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Response to long- and short-term salinity in populations of the C 4 nonhalophyte Andropogon glomeratus Walter B.S.P
Abstract
This research was undertaken to investigate differences in salt tolerance under conditions in which salinity is increased gradually and maintained for long periods or increased rapidly and maintained for shorter periods. The responses of populations of a C4 nonhalophytic grass, Andropogon glomeratus, to long- and short-term salinity were measured under controlled environment conditions. Additionally, plants from a salt marsh population and an inland population were transplanted into a salt marsh and their survival compared. The relative growth reductions in the salt marsh and the inland populations under long-term salinity were similar. Survival of seedlings of 4 populations inundated with full-strength seawater over a relatively short period indicated differential capacities to tolerate soil salinities imposed in a manner similar to tidal inundation in a salt marsh. The greater survival of plants from the marsh population transplanted into the salt marsh further indicated genetic differentiation between the populations. These results indicate that genetic differentiation to salt tolerance in A. glomeratus is better reflected by survival after shortterm salinity events, rather than growth inhibition due to long-term salinity imposed gradually.
... All grass species except A. gramineus had 37% to 79% reductions in shoot dry weight when irrigated with saline solution at an EC of 10.0 dS·m -1 , compared with the control. Similarly, with increasing salinity levels, there was a decrease in biomass production of Andropogon glomeratus (bushy bluestem) (Bowman and Strain, 1988). This also aligns with previous work documenting that Carex rigescens (rigescent sedge), Carex rostrata (beaked sedge), and Carex pilosa (hairy sedge) had reduced growth under salinity stress (Choo et al., 2001;Li et al., 2018). ...
Reclaimed water provides a reliable and economical alternative source of irrigation water for landscape use but may have elevated levels of salts that are detrimental to sensitive landscape plants. Landscape professionals must use salt-tolerant plants in regions where reclaimed water is used. Ornamental grasses are commonly used as landscape plants in the Intermountain West of the United States due to low maintenance input, drought tolerance, and unique texture. Six ornamental grass species, including Acorus gramineus (Japanese rush), Andropogon ternarius (silver bluestem), Calamagrostis ×acutiflora (feather reed grass), Carex morrowii (Japanese sedge), Festuca glauca (blue fescue), and Sporobolus heterolepis (prairie dropseed), were evaluated for salinity tolerance. Plants were irrigated every 4 days with a fertilizer solution at an electrical conductivity (EC) of 1.2 dS·m –1 (control) or with a saline solution at an EC of 5.0 dS·m –1 (EC 5) or 10.0 dS·m –1 (EC 10). At 47 days, most species in EC 5 exhibited good visual quality with averaged visual scores greater than 4.6 (0 = dead, 5 = excellent). In EC 10, most A. gramineus plants died, but C. ×acutiflora , F. glauca , and S. heterolepis had no foliar salt damage. At 95 days, C. ×acutiflora , F. glauca , and S. heterolepis in EC 5 had good visual quality with averaged visual scores greater than 4.5. Acorus gramineus , A. ternarius , and C. morrowii showed foliar salt damage with averaged visual scores of 2.7, 3.2, and 3.4, respectively. In EC 10, A. gramineus died, and other grass species exhibited moderate to severe foliar salt damage, except C. ×acutiflora , which retained good visual quality. Plant height, leaf area, number of tillers, shoot dry weight, and/or gas exchange parameters also decreased depending on plant species, salinity level, and the duration of exposure to salinity stress. In conclusion, A. gramineus was the most salt-sensitive species, whereas C. ×acutiflora was the most salt-tolerant species. Festuca glauca and S. heterolepis were more tolerant to salinity than A. ternarius and C. morrowii . Calamagrostis ×acutiflora, F. glauca , and S. heterolepis appear to be more suitable for landscapes in which reclaimed water is used for irrigation. Plant responses to saline water irrigation in this research could also be applied to landscapes in salt-prone areas and coastal regions with saltwater intrusion into aquifers and landscapes affected by maritime salt spray.
