum of Natural History, 1988.Everitt, B. L. “Ecology of Saltcedar-A Plea for Research.” Environmental Geology. 3:77-84, 1980.Gale, J. “Water Balance and Gas Exchange of Plants Under Saline Conditions.” in Plants in SalineEnvironments, ed by A. Poljakoff-Mayber and J. Gale. New York: Springer-Verlag. pp 165-185, 1995.Glenn, E. R. Tanner, S. Mendez, T. Kehret, D. Moore, J. Garcia, C. Valdes. “Growth rates, salttolerance, and water use characteristics of native and invasive riparian plants from the delta of theColorado River, Mexico.” Journal of Arid Environments. 40: 281-294, 1998.Goodman, P. J. “Physiological and Ecotypic Adaptations of Plants to Salt Desert Conditions in Utah.”Journal of Ecology, 61: 2. 473-494, 1973.Great Salt Lake Draft Comprehensive Management Plan. Prepared by Great Salt Lake Planning Team.Utah Department of Natural Resources. 11/3/1999.Gul, B and D. J. Weber. “Effect of salinity, lights, and temperature on germination in Allenrolfeaoccidentalis.” Canadian Journal of Botany, 77: 240-249, 1999.Khan, M. A., B. Gul, and D. J. Weber. “Seed germination in the Great Basin halophyte Salsola iberica”Canadian Journal of Botany, 80: 650-655, 2002.Kenkel, N. C, A. L. McIlraith, C. A. Burchill, G. Jones. “Competition and the response of three plantspecies to a salinity gradient.” Canadian Journal of Botany, 69: 2497-2502, 1991.Lambers, H, H. S. Chapin III, T. L. Pons. Plant Physiological Ecology. New York: Springer-Verlag,1998.Poljakoff-Mayber, A. “Morphological and Anatomical Changes in Plants as a Response to SalinityStress.” in Plants in Saline Environments, ed by A. Poljakoff-Mayber and J. Gale. New York: Springer-Verlag. pp 97-117, 1995Rawley, E. V. “Plant Life of the Great Salt Lake Study Area” in Great Salt Lake: A Scientific,Historical, and Economic Overview. ed. J. W. Gwynn. Salt Lake City, UT: Utah Geological andMineral Survey, 1980.Ungar, I. A. “Are Biotic Factors Significant in Influencing the Distribution of Halophytes in SalineHabitats?” The Botanical Review. 176-99, April-June 1998.Wagner, F. H. 2003. Natural Ecosystems III: The Great Basin. Pp 207-239 in F. H. Wagner (ed.). RockyMountain/Great Basin Regional Climate-Change Assessment. Report for the U.S. Global ChangeResearch Program. Utah State University, Logan, UT: IV + 240 pp.Zedler, J.B., H. Morzaria-Luna, K. Ward. “The challenge of restoring vegetation on tidal, hypersalinesubstrates.” Plant and Soil. 253: 259-273, 2003.Page 5 of 5