Salt Marsh Grass, Distichlis Spicata (Gramineae), and Environmental Factors Affecting Its Growth and Distribution!
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Amer. 1. Bot. 63(5): 635-650. 1976. ECOLOGICAL ADAPTATIONS OF SALT MARSH GRASS, DISTICHLIS SPICATA (GRAMINEAE), AND ENVIRONMENTAL FACTORS AFFECTING ITS GROWTH AND DISTRIBUTION! D. J. HANSEN, P. DAYANANDAN, PETER B. KAUFMAN, AND J. D. BROTHERSON2 Department of Botany, University of Michigan, Ann Arbor 48104 ABSTRACT Salt grass is an important pioneer plant in early stages of succession. The sharp-pointed rhizomes with numerous epidermal silica cells, and the aerenchymatous network of the rhizome, leaf sheath, and roots facilitate development of the plant in heavy clays, shales, and inundated soils. In salt marshes of southern Utah, salt grass contributes to a hummock-building process that favors localized removal of salts by capillary action and evaporation. This process provides a narrow strip of soil that is favorable for the rooting of extended rhizomes. In laboratory experiments, maximum growth for Disticlilis spicata, a perennial salt marsh grass, was obtained at 15,000 ppm soluble salts in nutrient solution cultures. Comparable concentrations of salts occurred in soils of the habitat from which plants were taken. Nearly equal concentrations of sodium and potassium were found in the plant tissue where the growth of the plants was optimal; such a ratio was maintained in the plants during most of the growing season. In the field the greatest amount of growth of salt grass takes place when temperatures are cool and soil moisture is quite high during the early spring. During mid-summer as air temperatures rise, crude protein in the plant decreases. During periods of high salt and water stress, morpho logical and anatomical adaptations of the stomata, salt glands, and trichomes of salt grass are important for survival. Stomata on exposed ridges of vascular bundles, where desiccation is greatest, usually are covered by four epidermal cells. In contrast, stomata found in the grooves between vascular bundles tend to be uncovered. The salt gland is composed of a large basal cell and a cap cell and actively excretes (in a diurnal rhythm) excess sodium, potassium, and chloride ions. A mechanism for salt excretion from this gland is postulated. The silica-contain ing trichomes on the leaves may playa role in cooling the leaf under conditions of high solar radiation and also serve to protect the plant against attack by herbivores. DISTICHLIS SPICATA (L.) Green, a perennial salt bundle sheaths were incorrect. Nielsen (1956) marsh grass, is found in all the states west of the did an extensive study of the variability of D, Mississippi except Arkansas and Louisiana, as well spicata from several geographical locations in the as in Mexico, western Canada and parts of South western United States. His aim was to provide in America (Nielsen, 1956). Despite the wide formation for establishing a selective breeding pro spread occurrence of this plant, and its potential gram on Distichlis so that the plant might be used as a source of fodder for animals, there has been more effectively in saline or marshy areas. In 2 little attempt to investigate the ecological factors more physiological approach, Detling (1969) de responsible for limiting the growth and distribu scribed net photosynthesis and dark respiration ol tion of this species or to describe adaptations D. spicata plants grown in several concentrations (morphological and physiological) that may have of salt solutions. Recently, Anderson (1974) evolved as a result of such factors. briefly reviewed the structure of this plant. Most of the work on the genus Distichlis is re The objectives of this paper are to: 1) repor1 stricted to the older literature. A description of the results of continuous monitoring of the en several features of plants in the genus, including vironmental parameters-air temperature, relative leaf tissue, was made by Holm (1891, 1901-2) humidity, and the soil conditions (pH, moisture content of the soil, individual ion concentrations and Prat (1936). However, Prat's work was and their total osmotic effect) in a typical D, criticized by Metcalfe (1960) who suggested that spicata community during the plant's normal his observations regarding the presence of double growing season; 2) discuss changes in internal concentrations of ions, crude protein, and growth 1 Received for publication 5 May 1975. as affected by environmental conditions both ill This work was supported in part by NSF grant BMS 75-16359. the field and in the laboratory; and 3) present the 2 Present address: Department of Botany, Brigham basic structural features of the plant that favor its Young University, Provo, Utah 84601. existence in saline habitats. 