Adaptations for the maintenance of water balance by three species of Antarctic mites

Three species of Antarctic mites, Alaskozetes antarcticus, Hydrogamasellus antarcticus and Rhagidia gerlachei, are abundant in the vicinity of Palmer Station, Antarctica. No single mechanism for reducing water stress was shared by all three species. A. antarcticus and R. gerlachei (both ca. 200 μg) are over twice as large as H. antarcticus (ca. 90 μg), but all had similar body water content (67%) and tolerated a loss of up to 35% of their body water before succumbing to dehydration. All imbibed free water and had the capacity to reduce water loss behaviorally by forming clusters. Alaskozetes antarcticus was distinct in that it relied heavily on water conservation (xerophilic classification) that was largely achieved by its thick cuticular armor, a feature shared by all members of this suborder (Oribatida), and abundant cuticular hydrocarbons. In comparison to the other two species, A. antarcticus was coated with 2–3× the amount of cuticular hydrocarbons, had a 20-fold reduction in net transpiration rate, and had a critical transition temperature (CTT) that indicates a pronounced suppression in activation energy (E _a) at temperatures below 25°C. In contrast, H. antarcticus and R. gerlachei lack a CTT, have lower amounts of cuticular hydrocarbons and have low E _as and high net transpiration rates, classifying them as hydrophilic. Only H. antarcticus was capable of utilizing water vapor to replenish its water stores, but it could do so only at relative humidities close to saturation (95–98 %RH). Thus, H. antarcticus and R. gerlachei require wet habitats and low temperature to counter water loss, and replace lost water behaviorally through predation. Compared to mites from the temperate zone, all three Antarctic species had a lower water content, a feature that commonly enhances cold tolerance.     

Organic matter and soil biota of upland wetlands in Taylor Valley,Antarctica

In January 2001, we surveyed streams and ponds above 300 m a.s.l. in Taylor Valley, South Victoria Land, Antarctica. One pond was examined in detail. Organic materials covered nearly 100% of the adjacent soil to 5–20 m from the shore, with intermittent patches to 80 m. Organic matter averaged 257 g C/m², and totaled 1,388 kg organic C on the soil around the pond. Soil-moisture content (0.56–12.41%) decreased with distance from shore, whereas pH (7.8–10.8) increased with distance. Electrical conductivity was lowest in the soils <10 m from the pond (416±94 µS/cm). Mineral soil organic C and total N concentrations were greatest between 10 and 30 m from the edge of the pond (1.21±0.37 and 0.13±0.05 mg/g soil, respectively). Soil invertebrates were present in only 50% of samples and included tardigrades, rotifers, and two nematodes, Scottnema lindsayae and Plectus antarcticus. A non-parametric, discriminant function analysis based on soil moisture, soil organic carbon, and electrical conductivity correctly predicted 87.0% of sites that had invertebrates and 70.8% of sites for which invertebrates were absent. Tardigrades, rotifers, and P. antarcticus were found only in the wettest soils nearest the pond whereas S. lindsayae was restricted to drier soils further from shore. Other ponds and streams also showed substantial accumulations of organic matter, suggesting that upland wetlands serve as resource islands in these polar deserts that provide a source of organic matter to nearby soils.     