... A. glomeratus is not tolerant to salt and generally will not grow at soil salinity levels above 0.5 ppt (Newman and Gates, 2006). However, Bowman and Strain (1988) found distinct differences in the salt tolerance of populations from salt marsh and fresh-water marsh and there is at least some tolerance of short-term salinity. ...
This datasheet on Andropogon glomeratus covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
The effects of NaCl stress on growth and development of rice {Oryza sativa L.) were studied and compared in varieties of various origins. During the vegetative stage, tall indica landraces (Nona Bokra, Buhra Rata, Panwell, and Pokkali) appeared to be resistant throughout while in japonica varieties (I Kong Pao (IKP) and Tainung 67) and elite breeding lines (IR 4630, IR 2153 and IR 31785), resistance fluctuated. Panwell, which was the only indica variety evaluated during the reproductive stage, also expressed salt resistance during booting, heading and grain maturation while varieties with the greatest variability in salt stress response during the vegetative phase (IR 4630, IR 31785 and IKP) also showed the greatest variability during reproductive development. Thus, varietal levels of resistance to salinity at different growth stages are not necessarily interdependent characteristics. Variability in salt resistance of different genotypes during the vegetative and reproductive phases of development was not correlated to their mean level of relative resistance.
There was an ontogenic evolution of salt resistance and the young seedling stage appeared to be the most sensitive to NaCI during vegetative growth. Nevertheless, short- and middle term effects of stress have to be distinguished for each genotype since some varieties showed better growth during the second week of stress than during the first, whilst others showed an opposite trend. Moreover, even at specific stages of development, plant responses to NaCI were quite variable according to the criterion used to quantify salinity resistance. The identification of genotypes resistant to NaCI at specific developmental stages is essential to improve the understanding of the effects of salt stress upon phenology and to elaborate further breeding programmes.
Andropogon glomeratus is a C4 nonhalophytic grass which exhibits population differentiation for tolerance to short-term salinity exposure. To investigate possible physiological mechanisms whch enable salt-tolerant individuals to survive short-term inundation, gas exchange and water relations parameters were measured before and during a 5-day watering treatment of half-strength synthetic seawater in plants from a tolerant and a non-tolerant population. Photosynthetic recovery was followed for 10 days after the salinity treatment. Photosynthetic CO2 uptake was substantially inhibited in both populations. Stomatal conductances decreased and intercellular CO2 concentrations increased, indicating non-stomatal factors were primarily responsible for the decrease in CO2 uptake. After termination of the salinity treatment photosynthetic capacity increased more rapidly in the tolerant population and reached the pretreatment level after 6 days, whereas the nontolerant population did not recover fully after 10 days. A-Ci curves measured before and after the salinity treatment indicated a decrease in the carboxylation efficiency, and suggested a proportionately greater metabolic inhibition relative to the increase in the stomatal limitation. Osmotic adjustment occurred in a 2-day period in the tolerant population, but there was no change in the osmotic potentials or the water potential at the point of turgor loss in the nontolerant population. Thus short-term salt tolerance in the marsh population is associated with rapid osmotic adjustment and recovcry of photosynthetic capacity shortly after the end of the salinity exposure, rather than maintenance of greater photosynthesis during the salinity treatment.
To examine the importance of Na+ and Cl- to osmotic adjustment in a salt-tolerant ecotype of the C4 nonhalophyte Andropogon glomeratus, plants were watered with sorbitol, a neutral osmoticum, and synthetic seawater, for five days. Gas exchange measurements were made during the course of the watering treatment and during a recovery period following treatment. Leaf osmotic adjustment occurred only in plants watered with seawater, and was associated with an increase in Na+ and Cl- concentrations. Estimates of the molar concentrations indicated these ions could account for 95% of the leaf osmotic adjustment. Net photosynthetic CO2 uptake was less effected during the watering treatment, and photosynthetic recovery was greater following the treatment in plants watered with seawater. Photosynthetic inhibition was related primarily to metabolic factors, including a decrease in carboxylation efficiency. A model is presented for a mechanism promoting tolerance to transient seawater inundation in A. glomeratus.
