TOLERANCES OF PLANTS TO DROUGHT AND SALINITY

IN THE WESTERN UNITED STATES By Parrel A. Branson, Reuben F. Miller, and Stephen K. Sorenson

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 88-4070

O I r^ CN O CO

Sacramento, California 1988 DEPARTMENT OF THE INTERIOR

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director

For additional information write to: Copies of this report may be purchased from:

District Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section Federal Building, Room W-2234 Federal Center, Bldg. 810 2800 Cottage Way Box 25425 Sacramento, CA 95825 Denver, CO 80225 CONTENTS

Page Abstract...... 1 Introduction...... 2 Purpose and scope...... 2 Concepts...... 2 Tolerances of plants to drought and salinity...... 4 Measurement of xylem pressure potentials...... 4 Measurement of cell osmotic potentials...... 5 Measurement of soil salinity and osmotic potentials...... 6 Osmotic potentials of plants...... 6 Range of xylem pressure potentials...... 6 Range of cell osmotic potentials...... 9 Range of soil osmotic potentials...... 10 Summary...... 13 References...... 13 Glossary...... 16

ILLUSTRATIONS

Page Figure 1. Map showing major desert classifications in the Western United States...... 3 2-5. Graphs showing: 2. Hypothetical energy profile for the soil-plant-atmosphere continuum for a habitat that has shallow ground water in a hot arid climate...... 5 3. Minimum, mean, and maximum total xylem pressure potentials for 71 plant species...... 7 4. Minimum, mean, and maximum cell osmotic potentials in 31 plant species measured by freezing-point depression method or by pressure-volume curve method...... 11 5. Minimum, mean, and maximum soil osmotic potentials at field capacity for the upper 10 centimeters of soils in 40 plant habitats...... 12

Contents III CONVERSION FACTORS

For use of readers who prefer inch-pound units rather than the metric (International System) units used in this report, the following conversion factors may be used:

Multiply metric unit By To obtain inch-pound unit meter (m) 3.281 feet centimeter (cm) 0.3937 inch megapascal (MPa) 0.1 bar

IV Conversion Factors TOLERANCES OF PLANTS TO DROUGHT AND SALINITY

IN THE WESTERN UNITED STATES

By Parrel A. Branson, Reuben F. Miller, and Stephen K. Sorenson

ABSTRACT

Differing capacities of plant species found to be the most drought tolerant. to tolerate drought and salinity are Saltbushes Atriplex confertifolia, A. causative factors for presence of species nuttallii, A. canescens, and A. torreyi and communities in various habitats. It had the lowest measured cell osmotic is proposed that minimum xylem pressure potential. Although pickleweed Alien- potentials are indicative of drought rolfea occidentalis grows in the tolerance and that minimum cell osmotic saltiest soil measured, it did not have potentials are indicative of salt the lowest cell osmotic potential. This tolerances of plant species. apparent inconsistency may be explained Of 85 species measured, Nuttall by the succulent characteristics of saltbush Atriplex nuttallii nuttallii was pickleweed.

Abstract 1 INTRODUCTION Published data of xylem pressure poten­ tial, cell osmotic potential, and soil The variation of species of plants salinity, along with extensive unpub­ from one habitat to another has intrigued lished data collected by the authors, mankind for centuries. Ecological in­ were reviewed and summarized. Xylem quiry is mostly directed towards ex­ pressure potential, cell osmotic poten­ plaining distribution patterns of organ­ tial, and soil salinity were calculated isms (Ritchie and Hinckley, 1975). Many for each species for which there were environmental factors affect the capacity data. Relative drought tolerances were of plants to grow in certain habitats, estimated by listing the plant species but most important are those factors according to the minimum xylem pressure associated with availability of water potentials reported. A similar index of (Kozlowski, 1964). Water is not only the drought tolerance was determined from driving variable of most importance for the data on cell osmotic potential. Data almost all contemporary desert community on soil salinity associated with differ­ interactions, but is probably the basis ent species of plants were compiled to of community evolution in the past estimate an index of tolerance to soil (McMahon and Schimpf, 1981). salinity.

Water is being pumped from aquifers in closed basins in the Western United Concepts States for various uses. This pumping is likely to cause a reduction in the Water moves through a plant in a amount of ground water available for continuous, cohesive hydraulic system existing vegetation. Responses of vege­ that extends from the roots to the tation to a reduction in water is now leaves. Water enters the system through and will continue to be of considerable the roots and is transpired from the interest to the residents of these system primarily through evaporation from areas. Questions that concern managers the leaves. Movement of water throughout of these lands include, which species this "soil-plant-atmosphere continuum" will survive if water availability is (Philip, 1957) is caused by differences greatly reduced and which species are in chemical potential from one part of likely to replace those present before the continuum to the next (Dileanis and pumping? By compiling published and Groeneveld, 1988). unpublished data on the drought toler­ ances of plants in the Western United Total water potential within a plant is States (fig. 1), it is possible to deter­ represented by the equation (Kramer, mine which plants will be most affected 1983): by the water-level declines caused by ground-water withdrawals. 0) IT m where = total water potential, Purpose and Scope 0) = osmotic potential, The purpose of this report is to pre­ sent data on xylem pressure potential, = pressure potential, cell osmotic potential, and soil salinity = matric potential, and that may be used to estimate the relative m drought and salinity tolerances of plants in the Western United States. = gravitational potential.