Nitrogen mineralization rates in salinevs. salt-amended soils

Studies were conducted to compare N mineralization rates in salt-amended nonsaline soils to naturally-occurring saline soils. NaCl, CaCl₂, and Na₂SO₄ were added to nonsaline soils at rates that produced electrical conductivities of the saturation extracts (EC_e) of 5, 10, 15, and 20 dS m⁻¹. Saline soils with similar properties were leached to the same EC_c levels. N mineralization in the Chino soil was inhibited by salt addition, particularly with sodium and calcium chlorides. In the Domino soil there was some inhibition of N mineralization with the chloride salts, but enhancement with Na₂SO₄ was observed. Nitrification in both soils was more sensitive to salt addition than ammonification. N mineralization occurred more slowly in both leached saline soils compared to the salt-amended soils. Leached saline soils often accumulated greater amounts of inorganic N compared to their native saline counterparts, particularly with the 5 dS m⁻¹ Chino soil (native, 44 dS m⁻¹) and with the 5, 10, 15 and 20 dS m⁻¹ Domino soils (native, 32 dS m⁻¹). Kinetic parameters were estimated by the linear least squares (LLS) and the nonlinear least squares (NLLS) methods. Generally, the LLS transformation estimated greater values of potentially mineralizable N (N_o) and lower rate constants (k). With the NLLS equation, N_o values for the leached saline soils were usually lower, and k values usually higher than in the salt-amended soils. The nonsaline controls generally had the highest N_o and lowest k estimates. Average LLS rate constants for the salt-amended and leached saline soils were 0.055 and 0.083 for the Chino, and 0.104 and 0.137 week⁻¹, respectively, for the Domino soils. With the NLLS equation, average k values for the salt-amended and leached saline soils were 0.087 and 0.089 for the Chino, and 0.181 and 0.387 week⁻¹, respectively, for the Domino soils. These results suggest that N mineralization rates obtained in salt-amended nonsaline soils may not be representative of those in naturally-occurring saline soils.     

Extraction of nematodes from Dry Valley Antarctic soils

Nematode density and taxonomic composition from Dry Valley soil processed by the sugar centrifugation (SC) method in Antarctica was compared to those extracted from soils shipped frozen to the USA and processed by either the SC or Baermann Funnel (BF) (at 5°C and 10°C) techniques. Soil selected for the extraction comparisons represented a wide range of soil properties found in the Dry Valleys. More nematodes were recovered from freshly collected Antarctic soil and from stored frozen soil using the SC technique than from BF at either temperature (P<0.05). Temperature had no effect on nematode densities extracted by the BF. Scottnema lindsayae was the most abundant species recovered by all extraction methods, but recovery was significantly lower from stored soils. Thus, nematodes can be extracted qualitatively following frozen storage using SC, but quantitative studies of nematode populations should be based on soils extracted following field sampling.     

Depth distribution of euryhaline halophilic bacteria in Suribati Ike, a meromictic lake in East Antarctica

Euryhaline halophiles grow over a wide range of salinity, from <3% NaCl (seawater equivalent) to >15% NaCl and even saturation level (about 30% NaCl). Several species of euryhaline halophiles occur worldwide, especially in marine environments and also in aquatic and terrestrial habitats of the Antarctic ice-free areas. A biogeographic view of Antarctic halophiles is that their migration among lakes on land is more difficult than in marine setting. Ponds and lakes on land may thus serve as “islands” which facilitate the selection and separation of unique species. We isolated euryhaline halophiles from the saline lake, Suribati Ike, near Syowa Station and placed them into seven groups, each demonstrating a clear depth-related distribution. Six of the seven groups probably represent new species of the genera Halomonas and Marinobacter. This result suggests that Antarctic saline lakes exhibit high selectivity of unique euryhaline halophiles and possibly of other microbial groups.     

Puccinellia festucaeformis (Host) Parl.: Germinazione e crescita iniziale in funzione della salinità del substrato

Abstract

Puccinellia festucaeformis (Host) Parl.: germination and early growth on different salt substrates. Germination behaviour of Puccinellia festucaeformis seeds and early growth of seedlings at different experimental conditions was analysed. The following growth substrates were utilized: NaCl, KCl, KNO₃, MgCl₂, MgSO₄, Na₂SO₄, NaNO₃, CaCl₂ at the decreasing concentrations of 0.50, 0.25, 0.12, 0.06M. Caryopses were allowed to imbibe and grow at alternating temperatures (10°-20°C or 20°-30°C) in the dark for 3 days. Seedling were grown for 15 days, at controlled light and temperature conditions, in the same nutrient substrates as those used for the germination experiments.