Online carbon isotope discrimination (Delta) and leaf gas exchange measurements were made with control and salt-stressed Zea mays and Andropogon glomeratus, two NADP-ME type C(4) grasses. Linear relationships between Delta and p(i)/p(a) (the ratio of intercellular to atmospheric CO(2) partial pressure) were found for control plants which agreed well with theoretical models describing carbon isotope discrimination in C(4) plants. These data provided estimates of phi, the proportion of CO(2) fixed by phosphoenolpyruvate carboxylase which leaks out of the bundle sheath and the component of fractionation due to diffusion in air. Salt-stressed plants had wider variation in Delta for the same or less range in p(i)/p(a). Additional work indicated Delta changed independently of p(i)/p(a) in both water- and salt-stressed plants, suggesting a possible diurnal change in phi as plant water status changed linked to a decrease in the activity of the C(3) photosynthetic pathway relative to C(4) pathway activity. The possible effect of stress-induced changes in phi on organic matter delta(13) C of C(4) plants is apt to be most apparent in chronically stressed environments.
Trifolium alexandrinum and Trifolium pratense were grown in solution culture at salinity levels of 50, 100, 150 and 200 mM NaCl. Trifolium alexandrinum survived at all salt treatments. Salt-induced growth reductions of 30 and 47% occurred at 50 and 100 mM NaCl, respectively, mostly affecting stems. Plants still survived at 150 and 200 mM NaCl. This species can therefore be considered moderately salt tolerant. Trifolium pratense showed a low survival potential at salt treatments of 100 mM NaCl or higher, and the dry weight production of all plant parts was considerably affected at moderate salt levels. Thus T. alexandrinum is considered more salt tolerant than T. pratense. The distribution and contents of K⁺, Na⁺ and Cl⁻ in both species indicate that T. pratense translocates Na⁺ and Cl⁻ linearly with increasing salt treatment into stems and leaves, whereas low foliar Na⁺ and Cl⁻ contents in T. alexandrinum suggest some mechanisms that control the ion distribution in the different plant parts. Salt-induced changes of the K⁺ and Ca²⁺ contents of the different plant parts of both species are discussed.
Betaine (glycinebetaine) accumulates in several plant families in response to salt or water stress. Although betaine is hypothesised to be central to cellular osmoregulation, there is little direct evidence for this. Betaine level in barley was therefore altered genetically by creating two F4 isopopulations with different mean betaine levels, and the osmoregulatory behaviour of these populations and of their parents was examined under saline conditions. To minimise linkage effects, the isopopulation procedure included several parents and two rounds of crossing. Mean betaine levels of the two populations in unstressed conditions were 23 and 32 μmol g⁻¹ dry weight; measurements of various morphological and developmental characters indicated that the populations were otherwise genetically comparable.
Salinising with 300 mM NaCl caused a decline of 0.5 MPa in solute potential (Ψs) and an 8- to 10-fold increase in betaine level in both isopopulations. The absolute difference in betaine level between the two populations remained constant as salt concentration was raised to 300 mM. Although selected only for differing betaine level, the parents and isopopulations differed also for Ψs; the high-betaine genotypes maintained a Ψs 0.1 MPa lower than the low-betaine genotypes at all salt levels. Furthermore, in both populations and parents, betaine level was linearly related to Ψs (r² Ͱ4; 0.97). These observations are consistent with coordinated genetic control of betaine level and Ψs and imply that betaine accumulation is a mandatory component of osmoregulation in barley.