2 Plant Tolerances to Drought and Salinity, Western United States EXPLANATION

~^ NORTHERN DESERT

T:] MOJAVIAN DESERT

>^y HIGHLANDS

j SONORAN DESERT

g^j CALIFORNIAN DESERT

'/N| CHICHUAHUAN DESERT

SAMPLING SITES

0 100 200 300 MILES I i " i r1 ' 0 100 200 300 KILOMETERS

FIGURE 1.-Major desert classifications in the Western United States. Dots on the map represent sites studied by F.A. Branson and R.F. Miller. Study areas of other authors cited in this report are not shown.

Gravitational water potential is not and others, 1965). For instance a 100- considered in shrubs because it repre­ meter-tall Sequoia would require 1 MPa sents only 0.01 MPa per meter of plant of gravitational potential to transport height. In tall trees, gravity effects water from the roots to the top. Matric are measurable and important (Scholander potential within the plant is also

Introduction 3 considered to be small in proportion to and thick cuticular layers reduce tran­ pressure potential and osmotic potential. spiration. Adjustment of stomatal openings is the most important regulator Differences in pressure potential of transpiration (Hsiao, 1973). The pri­ (usually measured as xylem pressure mary mechanism used by plants to enable potential) is primarily induced by atmos­ extraction of water from soils, as lower pheric potential, which is often less soil matric potentials develop, is osmot­ than -200 MPa in desert environments. ic regulation (Dileanis and Groeneveld, This low potential results in evaporation 1988). This mechanism, particularly well of water from substomatal chambers of developed in desert plants, concentrates leaves by transpiration. The loss of solutes in root cells where water is this water through transpiration results absorbed selectively through semipermea- in a negative potential within the sub­ ble membranes even when soil matric stomatal chambers , which in turn draw potentials are less than -2 to -3 MPa. water from areas of higher potentials in the xylem tissues. Water then moves into the root tissues in response to the TOLERANCES OF PLANTS TO potential gradient to replace that tran­ DROUGHT AND SALINITY spired through the leaves. The graph in In reviewing the available literature figure 2 illustrates the soil-plant- for drought and salinity tolerances of atmosphere continuum. The large differ­ plants, it is apparent that different ences in potentials from one end of the authors have used many different methods continuum to the other only occur during to evaluate the capacity of plants. In the day when large negative potential this section of the report the most differences develop between the atmos­ often used techniques to determine plant phere and the surface of the leaves. tolerances are briefly summarized and Transpiration is primarily a function of atmospheric potential (Van Bavel and compared. others, 1963) . During the night when atmospheric potential is high, there is Measurement of Xylem little movement of water, thus very Pressure Potentials little gradient within the continuum. During the day, atmospheric potential The most common method of measuring continues to control transpiration xylem pressure potential is the use of as long as soil water does not become the pressure chamber, developed by limiting. If transpiration rates exceed Scholander and others (1965). The pres­ the capacity of the plant to move water from the soil through the plant tissues, sure chamber is used by sealing a small leafy stem into the chamber with a gas- the plant must decrease transpiration tight rubber stopper. Pressurized air or by responses such as closing stomatal nitrogen is introduced into the chamber openings. until fluid appears at the surface of the cut stem. Xylem pressure potential is Total water potential must be less than calculated as the negative equivalent of matric and osmotic forces that retain the positive pressure required to force water in the soil. Plants adapted to xylem fluid from the stem. growing in desert environments have developed morphological and physiological Although the pressure chamber measures mechanisms to aid in extracting more xylem pressure potential, in most plants water from the soil or to reduce transpi­ it also gives an adequate estimate of ration. Morphological adaptations, such total water potential. This is because as sunken stomata, abundant leaf hairs, osmotic potential within the xylem is

4 Plant Tolerances to Drought and Salinity, Western United States J K L LEAF ATMOSPHERE

FIGURE 2.-Hypothetical energy profile for die soil-plant-atmosphere continuum for a habitat that has shallow ground water in a hot arid climate. As illustrated, die continuum consists of: (A-B) soil; (B) surface of root hairs; (C) cortex; (D) endodermis; (D-E) xylem vessels and tracheids leaf veins; (F) mesophyll cells; (F-G) intercellular space and substomatal chamber; (G-H) stomatal pore; (H-J) laminar boundary layer at leaf surface; (J-K) turbulent boundary layer; (K-L) free atmosphere. (Adapted from Philip, 1957.) usually high when few dissolved sub­ Osmotic adjustments permit cell enlarge­ stances are present and is therefore ment and growth to continue at total generally considered negligible (Richie water potential levels that would other­ and Hinckley, 1975; McMahon and Schimpf, wise be limiting (Kramer, 1983). The 1981). capacity of species to maintain low cell osmotic potentials also allows access to a greater volume of soil water (Monson Measurement of Cell Osmotic Potentials and Smith, 1982).