The germination experiments showed a high tolerance to salts up to 0.25M solution and for the whole range of MgSO₄ concentrations. High growth temperatures increased the depressive effects of salt concentrations. Seedling growth was highly reduced when salt concentration was higher than 0.12M. High salt tolerance - maximum shoot and root growth - was showed by seedling allowed to grow on 0.50M MgSO₄.

Germination and growth condition of Puccinellia festucaeformis is discussed in relation to the ecological features of this species and to its possible importance as bioindicator of MgSO₄ rich natural substrates.     

Physiological and antioxidant responses of <Emphasis Type="Italic">Mentha pulegium</Emphasis> (Pennyroyal) to salt stress

Mentha pulegium L. is a medicinal and aromatic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pronounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K⁺ uptake, as well as an increase in Na⁺ levels in all organs. Considering the response of antioxidant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equivalent g⁻¹ dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH· scavenging ability with the lowest IC₅₀ value (0.27 μg ml⁻¹) in comparison with control which exhibited IC₅₀ equal to 0.79 μg ml⁻¹.     

Optimization of fermentation conditions for production of anti-TMV extracellular ribonuclease by Bacillus cereus using response surface methodology

Bacillus cereus ZH14 was previously found to produce a new type of antiviral ribonuclease, which was secreted into medium and active against tobacco mosaic virus. In order to enhance the ribonuclease production, in this study the optimization of culture conditions using response surface methodology was done. The fermentation variables including culture temperature, initial pH, inoculum size, sucrose, yeast extract, MgSO₄·7H₂O, and KNO₃ were considered for selection of significant ones by using the Plackett–Burman design, and four significant variables (sucrose, yeast extract, MgSO₄·7H₂O, and KNO₃) were further optimized by a 2⁴ factorial central composite design. The optimal combination of the medium constituents for maximum ribonuclease production was determined as 8.50 g/l sucrose, 9.30 g/l yeast extract, 2.00 g/l MgSO₄·7H₂O, and 0.62 g/l KNO₃. The enzyme activity was increased by 60%. This study will be helpful to the future commercial development of the new bacteria-based antiviral ribonuclease fermentation process.     

Abiotic immobilization of nitrate in two soils of relic <Emphasis Type="Italic">Abies pinsapo</Emphasis>-fir forests under Mediterranean climate

Evidence for abiotic immobilization of nitrogen (N) in soil is accumulating, but remains controversial. Identifying the fate of N from atmospheric deposition is important for understanding the N cycle of forest ecosystems. We studied soils of two Abies pinsapo fir forests under Mediterranean climate seasonality in southern Spain—one with low N availability and the other with symptoms of N saturation. We hypothesized that biotic and abiotic immobilization of nitrate (NO₃ ⁻) would be lower in soils under these forests compared to more mesic temperate forests, and that the N saturated stand would have the lowest rates of NO₃ ⁻ immobilization. Live and autoclaved soils were incubated with added ¹⁵NO₃ ⁻ (10 μg N g⁻¹ dry soil; 99% enriched) for 24 h, and the label was recovered as total dissolved-N, NO₃ ⁻, ammonium (NH₄ ⁺), or dissolved organic-N (DON). To evaluate concerns about possible iron interference in analysis of NO₃ ⁻ concentrations, both flow injection analysis (FIA) and ion chromatography (IC) were applied to water extracts, soluble iron was measured in both water and salt extracts, and standard additions of NO₃ ⁻ to salt extracts were analyzed. Good agreement between FIA and IC analysis, low concentrations of soluble Fe, and 100% (±3%) recovery of NO₃ ⁻ standard additions all pointed to absence of an interference problem for NO₃ ⁻ quantification. On average, 85% of the added ¹⁵NO₃ ⁻ label was recovered as ¹⁵NO₃ ⁻, which supports our hypothesis that rates of immobilization were generally low in these soils. A small amount (mean = 0.06 μg N g⁻¹ dry soil) was recovered as ¹⁵NH₄ ⁺ in live soils and none in sterilized soils. Mean recovery as DO¹⁵N ranged from 0.6 to 1.5 μg N g⁻¹ dry soil, with no statistically significant effect of sterilization or soil type, indicating that this was an abiotic process that occurred at similar rates in both soils. These results demonstrate a detectable, but modest rate of abiotic immobilization of NO₃ ⁻ to DON, supporting our first hypothesis. These mineral soils may not have adequate carbon availability to support the regeneration of reducing microsites needed for high rates of NO₃ ⁻ reduction. Our second hypothesis regarding lower expected abiotic immobilization in soils from the N-saturated site was not supported. The rates of N deposition in this region may not be high enough to have swamped the capacity for soil NO₃ ⁻ immobilization, even in the stand showing some symptoms of N saturation. A growing body of evidence suggests that soil abiotic NO₃ ⁻ immobilization is common, but that rates are influenced by a combination of factors, including the presence of plentiful available carbon, reduced minerals in anaerobic microsites and adequate NO₃ ⁻ supply.     

