Western North American Naturalist Volume 60 Number 2 Article 8 5-24-2000 Effect of salinity and planting density on physiological responses of Allenrolfea occidentalis Bilquees Gul University of Karachi, Pakistan Darrell J. Weber Brigham Young University M. Ajmal Khan University of Karachi, Pakistan Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Recommended Citation Gul, Bilquees; Weber, Darrell J.; and Khan, M. Ajmal (2000) "Effect of salinity and planting density on physiological responses of Allenrolfea occidentalis," Western North American Naturalist: Vol. 60 : No. 2 , Article 8. Available at: https://scholarsarchive.byu.edu/wnan/vol60/iss2/8 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 60(2), © 2000, pp. 188–197 EFFECT OF SALINITY AND PLANTING DENSITY ON PHYSIOLOGICAL RESPONSES OF ALLENROLFEA OCCIDENTALIS Bilquees Gul1, Darrell J. Weber2, and M. Ajmal Khan1 ABSTRACT.—Physiological responses of Allenrolfea occidentalis to salinity and seedling density were investigated. Effects of salinity (0, 200, 400, 600, 800, and 1000 mM NaCl) and 3 planting densities (2000, 4000, 6000 plants m–2) on the growth, survival, and ecophysiology of A. occidentalis, a stem succulent inland halophyte, were studied under con- trolled greenhouse conditions. Plants were grown in a sand culture using subirrigation. Dry mass of roots was highest at 600 mM NaCl at low density (2000 plants m–2), but declined as salinity increased. Tissue water content was highest at the 200 mM NaCl treatment and decreased with increased salinity. Water potential of the plants became more negative with increasing salinity due to the accumulation of NaCl in the leaves. Inorganic ions, especially Na+ and Cl–, con- tributed substantially to dry mass. Na+ and Cl– concentration in shoots and roots increased when NaCl level was + ++ ++ –– – increased while K , Ca , Mg , SO4 , and NO3 contents decreased. Net photosynthesis increased at low salinity (200 mM), but photosynthesis at other salinities was not significantly different from the control. While A. occidentalis is very salt tolerant and photosynthesis functioned reasonably well at high salinities, extremely high salinity did decrease dry mass of roots and shoots. Key words: salinity, planting density, Allenrolfea occidentalis, halophyte, salt tolerance, pickleweed. Halophytes are plants that complete their usually do not recruit through seeds, and ram- life cycle at high salinities (Flowers et al. 1977), ets are competitively superior to genets at the and their survival in salt marshes depends on recruitment phase of the life cycle (Gul and salt tolerance at different stages of their life Khan 1999). In a saline habitat dominated by cycle (Adam 1990). Dry mass of halophytes perennials, drought, temperature, and salinity usually decreases with increases in salinity stress synergistically cause death of seedlings (Ungar 1991), although growth of several halo- and depress growth of adult plants. Mortality phytes is stimulated at some levels of salinity in perennial halophytes occurs at the seedling (Flowers and Yeo 1986, Munns et al. 1983, stage due to high salinity, temperature, or Khan and Aziz 1998). Nevertheless, high NaCl severe drought, while adult plants enter into a concentration is probably not essential for phase of dormancy to avoid death (Khan and optimal growth of most halophytes. There are Aziz 1998). several halophytes that show optimal growth Osmotic active adjustment under saline con- at NaCl concentrations of 400 mM or higher, ditions may be achieved by ion uptake, syn- e.g., Cress critic (425 mM NaCl; Khan and thesis of osmotica, or both (Cheesman 1988, Aziz 1998), Suaeda fruticosa (400 mM NaCl), Popp 1995). Halophytes differ widely in the Haloxylon recurvum (400 mM NaCl), and sev- extent to which they accumulate ions and eral cold-desert halophytic species like Sal- overall degree of salt tolerance (Glenn et al. icornia rubra, S. utahensis, Suaeda moquinii, 1996). Stem- and leaf-succulent chenopods are and Kochia scoparia (600 mM NaCl; Khan et commonly known as salt accumulators and al. unpublished data). have high Na+ and Cl– content (Breckle 1975, Intraspecific competition may influence Albert and Popp 1977, Gorham et al. 1980, survival, growth, and fecundity of annual pop- Neumann 1997, Khan and Aziz 1998). Halo- ulations in saline habitats (Ungar 1991). How- phytes have adapted to highly saline condi- ever, the role of competition in perennial pop- tions by their ability to adjust osmotically to ulations appears to be limiting in reference to increasing salinity levels (Reihl and Ungar new recruitment (Khan and Aziz 1998, Gul 1982, Clipson et al. 1985). Tolerance of photo- and Khan 1999). Most perennial halophytes synthetic systems to salinity is associated with 1Department of Botany, University of Karachi, Karachi-75270, Pakistan. 2Department of Botany and Range Science, Brigham Young University, Provo, UT 84602. Corresponding author. 