177,022 research outputs found
Drought responses in Aleppo pine seedlings from two wild provenances with different climatic features
No full textVolatile profile of perennial leaves of seven cultivated species of Ceratozamia (Cycads)
No full textCeratozamia (Zamiaceae) is a genus of New World Cycads, containing more than 20 species distributed in eastern and southern Mexico, with extensions into Central America [1]. Morphology, anatomy, and molecular data allowed resolution of some aspects of species relationships, suggesting phytogeographic hypotheses [2]. Renewed interest in cycads has also resulted in works focused on phytochemical topics [3 and literature therein], however data on the volatile emission profiles lack.
Seven Ceratozamia species belonging to clade “C” [2] and cultivated in a cold greenhouse at the Florence Botanic Garden were investigated: Ceratozamia fuscoviridis D. Moore, Ceratozamia hildae Landry & M. Wilson, Ceratozamia kuesteriana Regel, Ceratozamia latifolia Miq., Ceratozamia longifolia Miq., Ceratozamia mexicana Brongn., Ceratozamia vulgaris J. Schust. Perennial leaves were screened in February, July and September 2011 for the emission of volatile organic compounds (VOCs) by means of headspace solid phase microextraction coupled with gaschromatography and mass spectrometry (HS-SPME-GC/MS); two leaflets per species were sampled from coetaneous leaves, and analysed. In this study we assessed and compared the volatile profiles among species and across sampling periods, with the main objective to collect preliminary information to evaluate the potentiality of VOCs for taxonomic purposes.
The VOC analysis revealed the emission of overall 199 compounds, of which 144 identified. The unknown compounds dominated the volatile profiles, accounting for about 27%, followed by aldehydes, terpenes, alcohols, ketones and esters. The highest number of compounds (115) was found in C. fuscoviridis, the lowest (91) in C. longifolia. In all the examined species, February profiles invariably exhibited the major amount of volatiles in comparison to July and September.
Statistical data processing proved: (i) a low level of diversity among the VOC profiles of the examined species referred to each collection time; (ii) a great variability in the temporal emission patterns of all the species across the three sampling periods.
These evidences revealed the predominance of the environmental components at the study area in affecting the volatile profiles of Ceratozamia species, at the expense of the metabolic resilience related to the different climatic conditions of the native regions. Possible ecological roles of the VOC temporal variation in relation to the plant phenological stages are discussed
Plant species loss and community nestedness after leguminous tree Acacia pycnantha invasion in a Mediterranean ecosystem
No full textInvasions of ecosystems by alien species are one of the major threats to biodiversity. Among alien plant species, members of the family Fabaceae s.l. represent some of the most dangerous and well known global invaders. In Mediterranean ecosystems, many Australian acacias have been found to establish and rapidly spread, often determining severe impacts on understorey vegetation. In the present work, we report a case study of an Acacia pycnantha invasion in a typical Mediterranean matorral (Elba Island, central Mediterranean Sea, Italy). We conducted a survey of understorey plant communities across an invasion gradient from non-invaded to transitional and invaded areas, aiming to quantify the impacts on the understorey assemblage and to investigate the ecological processes involved in the changes in species composition. The understorey plant community was highly affected starting from the intermediate stage of invasion. Species richness, diversity and total cover were all lower in invaded than in non-invaded plots, with a transition generally in the middle. In addition, plant community composition severely changed along the invasion gradient. The species set we recorded showed a nested structure, with the composition of species in the invaded plots representing a subset of the others. According to our findings, A. pycnantha exerted detrimental impacts on the native vegetation, mainly causing a severe species loss in the understorey assemblage and the impoverishment of the invaded ecosystems
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Aleppo pine knot disease: Histology of the knots, detection of causal agent and mode of transmission
No full textKnot disease of Aleppo pine (Pinus halepensis subsp. halepensis) occurs in the western range of the host in the Mediterranean region. The disease, originally named Aleppo pine tuberculosis (from tubercle, i.e. knot) by Petri in 1924, causes a hyperplastic growth on the twigs and small branches, with knots that initially are small, green and lignified, and expand to 5–6 cm diameter at maturity. These knots have been associated with various bacterial species. In this study, only one bacterium was isolated from Aleppo pine knots, and this bacterium was constantly associated with the pine weevil Pissodes castaneus. The hyperplastic growth started either in the cortex or in the xylem, while the knot was formed in the cortical parenchyma. Bacteria were grouped in zoogloeae in the intercellular spaces or inside lysigenous cavities. Bacterial microcolonies have also been observed in the parenchyma cells. Inoculation of two of the bacterial strains on healthy Aleppo pine twigs did not induce knot formation. Knots did however form when adults of P. castaneus were externally contaminated with the bacteria and were then allowed to feed on pine saplings. These latter knots contained the same bacterial isolate as that which had been used to contaminate the weevils. All the isolates examined were tentatively assigned to the genus Erwinia. As this bacterium seems to be the causal agent of Aleppo pine knot disease, its complete identification and characterisation is needed
Soil and plant changing after invasion: the case of Acacia dealbata in a Mediterranean ecosystem
No full textAcacia dealbata Link (Fabaceae) is one of the most invasive species in the Mediterranean ecosystems of Europe, Africa and America, where it has been proved to exert strong effects on soil and plant communities. In Italy A. dealbata has been largely used for ornamental and forestry purpose and is nowadays spreading in several areas. The present study was addressed to evaluate the impacts on soil chemical properties, soil microbial communities and understory plant communities and to assess the relationships among these compartments after the invasion of A. dealbata in a typical Mediterranean shrubland. Towards these aims, a soil and vegetation sampling was performed in Elba Island where A. dealbata is invading the sclerophyllous native vegetation. Three levels of invasion status were differentiated according to the gradient from invaded, to transitional and non-invaded vegetation. Quantitative and qualitative alterations of soil chemical properties and microbial communities (i.e. bacterial and fungal communities) and above-ground understory plant communities were found. In particular, the invaded soils had lower pH values than both the non-invaded and transitional ones. High differences were detected for both the total N and the inorganic fraction (NH4+ and NO3-) contents, which showed the ranking: invaded>transitional>non-invaded soils. TOC and C/N ratio showed respectively higher and lower values in invaded than in non-invaded soils. Total plant covers, species richness and diversity in both the non-invaded and transitional subplots were higher than those in the invaded ones. The contribution of the nitrophilous species was significantly different among the three invasion statuses, with a strong increase going from native to transitional and invaded subplots. All these data confirm that A. dealbata modifies several compartments of the invaded ecosystems, from soil chemical properties to soil and plant microbial communities determining strong changes in the local ecosystem processes
