Salt accumulation and depletion in the root-zone of the halophyte Atriplex nummularia Lindl.: influence of salinity,leaf area and plant water use

Background and aims

Salt is known to accumulate in the root-zone of Na⁺ excluding glycophytes under saline conditions. We examined the effect of soil salinity on Na⁺ and Cl^? depletion or accumulation in the root-zone of the halophyte (Atriplex nummularia Lindl).

Methods

A pot experiment was conducted in soil to examine Na⁺ and Cl^? concentrations adjacent to roots at four initial NaCl treatments (20, 50, 200 or 400 mM NaCl in the soil solution). Plant water use was manipulated by leaving plants with all leaves intact, removing approximately 50 % of leaves, or removing all leaves. Daily evapotranspiration was replaced by watering undrained pots to weight with deionised water. After 35-38 days, samples were taken of the bulk soil and of soil loosely- and closely-adhering to the roots.

Results

In plants with leaves intact grown with 200 and 400 mM NaCl, average Na⁺ and Cl^? concentrations in the closely adhering soil were about twice the concentrations of the bulk soil. Ion accumulation increased with final leaf area and with cumulative transpiration over the duration of the trial. By contrast, in plants grown with the lowest salinity treatment (20 mM NaCl), Na⁺ and Cl^? concentrations decreased in the closely adhering soil with increasing leaf area and increasing cumulative water use.

Conclusions

Our data show that Na⁺ and Cl^? are depleted from the root-zone of A. nummularia at low salinity but accumulate in the root-zone at moderate to high salinity, and that the ions are drawn towards the plant in the transpiration stream.     

Effect of salt stress on growth parameters, enzymatic antioxidant system, and lipid peroxidation in wild chicory (Cichorium intybus L.)

Efficient utilization of saline land for food cultivation can increase agricultural productivity and rural income. To obtain information on the salt tolerance/susceptibility of wild chicory (Cichorium intybus L.), the influence of salinity (0–260 mM NaCl) on chicory seed germination and that of two salinity levels of irrigation water (100 and 200 mM NaCl) on plant growth, antioxidative enzyme activity, and accumulation of proline and malondialdehyde (MDA) were investigated. The trials were performed outdoors, in pots placed under a protective glass covering, for two consecutive years. Seeds showed a high capacity to germinate in saline conditions. The use of 100 mM NaCl solution resulted in 81 % germination, whereas seed germinability decreased below 40 % using salt concentrations above 200 mM NaCl. Wild chicory showed tolerance to medium salinity (100 mM NaCl), whereas a drastic reduction in biomass was observed when 200 mM NaCl solution was used for irrigation. MDA, present in higher amounts in leaves than in roots, decreased in both tissues under increasing salinity. Proline content increased remarkably with the level of salt stress, more so in roots than in leaves. In salt stress conditions, the activity of antioxidant enzymes (APX, CAT, POD, SOD) was enhanced. The electrophoretic patterns of the studied enzymes showed that the salinity of irrigation water affected only the intensity of bands, but did not activate new isoforms. Our results suggest that wild chicory is able to grow in soil with moderate salinity by activating antioxidative responses both in roots and leaves.     

Taste Responses to Fructose and Tannic Acid Among Gorillas (Gorilla gorilla gorilla)

We investigated the taste responses to fructose and tannic acid compounds among 6 western gorillas (Gorilla gorilla gorilla) at the San Francisco Zoo. We presented the subjects with 12 reference concentrations of 3–300 mM fructose, paired with tap water in paired-choice experimental trials. We subsequently presented them with tap water paired with 8 dilute concentrations of tannic acid (0.25–6 mM) dissolved in 100 mM fructose solutions and 8 concentrations (0.25–6 mM) dissolved in 300 mM fructose solutions. The gorillas exhibited a broadly similar preference threshold for fructose (50 mM) to those of other nonhuman primate and human samples. The gorillas tolerated moderate levels of tanninc acid, especially when presented in a very sweet package. The depressing effect of tannic acid on the ingestion of fructose solutions appeared to increase progressively with tannin concentration and was lower as fructose concentration increased. The inhibition threshold for tannic acid solutions was reached at 4 mM tannic acid in 100 mM fructose solution, and at 6 mM tannic acid in 300 mM fructose solutions. These results suggest that gorillas use sweetness as a criterion for food selection and regard those with moderate levels of tannins as palatable. Our findings corroberate food preference studies and nutritional analyses of wild gorilla foods indicating that they prefer sugary foods and readily consume ones containing moderate levels of tannins. Taste responses may facilitate a flexible frugivorous/folivorous diet among gorillas.     