The objective of ecological plant physiology is to explain processes in plant ecology, such as plant performance, survival, and distribution, in physiological, biophysical, biochemical, and molecular terms. It is a relatively young discipline and we are aware of only a few basic textbooks that have been written (Larcher 1973, 1980a, b; Kreeb 1974; Bannister 1976; Etherington 1975, 1978). Physiological plant ecology was first reviewed as a separate discipline by Billings (1957), but the knowledge since gained in ecological-physiological studies has been rapidly integrated into and has strongly influenced the parent disciplines of plant physiology and ecology. Nearly a century ago the necessity of ecophysiological work was recognized by Schimper in the introduction to his classical text (1898) Pflanzengeographie auf physiologischer Grundlage and was expressed succinctly: „Nur wenn sie in engster Fühlung mit der experimentellen Physiologie verbleibt, wird die Oekologie der Pflanzengeographie neue Bahnen eröffnen können, denn sie setzt eine genaue Kenntnis der Lebensbedingungen der Pflanzen voraus, welche nur das Experiment verschaffen kann.“ (In the original English translation: “the oecology of plant-distribution will succeed in opening new paths on condition only that it leans closely on experimental physiology, for it presupposes an accurate knowledge of the conditions of the life of plants which experiment alone can bestow.”) When introducing our perspectives as editors of four volumes dealing with physiological plant ecology in the New Series of the Encyclopedia of Plant Physiology, one of our tasks should be to consider the extent to which Schimper’s prediction has been fulfilled.
Anthoxanthum odoratum L. populations growing along a roadside and in adjacent pastures showed significant differences in morphological traits, flowering date and pollen fertility developed in less than 40 years. The marked differences between the populations were genetic adaptations to the contrasting soil environments. Application of deicing salt during the past 30 years had also caused evolution of appreciable salt tolerance. Large survival differentials of adult plants in alien sites indicate operation of high selection pressures against immigrant genes. Selection for early flowering in the roadside population has increasingly restricted pollen flow and thus facilitated differentiation of populations. The evidence indicates that rapid evolution of Anthoxanthum odoratum populations has occurred in response to selection with gene flow.
Phenotypic measurements of 35 individuals of Borrichia frutescens from different stands of vegetation on Sapelo Island, Georgia, showed few significant differences among stands, but all morphological characters measured showed significant differentiation along the salinity gradient within stands. Of the physiological characters measured, only those associated with water use (i.e., xylem water potential and leaf osmotic potential) were found to vary. Sexual and asexual reproduction varied significantly but in opposite directions along the gradient, with asexual reproduction greater in the high salt environment. Thus considerable phenotypic differentiation exists over very short distances (2-5 m). Experimental analysis of variation in quantitative characters among families and clones taken from different locations along the salinity gradient and grown under different salt treatments showed: (1) no significant treatment differences for any of the morphological characters, (2) significant location differences for several characters and (3) significant among-family or among-clone differences for most characters. Heritability estimates suggest that the genetic component of variation in morphological characters is greater than in physiological characters. Differentiation between locations on the salinity gradient shows the opposite trend: morphology is environmentally determined while physiology exhibits a high degree of genetic determination. Pollen-mediated gene flow between the low and high salt locations was approximately 10%. The stands of vegetation contain on average five neighborhoods, the diameter of which is about 1 m. These measures suggest at least moderate gene exchange along the salinity gradient. The phenotypic differentiation documented over short distances in this study is maintained in the face of gene flow, implying relatively strong selection. Man-made disturbances on the island suggest the differentiation has occurred in the last 100 years.
A cell line of Nicotiana tabacum L. var. Wisconsin 38 was selected (S-10 cells) which is capable of growth in medium containing 10 g liter−1 NaCl. The fresh and dry weights of S-10 cells at stationary phase in medium containing 10 g liter−1 NaCl were about 60 and 100% respectively, of that of S-10 cells grown without NaCl. When cells normally maintained in the
absence of the salt (S-0 cells) were transferred to medium containing 10 g liter−1 NaCl, they underwent a 14-day lag period before growth could be detected and they reached stationary phase 36 days after
inoculation compared to 14 days for S-10 cells. At stationary phase, fresh and dry weights of S-0 and S-10 cells were the
same in the presence of salt. The S-0 cells exhibited a reduced growth rate once growth began in medium with 10 g liter−1 NaCl. The cell mass doubling time of S-0 cells in medium with 10 g liter−1 NaCl was 4 days compared to 1.2 days for these cells grown in the absence of the salt and 1.6 days for S-10 cells grown in
medium with 10 g liter−1 NaCl. The resistance of the salt-selected cells was stable in the presence of the salt. However, after 5 cell mass doublings
following transfer into medium without NaCl, these cells lost their resistance to salt and responded to NaCl like the cell
population (S-0 cells) which had not been selected for growth on NaCl.