Maintainance and regulation of low cell Methods used to measure cell osmotic osmotic potentials are adaptations of potential include pressure-volume curves plants to saline and arid environments. (Scholander and others, 1965), refractive

Tolerances of Plants 5 index (Barrs f 1968), freezing-point Measurement of Soil Salinity depression (cryoscopy) , and by the use of and Osmotic Potentials various osmometers. All methods that use expressed sap to obtain freezing-point Soil osmotic potentials were measured depression are subject to dilution error in the upper 10 cm of soil by using elec­ caused by mixing cell wall or apoplastic trical conductivity of saturated paste of water with protoplasmic (symplastic) soil and water (a method proposed by water. Xylem water has been found to Richards, 1954). It is assumed that be relatively free of salts; thus, the soil-surface salt contents determine dilution error is avoided when using the species of plants that can become estab­ pressure-volume curve method. A concen­ lished in an area. Soil osmotic poten­ tration error is induced when sap is tials at field capacity (amount of water expressed from certain halophytes. In held in soil after drainage) are shown halophytes, such as species of Atriplex, because at this water content most of the salt accumulates in trichomes (vesicu- salts are in solution. lated hairs) on leaf surfaces; osmotic potentials in trichomes may reach -50 to -70 MPa (Mozafar and Goodin, 1970). When trichomes burst, salts are deposited on leaf surfaces causing possible error OSMOTIC POTENTIALS OF PLANTS when expressed sap is used to estimate cell osmotic potentials. Separating epidermal tissue containing trichomes Range of Xylem Pressure Potentials from leaves is extremely difficult, some­ No single factor determines the dis­ times impossible, but if not done, ques­ tribution of species, but differences tionable results are obtained. Washing in soil water availability and plant leaf surfaces to remove salts is unsatis­ responses to these differences must be factory because of possible dilution of important. Adaptations to high water leaf-tissue solutions. Most methods, stress or low potentials is substantially including the psychometric technique, may responsible for determining plant adapta­ yield erroneous results if leaf-surface tion and distribution in nature (Ritchie salts are not removed. Although suspect, and Hinckley, 1975). Pressure-chamber data derived from cell sap expressed from measurements have also been used to eval­ leaves by pressure are used in this uate drought tolerances of shrub species report because they represent the only considered useful for reclamation of available data for many species. disturbed lands (Wilkins and Klopatek, 1984). A number of studies show a direct Sholander and others (1965) were response of lowered xylem pressure poten­ the first to demonstrate field use of tial to lowered soil water potential pressure-volume curves to determine cell (Slatyer, 1961; Ellison, 1969; Moore and osmotic potentials of cell sap for others, 1972; Sucoff, 1972; Bamberg and species of moist and dry habitats. The others, 1975; Branson and Shown, 1975; method was refined and is now extensively Easter and Sosebee, 1975; Syvertsen and used (Tyree and Hammel, 1972; Tyree and others, 1975; Branson and others, 1976; others, 1973; and Cheung and others, Redmann, 1976; Campbell and Harris, 1977; 1975). Tyree and Hammel (1972) found Clark and others, 1980; Kleinkopf and that when enough liquid was expressed others, 1980; Nilsen and others, 1983; to approach the linear part of the and Wilkins and Klopatek, 1984). pressure-volume curve, the balancing pressure closely matched the cell osmotic Minimum, mean, and maximum total xylem potential of intracellular sap determined pressure potentials for 71 western plants by the freezing-point depression method. are shown in figure 3. As appears to be

6 Plant Tolerances to Drought and Salinity, Western United States SOURCES XYLEM PRESSURE POTENTIAL, SPECIES OF DATA IN MEGAPASCALS -2 -4 -6 -8 -10 -12 -14 I I l l I l Atriplex nuttallii nuttallii 1 E * - ^^ Ceratoides lanata 1,10 Atriplex conferti folia 1,10 Atriplex nuttallii gardneri 2 Atriplex corrugata 1,2 R =» =1 Suaeda fruticosa 2,6 l=* =1 Larrea tridentata 1 1,13 Gutierrezia sarothrae 1 M=* ^^ Allenrolfea occidentalis 1 | =*==^^ Sarcobatus vermiculatus 1,2 Ambrosia deltoidea 7 Kochia americana 1 Atriplex cuneata 1 \ Chrysothamnus greenei filifolius 2 Atriplex obovata 1 Coleogyne ramosissima 1 ES Artemisia tridentata tridentata 3,4 Atriplex (grayia) spinosa 1,2 1 4- | . . Lycium andersonii 1 Eriogonum fasciculatum 7 Krameria gray/ 7 1 % i Atriplex canescens 1 1 4- | Suaeda torreyana 1 Artemisia tridentata vaseyana 3 \ - f- | Simmondsia chinensis 12 1 Atriplex polycarpa 1,9 ^= *< Cercidium microphylum 1,7 )==% =j Juniperus osteosperma 1 Atriplex torreyi 1 s Ambrosia dumosa 1 [ fr -1 Tetradymia spinosa 1,2 Iva axilaris 1 Atriplex hymenelytra 1,8 m Encelia farinosa 9,13 i f i Prosopis glandulosa 12 i Atriplex parryi 1 Quercus gambelii 1 Chrysothamnus nauseosus 1,2 i 4- i Rosa arkansana 1 i i m i i 11

FIGURE 3.-Minimum, mean (*), and maximum total xylem pressure potentials for 71 plant species. Where only one measurement is available it is represented by a single vertical line. Species that tolerate the lowest potential are the most drought tolerant Sources of data are: (1) F.A. Branson, U.S. Geological Survey, written common., 1987; (2) Branson and others, 1976; (3) Branson and Shown, 1975; (4) Campbell and Harris, 1977; (5) Cunningham and Burk, 1973; (6) Detling and Klikoff, 1973; (7) Halvorson and Pattern, 1974; (8) Pearcy and others, 1974; (9) Monson and Smith, 1982; (10) Moore and others, 1972; (11) Syvertsen and others, 1975; (12) Nilsen and others, 1984; (13) Odening and others, 1974; (14) Wambolt, 1973; and (15) White and Carrie, 1984.