635 636 AMERICAN JOURNAL OF BOTANY [Vol. 63 MATERIALS AND METHODs-Description of the calcium were determined in the filtrate accord field study area-The field investigation was be ing to procedures outlined by Perkin-Elmer (1970) gun in April of 1972 and continued through on the Model 290B Atomic Absortpion Spectro August 1972 in order to represent a typical grow photometer by use of an air and acetylene fuel ing season for D. spicata. The study area chosen mixture. The anion, chloride, was detected in the for the investigation was a salt desert playa lo filtrate according to procedures outlined by Mar cated six miles north of Goshen, Utah. This site ius/Fiske (1972) with a Marius/Fiske Chlor-o was chosen because of the homogeneous nature counter. of the salt grass plants in this habitat or com munity. The ground was covered with a thin layer ANALYSIS OF PLANT SAMPLEs-Ion determina of dried algae (Oscillatoria) which may have in tion-Cation concentrations in plant samples were creased the moisture of the soil surface by form determined for sodium, potassium, magnesium, ing a very slight surface mulch. and calcium according to procedures of Perkin A hygrothermograph unit was used to monitor Elmer (1970) by the microkjeldhal method of air temperature and relative humidity continu digestion and the atomic absorption spectro ously. Measurements were recorded for the photometer. months of May to September 20, 1972. The chloride ion concentration in the plant tis sue was determined by freeze-drying the aerial ANALYSIS OF SOIL SAMPLES-Moisture content shoots in a New Brunswick Freeze Dryer B64. -Soil samples were taken with a core borer. The dried tissue was ground into a fine powder in Each core measured 2.54 em in diam and was ex a Wiley mill. Five gm of the powdered plant tis tended to a depth of 25.4 em. The cores were sue was soaked in 10 ml of distilled water over separated to provide surface and subsurface soil night and filtered. The remaining plant material samples. Surface samples consisted of the upper was further washed with three separate 5-ml vol 5 em of the core: subsurface samples consisted umes of distilled water. Distilled water was then of soil taken from 15.24 to 25.4 em in depth. added to the combined filtrates to obtain a final Five to eight core samples were taken at each site volume of 25 ml. The chloride concentration of and pooled to obtain a site soil sample. The sam the filtrate was then determined by use of the ples were placed in plastic bags, sealed, and im Marius/Fiske Chlor-o-counter, mediately taken to the laboratory for analysis. Samples were weighed to the nearest 0.01 gm and Crude protein analysis-The percentage of dried in an oven at 110 C for 48 hr. The samples crude protein in each plant was determined ac were reweighed and the percentage moisture was cording to the method of Horwitz (1970). calculated. Laboratory experimental methods-Salt grass Soil pH-Measurements of the soil pH were de plants were selected from the field site, the rhizo termined from saturated soil paste samples using matous clumps washed free of mud and soil, and the Sargent-Welch pH/Activity Meter, Model then potted in silicon sand in 16 oz polyvinyl PAX with a combination electrode (pH 0-14, 0 ethylene bottles that were drilled to allow for 80 C). drainage. Five randomly selected plants were as signed to a series of ten concentrations of a mix Osmotic potential of soil samples-Osmotic po ture of sodium sulfate and potassium sulfate in a tentials of soil samples were determined from a 3: 1 ratio of the cations, respectively. This was saturated soil pastes by freezing point depression made up with a complete, full-strength Hoagland's methods according to the procedure outlined by solution ranging from 375 to 24,000 ppm soluble Hansen and Weber (1974). salts. Treatment solutions were added twice weekly with sufficient weekend flushings to pre Ion determination-Soil samples were leached vent excess salt accumulation. Growth data on culm height and blade length of exchangeable cations and anions by placing 5 were taken weekly for four weeks, after which gm of a dry powdered soil sample in a filter paper time additional physiological measurements were which was flushed with four 25-ml volumes of taken. The measurements of blades and culms normal-neutral ammonium acetate. Each volume were obtained for the entire set of five plants, and was allowed to drain before the next was applied. the percentage increase was calculated for the en The normal-neutral ammonium acetate was pre tire set. Because of problems encountered with pared by adding 57.5 ml of glacial acetic acid to seedlings, as cited by Nielsen (1956), rhizome 800 ml of distilled water and then adding 65 ml of segments were used instead of seedlings. Plants concentrated NH40H. The pH was adjusted to were subsequently grown in the greenhouse. 7.0 with NH40H. The soil leachate was then diluted to one liter with distilled water. The Relative water content-Cut sections of the amounts of sodium, potassium, magnesium, and blade were first washed free of superficial salts, May-June, 1976] HANSEN ET AL.-SALT MARSH GRASS 637 TEMPERATURE G) OSMOTIC POTENTIAL OF SOIL PASTE 38.0 160 ,.: ..