The southernmost worm, <Emphasis Type="Italic">Scottnema lindsayae</Emphasis> (Nematoda): diversity,dispersal and ecological stability

The nematode worm Scottnema lindsayae (Cephalobidae) was found near the base of the Beardmore Glacier in the Transantarctic Mountains 83.48°S, over 5° further south than previously recorded. Identification was confirmed using morphological analyses of males, females and juvenile stages, and by DNA sequencing of the ITS1 region of the ribosomal RNA tandem repeat unit. These data revealed no discernable morphological or ITS rDNA sequence variation between the extreme southern population of S. lindsayae and disparate populations from the McMurdo Dry Valleys in south Victoria Land (77–78°S). Based on these results, we suggest that broadcast dispersal, with accompanying high rates of gene flow, establish the extreme southern distribution of the phylum Nematoda. High abundance, low rates of diversification and lack of an apparent biogeographic structure across latitudinal and environmental gradients implies that their presence in simple Antarctic soil ecosystems is stable, so long as physical and biological controls on their distributions remain within viable parameters. Recent evidence that S. lindsayae populations are in decline suggests that their high dispersal rates are insufficient to buffer current, unfavorable environmental changes and may foreshadow longer-term ecosystem disruption.     

Alleviation of Salt Stress in Common Bean (Phaseolus vulgaris) by Exogenous Abscisic Acid Supply

In this work the effect of abscisic acid (ABA) and 100 mM NaCl on common bean (Phaseolus vulgaris var. Coco) growth, nitrogenase activity, and nodule metabolism was studied. Experiments were carried out in a controlled environmental chamber and plants, at the vegetative growth stage (16 days old), were treated with ABA (1 μM and 10 μM) and 48 h later were exposed to saline treatment. Results revealed that plant dry weight, nodule dry weight, nitrogen fixation (acetylene reduction activity and ureides content), and most enzymes of ammonium and ureides metabolism were affected by both ABA and NaCl. The addition of 1 μM ABA to the nutrient solution before the exposure to salt stress reduced the negative effect of NaCl. Based on our results, we suggest that ABA application improves the response of Phaseolus vulgaris symbiosis under saline stress conditions, including the nitrogen fixation process and enzymes of ammonium assimilation and purine catabolism.     