Osmotic Potentials of Plants 7 SOURCES XYLEM PRESSURE POTENTIAL, SPECIES OF DATA IN MEGAPASCALS () -2 -4 -6 -8 -10 -12 i i i i i Distichlis spicata 6 1 Acacia greggii 12 1 Artemisia spinescens 1 1 Artemisia tridentata nova 1 E=^a E==*=j Artemisia tridentata vaseyana 3 Eriogonum multiceps 1 E Cercocarpus montanus 1 t=* i Hymenoclea salsola 1 Juniperus monosperma 1 1 Chrysothamnus viscidiflorus pumilus 1 iS Artemisia cana cana 15 !=*=! Cercidium microphyllum 1 E=*=^ Chilopsis linearis 13 N=*=i Artemisia ludoviciana 1 1 Juniperus scopulorum 1 [==*| Dalea fremontii 1 l=*=j Olynea tesota 12 1 Amalanchier alnifolia 1 1 Ephedra torreyana 1 1 Populus tremuloides 1 E^*^3 Eriogonum corymbosus 1 m Juniperus horizontalis 1 i Pseudotsuga menziesii 14 F^I Potentilla fruticosa 1 iS Artemisia filifolia 1 [*i Juniperus com munis 1 1 Bebbia juncea 1 1 Artemisia longifolia 1 1 Ephedra viridus 1 1 Tamarix pentandra 1 1 Pinus ponderosa 14 E*^i Pinus contorta 14 i i i i i FIGURE 3.-Minimum, mean (*), and maximum total xylem pressure potentials for 71 plant species-Continued. true of salinity tolerances (Daubenmire, drought-avoiding annuals, hydrophytes, or 1948), most negative potentials are more succulent species such as cacti. The indicative of drought tolerances than are order of species shown in figure 3 is the mean highest potentials. Maximum from lowest to highest measured xylem xylem pressure potentials, achieved when pressure potentials. Published refer­ soil water is readily available, are ences are included in the figure caption, similar for most species. Species shown but most of the data shown are from in figure 3 include xerophytes, halo- unpublished material collected by the phytes, and some mesophytes, but no authors.

8 Plant Tolerances to Drought and Salinity, Western United States Nuttall saltbush (Atriplex nuttallii All the tree species in this study nuttallii), had the lowest xylem pressure had high xylem pressure potentials. potential of hundreds of plants that were Lodgepole pine (Pinus contorta) has the measured. This low potential exceeds highest potential and various species that of plants growing in the lower part of juniper (Juniperus osteosperma, J. of Death Valley (see Atriplex hymenelytra monosperma, J. scopulorum, and J. hori- and Hymenoclea sal sol a, fig. 3) and zontalis) , have the lowest for tree many other desert areas. An area near species. Species that have intermediate Bridger, Montana, where these measure­ values are quaking aspen (Populus tremu- ments were made could be designated an loides) and Douglas fir (Pseudotsuga "edaphic desert" because of the high run­ menziesii) . Plants characteristic of wet off characteristics of the clayey soil. habitats are not shown, but many of them The second lowest measurements of xylem have negative xylem pressure potentials pressure potential was made on winterfat that do not exceed -1 MPa (Scholander and (Ceratoides lanata) by Moore and others others, 1965). (1972) in Utah. Even at this low poten­ tial (-12 MPa), the plants were actively It is probable that the order of the photosynthesizing. The results of Moore species shown in figure 3 from most neg­ and others (1972) differ from those of ative (top) to least negative (bottom) Branson and others (1976), who found xylem pressure potentials also represents seasonal minimum potential of winterfat most-to-least drought tolerance for the to be higher than those of Nuttall species shown. The graph would be more saltbush (Atriplex nuttallii), mat salt- useful if all species had been measured bush (A. corrugata), and shadscale (A. the same number of times. For some confertifolia). species, several hundred measurements were made and sampling extended over a Many of the Northern Desert shrubs wide geographic range for one or more (fig. 3) attain lower xylem pressure seasons. For some species the data potentials than do species of the hotter are for only one location at one time. Mojave Desert, such as creosote bush Nevertheless, the assumption of relative (Larrea tridentata) , bur-sage (Ambrosia drought tolerance may be valid for most deltiodea) , and Anderson wolfberry species shown. (Lycium andersonii) . Latitude and altitude do not seem to be significant factors affecting these results. In ex­ Range of Cell Osmotic Potentials tremely dry habitats in Death Valley, Mojave Desert species are usually The term "osmoregulation" has been restricted to areas where water accu­ applied to seasonal and diurnal changes mulates in shallow depressions or minor in cell osmotic potential in response to channels. Some desert shrub species decreasing soil matric and atmospheric survive without being restricted to such potentials. The capacity of plants to moisture collection sites. maintain low cell osmotic potential and to regulate it in response to soil matric Phreatophytes, which require readily and atmospheric potentials are elements available ground water, such as Nevada of a species tolerance to drought. Regu­ saltbush (Atriplex torreyi) , mesquite lation of osmotic potential was present (Prosopis glandulosa), rubber rabbit- in four of seven Arizona Sonoran Desert brush (Chrysothamnus nauseosus) , and species (Monson and Smith, 1982) and saltgrass (Distichlis spicata), are ranged from 0.3 to 0.8 MPa. For chapar­ characterized by intermediate xylem ral species of southern California pressure potentials. (Bowman and Roberts, 1985) , the seasonal

