Ecophysiological relevance of cuticular transpiration of deciduous and evergreen plants in relation to stomatal closure and leaf water potential

The water permeability of the leaves of three deciduous plants (Acer campestre, Fagus sylvatica, Quercus petraea) and two evergreen plants (Hedera helix, Ilex aquifolium) was analysed in order to assess its role as a mechanism of drought resistance. Cuticular permeances were determined by measurement of the water loss through adaxial, astomatous leaf surfaces. Minimum conductances after complete stomatal closure were obtained by leaf drying curves. The comparison of the water permeabilities determined with these two experimental systems revealed good agreement in the case of Acer, Fagus, Quercus, and Ilex. For Hedera the minimum conductance was 3-fold higher than the cuticular permeance indicating a significant contribution of residual stomatal transpiration. The leaf water potential was measured as a function of water content and analysed by pressure-volume curves. The influence of water potential as a component of the driving force for transpirational water loss was assessed in order to identify modifications of the cuticular barrier by the leaf water content. The ecophysiological meaning of the water relations parameters describing transpiration under drought conditions (cuticular transpiration, minimum transpiration, residual stomatal transpiration, effect of leaf water content on transpiration) and the water relations parameters derived from pressure-volume curves (osmotic potential at full saturation, turgor loss point, bulk modulus of elasticity) are discussed with regard to adaptations for drought resistance.     

Phosphatase activity in relation to phytoplankton composition and pH in Swedish lakes

SUMMARY. 1. Potential phosphatase activity and phytoplankton from several lakes of different character were compared in order to evaluate the importance of lake water pH and phytoplankton composition for the activity and pH optimum of lake water phosphatases.
2. In oligotrophic lakes, in which phytoplankton biomass was most often dominated by Ochromonadaceae spp., optimum phosphate activity was found at pH values <6. In eutrophic lakes, where species of Cyanophyceae and Bacillariophyceae dominated the phytoplankton biomass, optimum phosphatase activity was found at pH 7.5 or 8.5.
3. The pH optimum of phosphatase activity often differed from the corresponding lake water pH.
4. Experimental variation in phosphorus availability resulted in predictable changes in phosphatase activity. However, specific phosphatase activity, calculated per biomass of phytoplankton, was dependent on plankton species composition.     

The development of fungi as affected by pH and type of soil, in relation to the occurrence of bacteria and soil fungistatic activity

A study was made on the effect of liming (Ca(OH)2) on the numbers of colony-forming units (CFU) and the biomass of fungi in loamy sand (ls) and a loose sandy soil (lss) during 90 days under laboratory conditions. Liming inhibited the growth of fungi more strongly in the lighter soil. Raising the pH of lss from its native 4.5 to 7.0 and 9.0 decreased mean fungal CFU numbers by 50%, and their biomass by 42% and 68%, respectively, in comparison with control unlimed samples. Also in ls with its native pH of 7.7, when alkalinised to 9.0 and 11.0 the fungal CFU numbers were smaller than in the control by 25% and 50%, respectively, and the fungal biomass decreased by 40% and 56%, respectively. Although in a parallel research alkalinisation has been shown to stimulate bacterial growth very strongly, especially in lss, the total microbial biomass (fungal + bacterial) declined by an average of 30% (pH 9.0) and 40% (pH 11.0) in limed ls, and by 35% (pH 7.0) and as much as 50% (pH 9.0) in lss, in comparison with the control.     

The distribution of geophilic dermatophytes and other keratinophilic fungi in relation to the pH of the soil

Summary Keratinophilic fungi have been isolated from 178 (71.3 %) out of 250 soil samples taken from different sites in the surroundings of Berlin. The pH-values of the soils recorded vary within a range from 3.0 to 8.0. Most of the soils with the lowest pH (3.0–4.5) do not yield keratinophilic fungi while almost all of them with a pH higher than 5 do contain 1 to 6 kerationphilic species. The average pH of soils negative for these fungi is pH 4.1, the average pH of positive samples is 5.8. The distribution of individual species is also influenced by the pH of the soil. OnlyKerationmyces ajelloi is recovered in the same rate from soils with pH lower and higher than 6, the other species more frequently occur in weakly acid to weakly alkaline reacting soils. The development of keratinophilic and keratinolytic fungi generally seems to be favoured under nearly neutral to weakly alkaline conditions. A similar range of pH has proved to be the most favourable to several metabolic activities of these fungi. The pH-optima of enzymes excreted by dermatophytes have been found to be within this range. Enzyme activity is inhibited if the pH of the substrate decreases below 4.0. The absence of keratinophilic fungi in strongly acid soils may therefore be due to the inhibition of enzyme activities under these conditions.