Summary Inland and sea cliff populations of bothAgrostis stolonifera L. andHolcus lanatus L. were subjected to soil NaCl treatments, of 100 and 200 mol m−3 NaCl, and tolerance examined using plant dry weight data. A parallel experiment subjected them to salt spray treatments of
2.5%, 5% and 10% NaCl in distilled water, and tolerance assessed from leaf damage.
Both populations of each species were equally sensitive to soil NaCl. When subjected to salt spray the sea cliff populations
however showed marked resistance to leaf damage. Soil salinity resistance and salt spray resistance thus appear to be independent
characteristics in these two species.
Eight populations ofAgrostis stolonifera, collected from maritime and inland habitats, were grown in solution culture and in sand culture at various concentrations of sodium chloride from 0 ppm to 5,000 ppm Na.
NaCl had less effect upon the dry weight yield of populations from maritime habitats, with soils of high Na content, than upon populations from inland or maritime habitats with soils of low Na content. The correlation between per cent reduction in dry weight yield and the Na content of the native soil of each population was r=−0.73. Populations from inland or maritime habitats, with soils of low Na content, contained more Na in their shoot materials, and higher Na/K ratios, than did populations from high Na soils, at all Na concentrations.
The effect of NaCl upon the root elongation of each population was not correlated with the effect upon dry weight yield, nor with the Na content of their native soil. The effect of Na Cl upon root elongation was highly dependent upon the composition of the culture solution used. It is concluded that the effect of NaCl on root elongation is not an adequate measure of salinity tolerance in this species.
ALTHOUGH the tolerance of plants to salt is of great economic importance and has received detailed attention, data for contrasting populations of species that occur naturally in saline and non-saline habitats are limited. Demonstrations of the significance of salt in the distribution of forms of Typha by McMillan1 and McNaughton2 are notable exceptions. We have therefore examined the salt tolerance of populations of Festuca rubra L., which occurs in both the lower and upper regions of salt marshes and in the adjacent non-saline uplands, and of Agrostis stolonifera L. which coexists with Festuca in the upper marsh and upland. Five such populations were collected from each of two geographically separate but otherwise similar sites (Aber, Caernarvonshire and Malltraeth, Anglesey).
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Selected NaCl‐tolerant lines of Trifolium alexandrinum L., Medicago sativa L., and Trifolium protease L. produced significantly greater dry matter than unselected control lines after 4 weeks of growth in sand culture with different NaCl concentrations.
Tolerant lines of all three species generally contained less Na ⁺ but more Cl ⁻ in their shoots than normal lines, although these differences were not statistically significant. Selected lines also contained less K ⁺ in their shoots than unselected lines. Ca ²⁺¹ distribution was similar in T. allexandrinum and M. sativa but not in T. pratense , in which the tolerant line had significantly higher Ca ²⁺ in the shoot than the unselected line.
S ummary
After 7 weeks' growth in varying NaCl concentrations in sand culture, dry matter production and tiller number were compared for the progenies of NaCl–tolerant selection lines and the Progenies of unselected control lines of Holcus lanatus L., Lolium perenne L., Dactylis glomerata L. and Festuca rubra L. The tolerant lines had been produced by selection at the seedling stage. In each species, selected lines produced significantly more dry matter and had greater tiller numbers than unselected material, particularly at high levels of NaCl. Shoot/root ratios differed significantly only in L. perenne , unselected material having a higher shoot/root ratio. These data confirm that for these four species, selection based upon differences in seedling root growth is a valid means of selecting for improved NaCl tolerance in adult plants, and that this tolerance does not lead to any reduced performance in the absence of NaCl.
High salt stresses were exerted upon seedlings of the common variety of Rhodes grass (Chloris gayana Kunth.) in order to select a salt resistant strain and to ascertain the characteristics which differentiate between the original parent population and the currently selected one. Five generations of seedlings were grown on sand culture and irrigated with NaCl solutions up to 0.7 M. The most successful survivors of each generation were selected and grown to maturation and seed production. Plants of the F5-selected population showed a marked improvement in their survival and regeneration capabilities after harvesting. Some effects of selection were found in seed germination and in water use. No apparent differences between the parent and the F5 populations were found in growth of unclipped plants, ion content or protein synthesis. The data presented indicate that the capability to survive through salt stresses can be raised in Rhodes grass by mass selection. Fundamentally this is achieved by improving the regeneration capability of the plants after multiple clippings.