The influence of mangrove-derived tannins on intertidal meiobenthos in tropical estuaries

Summary Mangrove-derived tannins negatively effected laboratory-reared nematode populations and natural communities of meiobenthos in tropical mangrove forests along the northeastern coast of Australia. In the low and mid intertidal zones of five mangrove estuaries, nearly all of the dominant meiofaunal taxa correlated negatively with concentrations of sediment tannins. Only nematodes correlated with low tannin concentrations in the high intertidal zones. The negative exponential equation y=be ^-mx represented the best-fit for most of the meiofauna-tannin relationships. The mangrove-dwelling nematode, Terschellingia longicaudata did not grow (r=0.001) in the laboratory on fresh, tannin-rich leaves of the red mangrove, Rhizophora stylosa. Population growth of the nematode was significantly greater on fresh, tannin-poor leaves of the grey mangrove, Avicennia marina (r=0.081) with best growth (r=0.112) attained on a diet of tannin-free, mixed cereal. These preliminary field and laboratory results suggest that hydrolyzable tannins leached from mangrove roots and leaf litter are an important factor regulating intertidal meiobenthic communities in tropical mangrove forests along the northeastern Australian coast.     

Leaf silicon content in banana (Musa spp.) reveals the weathering stage of volcanic ash soils in Guadeloupe

Several plant species accumulate silicon, which is taken up by roots in soil solution. The Si concentration in soil solution can be governed by silicate dissolution and formation, and thus soil constitution. Here, we study the Si leaf content of mature banana plants (Musa acuminata cv Grande Naine) cropped on soils derived from andesitic ash in Guadeloupe through standard foliar analysis. The soils strongly differ in weathering stage and total Si content. The most desilicated soils (Andosol–Nitisol–Ferralsol) occur in the wettest areas, on the Eastern slopes (Es) of the volcano exposed to rain bearing winds. Least weathered soils (Andosol–Cambisol) occur on Western slopes (Ws). The average leaf Si concentration ranges from 2.7 to 3.9 g kg^?1 for bananas cropped in Es soils, and from 7.7 to 9.6 g kg^?1 in Ws soils. The leaf Si concentrations are lowest for the Es gibbsite-rich Andosols and Ferralsols. The leaf Si concentration is positively correlated with soil CaCl₂-extractable Si content, soil Si content and total reserve in weatherable minerals. The silicon content of banana leaves thus reveals the weathering stage of volcanic ash soils in Guadeloupe.     

The role of cotyledons in the establishment of Suaeda physophora seedlings

The role of cotyledons in seedling establishment of the euhalophyte Suaeda physophora under non-saline and saline conditions (addition of 1 mM or 400 mM NaCl) was investigated. Survival and fresh and dry weights were greater for seedlings grown in the light (12-h light/12-h dark) than in the dark (24-h dark). The shading of cotyledons tended to decrease shoot height, shoot organic dry weight, number of leaves, and survival of seedlings regardless of NaCl treatment, but the effect of cotyledon shading was greater with 400 mM NaCl. Concentrations of Na⁺ were higher in cotyledons than in leaves, regardless of NaCl treatment. The K⁺/Na⁺ ratio was lower in cotyledons than in leaves for seedlings treated with 1 mM NaCl but not for seedlings treated with 400 mM NaCl. Addition of 400 mM NaCl decreased oxygen production in cotyledons but especially in leaves. These results are consistent with the hypothesis that, by generating oxygen via photosynthesis and by compartmentalizing Na⁺, cotyledons are crucial for the establishment of S. physophora seedlings in saline environments.     