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Zusammenfassung Aus 178 von 250 in der Umgebung von Berlin gesammelten Bodenproben wurden keratinophile Pilze isoliert (71,3%). Die untersuchten Böden wiesen pH-Werte zwischen 3,0 und 8,0 auf. Es bestanden enge Beziehungen zwischen dem pH-Wert des Bodens und dem Vorkommen keratinophiler Pilze. In den meisten Proben mit pH-Werten unter 4,5 fehlten diese Pilze, während in fast allen Proben mit pH-Werten über 5,0 mindestens eine, oft mehrere keratinophile Arten nebeneinander vorkamen. Der Durchschnitts-pH-Wert aller Proben, die keine keratinophilen Pilze aufwiesen, betrug 4,1, der entsprechende Wert für solche Pilze enthaltende Proben 5,8. Die einzelnen Arten zeigten eine unterschiedlich starke Bevorzugung der schwach sauer bis schwach alkalisch reagierenden Böden. NurKeratinomyces ajelloi war in Böden mit pH-Werten unter und über 6,0 gleichmäßig verteilt, während alle anderen Arten in fast neutralen Böden gehäuft auftraten. Wachstum und Stoffwechsel keratinophiler und keratinolytischer Pilze werden anscheinend grundsätzlich unter neutralen bis schwach alkalischen Bedingungen gefördert. Die pH-Optima von Dermatophyten ins Nährmedium ausgeschiedener Enzyme liegen auch in diesem Bereich. Sinkt der pH-Wert des Substrates unter pH 4,0, wird die Aktivität dieser Enzyme fast völlig unterbunden. Das Fehlen keratinophiler Pilze in stark sauren Böden läßt sich daher wahrscheinlich auf eine Hemmung iher für den Aufschluß des Keratins notwendigen Ektoenzyme zurückführen.

     

Ecophysiological adaptations of two Mediterranean red algae in relation to distribution

Effects of irradiance and temperature on the Mediterranean red algae Eupogodon spinellus and Eupogodon planus were tested. Growth of both species was saturated at an irradiance of 10–20?μmol?m^?2?s^?1, which is in accordance with their sublittoral habitat. Eupogodon spinellus and E. planus survived permanently at temperatures between 8 and 30?°C. The temperature optimum for growth was 25?°C with suboptimal growth occurring at (10?)15 and 30?°C in both species. At their collection locality (Corsica), potential monthly growth yields would be highest in summer and in winter would be only about 20% of the maximum. Reproductive requirements could be determined only in E. planus. Gametophytes reproduced both in long and in short days but only at 20?°C. Tetrasporophytes reproduced at 15–20?°C but only in short days. Geographic distribution boundaries are not set by growth or survival limits. However, the reproductive requirements of E. planus did account for its restricted distribution in the Mediterranean and on the Canary Islands.     

Effects of Neotyphodium fungi on Lolium multiflorum seed germination in relation to water availability

BACKGROUND AND AIMS: Temperate endophyte-infected (Neotyphodium sp.) grasses have been shown to exhibit an ecological advantage over endophyte-uninfected grasses under abiotic stressful conditions. It is predicted that endophyte-infected plant populations will display higher rates of germination and proportion of germinated seeds under limiting water conditions. METHODS: The hydrotime regression model was used to describe the effect of Neotyphodium endophyte on seed germination of Lolium multiflorum at different water potentials. Additionally, seed mortality after water stress exposure was estimated in endophyte-infected and -uninfected seeds. KEY RESULTS: Endophyte infection inhibited seed germination at all water potentials. The hydrotime model described satisfactorily the germination responses, and revealed that endophyte-free seeds exhibited higher rates of and final percentage germination, probably due to a lower base water potential compared with endophyte-infected seeds. However, Neotyphodium endophyte conferred a higher rate of survival in those seeds that remained ungerminated when exposed to highly water stress conditions. CONCLUSIONS: Changes produced by Neotyphodium endophyte in L. multiflorum seeds might affect fitness in particular ecological scenarios. For example, the presence of the endophyte may curtail seed germination when water is limiting, reducing the risk of seedling death. Conversely, endophyte-free seeds would display an enhanced germination, ensuring a more rapid seedling establishment if later water conditions do not restrict plant growth.     