The tolerance to sodium chloride of clones of Agrostis stolonifera from salt marsh, spray zone, and inland habitats was measured in water cultures by a rooting technique and by growth analysis. The order of tolerance was found to be: salt marsh > spray zone > inland. The two methods of measurement of tolerance were found to show good agreement. Salt marsh plants were found to be more resistant to low dissolved oxygen concentrations in the culture solution than plants from the spray zone and inland habitats. With polyethylene glycol 6000 in culture solution, the pattern of resistance to osmotic stress in the absence of sodium chloride was similar to the pattern of resistance to salt.
1) This review concentrates on the effect of sodium chloride on the growth of higher plants, being primarily concerned with relatively high concentrations i.e. 50 mmol 1 ‐1 and above, though something is also said about those instances when sodium acts as a micronutrient. Emphasis is placed on particular species or genera for which enough information is available to discuss possible mechanisms.
(2) Trace amounts of sodium are required for the growth of plants using the C 4 pathway of carbon fixation and may also be important in plants with Crassulacean acid metabolism.
(3) The increased growth of Beta vulgaris brought about by sodium chloride can in part be explained by a sparing effect on potassium. However, growth is still increased when sufficient potassium is available. Complementary studies with rubidium indicate that the hormone balance in the plant may be changed. Sodium chloride also increases the level of sucrose in storage roots and allows beet plants to withstand water stress more readily, possibly by increased turgor pressure.
(4) Sodium chloride increases production of dry matter in C 4 species of Atriplex under conditions of low relative humidity because water loss is reduced and photo‐synthesis hardly affected.
(5) Succulence in many plants is stimulated by salinity. The essential basis of the phenomenon is an increased water potential gradient between the leaf and the external medium. In some instances, it is the accumulation of chloride which is important; in others it is the accumulation of cations, when potassium can be as effective as sodium.
(6) Salinity reduces the final area achieved by growing leaves. Most of the studies have been made on Phaseolus vulgaris and an important early event is the reduction in the rate of expansion of the epidermal cells and this may be accompanied by a decrease in their number. Reduction of epidermal cell size is a result of water stress; sodium chloride may directly affect cell division, though water stress cannot be ruled out. Whether salinity brings about inhibition of cell division depends upon the calcium content of the medium – a high content is accompanied solely by a reduction in epidermal cell size.
(7) Hormones, as yet unspecified, may play an important part in response of a growing leaf to salinity. However, there is no evidence that sodium chloride per se has an effect on hormone balance within the plant. So far, any measured changes in levels of specific hormones can be ascribed to the osmotic effects of the saline medium.
(8) Two estimates by flux analysis of cytoplasmic concentration of sodium in plants growing in conditions of high salinity give a value of around 150 mmol 1 ‐1 . There is no similar information for chloride. Other techniques (histochemistry and X‐ray micro‐probe analysis) give questionable information.
(9) There is now extensive information to show that enzymes of halophytes (other than ATPases) do not differ significantly from those of other higher plants with respect to their sensitivity in vitro to sodium chloride. There is a need for further work with respect to the activity of enzymes in the presence of those metabolites which have the highest cytoplasmic concentration.
(10) Sodium‐stimulated ATPases have been isolated from plant cells but their distribution amongst higher plants is restricted.
(11) There are a number of reports of changed metabolism brought about by saline treatments but it is not clear how far the effects of sodium chloride and water stress are confounded.
(12) Sodium appears to increase the sucrose levels in sugar beet by an inhibitory effect on product starch‐granule‐bound ADP‐glucose starch synthase.
(13) Reversal of a sodium pump located at the plasmalemma might have an effect on cell turgor.