Bitter problems in ecological feeding experiments: Commercial tannin preparations and common methods for tannin quantifications

In the field of plant–herbivore interactions, research methods where plant secondary metabolites are manipulated are becoming more and more popular. Among the most commonly used is tannic acid. However, recent studies have shown that different tannic acid preparations are not comparable in their tannin structures. While tannic acids are meant to contain only gallotannins (GTs), some commercial preparations compose mainly of more simple galloylglucoses (that have, e.g. much lower protein precipitation capacity than GTs) or even of gallic acid (the hydrolysis product of GTs). Another group of tannins used in feeding trials is condensed tannins (CTs), usually in the form of quebracho tannin. Quebracho, however, contains different CT structures than, e.g. leaves of many deciduous trees. Additionally, when analysed with the common acid-butanol assay for total CTs, quebracho tannins give even 30-fold lower absorbance than the CTs of those deciduous trees. In addition to above problems it has been shown that different tannins can give different response even within the same herbivore species, and that the same tannin structure can cause different response in different herbivores. Below we review these problems, as well as some means to deal with them.     

Separation of polymeric tannins from white wine by a combination of 2-butanol extraction and column chromatography

A new procedure was developed for the separation of polymeric tannins from a high-tannin white table Koshu wine by extraction with organic solvent and adsorption chromatography. The wine was adjusted to pH 1.0, sodium chloride was added to give a final concentration of 12.5% NaCl, then phenolic compounds including phenolic acids and tannin phenolics were extracted with 2-butanol. About 95% of the total phenolics was extractable.Polymeric tannins were separated from the extract by chromatography on Bio-Gel P-2, which adsorbs polymeric tannins in the presence of 10% acetic acid-50% ethanol, and recovered quantitatively by subsequent elution with 50% acetone. The phenolic acids and flavonoid tannins of low molecular weight that were eluted first using 10% acetic acid-50% ethanol, and the tannin phenolics of high molecular weight subsequently eluted using 50% acetone, were both free of potassium and sodium ions.This method, including the extraction and chromatography, is useful for rough separation of polymeric tannins and other phenolics from white wines.     

SOME EFFECTS OF TANNIC ACID AND OF LEAF EXTRACTS WHICH CONTAIN TANNINS ON THE INFECTIVITY OF TOBACCO MOSAIC AND TOBACCO NECROSIS VIRUSES

The inhibition of infection by tobacco necrosis and tobacco mosaic viruses by tannic acid, and by extracts of raspberry and strawberry leaves, was associated with the precipitation of the viruses. Precipitation and inhibition were reversible, and infective virus was obtained from the precipitate formed between the viruses and tannins. Infectivity was fully restored by diluting mixtures of virus and tannin adequately and partially restored by adding alumina or nicotine sulphate.
Viruses and tannins are thought to form non-infective complexes, in which the virus and tannin components are held together by co-ordinate linkages or hydrogen bonds.
Macerating tobacco leaves infected with tobacco mosaic virus together with raspberry leaves greatly decreased the infectivity of the extracts; adding nicotine sulphate to the mixture of leaves before it was ground increased the infectivity, even though nicotine sulphate alone decreases the infectivity of tobacco mosaic virus. Even in the presence of nicotine sulphate, much of the virus was precipitated by substances from the raspberry leaves.
Extracts of roots of Fragaria vesca plants, infected with a tobacco necrosis virus, were more infective when made by macerating the roots with four times their weight of buffer at pH 8 than when made without buffer. Various methods are suggested for facilitating the transmission of viruses from plants that contain tannin.     

Iron and phosphorus fertilizations and the development of proteoid roots in macadamia (Macadamia integrifolia)

Proteoid roots are reportedly an adaptation to soils with either low phosphorus (P) or iron (Fe) or both. Since macadamia (Macadamia integrifolia, a member of the family Proteaceae) is an important crop in Hawaii, a factorial experiment with soil P levels of 0, 150, and 500 mg/kg and Fe levels of 0, 5, and 10 mg/kg was conducted to evaluate the effects of P and Fe fertilizations and possible Fe x P interactions on proteoid root development and macadamia growth. The soil was a highly weathered Oxisol having 0.015 mg P/L and 0.03 mg Fe/L in the soil solution in its unamended state. Proteoid roots were reduced in number and as a percentage of the total root mass at the highest levels of P and Fe. Phosphorus, however was a major controlling factor. Optimum dry matter associated with at least 10% proteoid roots, corresponding to a P concentration approximately of 0.035 mg/L in soil solution and 0.10% P in leaves. Total Fe in leaves or the amount of Fe applied was not a good predictor of plant growth. In contrast, chlorophyll content, a surrogate of biologically active Fe, was. Soil-solution ratio of Fe ^1/3/ P (molar basis) could be used to predict the response of macadamia growth to P and Fe fertilizations.     