pH and temperature optima for growth and sporulation in some common fungi from city waste

Relationships between the growth of certain fungi isolated from city waste and pH and temperature were examined by two methods. The tested isolates showed their maximum growth and sporulation at different pHs while temperature requirements were the same (28°C), except forHumicola grisea (43°C).Cladosporium herbarum andH. grisea showed double pH optima. The ranges of pH and temperature for sporulation were more limited than those for the vegetative growth. Although all the tested isolates showed wide tolerances to pH and temperature, the degree of tolerance varied with the isolates. A considerable change from the initial pH of the liquid medium was noted at the end of the experiment.     

The effect of water activity and pH on the production of mycotoxins by fungi growing on a bread analogue

Mycotoxin production by various toxigenic fungi, growing on a bread analogue, was investigated at various water activities (a_w) and pH combinations. Citrinin, ochratoxin A and sterigmatocystin could be detected at a_w > 0·80, while patulin was only observed at a_w= 0·95. These results show that some toxins may be produced at lower water activities than have been reported on synthetic media and suggest that, where possible, natural substrates should be used to investigate factors affect-ing mycotoxin production in foodstuffs.     

Differentiations of determinants for the community compositions of bacteria,fungi, and nitrogen fixers in various steppes

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Ecophysiological characterization of carnivorous plant roots: Oxygen fluxes,respiration, and water exudation

Various ecophysiological investigations on carnivorous plants in wet soils are presented. Radial oxygen loss from roots of Droseraceae to an anoxic medium was relatively low 0.02 – 0.07 mol(O₂) m^{– 2} s^–1 in the apical zone, while values of about one order of magnitude greater were found in both Sarracenia rubra roots and Genlisea violacea traps. Aerobic respiration rates were in the range of 1.6 – 5.6 mol kg^–1 (f.m.) s^–1 for apical root segments of seven carnivorous plant species and 0.4 – 1.1 mol kg^–1 (f.m.) s^–1 for Genlisea traps. The rate of anaerobic fermentation in roots of two Drosera species was only 5 – 14 % of the aerobic respiration. Neither 0.2 mM NaN₃ nor 0.5 mM KCN influenced respiration rate of roots and traps. In all species, the proportion of cyanide-resistant respiration was high and amounted to 65 – 89 % of the total value. Mean rates of water exudation from excised roots of 12 species ranged between 0.4 – 336 mm 3 kg^–1 (f.m.) s^–1 with the highest values being found in the Droseraceae. Exudation from roots was insensitive to respiration inhibitors. No significant difference was found between exudation rates from roots growing in situ in anoxic soil and those kept in an aerated aquatic medium. Carnivorous plant roots appear to be physiologically very active and well adapted to endure permanent soil anoxia.     

Ecophysiological diversity of alpine populations of Gammarus lacustris in relation to environmental calcium

1. The contribution of environmental calcium to ecophysiological diversity among populations of Gammarus lacustris was investigated by comparing five alpine lakes in France.
2. Calcium concentrations in the water varied with substratum lithology, ranging from 6 mg L^–1 in lakes on crystalline (igneous) rocks to 32.7 mg L^–1 in lakes on limestone, and up to 248 mg L^–1 in a lake with a gypsum environment.
3. The duration of the moult cycle and mortality rate were compared between populations by means of field and in situ laboratory and translocation experiments on adult males. Animals from water with low calcium concentrations showed a significantly longer moult cycle and higher mortality rate than those from water with high calcium concentrations. A significant increase in the duration of the moult cycle was observed in animals translocated to water of lower calcium concentration and vice versa.
4. These results suggest the existence of different physiological races of G. lacustris with an ecophysiological plasticity of calcium metabolism narrower than that of river-dwelling gammarids such as G. fossarum. This may be a consequence of geographic isolation among lacustrine populations together with the relatively stable environmental parameters in lakes.