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Element concentrations in the forest moss Hylocomium splendens: variation associated with altitude, net primary production and soil chemistry
No full textNet primary production (NPP) of the forest moss Hylocomium splendens increased significantly along an elevational gradient in the southern Alps of Italy. Extracellularly bound metals (Al, Ca, Co, Cr, Fe, Ni, Mo, Ni, Pb) showed declining concentrations in moss tissue with increasing altitude, presumably because the amount of exchange sites on the cell wall increases less than total biomass. Concentrations of intracellular elements did not vary (Cd, Cu, Mg, Na, Zn), or even increased (K) with altitude. The observed patterns were always independent of precipitation amount and soil concentrations of exchangeable elements. A higher soil nutrient status only enhanced K uptake by the moss. We concluded that variations in moss NPP, associated with elevational gradients, may significantly affect estimates of atmospheric deposition based on moss analysis in mountainous regions. © 2001 Elsevier Science Ltd. All rights reserved
Reed (Phragmites australis) decline in a brackish wetland in Italy
No full textA comparative field study was carried out at two sites (a healthy site and a declining site) in a brackish wetland in northern Italy, with the objective to investigate the symptoms and the possible causes leading to reed (Phragmites australis) decline in this area. The declining reed plants presented many of the symptoms (clumping habit, smaller size, weaker culms, abnormal rhizome and root anatomy, low starch levels in rhizomes) comprised within the so-called reed die-back syndrome, frequently observed in central European wetlands but never recorded previously in (Sub)Mediterranean regions. Soil nutrient levels did not differ much between the two sites, with nitrate concentrations in the soil being even higher at the healthy site (1.54 μg g-1; die-back site 0.76 μg g-1). Hence, eutrophication did not seem to represent a major cause in determining reed decline in this area. High sulphate concentrations in saltwater associated with low soil redox potentials (-215 mV) due to waterlogging resulted in high soil sulphide concentrations. Concentrations of organic acids, especially acetic acid, did not differ remarkably between sites. High sulphide levels presumably accounted for abnormal anatomical formations (callus blocking aerenchyma channels), lower rates of net CO2 exchange and reduced reserve storage, observed at the die-back site. This was associated with a lower mechanical resistance of reed culms which accelerated reed mortality in the die-back areas. We concluded that high sulphide levels in permanently waterlogged soils may result in die-back of reed stands in Mediterranean wetlands. © 2002 Elsevier Science Ltd. All rights reserved
Monitoring temporal trends of air pollution in an urban area using mosses and lichens as biomonitors.
No full textMonitoring air quality by using living organisms as biomonitors has received increasing attention in recent years. However, rather few studies were based on the concomitant use of passive biomonitoring (based on the different sensitivity of living organisms to air pollution) or active biomonitoring (based on their capacity to accumulate pollutants in the tissues). We carried out a repeated survey of an urban area in Northern Italy, with the objective of comparing temporal trends of different kinds of air pollutants with bioindication (passive biomonitoring) and bioaccumulation (active biomonitoring) techniques. During a five-year interval, temporal patterns of moss metal concentrations underwent significant changes probably due to intercurring variations in the importance of different pollution sources. Nitrogen (N) concentration in moss tissues also decreased and was paralleled by increasing diversity of epiphytic lichens. Increasing δ15N in moss tissues suggested a higher contribution of oxidized N species compared with reduced N species
Response of dwarf shrubs to neighbour removal and nutrient addition and their influence of community structure in a subalpine heath
No full text1. A 3-year experiment revolving nutrient addition and removal of one of two coexisting dwarf shrub species was conducted in two community types in a subalpine heathland on the northern Apennines (Italy). Vaccinium uliginosum occurred at all sites but was associated with the deciduous Vaccinium myrtillus at more sheltered nutrient-rich sites (HV community), and with the evergreen Empetrum hermaphroditum where the habitat was poorer and more exposed (EV community). Length of current-year shoots and fruit production of each species were determined in each of the 3 years, and standing crop at the beginning and end of the experiment. 2. The length of current-year shoots of both deciduous species, but not of the evergreen, varied considerably between years, presumably due to varying temperatures at the beginning of the three growing seasons. Fruit production also varied. 3. Fertilization promoted an increase in the length of V. uliginosum shoots at the HV community but not at the EV community. The removal of V. uliginosum enhanced shoot elongation in V. myrtillus (HV community) but reduced shoot elongation in E. hermaphroditum (EV community). Neighbour removal did not affect shoot length of V. uliginosum at either community. There were few treatment effects on fruiting of these clonal species. 4. The standing crop in untreated stands did not change during the experimental period. Changes in shoot length resulting from environmental manipulations were not accompanied by consistent variation in the standing crop of any species. Standing crop increased only for V. myrtillus after removing V. uliginosum at the HV community (same direction as shoot length). The standing crop of E. hermaphroditum did not change after removing V. uliginosum at the EV community, although shoot length was significantly reduced. The standing crop of V. uliginosum was unaffected by neighbour removal and was decreased by nutrient addition at both communities. 5. None of the shrubs appeared able to utilize more abundant resources to increase above-ground biomass. However, increased shoot length in nutrient-rich habitats gave V. uliginosum a superior ability to capture light compared with V. myrtillus, the latter being more successful when the coexisting competitively superior species was removed. This would support Grime's theory, indicating that competition becomes more important as soil resource levels increase. Positive interactions appeared to play a role in the more extreme habitat, where E. hermaphroditum normally benefitted from the shelter of the V. uliginosum canopy but was able to adapt its architecture when exposed
