Proline as a biochemical marker in relation to the ecology of two halophytic Juncus species

Aims Osmolytes, used for maintaining osmotic balance and as 'osmoprotectants', are synthesized in plants as a general, conserved response to abiotic stress, although their contribution to stress-tolerance mechanisms remains unclear. Proline, the most common osmolyte, accumulates in many plant species in parallel with increased external salinity and is considered a reliable biochemical marker of salt stress. We have measured proline levels in two halophytic, closely related Juncus species under laboratory and field conditions to assess the possible relevance of proline biosynthesis for salt tolerance and therefore for the ecology of these two taxa.Methods Proline was quantified in plants treated with increasing NaCl concentrations and in plants sampled in two salt marshes located in the provinces of Valencia and Alicante, respectively, in southeast Spain. Electrical conductivity, pH, Na + and Cl ? concentrations were measured in soil samples collected in parallel with the plant material.Important findings Treatment with NaCl inhibited growth of J. acutus plants in a concentration-dependent manner, but only under high salt conditions for J. maritimus. Salt treatments led to proline accumulation in both species, especially in the more salt-tolerant J. maritimus. The results, obtained under laboratory conditions, were confirmed in plants sampled in the field. In all the samplings, proline contents were significantly lower in J. acutus than in the more tolerant J. maritimus growing in the same area. No direct correlation between soil salinity and proline levels could be established, but seasonal variations were detected, with increased proline contents under accentuated water deficit conditions. Our results suggest that proline biosynthesis is not only an induced, general response to salt stress but also an important contributing factor in the physiological mechanisms of salt tolerance in Juncus, and that it therefore correlates with the ecology of both species.     

Vesicular arbuscular mycorrhiza (VAM) in pioneer salt marsh plants of the Ganges river delta in West Bengal (India)

VA mycorrhizal colonization of four species of pioneer salt marsh plants including two species of chenopodiaceae at the terminal Gangetic delta in India, is reported. Five common species of VAM fungi were recorded from rhizosphere soils of the plant species. Population of spores of VAM fungi and effective inoculum potential of these fungi in rhizosphere soils as determined by the MPN-method were rather low.     

Growth responses and ion accumulation in the halophytic legume Prosopis strombulifera are determined by Na2SO4 and NaCl

Halophytes are potential gene sources for genetic manipulation of economically important crop species. This study addresses the physiological responses of a widespread halophyte, Prosopis strombulifera (Lam.) Benth to salinity. We hypothesised that increasing concentrations of the two major salts present in soils of central Argentina (Na₂SO₄, NaCl, or their iso‐osmotic mixture) would produce distinct physiological responses. We used hydroponically grown P. strombulifera to test this hypothesis, analysing growth parameters, water relations, photosynthetic pigments, cations and anions. These plants showed a halophytic response to NaCl, but strong general inhibition of growth in response to iso‐osmotic solutions containing Na₂SO₄. The explanation for the adaptive success of P. strombulifera in high NaCl conditions seems to be related to a delicate balance between Na ⁺ accumulation (and its use for osmotic adjustment) and efficient compartmentalisation in vacuoles, the ability of the whole plant to ensure sufficient K⁺ supply by maintaining high K ⁺ /Na ⁺ discrimination, and maintenance of normal Ca^{2 +} levels in leaves. The three salt treatments had different effects on the accumulation of ions. Findings in bi‐saline‐treated plants were of particular interest, where most of the physiological parameters studied showed partial alleviation of SO₄^2?‐induced toxicity by Cl^?. Thus, discussions on physiological responses to salinity could be further expanded in a way that more closely mimics natural salt environments.     

Tidal asymmetry in creeks surrounded by saltflats and mangroves with small swamp slopes

Most mangrove swamp/salt flat systems have tidal currents that are ebb dominated, however, some systems show only slight ebb dominance despite having a very large swamp volume relative to the creek volume. Cocoa Ck in northern Australia is such a system. Results are presented from a simple analytical model for flow in Cocoa creek together with detailed water level observations in the swamps. It was found that the primary factor reducing the ebb dominance of this system was the very low slope of the swamp surface. During rising tides, water floods as sheet flow; however, on ebb tides, the surface water slope in the swamp becomes greater than the swamp surface slope, with the result that areas of swamp closest to the main feeder creek (Cocoa Ck) dry before areas furthest from the creek. Thus, about an hour after ebb tide commences, there is a large quantity of water perched on the salt flats/mangroves, tens of centimetres higher than the water in the creek. This water cannot leave the swamp via sheet flow, but must leave through a very small and shallow creek which is also highly constricted by vegetation. This effectively increases the friction on ebb tides and results in a delay in water leaving the swamps and salt flats, reducing any tendency towards ebb dominance.     

