Characterization of a microbial community capable of reducing perchlorate and nitrate in high salinity

Denitrifying up-flow packed-bed bioreactors fed with perchlorate and nitrate allowed for the examination of the impact of a variety of salt conditions (up to 10% w/v NaCl) on the complete perchlorate and nitrate removal capacity of the reactor using activated sludge taken from a municipal wastewater treatment plant. Based on the evaluation of the microbial community in the bioreactor by cloning analysis, Clostridium sp. and a Rhodocyclaceae bacteria were identified as the dominant clones. This suggests that they may be tolerant to high salt and can reduce both nitrate and perchlorate in such conditions.     

Assessment of Potential Impacts of Exotic Species on Populations of a Threatened Species, White Sands Pupfish, Cyprinodon tularosa

The potential impact of introduced species on rare taxa is of particular concern to conservation biologists. We evaluate the impacts of western mosquitofish (Gambusia affinis) and virile crayfish (Orconectes virilis) on experimental populations of a threatened species, the White Sands pupfish (Cyprinodon tularosa). Forty experimental pupfish populations were exposed to one of four treatments; (a) 1 crayfish, (b) 4 crayfish, (c) 5 adult mosquitofish and (d) control. Pupfish population size and biomass was monitored over the duration of one breeding season. A repeated measure multiple analysis of covariance revealed a significant effect of treatments on response variables (population size and biomass) (P<0.0001). Mosquitofish had a significant effect on population size and biomass (P=0.0330). The effect of one crayfish was not significant (P=0. 0683). However, 4 crayfish had a significant effect (P<0.0001) on population size. We use these data, along with information on environmental tolerances of crayfish and mosquitofish, to evaluate risks for specific pupfish populations. An erratum to this article is available at .     

Rhizosphere salinity and phytoalexin accumulation in soybean

Summary Rhizosphere salinity decreased the capacity of soybean to accumulate a pterocarpanoid phytoalexin (glyceollin) in the stem in response toPhytophthora megasperma var.sojae. Rapid (48h) accumulation was depressed by NaCl, Na₂SO₄, CaCl₂ and MgSO₄ applications. Time-course accumulations was slowed by applications. Time-course accumulation was slowed by application of 0.131M NaCl. Glyceollin accumulation was also reduced in plants subjected to a period of high salinity stress (0.177M NaCl, 72 h) after a period of nonsalinized growth. Calcium chloride completely suppressed glyceollin accumulation in normally-resistant plants but no susceptibility to the fungus was observed.     

Osmotic adaptation in Ulva lactuca under fluctuating salinity regimes

A study has been made of the osmotic responses of the green intertidal alga, Ulva lactuca, under two fluctuating salinity regimes; sinusoidal and square-wave fluctuations between 30 and 100% sea water in a 12 h cycle. These regimes closely resemble the tidal fluctuation of salinity encountered by the alga in its natural estuarine habitat. Data on changes in the inorganic ions, potassium, sodium, chloride and sulphate; in the organic solute, dimethylsulphoniopropionate; in the total sugar levels and estimated osmotic and turgor pressures under the two salinity regimes are reported. Significant differences in the solute responses under these different conditions were detected. In general, better control of ion fluxes appeared to be exercised under the sinusoidal conditions which also buffered changes in dimethylsulphoniopropionate levels. Influxes of potassium were highly light-dependent. Chloride levels conspicuously failed to reach the steady-state levels in the 6-h-hyper-osmotic part of either the abrupt or gradual cycle. The possible significance of these data, which may better reflect osmotic changes in the natural environment, and some of the problems encountered, particularly in accounting for charge balance under some conditions, are discussed.Abbreviations DSMP 3-(dimethylsulphonio)propionate - FW fresh weight     

Genetic diversity and morphological differentiation in Liatris helleri (Asteraceae), a threatened plant species

Liatris helleri (Asteraceae) is an insect-pollinated herbaceous perennial endemic to several high-elevation sites in the Blue Ridge Mountains of North Carolina. Allozymes were used to describe the genetic diversity and population structure in nine populations of this rare, federally listed species. Differences in leaf morphology were also examined for greenhouse-grown plants representing several populations. The proportion of the total genetic diversity found among populations, as indicated by the allozyme data, was 16%. Higher levels of population differentiation were found for differences in leaf shape; population of origin accounted for 37% of the variation in maximum leaf width, while families within populations accounted for 7%. In contrast to many endemic species, L. helleri maintains fairly high levels of genetic diversity. For the species, the percent polymorphic loci was 87.5, the average number of alleles at variable loci was 3.00 and the gene diversity was 0.276. Mean population values were percent polymorphic loci =58.4, mean number of alleles per polymorphic locus =2.59 and gene diversity =0.219. The estimated gene flow was low (Nm=0.85–1.32) and a relatively high correlation (r=0.55; p<0.005) was found between linear geographic and genetic distance. This suggests that the populations are partially isolated by distance, despite the limited range (<60 km) of the species. We recommend that population distinetiveness be maintained in restoration efforts.     