The modulation of various physiochemical changes in <Emphasis Type="Italic">Bruguiera cylindrica</Emphasis> (L.) Blume affected by high concentrations of NaCl

Bruguiera cylindrica is a major mangrove species in the tropical mangrove ecosystems and it grows in a wide range of salinities without any special features for the excretion of excess salt. Therefore, the adaptation of this mangrove to salinity could be at the physiological and biochemical level. The 3-month-old healthy plantlets of B. cylindrica, raised from propagules were treated with 0 mM, 400 mM, 500 mM and 600 mM NaCl for 20 days under hydroponic culture conditions provided with full strength Hoagland medium. The modulation of various physiochemical changes in B. cylindrica, such as chlorophyll a fluorescence, total chlorophyll content, dry weight, fresh weight and water content, Na⁺ accumulation, oxidation and antioxidation (enzymatic and non-enzymatic) features were studied. Total chlorophyll content showed very minute decrease at 500 mM and 600 mM NaCl treatment for 20 days and the water content percentage was decreased both in leaf and root tissues with increasing concentration. A significant increase of Na⁺ content of plants from 84.505 mM/plant dry weight in the absence of NaCl to 543.38 mM/plant dry weight in plants treated with 600 mM NaCl was recorded. The malondialdehyde and the metabolites content associated with stress tolerance (amino acid, total phenols and proline) showed an increasing pattern with increasing NaCl concentration as compared to the control in both leaf and root tissues but the increase recorded in plantlets subjected to 500 mM was much less, indicating the tolerance potential of this species towards 500 mM NaCl. The significant decrease of sugar content was found only in 600 mM NaCl on 20 days of treatment, showing that the process of sugar synthesis was negatively affected but the same process remains less affected at 500 mM NaCl. A slight reduction in ascorbate and glutathione content and very less increase in carotenoid content were observed at 500 mM and 600 mM NaCl stress. Antioxidant enzymes (APX, GPX, SOD and CAT) showed an enhanced activity in all the treatments and the increased activity was more significant in 600 mM treated plants. The result establishes that B. cylindrica tolerates high NaCl concentration, to the extent of 500 mM NaCl without any major inhibition on photosynthesis and metabolite accumulation. Understanding the modulation of various physiological and biochemical changes of B. cylindrica at high levels of NaCl will help us to know the physiochemical basis of tolerance strategy of this species towards high NaCl.     

Compost alleviates the negative effects of salinity via up-regulation of antioxidants in Solanum lycopersicum L. plants

The aim of this study was to investigate the effectiveness of compost in alleviating the negative impacts of salinity on tomato (Solanum lycopersicum cv. Hybrid Guardian F1) plants. An experiment was performed to evaluate the response of plants to compost addition to soil at a rate of 55 g kg^?1 soil and NaCl salinity at 0, 50, 100 mM. The results obtained showed a significant decrease in growth-related parameters, i.e. shoot- and root-fresh weight (FW), fruit FW, and fruit yield. Meanwhile, salinity resulted in a significant increase of Na⁺, electrolyte leakage, lipid peroxidation and hydrogen peroxide in the leaves, but a decrease of N, P, S, K⁺, Ca²⁺ and Mg²⁺ level, as well as K⁺/Na⁺ ratio in a dose dependent manner. Under these conditions compost nullified the above negative impacts of salinity caused by 50 mM NaCl and to some extent at 100 mM NaCl. The salinity mediated enhancement in biomarkers of oxidative stress was considerably decreased by compost application which increased the level of ascorbate (ASC) and glutathione (GSH) and the ratios of ASC/dehydroascorbate (DHA) and GSH/glutathione disulfide, as well as the activities of ASC peroxidase, monodehydroascorbate reductase, DHA reductase and GSH reductase in NaCl-treated plants, implying a better reactive oxygen species scavenging system. Data also indicated that compost application resulted in higher activities of leaf carbonic anhydrase, ribulose bisphosphate carboxylase, nitrate reductase and adenosine triphosphate-sulfurylase. These findings collectively suggest that compost plays a pivotal role in inducing salinity tolerance via enhancing an efficient antioxidant system and key C, N and S assimilatory enzymes.     