Osmoregulation in halophytic higher plants: a comparative study of soluble carbohydrates, polyols, betaines and free proline

Abstract. The levels of soluble carbohydrates, polyols, betaines and free proline have been determined in different organs of sixteen plants collected on coastal salt marshes. Among the carbohydrates, sucrose, fructose and glucose accumulated at quite high levels. Sucrose is particularly abundant in the monocots Juncus maritima, Phragmites communis and Scirpus maritimus. Maltose is quite abundant in Atriplex hastata and rhamnose in Plantago maritima roots. High levels of polyols were detected in Aster tripolium, Juncus maritimus, Plantago maritima and Phragmites communis. According to their capacity to accumulate carbohydrates and (or) nitrogenous solutes, halophytic higher plants can be divided into three main groups: (1) species producing high levels of soluble carbohydrates only, (2) species accumulating both carbohydrates and nitrogenous compounds, (3) species producing more nitrogenous solutes than soluble carbohydrates. The possible functions of these various organic solutes, including a role in equalizing the relative water potentials of cytoplasm and vacuole and to lower the internal potential, are discussed.     

Feeding ecology and postural behaviour of the three-toed sloth (Bradypus variegatus flaccidus) in northern Venezuela

We studied the diet, activity budget, vertical ranging, and postural behaviour in relation to weather of the three-toed sloth (Bradypus variegatus flaccidus) in disturbed montane forest remnants (1150 m asl) in northern Venezuela. Sloths spent most (72.9%) of their time resting and had a nearly exclusive (99.4%) leaf diet. While resting they assumed a sitting – not hanging – posture mostly (90.2% of observations). Species of three families, Clethraceae, Cecropiaceae, and Clusiaceae accounted for 77% of feeding records. Young leaves (67.2%) accounted for most of the leaf diet. Activity and posture were dependent on weather conditions. Sloths fed more often during mid-day hours and tended to rest more at dawn and dusk. In northern Venezuela sloths tended to use more frequently the upper strata of the canopy, while in warmer lowland sites they use intermediate levels more often. They adopted postures that maximized exposure of ventral surfaces to incident solar radiation when sunny, but minimized their surface area by huddling when cloudy, foggy or rainy. We propose that sunning behaviour of sloths may speed up their fermentation rate, and ultimately, might have been an important selective factor in the evolution of derived upside-down posture of sloths.     

Differential salt tolerance of two Artemisia species growing in contrasting coastal habitats

To investigate factors determining the differences in their salt tolerance, growth and germination, experiments were conducted on two plant species belonging to genus Artemisia: Artemisia fukudo Makino, a biennial salt marsh plant and Artemisia stelleriana Bess, a perennial coastal hind dune plant. Growth experiments revealed that salinity (100 and 300 m m NaCl) inhibited the relative growth rate (RGR) in A. stelleriana significantly but not in A. fukudo. These specific differences in salt tolerance were mainly attributed to differential responses of net assimilation rate (NAR). That is, the reduction in RGR in A. stelleriana was mainly due to the reduction in NAR, whereas no significant reduction in NAR was observed in A. fukudo. The reduction in RGR in A. stelleriana in the salt treatment was also attributable to a reduced leaf area ratio (LAR). Specific leaf area (SLA) in the two species decreased in the 300 m m treatment. The decrease in SLA in A. fukudo was, however, compensated for partly by an increase in leaf weight ratio (LWR). Germination experiments also showed that A. fukudo has a higher salt tolerance than does A. stelleriana. These results are consistent with the differences in the salinity conditions between the native habitats of the two species.     

Genetic structure of coastal and inland populations of the annual halophyte Suaeda maritima (L.) dumort. in Central Europe, inferred from amplified fragment length polymorphism markers

Naturally occurring inland salt habitats are highly threatened due to increasing fragmentation and area reduction, while the surroundings of former potash mining dumps have experienced a massive invasion by halophytes over the last 20 years. We reconstructed colonisation patterns of these purely anthropogenic inland salt sites using molecular markers in the obligate halophyte Suaeda maritima (L.) dumort. (Chenopodiaceae), a typical plant in such areas. In the present study, 120 individual plants from 40 coastal and inland populations in Central Europe were subjected to AFLP analysis with nine primer combinations. A total of 243 AFLP band positions were scored as presence/absence characters. Genetic diversity values were not significantly different in populations from natural and anthropogenic inland salt sites as compared to coastal habitats. Results from principal coordinate analysis, neighbour-joining analysis and analysis of molecular variance ( amova ) all indicated that most of the genetic variation is preserved within populations, while genetic differentiation among populations is comparatively low. We conclude that S. maritima has repeatedly and independently colonised the surroundings of former potash mining dumps in Central Germany. However, the absence of founder effects and the lack of phylogeographic structure prevented us from identifying putative donor populations.     