Genetic structure of wild populations of the endangered Desert Pupfish complex (Cyprinodontidae: Cyprinodon)

Data from 10 microsatellite DNA loci were used to describe the genetic structure of the two extant species (Cyprinodon macularius and C. eremus) of the endangered Desert Pupfish complex of southwestern United States and northwestern Mexico. Variation at microsatellite loci was significantly correlated (Mantel test) with that of previous mtDNA results, both for the complex and for the relatively wide-ranging C. macularius alone. Both species showed unusually high levels of microsatellite diversity for non-marine fish (H _e = 0.84–0.93; A_R = 11.9–17.0). There was evidence (R _ST > F _ST) that the two extant populations of C. eremus have been isolated sufficiently long for mutation to contribute significantly to genetic divergence, whereas divergence among the nine assayed populations of C. macularius could be attributed to genetic drift alone. Correspondingly, 10% of the diversity in C. eremus was attributable to differences between the two populations, whereas, for C. macularius, only 2.7% was attributable to among-population variation. Within C. macularius, a small (0.8%), but statistically significant, portion was attributable to differences between populations in the Salton Sea area and those on the lower Colorado River delta. The two populations of C. eremus and five groups of populations of C. macularius are recommended as management units for conservation genetics management of the two species.     

Growth and mineral nutrition of six rapid-cycling Brassica species in response to seawater salinity

The growth of six rapid-cycling lines of Brassica species, B. napus, B. campestris, B. nigra, B. juncea, B. oleracea and B. carinata was inhibited by seawater salinity. Based on the change in dry matter reduction relative to the control at varying concentrations of salts (4, 8 and 12 dS m^-1), the relative salt tolerance of these species was evaluated. B. napus and B. carinata were the most tolerant and most sensitive species, respectively, while the other four species were moderately tolerant. The influence of seawater on the concentrations of 12 elements including macronutrients and micronutrients in the shoots of these Brassica plants was characterized to determine the relationship between nutritional disturbance and relative salt tolerance. It was found that seawater salinity had a significant effect on the concentrations of Ca, Mg, K, Cl, Na and total N in the shoots of these plants but only the change in Ca concentration was significantly related to the relative salt tolerance of these six rapid-cycling Brassica species according to a rank analysis of the data. This finding indicates that Ca may play a regulatory role in the responses of Brassica species to saline conditions.     

Ecological studies on sporobolus virginicus (L.) kunth with particular reference to salinity and inundation

Sporobolus virginicus is shown to occupy low-lying areas on the shores of Lake St. Lucia, where it is subjected to periodic inundation and widely varying salinities. Whilst seeds are not permanently affected by storage under waterlogged saline conditions, young plants are markedly influenced by both inundation and salinity. Older plants are more tolerant of these conditions.     

Relationship between morphological and physiological responses to waterlogging and salinity in Sporobolus virginicus (L.) Kunth

The effects of waterlogging and salinity on morphological and physiological responses in the marsh grass Sporobolus virginicus (L.) Kunth were investigated in a 4×2 factorial experiment. Plants were subjected to four salinity levels (0, 100, 200 and 400 mol m^–3 NaCl) and two soil inundation conditions (drained and flooded) for 42 days. Flooding at 0 mol m^–3 NaCl caused initiation of adventitious surface roots, increased internal acration and plant height, induced alcohol dehydrogenase activity (ADH), and decreased belowground biomass and the number of culms per plant. Salinity increase from 0 to 400 mol m^–3 NaCl under drained conditions increased leaf and root proline concentrations and decreased photosynthesis, aboveground biomass, number of culms per plant and number of internodes per culm. Concurrent waterlogging and salinity induced ADH activity and adventitious surface roots but decreased plant height and aboveground biomass. Internal air space increased with waterlogging from 0 to 100 mol m^–3 NaCl but further increases in salinity to 400 mol m^–3 reduced air space. Combined waterlogging and salinity stresses, however, had no effect on photosynthesis or on the concentrations of proline in leaves or roots. These results are discussed in relation to the widespread colonization by S. virginicus of a wide range of coastal environments varying in soil salinity and in the frequency and intensity of waterlogging.     