Osmotic Potentials of Plants 9 trend was toward increasingly negative Bennert and Mooney (1979) classified this cell osmotic potentials with little or no species as drought tolerant with the recovery at the end of the summer drought ability to adjust osmotic components to period, however, turgor-loss point varied changes in the hydrologic environment. both seasonally and diurnally. Monson and Smith (1982), whose measurements were Some phreatophytes, such as Nevada for an entire year for Sonoran Desert saltbush (Atriplex torreyi) and saltgrass plants of Arizona, found both seasonal (Distichlis spicata, fig. 4) have low adjustments and recovery of cell osmotic cell osmotic potentials, but some, such potentials in midwinter. as greasewood (Sarcobatus vermiculatus) and mesquite (Prosopis velutina and Species are listed in order of minimum P. glandulosa) have relatively high cell osmotic potentials to maximum poten­ potentials. tials (fig. 4) . It is not possible to estimate the errors that may be present in the freezing-point depression measure­ ments for some of the halophytes, but Range of Soil Osmotic Potentials perhaps the order would be the same had other methods been used. As one Figure 5 shows the range of soil example of the possible magnitude of the osmotic potentials associated with 40 discrepancy between methods, Bennert and different western plant species. One Mooney (1979) measured cell osmotic would expect pickleweed (Allenrolfea potentials as low as -13 MPa for desert occidentalis), which grows in very salty holly (Atriplex hymenelytra) in Death environments such as the salt pan in Valley by the cryoscopic method, but Death Valley and salt marshes adjacent to -4.26 MPa was the lowest value determined the Great Salt Lake, to have lower by pressure-volume curves. cell osmotic potentials than those shown. Perhaps the succulent characteristics of The halophytes listed in this study the pickleweed permits the retention of have the lowest cell osmotic potentials. enough water to dilute cell-sap salts. Shadscale (Atriplex confertifolia), al­ Pickleweed grows in the saltiest habi­ though often found growing in nonsaline tats, but is also found in a wide sites (Billings, 1949; Branson and range of sites including some that are others, 1976) has the lowest cell osmotic nonsaline. It is by far the most potential. Nuttall saltbush Atriplex salt-tolerant species studied. nuttallii has very low cell osmotic potential, as is true of xylem pressure potential (fig. 3) . It is surprising Species which grow in relatively that big sagebrush (Artemisia tridentata) moist habitats, such as big bluestem has such low cell osmotic potential, ex­ (Andropogon gerardi) (Hake and others, ceeding that of many halophytes. Harris 1984) and giant reed (Pharagmites (1934) gave the locations for each of the communis) (Harris, 1934), have high cell 208 sites where this species was studied osmotic potentials. so it might be possible to reevaluate some of the more anomalous values. One A number of the saltbushes (Atriplex possibility for the low values is that sp.) are extremely salt tolerant. Mat windblown salts may have accumulated saltbush (Atriplex corrugata), Parry on the leaves. Another upland, nonhalo- saltbush (A. parryi), and fourwing salt- phytic species that attains relatively bush (A. canescens) are commonly found low cell osmotic potential is creosote where water tables are at shallow bush (Larrea tridentata) . depths that permit the migration of

10 Plant Tolerances to Drought and Salinity, Western United States METHOD AND SOURCE SPECIES OF DATA CELL OSMOTIC POTENTIALS, IN MEGAPASCALS 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 I I I I I I I I I I I I I I 1 I I I I 1 1 Atrip lex con fertifolia A-1 Atriplex nuttallii A-1 Atriplex canescens A-1 Atriplex torreyi A-1 ^=*=l Distichlis stricta A-1 Atriplex polycarpa A-1 Artemisia tridentata B-4, A-1 Salicornia rubra A-1 1 # 1 Atriplex lentiformis A-1 EJ[=I Allenrolfea occidentalis A-1 1 # 1 Artemisia tridentata B-2 | 5(C | Suaeda torreyana A-1 E=*=j Larrea tridentata A-2 E * i Larrea tridentata B-6 | # | Gray/a spinosa A-1 | ___ ^ ___| Simmondsia chinensis B-6 | # | Schizachyrum scoparius B-5 |=*=j Suaeda fruticosa A-1 Sarcobatus vermiculatus A-1 | # | Sporobolus airoides A-1 Atriplex hymenelytra B-3 E*3 Prosopis velutina A-2 [= * i Prosopis glandulosa B-6 Olneya tesota B-6 Juniperus utahensis A-2 Ephedra trifurca A-2 ffi Encelia farinosa B-6 Chilopsis linearis B-6 F*l Phragmites communis A-1 H Andropogon gerardi B-5 Hyptis emoryi B-6 E"*l i i i i i i i i i i i i i i i i i i i i i

FIGURE 4. Minimnm, mean (*), and maximum cell osmotic potentials in 31 plant species measured by freezing-point depression method (A) or by pressure-volume curve method (B). Sources of data are: (1) Harris, 1934; (2) Walter and Stadelmann, 1974; (3) Bennert and Nooney, 1979; (4) Campbell and Harris, 1977; (5) Hake and others, 1984; and (6) Nilsen and others, 1984.

salts to the soil surface. Other phre- intermediate tolerances. Not all salt- atophytic species, such as rubber rabbit- bushes were found growing in saline soils brush (Chrysothamnus nauseosus) and (for example, Atriplex polycarpa and A. greasewood (Sarcobatus vermiculatus) show hymenelytra).