(14) Sodium (like other monovalent cations) causes loss of materials from plant cells, possibly through an effect on carrier proteins; calcium prevents this from happening. Calcium also allows plants to grow better in saline conditions by a depression of sodium uptake by and transport within the plant. The properties and composition of the membranes of mesophytes and halophytes need to be compared.
(15) A saline medium exerts a major effect on plant growth through water stress to which a halophyte must adapt. As well as this, the cytoplasmic concentration of sodium chloride must be kept lower than the total cellular concentration of the salt. Unless this happens, it is likely that enzymic activity will be reduced due, in some instances, to an unspecific effect of a high concentration of monovalent cations and/or chloride and in other instances to competition between sodium and other cations, specifically potassium, for activation sites on enzymes, e.g. pyruvate kinase.
(16) Further work is required to separate the osmotic effects from the specific effect of sodium chloride after it has entered the plant. As well as this, it has become clear that more information is needed about the mineral nutrition of halophytes.
Properties of the leaf surface associated with wettability were studied in ecotypes of Agrosti stolonifera from salt marsh, spray zone and inland habitats. The maritime ecotypes retained much less salt than the inland ecotype after immersion in salt water. Retention of salt after spraying was highest by leaves of the inland ecotype and least by those of the spray zone ecotype. Differences in retention of salt can be correlated with differences in wettability (indicated by measurement of advancing contact angle) and these differences are, in turn, related to differences in the structure and distribution of extracuticular waxes on the surfaces of leaves of the ecotypes. The differences are considered to be adaptations to the environments in which the ecotypes grow.
Andropogon glomeratus is a C4 nonhalophytic grass which exhibits population differentiation for tolerance to short-term salinity exposure. To investigate possible physiological mechanisms whch enable salt-tolerant individuals to survive short-term inundation, gas exchange and water relations parameters were measured before and during a 5-day watering treatment of half-strength synthetic seawater in plants from a tolerant and a non-tolerant population. Photosynthetic recovery was followed for 10 days after the salinity treatment. Photosynthetic CO2 uptake was substantially inhibited in both populations. Stomatal conductances decreased and intercellular CO2 concentrations increased, indicating non-stomatal factors were primarily responsible for the decrease in CO2 uptake. After termination of the salinity treatment photosynthetic capacity increased more rapidly in the tolerant population and reached the pretreatment level after 6 days, whereas the nontolerant population did not recover fully after 10 days. A-Ci curves measured before and after the salinity treatment indicated a decrease in the carboxylation efficiency, and suggested a proportionately greater metabolic inhibition relative to the increase in the stomatal limitation. Osmotic adjustment occurred in a 2-day period in the tolerant population, but there was no change in the osmotic potentials or the water potential at the point of turgor loss in the nontolerant population. Thus short-term salt tolerance in the marsh population is associated with rapid osmotic adjustment and recovcry of photosynthetic capacity shortly after the end of the salinity exposure, rather than maintenance of greater photosynthesis during the salinity treatment.
Seed and transplanted adult plants from populations of Festuca rubra, collected from inland, salt-marsh and sand-dune sites were grown on culture solution with added sodium chloride. The growth of the populations of the three habitats was reduced differentially by salt. The salt marsh ecotype Festuca rubra ssp. litoralis was only slightly affected and the inland ecotype F. rubra ssp. rubra was severely retarded at 60 mM NaCl. The dune ecotype F. rubra ssp. arenaria had an intermediate tolerance. The tolerant ecotypes accumulated less sodium chloride as compared to the sensitive ecotype, suggesting that salt tolerance is caused in part by salt exclusion.
In addition, the dune ecotype F.r. arenaria appeared to be more drought tolerant than the salt marsh ecotype. Abscission of salt-saturated leaves does not function as an adaptation to salinity in Festuca rubra.
All three ecotypes accumulated proline with increased salinity. The response was most pronounced in the drought tolerant F.r. arenaria, indicating that proline accumulation is a response to osmotic stress rather than to ion-specific effects of salinity. The observed differences in salt tolerance may be explained by differential sensitivity to toxic effects of sodium chloride.
The occurrence on a beach plain of closely adjacent populations of F.r. arenaria and F.r. litoralis, differing markedly in salt tolerance, is briefly discussed.
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