Induced water stress affects seed germination response and root anatomy in Robinia pseudoacacia (Fabaceae)
No full textThe different germination behaviours of the seeds under induced water limitations may be related to the different adaptive capacities acquired at the diverse collection sites, as a response to the different environmental parameters. The island of Pianosa resulted the most performant in term of germination responses and the co-occurrence of xeromorphic anatomical evidences at root level confirmed this trend. Abstract: Regeneration from seeds is an important co-determinant in the invasion ecology of black locust. In the attempt of providing new information on its invasion potential in Mediterranean Europe under the future scenario of global warming, we investigated the effects of induced water-deficit regimes on: (1) seed germination performance and (2) root growth and anatomy. Ripe seeds were collected from four populations established in Tuscany (Central Italy): mechanically scarified seeds were incubated in a range (− 0.2/− 0.8 MPa) of constant water stress conditions at 21 °C. The final germination rate drastically declined with increasing induced water-deficit conditions, with the highest value at control and at − 0.2 MPa (ca 50–97%), and the lowest at − 0.6 MPa (ca 10–33%). The mean germination time decreased with increasing water stress. At root level, xeromorphism relies on the combination of different anatomical traits which co-optimize water uptake/loss: thinner roots, higher number of xylem vessels, vessels with small-sized lumen and thinner cell walls. Seeds collected in sites characterized by different environmental parameters display a noteworthy difference in the germination dynamics: as far as the beginning and ongoing of germination, as well as the germination response in time is concerned, the seeds from the island of Pianosa showed the highest performance; the major arid conditions in Pianosa could have caused a “stress imprint” able to facilitate a fast and protective response to future drought events. As a whole, our results confirmed the great phenotypic plasticity of black locust as a response to variable water availability and provided evidence for the potential high germination capacity in drier environments, as seems to be the future Mediterranean Europe
Morphological and ultrastructural aspects of dehydration and rehydration in leaves of Sporobolus stapfianus.
No full textThe resurrection species Sporobolus stapfianus Gandoger has been studied by LM, TEM and SEM in order to
define the leaf morphology and fine structure and to analyse the cellular changes occurring during the processes of
dehydration and rehydration of the plant. Some characteristics of the fully hydrated leaf and some ultrastructural
and physiological events which take place during leaf wilting are discussed in relation to their possible role in plant
desiccation-tolerance.
The leaves of S. stapfianus show several characteristics common among xerophytic species. In the resurrection
leaf they could play a role in slowing down the drying rate, thus leaving time to activate the mechanisms protecting
the cell structures against drought damage. Actually, the S. stapfianus leaves do not undergo important cellular
alterations during dehydration. The chloroplasts, in particular, retain part of their photosynthetic pigments and
thylakoid membranes. Upon rewatering leaf recovery is rather fast and the tissue structure and cell organization of
the fully hydrated state are already regained after two days
Inter-population and temporal variation of VOC emission from Mediterranean Helichrysum Mill. (Asteraceae)
No full textMediterranean Helichrysum species are highly diverse with respect to both phenotype and metabolite profile [1].
Volatile organic compounds (VOCs) were recently recognized as valuable tools for studying Helichrysum systematics at population level [2]. In seeking carry on the studies on the phytochemical typification for taxonomic purposes, we examined the diversity and temporal variation of volatile profiles in eight selected Mediterranean populations, included within the H. italicum complex, H. litoreum and H. stoechas. The goals of this study are: (i) to evaluate and compare the differences of volatile profiles across populations and collection time, and (ii) to characterize the intra-population variation over time.
After collection in the wild, plants were cultivated in standard growing conditions at the Florence Botanical Garden, to remove the effects due to the different ecological conditions of the collection sites. The emissions of VOCs from annual leafy shoots were analysed in May, July and September 2012, by means of headspace solid phase microextraction coupled with gas-chromatography and mass spectrometry (HS-SPME-GC/MS).
The VOC analysis revealed the production of overall 417 compounds, with terpenes being the dominant compound class, followed by esters and alcohols.
Statistical data processing, based on a Permutational Multivariate Analysis of Variance and on a subsequent Variance Partitioning Analysis on the relative quantitative data of VOCs, showed a great variability in the volatile profiles across populations (69%, p<0.001), with a weak contribution due to time (5%, p<0.001), whereas the additional variance explained by the interaction term between these two factors is 19% (p<0.001). The volatile profiles of each population were consistent over time, as indicated by the high correlation coefficients (ca 65%), with the exception of only one provenance.
In conclusion, VOC profiles as a whole varied considerably from one population to another, and over time. Conversely, the low diversity of time-to-time emission pattern within each population suggests that the volatile profiles exhibit phytochemical consistency, presumably due to the standardization of the plant growing conditions. These data further enhance the potentiality of VOCs as diacritical characters in discriminating among populations and in solving taxonomic problems
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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