Effects of inundation and salt on the survival of ants in a sandy coastal plain

Abstract. 1. Survival of four species of ants, Myrmica rubra, Myrmica scabrinodis, Lasius niger and Lasius flavus , exposed to prolonged inundation and the drinking of brackish water, was experimentally determined.
2. In most of the experiments, survival of Lasius flavus workers was much worse than either Lasius niger or Myrmica scabrinodis .
3. After inundation with brackish water, and drinking of brackish water for more than 3 weeks, survival of workers of Myrmica rubra was also more affected than that of Lasius niger and Myrmica scabrinodis .
4. As a rule, survival of dealated queens after inundation appeared to be better in Lasius flavus and Lasius niger , but worse in Myrmica rubra , compared with worker survival.
5. After surviving inundation, the capacity to produce eggs and workers was only slightly affected in queens of both Lusius species.
6. The conclusions based on the experimental mortality rates seem to be consistent both with ant species distribution and with frequency of inundation and salt stress in different parts of the coastal plain and surrounding sand-dunes on the Dutch Wadden island Schiermonnikoog.     

Sporotrichosis in the Orinoco river basin of Venezuela and Colombia

Six cases of sporotrichosis from the Orinoco river basin of Venezuela and Colombia are described; two are of the localized cutaneous type and four are lymphocutaneous. Diagnosis was based on the patient's clinical history and mycological culture. Epidemiology and distinctive cultural habits of the patients are discussed in connection with disease etiology.Abbreviations CAICET Amazonas Center for Investigation and Control of Tropical Diseases - TFA Amazonas Federal Territory     

Germination ecology of coastal plants in relation to salt environment

Responses of seed germination to salinity were examined using 37 species collected from salt marshes, cliffs, and fore (unstable) and hind (stable) sand dunes along Japanese coasts. For comparison, seed germination of nine inland species was also examined. The soil salinities in salt marshes ranged from 150 to 300 mmol/L NaCl, whereas those in fore and hind dunes ranged from 0 to 150 mmol/L NaCl, with a few exceptions. Cliff soils showed relatively high salinities up to 300 mmol/L NaCl. Ciff and foredune soils that encountered a typhoon and storm showed high salinities >300 mmol/L NaCl. Salt tolerance in seed germination of coastal plants was ordered by comparing the responses of percentage and rate of germination to salinity conditions up to 200 mmol/L NaCl, being in the order of salt marsh>cliff>foredune≅hind dune≅inland. Thse results indicate that salt tolerance in seed germination of coastal plants is closely related to the salinity conditions of their habitats. Germination experiments under favorable conditions showed that a high percentage of the seeds of salt marsh species germinate rapidly, those of diff species germinate slowly and those of foredune species exhibit a low percentage and low rate of germination. It seems that these germination characteristics contribute to the success of germination at the ‘safe site’ and the subsequent survivorship of emerged plants in their natural habitats.     

Ecophysiology in Relation to Exposure of Pendant Epiphytic Bryophytes in the Canopy of a Tropical Montane Oak Forest1

We investigated ecophysiological and morphological traits affecting light and water use of four commercially important pendant epiphytic bryophyte species in a montane oak‐bamboo forest in Costa Rica. Predictions based mostly on ecophysiological studies of temperate bryophytes and vascular plants were experimentally tested on tropical montane bryophyte species ranked on the basis of their distributions in the canopy from the most protected (1) to the most exposed sites (4): (1) Phyllogonium viscosum; (2) Pilotrichella flexilis; (3) Dendropogonella rufescens; and (4) Frullania convoluta. As predicted, highly exposed species tended to have higher light saturation and compensation points, higher dark respiration rates, more chlorophyll, higher chlorophyll a:b ratios, and higher nitrogen concentrations. Contrary to predicted trends, exposed‐site species had lower water contents at full saturation; there were no detectable differences among species in the rate of water loss. Rates of carbon gain in all species reached asymptotes with increasing water content, but the moisture compensation point for carbon uptake of the moss D. rufescens was substantially higher than in the other species. Observed patterns result from interactions among processes related to water storage and transport operating at different scales and are determined by various morphological traits including the density, size, and disposition of phylloids, as well as by whole‐clump architecture.     