188 2000] PHYSIOLOGICAL RESPONSES OF ALLENROLFEA OCCIDENTALIS 189 the capacity of plant species to effectively after planting. Seedlings were thinned by compartmentalize ions in the vacuole, cyto- removing excess plants from the pots to pro- plasm, and chloroplast (Reddy et al. 1997). duce 3 treatment densities equal to 2000, Chlorophyll fluorescence, an analytical tool for 4000, and 6000 plants m–2. Plants were grown investigating stress damage mechanisms, has for 1 wk in a greenhouse by subirrigation by been used for detecting tolerance to chilling, placing the pots in plastic trays containing freezing, drought, and air pollution stress. It half-strength Hoagland’s solution; the 2nd wk may prove equally useful for salinity tolerance different salinities were applied. Plants were screening (Mekkaoui et al. 1989, Monnieveux subirrigated by placing the pots in plastic et al. 1990) or for detecting salt effects before trays and adjusting the water level daily to visible damage occurs (West 1986). correct for evaporation. Once weekly we com- Allenrolfea occidentalis (Wats.) Kuntze pletely replaced salt solutions to avoid buildup (Chenopodiaceae), a C3 plant common in the of salinity in pots. At the initiation of the western U.S., is found in an environment experiment, we gradually increased salinity where halomorphic soil induces extreme concentrations by 200 mM at 1-d intervals osmotic stress in concert with erratic and low until the maximum salinity level of 1000 mM precipitation during the growing season (Trent NaCl was obtained. Seedlings were grown in a et al. 1997). During drought this species ex- greenhouse at a thermoperiod of 25°C:35°C hibits low photosynthesis, stomatal conductance, (night:day) for a total of 90 d after final salinity and transpiration in comparison to years with concentrations were reached. high moisture (Skougard and Brotherson 1979). Dry mass of plant shoots and roots was Allenrolfea occidentalis is restricted to a few measured 90 d after the highest salt concen- communities directly at the margin of playas tration was reached. Dry mass of plants from where soils are often poorly drained and have an individual pot was determined after drying high soil salinity (Hansen and Weber 1975). for 48 h in a forced-draft oven at 80°C. Ion Because little information is available on concentration was determined by boiling 0.5 g the growth and salt tolerance of Allenrolfea of plant material in 25 mL of water for 2 h at occidentalis, the objective of this study was to 100°C using a dry-heat bath. This hot water determine the physiological responses of A. extract was cooled and filtered using Whatman occidentalis to salinity and seedling density. no. 2 filter paper. One mL of hot water extract We hypothesized that increased salinity and was diluted with distilled water for ion analy- seedling density would decrease the growth sis. Chloride, nitrate, and sulfate ion contents response of A. occidentalis. were measured with a DX-100 ion chromato- graph. Cation contents, Na+, K+, Ca2+, and MATERIALS AND METHODS Mg2+, of plant organs were analyzed using a Perkin Elmer model 360 atomic absorption We collected Allenrolfea occidentalis seed- spectrophotometer. lings from an inland salt playa located on the Using an LI-6200 portable photosynthesis east of Goshen, in northwestern Utah (39:57: system (LI-COR, Inc., Lincoln, NE), we mea- 06N 111:54:03W, 4530 ft). Equal-sized seed- sured the net CO2 assimilation rate of 4 plants lings (about 1 sq cm in size) were transplanted for each treatment. Level of stress in plants into 12.7-cm-diameter × 12.7-cm-tall plastic growing at different salinities was determined pots containing nutrient-free sand. We used 3 to be the amount of fluorescence measured planting densities (low, 25 plants per pot, from photosystem II with a Morgan CF-1000 which was equal to the rate of 2000 plants chlorophyll fluorescence measurement system m–2; medium, 50 plants per pot, equal to the (P.K. Morgan Instruments, Andover, MA). Stress –2 rate of 4000 plants m ; and high, 75 plants is measured as a ratio of Fv (variable fluores- –2 per pot, equal to the rate of 6000 plants m ). cence) to Fm (maximum fluorescence). Water Six salinity (0, 200, 400, 600, 800, and 1000 potential was measured at midday with a pres- mM NaCl) treatments were used. Four repli- sure chamber (PMS Instrument Co., Corvallis, cate pots were used for each saline treatment OR). Results of growth, ion contents, net CO2 group, and pots were placed in plastic trays exchange rate, water potential, and stress were containing half-strength Hoagland’s nutrient analyzed with a 3-way ANOVA to determine if solution. All pots were watered immediately significant differences were present among 190 WESTERN NORTH AMERICAN NATURALIST [Volume 60 means. A Bonferroni test determined whether creased with increased density, but there was significant (P < 0.05) differences occurred be- no density effect at higher salinities (Fig.