Identification of tannin–degrading microorganisms in the gut of plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus)

Gut microorganisms are thought to play a role in the degradation of plant secondary metabolites in herbivores. Here, we examined the presence of tannin–degrading microorganisms in the gut of two herbivores, plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus). Tannase activity in the feces of wild plateau pikas and root voles increased from June to August, corresponding to the increase in condensed and hydrolyzable tannin concentrations in plants during this period. Using intragastric tannic acid infusion, we found that tannase activities were significantly higher following administration of three concentrations of tannic acid than that in the control group for root voles. In contrast, for plateau pikas, animals administered tannic acid exhibited lower tannase activity in low–dose and high–dose groups than that in the control group. Tannase activities in root voles were higher than those in plateau pikas among different months and in different tannic acid infusion groups. Three tannin–degrading anaerobic strains were isolated from the cecum of plateau pikas (termed A1, A2, and A3) and root voles (termed M1, M2, and M3). 16 s rDNA sequencing assigned isolates A1 and M1 to the genus Enterobacter, A2 and M2 to the genus Shigella, and A3 and M3 to the genus Staphylococcus. These data provided the first evidence of microorganisms with tannin–degrading activity in the gut of plateau pikas and root voles. We speculated that both animals could degrade tannins in the gut, but that root voles would have a greater ability to process tannins than plateau pikas.     

Recent trends and advancements in microbial tannase-catalyzed biotransformation of tannins: a review

The outburst of green biotechnology has facilitated a substantial upsurge in the usage of enzymes in a plethora of industrial bioconversion processes. The tremendous biocatalytic potential of industrial enzymes provides an upper edge over chemical technologies in terms of safety, reusability, and better process control. Tannase is one such enzyme loaded with huge potential for bioconversion of hydrolysable tannins to gallic acid. Tannins invariably occur in pteridophytes, gymnosperms, and angiosperms and predominately cumulate in plant parts like fruits, bark, roots, and leaves. Furthermore, toxic tannery effluents from various tanneries are loaded with significant levels of tannins in the form of tannic acid. Tannase can be principally employed for debasing the tannins that predominately occur in the toxic tannery effluents thus providing a relatively much cheaper measure for their biodegradation. Over the years, microbial tannase-catalyzed tannin degradation has gained momentum. The plentious availability of tannin-containing agro- and industrial waste paves a way for efficient utilization of microbial tannase for tannin degradation eventually resulting into gallic acid production. Gallic acid has received a great deal of attention as a molecule of enormous therapeutic and indusrial potential. The current worldwide demand of gallic acid is 8000 t per annum. As a matter of fact, bioconversion of tannins into gallic acid through fermentation has not been exploited completely. This necessitates further studies for development of more efficient, economical, productive processes and improved strains for gallic acid production so as to meet its current demand.     

The role of xylopodium in Na+ exclusion and osmolyte accumulation in faveleira [Cnidoscolus phyllacanthus (d. arg.) Pax et K. Hoffm] under salt stress

The aim of this work was to evaluate physiological and biochemical responses of faveleira under salinity. Plants were grown in nutrient solution containing 0, 50, 100 or 150 mM NaCl. After 8 days of stress, plants were harvested and separated into roots, xylopodium, stem + petiole (SP), and basal, median and apical leaves. Salinity reduced the dry weight of all plant parts, although the indicators of water status were not changed. Salt stress increased the content of Na⁺ in the different plant parts, especially in xylopodium, in which it increased approximately eightfold while the content of K⁺ decreased by approximately 40 % under 150 mM NaCl. As a consequence, the K⁺/Na⁺ ratio decreased in all plant organs. In stressed plants, the content of soluble sugars was increased in the roots, SP and leaf strata and the content of soluble proteins increased in all organs. The content of total free amino acids increased in the roots, SP and apical leaves, while the proline content increased in all organs except in xylopodium. It is suggested that the xylopodium may be involved in a mechanism of exclusion and/or compartmentalization of Na⁺ in faveleira under salinity to avoid ionic toxicity in the leaves.     

5-Aminolevulinic acid improves photosynthetic gas exchange capacity and ion uptake under salinity stress in oilseed rape (Brassica napus L.)