Osmotic Potentials of Plants 11 NUMBER SOIL OSMOTIC POTENTIAL AT FIELD SPECIES OF SITES CAPACITY, IN MEGAPASCALS C -1 -2 -3 -4 -5 -6 -7 -8 i i i i i i i i i Allenrolfea occidentalis Atriplex obovata

Atriplex corrugata gw p Atriplex parryi 2 i i ^ ~~| 1 , Atriplex canescens 5*J , ' Atriplex nuttallii nuttallii 59 :fr | i Suaeda torreyana ramosissima 2 Suaeda fruticosa 4 !t=*=i Tetradymia spinosa 5 i Chrysothamnus nauseosus 6 i Atriplex confertifolia 76 Sarcobatus vermiculatus 11 (='*=! Kochia americana 3 ^*^ Ceratoides lanata 22 [*p Atriplex nuttallii gardneri 3 IP Artemisia longifolia 1 | 1 2 Gutierrezia sarothrae i Artemisia tridentata tridentata 68 m Atriplex (grayia) spinosa 6 % SALINE SOILS * Artemisia tridentata vaseyana 18 Chrysothamnus viscidiflorus pumillus 8 Artemisia tridentata nova 9 E Artemisia cana 2 g Chrysothamnus greenei filifolius 20 1 Artemisia spinescens 1 1 Atriplex polycarpa 3 B Pinus edulis 6 1 Artemisia pedatifida 2 1 Eriogonum corymbosum 1 1 Chrysothamnus viscidiflorus purberulus 1 1 Juniperus osteosperma 3 1 Quercus gambellii 2 1 Larrea tridentata 3 1 Coleogyne ramosissima 2 1 Atriplex hymenelytra 2 1 Cercocarpus montanus 1 1 Ambrosia dumosa 2 1 Chrysothamnus vaseyi 1 1 Pinus ponderosa 2 1 1 Potentilla fruticosa i i i i i i i i FIGURE 5. Minimum, mean (*), and maximum soil osmotic potentials at field capacity for the upper 10 centimeters of soils in 40 plant habitats. Where only one measurement is available it is represented by a single vertical line. Sources of data are: F.A. Branson and R.F. Miller, U.S. Geological Survey, written commnn., 1987; Branson and others, 1976; and Miller and others, 1982. All soils to the right of the vertical dashed line are saline.

12 Plant Tolerances to Drought and Salinity, Western United States SUMMARY REFERENCES

The distribution of plant species in Bamberg, S.A., Kleinkopf, G.E., Wallace, the Western United States is caused by A., and Vollmer, A., 1975, Comparative variations in the capacities of different photosynthetic production of Mojave species to tolerate dry conditions and Desert shrubs: Ecology, v. 56, p. different amounts of soil salinity. It 732-736. is proposed that minimum xylem pressure Barrs, H.D., 1968, Determination of potentials, which were measured over a water deficits in plant tissues, in large part of the Western United States, Kozlowski, T.T., ed., Water deficits are indicative of drought tolerance, and and plant growth, Volume I: New York, that minimum cell osmotic potentials are Academic Press, p. 236-368. indicative of salt tolerances of plant species. Bennert, W.H., and Mooney, H.A., 1979, The water relations of some desert plants in Death Valley, California: Of the species measured, Nuttall Flora, v. 168, no. 4, p. 405-427. saltbush (Atriplex nuttallii nuttallii) was found to be the most drought toler­ Billings, W.D., 1949, The shadscale zone ant. Although pickleweed (Allenrolfea of Nevada and eastern California in occidentalis) grows in the saltiest soil relation to climate and soils: American measured, it did not have the lowest cell Midland Naturalist, v. 42, p. 87-109. osmotic potential. This apparent anomaly may be explained by the succulent charac­ Bowman, W.D., and Roberts, S.W., 1985, teristics of pickleweed. Saltbushes Seasonal and diurnal water rela­ (Atriplex confertifolia, A. nuttallii, tions adjustments in three evergreen A. canescens, and A. torreyi) had the chaparral shrubs: Ecology, v. 66, p. lowest cell osmotic potentials measured. 738-742. Branson, F.A., Miller, R.F., and McQueen, Sites that have vegetation with high I.S., 1976, Moisture relationships in cell osmotic potentials can be very dry twelve northern desert shrub communi­ (such as areas where bur-sage [Ambrosia ties near Grand Junction, Colorado: dumosa] grows) or wet (where shrubby Ecology, v. 57, no. 6, p. 1104-1124. cinquefoil [Potentilia fruticosa] grows) Branson, F.A., and Shown, L.M., 1975, or can have soils with an intermediate Soil-moisture stress as related to moisture content (where little bluestem plant-moisture stress in big sagebrush: [Schizachyrun scoparius] grows). Gener­ Journal of Range Management, v. 28, no. ally, only low soil osmotic potentials 3, p. 212-215. in salty to moderately salty soils, markedly influence plant distribution. Campbell, G.S., and Harris, G.A., 1977, Water relations and water use pat­ In areas with low salinity soils, soil terns for Artemisia tridentata water availability is a more selective Nuttallii in wet and dry years: influence. Ecology, v. 58, p. 652-659.