Isotopic signatures and nutrient relations of plants inhabiting brackish wetlands in the northeastern coastal plain of Venezuela

The semi-diurnal tidal regime (≥2 m) in the Paria Gulf on the Atlantic coast of Venezuela, and the flat landscape of the region, allow the penetration for tens of km of marine waters into the rivers draining the northeastern coastal plain of the country. The levels of salinity, tidal flooding, and sedimentation decrease perpendicularly from the river channel toward the back swamps. The vegetation varies sequentially from fringe mangroves along the river margins, to back swamps containing forests dominated by Pterocarpus officinalis, herbaceous communities of Lagenocarpus guianensis, and palm swamps with Mauritia flexuosa, Chrysobalanus icaco, and Tabebuia spp. This environmental structure was used to test the hypotheses that: (a) mangrove distribution is strongly associated with salinity of interstitial water, and (b) they occupy areas where tidal influence and sediment dynamics determine a relatively open N cycle. Analyses of soil, water, and plants along a 1.5 km transect located near the confluence of the Guanoco and San Juan Rivers (Sucre and Monagas States, Venezuela) revealed that: (a) conductivity decreased from 11 to 0.2 mmhos cm⁻¹ from the river fringe to the internal swamp, whereas Na in the same stretch decreased from 100 to 2 μM; (b) average leaf tissue concentrations of Na, P, and N decreased significantly along the transect; (c) P. officinalis showed a large Na-exclusion capacity indicated by positive K/Na ratios from 8 to 200, and Crinum erubescens counteracted Na by accumulating K above 1,000 mmol kg⁻¹; (d) leaves varied widely in δ ¹³C (−25.5 to −32‰) and δ ¹⁵N (4 to −10.5‰) values. Samples were aggregated according to soil carbon content corresponding to those of the mangrove forest belt (5–28 mol C kg⁻¹; 0–650 from river fringe) and those of the back swamps (40–44 mol C kg⁻¹; 700–1,500 m from river fringe). The concentrations of Na, P, and N (in mmol kg⁻¹) and δ ¹⁵N values (in ‰) were significantly higher in the mangrove forest compared to the back swamp (Na 213 vs. 88; P 41 vs. 16; N 1,535 vs. 727; δ ¹⁵N 1.5 vs. −3.7), indicating that the fringe forest was not nutrient limited. These results support the hypotheses that mangroves are restricted to the more-saline sections of the transect, and that the fringe forest has a more open N cycle, favoring ¹⁵N accumulation within the system.     

The role of alien plants in the natural coastal vegetation in central-northern Spain

Alien plants in coastal habitats and their influence on natural vegetation are studied. After 5 years working on this subject in the Basque Country and surrounding areas, a number of results from the coastal ecosystems are presented. These ecosystems are one of the most threatened and affected by the invasion of alien plants, especially shore dunes, saltmarshes and cliffs. These kinds of habitats, especially the dunes, experience significant pressure from human activities which favours the expansion of some of these species: Arctotheca calendula, Sporobolus indicus and Oenothera spp. The presence and abundance of these invasive plants and others such as Baccharis halimifolia, Cortaderia selloana, Spartina patens and Carpobrotus edulis in the plant communities in an area between the French border and the western part of the region of Cantabria have been studied. The degree of invasion of each plant in each syntaxonomic unit has been analysed.     

Simulium metallicum cytospecies E larval habitat characterization in the Altamira focus of onchocerciasis, northern Venezuela

Abstract. Simulium metallicum sibling species E was identified cytotaxonomically from an onchocerciasis focus at Altamira in northern Venezuela. S. metallicum E larvae were sampled monthly from two small mountain streams over a 15-month period (July 1990 to September 1991) and eleven habitat variables were measured at two altitudes. One stream consistently harboured much higher densities of S. metallicum E larvae than the other, with three annual peaks of abundance: during the dry season and at the beginning and end of the rainy season. These peak densities were correlated with high rainfall 4 months previously. Larvae were most abundant on submerged rocks and fallen leaves, in small shallow areas characterized by slow water current, high conductivity and sparse terrestrial vegetation cover. Stream variables which best explained the temporal changes in abundance were water discharge and conductivity. The population dynamics of S. metallicum E appeared to be influenced primarily by interactions between stream discharge and substrate stability. Relevance of these results to vector control with larvicides is discussed.     