Water- and nutrient-use efficiency of a deciduous species, Vaccinium myrtillus, and an evergreen species, V. vitis-idaea, in a subalpine dwarf shrub heath in the southern Alps, Italy
No full textPeriodic measurements of gas-exchange rates and determinations of foliar N and P concentrations were used for evaluating instantaneous water-use efficiency and photosynthetic nutrient-use efficiency in two co-existing dwarf shrubs of different growth form (V. myrtillus, deciduous, and V. vitis-idaea, evergreen) in a subalpine heath in the southern Alps of Italy. Those data were compared with cumulative assessments of water-use efficiency and photosynthetic nutrient-use efficiency obtained by measuring leaf carbon isotope discrimination in leaf tissues and by estimating nutrient resorption from senescing leaves. V. myrtillus presented higher dry-weight based rates of net photosynthesis (A(weight)) compared to V. vitis-idaea. A(weight) was positively correlated with foliar-nutrient status and intercellular-to-ambient gradient in CO2 concentrations. A(weight) was, furthermore, negatively correlated with leaf specific mass. Instantaneous photosynthetic nutrient-use efficiency did not differ between the two species but the percentages of N and P pools resorbed from senescing leaves were somewhat higher in the deciduous species. The evergreen species showed lower P concentrations in senescing leaves which indicated a higher proficiency in resorbing phosphorus compared to the deciduous species. In addition, the evergreen species achieved a higher carbon gain per unit foliar N and P, due to a longer mean residence time of both nutrients. The two species did not differ from each other with respect to both instantaneous and long-term water-use efficiency. This was consistent with the climatic pattern, showing no sign of water deficiency through the growing season. Current-year V. vitis-idaea leaves had a significantly higher δ13C compared to previous-year leaves, possibly mirroring a long term acclimation of evergreen leaves, as far as they age, to the habitat conditions in the understory where evergreen species are usually confined within mixed dwarf-shrub communities
Nutrient and carbon relations in subalpine dwarf shrubs after neighbour removal or fertilization in northern Italy
No full textTwo subalpine dwarf-shrub heath communities with differing levels of soil nutrient availability were subjected to a 3-year experimental manipulation, including nutrient addition or removal of one of the two co-dominant species from each community. The main objective of our study was to assess the relative importance of interspecific competition versus nutrient limitation in relation to soil fertility. We also aimed to investigate if and to what extent current-year shoot size, leaf-based rates of net photosynthesis and foliar nutrient status accounted for the observed changes in the aboveground biomass of the shrubs. At the end of the experiment, neighbour removal increased the aboveground biomass of all shrubs, especially in the more fertile community, while fertilization did not. We concluded that: (1) competition is more effective than nutrient limitation in structuring the vegetation of subalpine heathlands; and (2) competition intensity is stronger in the more fertile community. The observed patterns of variations in aboveground biomass were not consistently related to net photosynthetic rates, size of individual shoots and foliar nutrient status. Hence, we also concluded that the growth response of dwarf shrubs to altered environmental conditions is primarily determined by developmental plasticity
Growth response of sphagnum capillifolium to nighttime temperature and nutrient level: Mechanisms and implications for global change
No full textIndividuals of Sphagnum capillifolium were cultured for 2 mo under six different combinations of nighttime temperature and nutrients. Low nighttime temperature caused a five-fold reduction of growth. Growth was also reduced when the plants were cultured without any addition of nutrient in the growing medium, but only when nutrient deficiency was coupled with high nighttime temperature. Growth reduction was associated with decreased rates of net photosynthesis, but was not accompanied by a degradation of photosynthetic pigments and/or variations in the pigment ratios, nor was the ultrastructure of chloroplasts significantly altered. The decline in the net photosynthetic rate may be due to a limitation in the enzymatic reactions at unfavorable temperatures. Nitrogen and, especially, phosphorus appeared to limit growth of Sphagnum capillifolium at optimal temperatures. A nighttime temperature of 5°C was above the lower threshold triggering the synthesis of red wall-pigments, known to be promoted by nighttime chilling. Climate warming is expected to increase the growth rates of Sphagnum, but the consequences on the carbon balance of peatlands cannot be predicted because temperature rise may also enhance breakdown of peat
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Morpho-physiological and biochemical responses in the floating lamina of Trapa natans exposed to molybdenum
No full textThe response to molybdenum (Mo) was studied in the metal-tolerant hydrophyte Trapa natans L. Previously, it was shown that the plant accumulates Mn in the floating lamina by means of phenolic compounds and responded with acclimation responses of the chloroplast. Since the involvement of phenolics has been proposed also in Mo resistance, we tested the response of T. natans to increasing doses (5, 50, 150, 600 μM) of Mo using the photosynthetic apparatus as an indicator of cellular stress. Only 5 μM Mo did not cause evident modifications with respect to controls. Conversely, 50 to 600 μM Mo induced progressively marked alterations of the lamina morphology. The chloroplast ultrastructure showed disorganisation of the thylakoid system, and correspondingly, the photosynthetic pigment pattern was altered with a fall-down in photosynthesis. Microspectrofluorimetry indicated alterations of photosystem II, with differences among the three cell layers (first and second palisade and spongy tissues). While the highest dose caused plant death, 50 and 150 μM Mo-treated plants underwent partial recovery, and the plant survived up to the end of the vegetative season. However, reproduction was unsuccessful. Mo treatment did not induce increase in total phenolics, but only in anthocyanin. In contrast to Mn, detoxification of Mo by chelation inside vacuoles, possibly by anthocyanins, is suggested to be an insufficient mechanism to reduce Mo toxicity, which probably
includes an impairement of nitrogen metabolism. However, the metal was accumulated in the lamina. On the whole, T. natans showed limited capabilities to survive Mo excess as compared with Mn
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