Salinity is one of the major constraints in oilseed rape (Brassica napus L.) production. One of the means to overcome this constraint is the use of plant growth regulators to induce plant tolerance. To study the plant response to salinity in combination with a growth regulator, 5-aminolevulinic acid (ALA), oilseed rape plants were grown hydroponically in greenhouse conditions under three levels of salinity (0, 100, and 200 mM NaCl) and foliar application of ALA (30 mg/l). Salinity depressed the growth of shoots and roots, and decreased leaf water potential and chlorophyll concentration. Addition of ALA partially improved the growth of shoots and roots, and increased the leaf chlorophyll concentrations of stressed plants. Foliar application of ALA also maintained leaf water potential of plants growing in 100 mM salinity at the same level as that of the control plants, and there was also an improvement in the water relations of ALA-treated plants growing in 200 mM. Net photosynthetic rate and gas exchange parameters were also reduced significantly with increasing salinity; these effects were partially reversed upon foliar application with ALA. Sodium accumulation increased with increasing NaCl concentration which induced a complex response in the macro-and micronutrients uptake and accumulation in both roots and leaves. Generally, analyses of macro- (N, P, K, S, Ca, and Mg) and micronutrients (Mn, Zn, Fe, and Cu) showed no increased accumulation of these ions in the leaves and roots (on dry weight basis) under increasing salinity except for zinc (Zn). Foliar application of ALA enhanced the concentrations of all nutrients other than Mn and Cu. These results suggest that under short-term salinity-induced stress (10 days), exogenous application of ALA helped the plants improve growth, photosynthetic gas exchange capacity, water potential, chlorophyll content, and mineral nutrition by manipulating the uptake of Na⁺.     

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na⁺ and Cl^? content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries.     

Distribution of mangrove vegetation along inundation, phosphorus, and salinity gradients on the Bragança Peninsula in Northern Brazil

Background and aims

The Bragança Peninsula, in northern Brazil is characterized by macrotides (4 m) and specific edaphic conditions, which determine the local mangrove forest’s development. This study, conducted during the dry season evaluated the spatial patterns of Rhizophora mangle and Avicennia germinans species across an inundation gradient.

Methods

Along a transect of 700 m, measurements of structure forest, soil moisture, porewater salinity, extractable phosphorus (extr.-P) in sediments, and phosphorus in the leaves (leaf-P) were conducted.

Result

The A. germinans (100 %) occurred in high intertidal (HI) zone. A. germinans (59 %) and R. mangle (41 %) co-occurred in mid intertidal (MI) zone, while R. mangle (58 %) predominated in low intertidal (LI) zone, followed by A. germinans (37 %) and Laguncularia racemosa (5 %). Covariance analysis (ANCOVA) indicated that salinity and soil moisture means are significantly different between the mangrove forests, but do not correlate with inundation frequency (IF). The means of extr.-P were significantly different in mangrove forests and correlated with IF and leaf-P.

Conclusion

The inundation frequency, the availability of P in the sediments, phosphorus in the leaves and interstitial salinity are all important factors contributing to the distribution of the mangrove tree species A. germinans and R. mangle on the Bragança Peninsula.     

Inhibitory activity of pine needle tannin extracts on some agriculturally resourceful microbes

Crude extracts of water and solvent extractable tannin fractions from pine needles were found to contain tannin concentrations of 10.15% and 13.15% tannic acid equivalents respectively. Thin Layer Chromatography revealed the presence of four distinct phenolic compounds, amongst which two were tannic acid like compounds. Both the extracts were found to be inhibitory to several microbes of agricultural importance. Amongst the bacterial strains studied, Azotobacter sp (VL-A2) was able to tolerate upto 1000 ppm of crude tannin concentration without any growth inhibition. While growth of Rhizobium (VL-R1) and Bacillus halodurans (MTCC 7181) was inhibited by crude tannin concentrations of 50 and 100 ppm respectively of both water and solvent extracted tannins. Among the fungal genera, Pleurotus djamor was found to tolerate up to 10000 ppm of crude tannins, while Trichoderma virescens (MTCC 6321) and T. reesii could tolerate up to 3000 ppm of both water extractable and acetone extractable crude tannins without any growth inhibition.     

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Background

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity.

Aims and methods

The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl).

Results

Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production.

Conclusions

This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.