References 13 Cheung, Y.N.S., Tyree, M.T., and Dainty, Halvorson, W.L., and Patten, D.T., 1974, J., 1975, Water relations parameters on Seasonal water potential changes in single leaves obtained in a pressure Sonoran Desert shrubs in relation to bomb and some ecological interpreta­ topography: Ecology, v. 55, p. 173- tions: Canadian Journal of Botany, v. 177. 53, no. 13-18, p. 1342-1346. Harris, J.A., 1934, The physio-chemical Clark, S.G., Letey, J., Jr., Lunt, 0. R., properties of plant saps in relation to Wallace, A., Kleinkopf, G.E., and plant geography: Minneapolis, Univer­ Romney, E.M., 1980, Transpiration and sity of Minnesota Press, 339 p. carbon dioxide fixation of selected Hsiao, T.C., 1973, Plant responses to desert shrubs as related to soil water water stress: Annual Review of Plant potential: Great Basin Naturalist Physiology, v. 24, p. 519-570. Memoir, v. 0, no. 4, p. 110-116. Kleinkopf, G.E., Hartsock, T.L., Wallace, Cunningham, G.L., and Burk, J.H., 1973, A., and Romney, E.M., 1980, Photosyn- The effect of carbonate deposition thetic strategies of 2 Mojave Desert layers ("caliche") on the water status USA shrubs: Great Basin Naturalist of Larrea tridentata: American Midland Naturalist, v. 90, p. 474-480. Memoir, v. 0, no. 4, p., 100-109. Kozlowski, T.T., 1964, Water metabolism Daubenmire, R.F., 1948, Plants and environment: New York, John Wiley, in plants: New York, Harper and Row, 227 p. 424 p. Kramer, P.J., 1983, Water relations of Detling, J.K., and Klikoff, L.G., 1973, plants: New York, Academic Press, 489 Physiological response to moisture stress as a factor in halophyte distri­ P- McMahon, J.A., and Schimpf, D.J., 1981, bution: American Midland Naturalist, v. Water as a factor in the biology of 90, p. 307-318. North American desert plants, p. 114- Dileanis, P.D., and Groeneveld, D.P., 1988, Osmotic potential and projected 171, in Evans, D. D., and Thames, J. L., eds., Water in desert ecosystems: drought tolerance of four phreatophytic Stroudsburg, Pennsylvania, Dowden, shrub species in Owens Valley, Califor­ nia: U.S. Geological Survey Open-File Hutchinson and Ross, Inc., 280 p. Report SB-71, 45 p. Miller, R.F., Branson, F.A., McQueen, Easter, S.J., and Sosebee, R.E., 1975, I.S., and Snyder, C.T., 1982, Water Influence of soil water potential on relations in soils as related to plant water relationships of honey mesquite: communities in Ruby Valley, Nevada: Journal of Range Management, v. 28, p. Journal of Range Management v. 35, no. 230-232. 4, p. 462-468. Ellison, S.L., 1969, Leaf water potential Monson, R.K., and Smith, S.D., 1982, in Pinus taeda L. as related to fluc­ Seasonal water potential components of tuations in soil water and atmospheric Sonoran Desert Arizona: Ecology, v. conditions: Dallas, A and M Univer­ 63, no. 1, p. 113-123. sity, M. S. thesis, 85 p. Moore, R.T., White, R.S., and Caldwell, Hake, J. P., McPherson, J. K. , Claypool, M.M., 1972, Transpiration of Atriplex P. L., and Dunn, G. L., 1984, Water confertifolia and Eurotia lanata in stress of tallgrass prairie plants in relation to soil, plant, and atmos­ central Oklahoma: Journal of Range pheric moisture stress: Canadian Management, v. 37, p. 147-151. Journal of Botany, v. 50, p. 2411-2418.