干旱、半干旱区湖泊周围盐生植物群落的多样性格局及特点

干旱、半干旱地区湖泊周围是盐渍化土壤的主要分布区,盐渍化是荒漠化的主要类型之一。目前,关于盐生植被的分布格局及群落多样性随着盐渍化程度加深的动态变化的研究仍很缺乏, 为阐释这种关系,作者在内蒙古干旱、半干旱地区选择吉兰泰(盐池)、乌梁素海、查干诺尔(碱矿)以及额吉诺尔(盐池)等4个湖泊,研究了其周围盐生植物群落的物种组成、分布特征以及群落结构的差异, 讨论了群落多样性沿盐分梯度的变化特点, 并在此基础上探讨了盐生植物群落对土壤盐分环境的指示意义。为建立群落耐盐值与群落多样性的关系,我们计算了群落耐盐值。结果表明, 盐生植物群落沿盐湖呈明显的环带状分布;随着土壤盐渍化程度的增加, 按照芨芨草群落(Comm. Achnatherum splendens)、盐爪爪群落(Comm. Kalidium foliatum)、盐角草群落(Comm. Salicornia europaea)和碱蓬群落(Comm. Suaeda glauca)的顺序演替, 而且物种种类趋向单一化, 群落结构趋向简单化。群落的物种多样性和群落间物种的替代速率都随土壤盐分的增加而减小, 而群落间物种的相似性则增加。区域性气候特点对盐生植物群落的特征也会产生一定的影响, 特别是在低盐渍化的条件下, 这种影响比较显著, 使得盐生植物群落体现出地带性的特点, 而随着土壤盐渍化程度的提高, 盐生植物群落的隐域性特征更为突出。因此, 这一地区的盐生植被又呈现出非常明显的地带性植被向非地带性植被过渡的特点。     

Occurrence and relative incidence of viruses infecting papaya in Venezuela

A survey of the main papaya (Carica papaya L.) production fields in Venezuela during 1997, indicated that crops were heavily affected with various virus‐like symptoms. A total of 745 samples from papaya plants showing symptoms suggestive of virus infection were collected and analysed using electron microscopy and enzyme‐linked immunosorbent assay (ELISA). Papaya ringspot virus (PRSV) and Papaya mild yellowing virus (PMYV) were the most frequently found viruses, which also occurred, in mixed infections. Rhabdovirus‐like particles were found only in samples collected in Distrito Federal (D.F). Papaya mosaic virus (papMV) and Tomato spotted wild virus (TSW V) were not detected during the survey.     

Gas Exchange and Water Vapor Uptake in the Atmospheric CAM Bromeliad Tillandsia recurvata L.: The Influence of Trichomes

Tillandsia recurvata is an epiphytic atmospheric CAM bromeliad without functional roots. As an adaptation to very exposed and often dry habitats T. recurvata takes up liquid water via trichomes, which cover the plant. Gas exchange measurements also show an absorption of water vapor at the trichomes simultaneously with an increase in relative humidity at the beginning of the dark period. A similar amount of water is lost again when the relative humidity is decreased. Experiments with heat-killed plants show that this was due exclusively to physical equilibration of the hygroscopic walls of the dead trichome cells. This effect would have prevented an accurate calculation of transpiration and conductance, but can be accounted for by substracting water vapor exchange of heat-killed plants from that of the living tissue which yields the true water vapor conductance of the tissue. This is found to be rather low (3.37 mmol H₂O kg^?1 s^?1) in comparison to other plants, and the proportion of total conductance due to trichomes is relatively high (0.53 mmol H₂O kg^?1 s^?1). This explains the slow rates of photosynthesis and growth found in this plant.     

Sinusichnus, a trace fossil from Antarctica and Venezuela: expanding the dataset of crustacean burrows

The sinusoidal decapod crustacean burrow Sinusichnus sinuosus is documented from the Upper Cretaceous Hidden Lake Formation of James Ross Island (Antarctica), the Upper Oligocene-Lower Miocene Naricual Formation of the Eastern Venezuela Basin, and the Middle Miocene Socorro Formation of the Falcón Basin of Western Venezuela, significantly expanding its geographical and palaeolatitudinal range. These burrows may have served for bacterial farming in relatively stressful settings characterized by deltaic progradation. Sinusichnus sinuosus seems to display a broad latitudinal range, from low latitude tropical settings (Venezuela) to intermediate latitude temperate areas (Spain and France), and high latitude cold waters (Antarctica). The appearance of S. sinuosus in the Cretaceous reveals the acquisition of more sophisticated feeding strategies by decapod crustaceans, reflecting the dominance of the Modern Evolutionary Fauna.