Effects of various mixed salt-alkaline stresses on growth,photosynthesis, and photosynthetic pigment concentrations of <Emphasis Type="Italic">Medicago ruthenica</Emphasis> seedlings

Soil salinization and alkalinization frequently co-occur in naturally saline and alkaline soils. To understand the characteristics of mixed salt-alkali stress and adaptive response of Medicago ruthenica seedlings to salt-alkali stress, water content of shoots, growth and photosynthetic characteristics of seedlings under 30 salt-alkaline combinations (salinity 24–120 mM and pH 7.03–10.32) with mixed salts (NaCl, Na₂SO₄, NaHCO₃, and Na₂CO₃) were examined. The indices were significantly affected by both salinity and pH. The interactive effects between salt and alkali stresses were significant, except for photosynthetic pigments. Water content of shoots, relative growth rates of shoots and roots and pigment concentrations showed decreasing trends with increasing salinity and alkalinity. The root activity under high alkalinity and salinity treatments gradually decreased, but was stimulated by the combined effects of low alkalinity and salinity. The survival rate decreased with increased salinity, except at pH 7.03–7.26 when all plants survived. Net photosynthetic rate, stomatal conductance and intercellular CO₂ concentration decreased with increased salinity and pH. M. ruthenica tolerated the stress of high salt concentration when alkali concentration was low, and the synergistic effects of high alkali and high salt concentrations lead to the death of some or all seedlings. M. ruthenica appeared to be saltalkali tolerant. Reducing the salt concentration or pH based on the salt components in the soil may be helpful to abate damage from mixed salt-alkaline stress.     

Influence of growth regulators and elicitors on cell growth and α-tocopherol and pigment productions in cell cultures of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis> L.

The present study examined the effects of plant growth hormones, incubation period, biotic (Trametes versicolor, Mucor sp., Penicillium notatum, Rhizopus stolonifer, and Fusarium oxysporum) and abiotic (NaCl, MgSO₄, FeSO₄, ZnSO₄, and FeCl₃) elicitors on cell growth and α-tocopherol and pigment (red and yellow) productions in Carthamus tinctorius cell cultures. The cell growth and α-tocopherol and pigment contents improved significantly on Murashige and Skoog (MS) liquid medium containing 50.0 μM α-naphthalene acetic acid (NAA) and 2.5 μM 6-Benzyladenine (BA) at 28 days of incubation period. Incorporation of T. versicolor (50 mg l⁻¹) significantly enhanced the production of α-tocopherol (12.7-fold) and red pigment (4.24-fold). Similarly, supplementation of 30 mg l⁻¹ T. versicolor (7.54-fold) and 70 mg l⁻¹ Mucor sp. (7.40-fold) significantly increased the production of yellow pigment. Among abiotic elicitors, NaCl (50–70 mg l⁻¹) and MgSO₄ (10–30 mg l⁻¹) significantly improved production of α-tocopherol (1.24-fold) and red pigment (20-fold), whereas yellow pigment content increased considerably by all the abiotic elicitor treatments. Taken together, the present study reports improved productions of α-tocopherol and the pigment as a stress response of safflower cell cultures exposed to these elicitors.     

Nematodes from saline and freshwater lakes of the Vestfold Hills,East Antarctica,including the description of <Emphasis Type="Italic">Hypodontolaimus antarcticus</Emphasis> sp. n.

The invertebrate fauna of many Antarctic ice-free areas, even those close to permanent research stations, can be poorly known. Here we describe some nematodes from freshwater and saline, marine-derived lakes of the Vestfold Hills, East Antarctica. The freshwater lakes contained the widespread East Antarctic endemic species, Plectus frigophilus Kirjanova, 1958. The saline lakes were inhabited by two recently described species, Halomonhystera halophila Andrássy, 2006 and Halomonhystera continentalis Andrássy, 2006, and by a new species described in this report, Hypodontolaimus antarcticus sp. n. Originally marine but now brackish Highway Lake contained a nematode fauna with both freshwater and marine-derived components. The nematode fauna of Antarctica now consists of 54 named species, 22 of which are found in East Antarctica.     