14 Plant Tolerances to Drought and Salinity, Western United States Mozafar, L.A., and Goodin, J.R., 1970, Scholander, P.P., Hammel, H.T., Vesiculated hairs: a mechanism for salt Bradstreet, E.D., and Hemmingsen, E.A., tolerance in Atriplex halimus L. : 1965, Sap pressure in vascular plants: Plant Physiology, v. 45, p. 62-65. Science, v. 148, p. 339-346. Slatyer, R.O., 1961, Internal water Nilsen, E.T., Sharifi, M.R., and Rundel, balance of Acacia aneura F. Muell. in P.W., 1984, Comparative water relations relation to environmental conditions, of phreatophytes in the Sonoran Desert in Plant-water relationships in arid of California: Ecology, v. 65, no. 3, and semi-arid conditions: Proceedings, p. 767-778. Madrid Symposium, Paris, UNESCO, p. Nilsen, E.T., Sharifi, M.R., Rundel, P. 137-146. W., Jarrell, W.M., and Virginia, R.A., Sucoff, Edward, 1972, Water potential in 1983, Diurnal and seasonal water rela­ red pine: soil moisture, evapotran- tions of the desert phreatophyte spiration, crown position: Ecology, v. Prosopis glandulosa (honey mesquite) in 53, p. 681-686. the Sonoran Desert of California: Syvertsen, J.P., Cunningham, G.L., and Ecology, v. 64, no. 6, p. 1381-1393. Feather, T.V., 1975, Anomalous diurnal Odening, W.R., Strain, B.R., and Oechel, patterns of stem xylem water potentials W.C., 1974, The effect of decreasing in Larrea tridentata: Ecology, v. 56, water potential on net CO 2 exchange of p. 1423-1428. intact desert shrubs: Ecology, v. 55, Tyree, M.T., Dainty, J. , and Benis, M. , p. 1086-1095. 1973, The water relations of hemlock Pearcy, R.W., Harrison, A.T., Mooney, (Tsuga canadensis I.), Some equilibrium H.A., and Bjorman, D., 1974, Seasonal water relations as measured by the changes in net photosynthesis of pressure-bomb technique: Canadian Atriplex hymenelytra shrubs growing in Journal of Botany, v. 51, no. 5, p. Death Valley, California: Oecologia, v. 1471-1480. 17, p. 111-124. Tyree, M.T., and Hammel, H.T., 1972, The measurement of the turgor pressure and Philip, J.R., 1957, The physical princi­ the water relations of plants by the ples of soil water movement during the pressure-bomb technique: Journal of irrigation cycle: Proceedings, Inter­ Experimental Botany, v. 23, p. 267-282. national Congress of Irrigation and Van Bavel, C.H.M., Fritschen, L.J., and Drainage, v. 8, p. 125-154. Reeves, W.E., 1963, Transpiration by Redmann, R.E., 1976, Plant water rela­ sudangrass as an externally controlled tionships in a mixed grassland: process: Science, v. 141, p. 269-270. Oecologia, v. 23, no. 4, p. 283-295. Walter, H., and Stadelmann, E., 1974, A Richards, L.A., ed., 1954, Diagnosis and new approach to the water relations of improvement of saline and alkali soils: desert plants, in Brown, G.W., ed. , U.S. Department of Agriculture, Agri­ Desert Biology: New York, Academic culture Handbook 60, 160 p. Press, p. 114-310. Ritchie, G.A., and Hinckley, T.M., 1975, Wambolt, C.L., 1973, Conifer water poten­ The pressure chamber as an instrument tial as influenced by stand density and for ecological research, in Advances in environmental factors: Canadian ecological research, v. 9, p. 165-25: Journal of Botany, v. 51, no. 12, p. New York, Academic Press, 385 p. 2333-2337.

References 15 White, R.S., and Currie, P.O., 1984, osmotic components in response to Phenological development and water changes in the hydrologic environment. relations in plains silver sagebrush: Hydrophytes. Plants that grow partly or Journal of Range Management v. 37, no. wholly immersed in water. 4, p. 503-507. Mesophytes. Plants that grow under Wilkins, S.D., and Klopatek, J.M., 1984, conditions of intermediate environ­ Water stress, Atriplex species, and reclamation at Black Mesa, Arizona, mental wetness. in Proceedings, Symposium on the Osmotic potential. That part of total Biology of Atriplex and related cheno- potential that is caused by dis­ pods: U.S. Department of Agriculture, solved salts. Forest Service General Technical Report Phreatophyte. A plant which derives at INT-172, p. 97-107. least part of its water supply from ground water and is more or less GLOSSARY independent of rainfall. Pressure-volume curve. Obtained by plac­ Apoplastic water. Water that in cell ing a turgid twig or stem in a walls and xylem elements is water outside the protoplast. pressure chamber and subjecting it to stepwise increases in pressure, Atmospheric potential. The force exerted while the volume of sap expressed by the atmosphere to remove water at each pressure is measured and the from plants, soils, and water surfaces. data used to construct a curve. Stress values are positive and potential values are negative. Soil osmotic potential. That part of total soil water potential attri­ Cell sap. The watery solution of various butable to dissolved salts. substances, including salts, alkaloids, and sugars that occurs within cells. Symplastic water. That water occurring in vacuoles and cytoplasm. Cortex. The tissue between the epidermis (outer layer of cells) and the stele Total water potential. The difference (inner tissues of stems and roots). between free energy of water in a particular system and that of pure Edaphic desert. Desert conditions in a water. Water potential is decreased by non-desert climate caused by high run­ factors that decrease vapor pressure. off from clayey soils. Transpiration. The loss of water from Euryhydric. Refers to the capacity of plants to the atmosphere. certain species to withstand large water deficits. Turgor-loss point. Synonymous with per­ manent wilting percentage and is Field capacity. Amount of water held in the point in the drying curve at soil after drainage by gravity. which positive turgor pressure in Halophyte. Plants that tolerate high plant cells cannot be regained. concentrations of soil salts. Xerophyte. A plant which can subsist Hydrolabile.--Species that adjust osmotic with a small amount of moisture components to changes in the hydrologic (such as a desert plant). environment. Xylem potential. Refers to the water Hydrolabile behavior. Adjustments that potential of water in the xylem are made by certain species of their portion of the transpiration stream.

16 Plant Tolerances to Drought and Salinity, Western United States