Differential effects of salinity on leaf elongation kinetics of three grass species

This study focuses on the inhibitory effect of salinity on the leaf extension of three different grass species: Hordeum jubatum L., Hordeum vulgare L. and Zea mays L. Leaf elongation rates (LER) were measured on the third leaf of the plants. NaCl was added to the hydroponic solution (0, 40, 80 and 120 mM) and changes in LER were measured over time with a displacement transducer. Salinity inhibited LER immediately in all three species, and a new, but lower steady-state LER was reached within 5 h. The decrease in LER was proportional to the salinity level. Differences in salt tolerance (% of control LER) were evident between genotypes within 5 h after salinization, but the relative salt tolerance of the plant at this stage was not necessarily indicative of the long-term salt tolerance of the species. In general, H. jubatum was more tolerant than maize, which was more tolerant than barley to these short-term salinity stresses. In contrast, barley is more salt tolerant than maize over the long term. The mechanisms of inhibition of LER by salinity, as tested by the applied-tension technique, varied with the species examined, affecting either the apparent yield threshold, the hydraulic conductance of the whole plant or both. The cell wall extensibility was not significantly affected by salinity in the three species tested in this study.     

Accumulation of selenium by different plant species grown under increasing sodium and calcium chloride salinity

High levels of naturally occurring selenium (Se) are often found in conjunction with different forms of salinity in central California. Plants considered for use in phytoremediation of high Se levels must therefore be salt tolerant. Selenium accumulation was evaluated for the following species under increasing salt (NaCl and CaCl) conditions:Brassica napus L. (canola),Hibiscus cannibinus L. (kenaf),Festuca arundinacea L. (tall fescue), andLotus tenuis L. (birdsfoot trefoil). The experimental design was a complete randomized block with four salt treatments of <1, 5, 10, and 20 dS m^-1, four plant species, three blocks, and six replicates per treatment. Ninety days after growing in the respective salt treated soil with a Se concentration of 2 mg Se kg^-1 soil, added as Na₂SeO₄, all plant species were completely harvested. Among the species tested, shoot and root dry matter yield of kenaf was most significantly (p<0.001) affected by the highest salt treatment and tall fescue and canola were the least affected species. Generally there was a decrease in tissue accumulation of Se with increasing salt levels, except that low levels of salinity stimulated Se accumulation in canola. Canola leaf and root tissue accumulated the highest concentrations of Se (315 and 80 mg Se kg^-1 DM) and tall fescue the least (35 and 7 mg Se kg^-1 DM). Total soil Se concentrations all harvest were significantly (p<0.05) lower for all species at all salt treatments. Removal of Se from soil was greatest by canola followed by birdsfoot trefoil, kenaf and tall fescue. Among the four species, canola was the best candidate for removing Se under the tested salinity conditions. Kenaf may be effective because of its large biomass production, while tall fescue and birdsfoot trefoil may be effective because they can be repeatedly clipped as perennial crops.     

Responses of a novel salt-tolerant Streptomyces albidoflavus DUT_AHX capable of degrading nitrobenzene to salinity stress

A novel salt-tolerant strain DUT_AHX, which was capable of utilizing nitrobenzene (NB) as the sole carbon source, was isolated from NB-contaminated soil. Furthermore, it was identified as Streptomyces albidoflavus on the basis of physiological and biochemical tests and 16S ribosomal DNA (rDNA) sequence analysis. It can grow in the presence of NaCl up to 12% (w/v) or NB up to 900 mg/l in mineral salts basal (MSB) medium. The exogenously added osmoprotectants such as glycin, glutamic acid, proline, betaine and ectoine can improve growth of strain DUT_AHX in the presence of 10% (w/v) NaCl. NB-grown cells of strain DUT_AHX in modified MSB medium can degrade NB with the concomitant release of ammonia. Moreover, crude extracts of NB-grown strain DUT_AHX mainly contained 2-aminophenol 1,6-dioxygenase activity. These indicate that NB degradation by strain DUT_AHX might involve a partial reductive pathway. The proteins induced by salinity stress or NB were analyzed by native-gradient polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS)-PAGE. In NB-induced proteins de novo, 141 kDa protein on the native-gradient PAGE gel was excised and electroeluted. Furthermore, enzyme tests exhibit the 2-aminophenol 1,6-dioxygenase activity of purified 141 kDa protein is 11-fold that of the cell-free extracts. The exploitation of strain DUT_AHX in salinity stress will be a remarkable improvement in NB bioremediation and wastewater treatment in high salinity.     