Unique Similarity of Faunal Communities across Aquatic–Terrestrial Interfaces in a Polar Desert Ecosystem

Abstract Critical transition zones, such as aquatic–terrestrial interfaces, have been recognized as important features in landscape ecology. Yet changes in the community structure of soil and sediment biota across aquatic–terrestrial boundaries remain relatively unstudied. We investigated the community structure of the dominant fauna, namely nematodes, rotifers and tardigrades, across lake sediment–soil transects in three basins in a species-poor, polar desert ecosystem (McMurdo Dry Valleys, Antarctica). We also examined substrate (that is, soil and sediment) properties, including moisture, salinity, carbon, nitrogen and phosphate concentration, across these transects. Differences in faunal community structure and biochemical properties were typically explained by hydrologic basin and the sediment–soil gradient, but not by transects within each basin. Bonney Basin contained the least organic carbon, chlorophyll a, nematodes and taxa, whereas there was little difference in many of these measures between Fryxell and Hoare Basins. Nematode (Scottnema lindsayae and Plectus sp.) and rotifer abundance varied along sediment–soil transects. Scottnema lindsayae, the most abundant and widely distributed soil animal in this ecosystem, increased in abundance from sediments to soils, whereas Plectus sp. and rotifer abundance, and taxa richness (that is, nematodes, rotifers and/or tardigrades), decreased; Eudorylaimus sp. and tardigrade abundance did not differ significantly along the transects. Previous studies of soil biodiversity and faunal abundance in this ecosystem have revealed a positive association between these measures and biogeochemistry, if this holds true for lake sediments, our findings suggest sediments in Lake Bonney experience lower rates of nutrient cycling than either Lakes Fryxell or Hoare. Despite differences in faunal abundances along the sediment–soil transects, taxa occurrence was surprisingly similar in soil and sediment, only S. lindsayae was restricted to soil or the lake shore. In contrast, in other ecosystems, soil community composition differs greatly from lake sediments, suggesting that the observed similarity in species occurrence in both soils and sediments may be unique to Antarctica. This finding might result from the extreme low diversity of this ecosystem, presumably limiting competition among fauna, and thus promoting broad ecological niches. Alternatively, environmental conditions in Antarctica may select for species with broad ecological niches.     

The impact of salinity exposure on survival and temperature tolerance of the Antarctic collembolan Cryptopygus antarcticus

The collembolan Cryptopygus antarcticus Willem is potentially exposed to habitat salinities equal to (or greater than) sea water, as a result of sea spray, drying of littoral habitats, dispersal or temporary entrapment on the surface of sea water, or exposure to localized salt deposits from dense vertebrate populations on terrestrial habitats. To test the impact of this exposure on C. antarcticus, the tolerance of the collembolan to being placed on the surface of sea water and solutions of higher salt concentrations is investigated. The effects of acclimation to exposure to liquids of different salinities [44, 100 and 200 parts per thousand (ppt) sea salt] on cold and heat tolerance, as well as thermal activity thresholds, are also explored. Cryptopygus antarcticus shows > 75% survival after 10 days of exposure to both sea water and 100‐ppt salt, whereas it exhibits significantly lower survival after 5 days (60% survival) and 10 days (40%) of exposure to a 200‐ppt solution. Body water content also decreases after exposure to all salinities, and particularly to the 200‐ppt solution, in which > 50% of body water is lost after 10 days. Acclimation results in greater cold tolerance, although heat tolerance at 33, 35 and 37 °C is either unaltered or reduced. The thermal activity thresholds of C. antarcticus at both high and low temperatures are also negatively affected by saline exposure. The data demonstrate the capacity of C. antarcticus to tolerate periods of exposure to saline conditions, and also show that this exposure can enhance cross‐tolerance to low temperatures. The present study also demonstrates that salinity‐associated stress at moderately low and high temperatures narrows the thermal range of activity, thus reducing the ability of collembolans to forage, develop and reproduce. © 2013 The Royal Entomological Society     

Efficient production of protocorm-like bodies and plant regeneration from flower stalk explants of the sympodial orchid <Emphasis Type="Italic">Epidendrum radicans</Emphasis>