Effect of salinity on tissue architecture in expanding wheat leaves

Salinity greatly reduces the leaf cross-sectional area of wheat (Triticum aestivum L.) during its development, which may lead to variation in the architectural properties of growing leaves that would result in a change in leaf physiological functions. Our objective was to characterize the effect of salinity on the spatial distribution of the cross-sectional area and the anatomy of large and small veins of a growing wheat leaf. Spring wheat was grown in a growth chamber in soils with or without 120 mM NaCl. Leaf 4 in both treatments was harvested 2–3 days after its emergence and then cut into five transverse segments. Examination of the transverse sections revealed that salinity significantly reduced the cross-sectional area, width, and radii of both epidermal and mesophyll cells along the leaf axis. Reduction in the cross-sectional area and width occurred mainly at the leaf base, indicating that these reductions occur during the period of leaf initiation. The reduction in cross-sectional area was attributed to a decrease in the size of the vein segments and a reduced number of medium and small veins. The thickness of the leaf was also reduced under the 120 mM NaCl treatment. A greater intercellular air space in the large vein segments under saline conditions was also found. The approximately 35% reduction observed in the number of veins under saline conditions (mainly in the number of small veins) may suggest that salinity reduces the capacity for re-translocation of mineral nutrients and assimilates. The reduced area of protoxylem and metaxylem in midrib and large vein segments in growing tissues may be responsible for lower water deposition into the growth zone under saline conditions.     

In vitro multiplication ofVella lucentina M. B. crespo (Brassicaceae), a threatened Spanish endemic species

Summary Vella lucentina M. B. Crespo is a threatened Spanish species that is endemic to a small area in eastern Alicante Province (SE Spain). Micropropagation techniques were applied forex situ conservation of this plant. Aseptic epicotyls bearing the apical bud were grown in Murashige and Skoog medium supplemented with 6-furfurylaminopurine (Kin), N⁶-benzyladenine (BA) or 6-(γ,γ,-dimethilalylamino) purine (2iP). High multiplication rates were obtained with 0.5, 1, or 2 mg·liter⁻¹ BA, or 1 or 2 mg·liter⁻¹ 2iP. Indole-3-acetic acid and indole-3-butyric acid were utilized for rooting in half-strength Murashige and Skoog medium. Regenerated plants were transferred to a potting mix and gradually acclimated to field conditions. No morphological differences were observed amongin vitro andin vivo plants.     

Nitrification and seasonal changes in bacterial populations in the rhizosphere ofSuaeda andArthrocnemum species growing in saline soils

Summary The nitrification rate in the rhizosphere of Suaeda and Arthrocnemum plants growing in saline soils, as affected by microbial populations, temperature, pH, and organic matter, was examined in the field throughout the year. The genera Nitrosomonas and Nitrobacter were most common in the rhizosphere soil. The bacterial counts in the rhizosphere of both plants fluctuated during the study period, reaching peak values during February–March and in August. The nitrate concentration in the rhizosphere soil could be related with the observed increase in the numbers of ammonium-oxidizers and nitrite-oxidizers in the latter part of the study period. The pH of the rhizosphere soils did not have any influence on the nitrification rate at the values measured. The rhizosphere organic content varied between 1.8 and 4% (w/w), showing the continuous availability of organic matter in the soil. The seasonal changes in bacterial populations in the rhizospheres of both plants was described as the result of the combination of several factors.     

Parasites promote host gene flow in a metapopulation

Local adaptation is a powerful mechanism to maintain genetic diversity in subdivided populations. It counteracts the homogenizing effect of gene flow because immigrants have an inferior fitness in the new habitat. This picture may be reversed in host populations where parasites influence the success of immigrating hosts. Here we report two experiments testing whether parasite abundance and genetic background influences the success of host migration among pools in a Daphnia magna metapopulation. In 22 natural populations of D. magna, immigrant hosts were found to be on average more successful when the resident populations experienced high prevalences of a local microsporidian parasite. We then determined whether this success is due to parasitism per se, or the genetic background of the parasites. In a common garden competition experiment, we found that parasites reduced the fitness of their local hosts relatively more than the fitness of allopatric host genotypes. Our experiments are consistent with theoretical predictions based on coevolutionary host-parasite models in metapopulations. A direct consequence of the observed mechanism is an elevated effective migration rate for the host in the metapopulation.     