Summary A simple and efficient micropropagation method was established for direct protocorm-like body (PLB) formation and plant regeneration from flower stalk internodes of a sympodial orchid, Epidendrum radicans. Small transparent tissues formed on surfaces and cut ends of flower stalk internodes on a modified half-strength Murashige and Skoog basal medium with or without thidiazuron (TDZ) after 1–2 wk of culture. In the light, the transparent tissues enlarged and turned into organized calluses on most of the explants. However, PLBs formed only on a medium supplemened with 0.45 μM TDZ within 2 mo. of culture. Sucrose, NH₄NO₃, and KNO₃ were used in media to test their effects on PLB proliferation and shooting. The best response on number of PLBs per tube was 23.6 at 40 gl⁻¹ sucrose, 825 mgl⁻¹ NH₄NO₃, and 950 mgl⁻¹ KNO₃, and the highest number of PLBs with shoots was found at 10 gl⁻¹ sucrose, 825 mgl⁻¹ NH₄NO₃, and 950 mgl⁻¹ KNO₃. Homogenized PLB tissues produced by blending were used to test the effects of four cytokinins [TDZ, N⁶-benzyladenine (BA), zeatin-riboside, and kinetin] on PLB proliferation and shoot formation. The best responses on number of PLBs per tube, proliferation rate, and number of PLBs with shoots per tube were obtained at 4.44 μM BA, 0.28 μM zeatin-riboside, and 1.39 μM kinetin, respectively. Normal plantlets converted from PLBs on the same TDZ-containing medium after 1 mo. of culture. The optimized procedure required about 12–13 wk from the initiation of PLBs to plantlet formation. The regenerated plants grew well with an almost 100% survival rate when acclimatized in a greenhouse.     

Effects of various salts on the germination of three perennial salt marsh species

We studied the germination responses of Arthrocnemum macrostachyum, Juncus acutus and Schoenus nigricans to saline stress caused by different salt types. The germination percentage and mean time to germination data were obtained by incubating seeds for 30 d in 1, 2, 3, 4 or 5% saline solutions of NaCl, MgCl₂, MgSO₄ and Na₂SO₄ at 30/20 °C and with a 12 h photoperiod. A. macrostachyum was the most tolerant species to salinity during the germination (65% in 2% NaCl). S. nigricans showed the lowest germination (none germinated in salt and only 26% in distilled water). J. acutus showed intermediate behaviour between the two above species, its germination being inhibited by high salt concentrations. The sulphates had less inhibitory effect than the equivalent chloride concentrations.     

Wind dispersal of soil invertebrates in the McMurdo Dry Valleys, Antarctica

Dispersal of soil organisms is crucial for their spatial distribution and adaptation to the prevailing conditions of the Antarctic Dry Valleys. This study investigated the possibility of wind dispersal of soil invertebrates within the dry valleys. Soil invertebrates were evaluated in (1) pockets of transported sediments to lake ice and glacier surfaces, (2) wind-transported dust particles in collection pans (Bundt pans) 100 cm above the soil surface, and (3) sediments transported closer to the surface (<50 cm) and collected in open top chambers (OTCs). Invertebrates were extracted and identified. Nematodes were identified to species and classified according to life stage and sex. Three species of nematodes were recovered and Scottnema lindsayae was the most dominant. There were more juveniles (∼71%) in the transported sediments than adults (29%). Tardigrades and rotifers were more abundant in sediments on lake and glacier surfaces while nematodes were more abundant in the dry sediment collections of Bundt pans and OTCs. The abundance of immobile (dead) nematodes in the Bundt pans and OTCs was three times greater than active (live) nematodes. Anhydrobiosis constitutes a survival mechanism that allows wind dispersal of nematodes in the McMurdo Dry Valleys. Our results show that soil invertebrates are dispersed by wind in the Dry Valleys and are viable in ice communities on lake surfaces and glaciers.