Germination responses of Diplotaxis harra to temperature and salinity

Diplotaxis harra (Forssk.) Boiss, an annual herb in the family of Brassicaceae, is widely distributed in many sandy and gypseous areas in southern Tunisia. Laboratory experiments were carried out to assess the effects of temperature and salinity on seed germination and recovery responses after seed transfer to distilled water. The germination responses of the seeds in complete darkness were determined over a wide range of temperatures (5, 10, 15, 20, 25 and 30 °C) and salinities (0, 50, 100, 150 and 200 mM NaCl). Germination was inhibited by either an increase or decrease in temperature from the optimal temperature (15 °C). Highest germination percentages were obtained under non-saline conditions and an increase in NaCl concentrations progressively inhibited seed germination. Rate of germination decreased with an increase in salinity at all temperatures but comparatively higher rates were obtained at 15 °C. Salt stress decreased both the percentage and the rate of germination. An interaction between salinity and temperature yielded no germination at 200 mM NaCl. Seeds were transferred from salt solution to distilled water after 20 days, and those from low salinities recovered at all temperatures. At NaCl concentration of 200 mM, the recovery of germination was completely inhibited.     

Screening of rice (Oryza sativa L.) genotypes for physiological characters contributing to salinity resistance,and their relationship to overall performance

Summary Phenotypic resistance of salinity is expressed as the ability to survive and grow in a salinised medium. Some subjective measure of overall performance has normally been used in plant breeding programmes aimed at increasing salinity resistance, not only to evaluate progeny, but to select parents. Salinity resistance has, at least implicitly, been treated as a single trait. Physiological studies of rice suggest that a range of characteristics (such as low shoot sodium concentration, compartmentation of salt in older rather than younger leaves, tolerance to salt within leaves and plant vigour) would increase the ability of the plant to cope with salinity. We describe the screening of a large number of rice genotypes for overall performance (using an objective measure based on survival) and for the aforementioned physiological traits. There was wide variation in all the characters studied, but only vigour was strongly correlated with survival. Shoot sodium concentration, which a priori is expected to be important, accounted for only a small proportion of the variability in the survival of salinity. Tissue tolerance (the cellular component of resistance reflecting the ability to compartmentalise salt within leaves) revealed a fivefold range between genotypes in the tolerance of their leaves to salt, but this was not correlated positively with survival. On the basis of such (lack of) correlation, these traits would be rejected in normal plant breeding practice, but we discuss the fallacies involved in attempting correlation between individual traits and the overall performance of a salt-sensitive species in saline conditions. We conclude that whilst overall performance (survival) can be used to evaluate the salt resistance of a genotype, it is not the basis on which parents should be selected to construct a complex character through breeding. It was the norm for varieties which had one good characteristic affecting salt resistance to be unexceptional or poor in the others. This constitutes experimental evidence that the potential for salt resistance present in the rice genome has not been realised in genotypes currently extant. The results are discussed in relation to the use of physiological traits in plant breeding, with particular reference to environmental stresses that do not affect a significant part of a species' ecological range.     

Effects of salinity on competitive interactions between two Juncus species

A glasshouse study investigated the effect of salinity on growth and competitive interactions between two closely related rush species, an Australian native (Juncus kraussii) and an exotic (J. acutus) species. Overall, both species exhibited decreases in height and total biomass with increasing salinity, although tolerance of J. acutus was marginally lower. We observed asymmetric responses at each salinity, due to the presence of the other species. In fresh-water, co-presence of J. kraussii facilitated the growth (increases in height and total biomass) of J. acutus. However, at 10 ppt salinity direct interspecific competition with J. kraussii adversely affected total biomass of J. acutus. When grown with J. acutus, at 5 ppt but not at 10 ppt, salinity reduced total biomass of J. kraussii. We suggest that interspecific interactions vary with salinity, dependant on relative salinity tolerance of each species. It would appear that in areas receiving regular fresh-water inputs, which reduce salinity stress, J. acutus has the potential to displace J. kraussii.