196,228 research outputs found
Tre figure. Achille, Meleagro, Cristo
No full textPer una serie di circostanze imprevedibili le immagini di Achille, Meleagro e Cristo, usate e riusate per secoli, s'intrecciarono, sovrapponendosi. Che cosa spiega la loro ibridazione, la loro persistenza, la loro migrazione attraverso il tempo e lo spazio? Quanto contarono, nella fortuna di queste figure, le formule compositive originarie e quanto il contesto che di volta in volta le fece proprie? Questo libro cerca di rispondere a queste domande. Chi legge entra in un cantiere dove hanno lavorato, separati da secoli o millenni, scultori e pittori, storici e storici dell'arte. Luca Giuliani analizza la genesi e il precoce riuso nell'antichità romana dell'iconografia di Achille in lutto presso il cadavere di Patroclo; Maria Luisa Catoni, la possibile genesi e il riuso in età post-antica di una formula della disperazione di fronte alla morte; Salvatore Settis, la fortuna rinascimentale di uno schema iconografico antico usato per rappresentare il corpo esanime di Cristo; Carlo Ginzburg, la genesi della nozione di Pathosformel (formula di pathos) coniata da Aby Warburg
Morphological and physiological adaptive traits of Mediterranean narrow endemic plants: The case of Centaurea gymnocarpa (Capraia Island, Italy)
No full textA case study on Centaurea gymnocarpa Moris & De Not., a narrow endemic species, was carried out by analyzing its morphological, anatomical, and physiological traits in response to natural habitat stress factors under Mediterranean climate conditions. The results underline that the species is particularly adapted to the environment where it naturally grows. At the plant level, the above-ground/below-ground dry mass (1.73 +/- 0.60) shows its investment predominately in the above-ground structure with a resulting total leaf area per plant of 1399 +/- 94 cm(2). The senescent attached leaves at the base of the plant contribute to limit leaf transpiration by shading soil around the plant. Moreover, the dense C gymnocarpa leaf pubescence, leaf rolling, the relatively high leaf mass area (LMA = 12.3 +/- 1.3 mg cm(-2)) and leaf tissue density (LTD = 427 +/- 44 mg cm(-3)) contribute to limit leaf transpiration, also postponing leaf death under dry conditions. At the physiological level, a relatively low respiration/photosynthesis ratio (R/P-N) in spring results from high R [2.26 +/- 0.59 mu mol (CO2) m(-2) s(-1)] and P-N [12.3 +/- 1.5 mu mol (CO2) m(-2) s(-1)]. The high photosynthetic nitrogen use efficiency [PNUE = 15.5 +/- 0.4 mu mol (CO2) g(-1) (N)s(-1)] shows the large amount of nitrogen (N) invested in the photosynthetic machinery of new leaves, associated to a high chlorophyll content (Chl = 35 +/- 5 SPAD units). On the contrary, the highest R/PN ratio (1.75 +/- 0.19) in summer is due to a significant PM decrease and increase of R in response to drought. The low PNUE [1.5 +/- 0.2 mu mol (CO2) g(-1) (N) s(-1)] in this season is indicative of a greater N investment in leaf cell walls which may contribute to limit transpiration. On the contrary, the low RIPN ratio (0.05 +/- 0.02) in winter is resulting from the limited enzyme activity of the respiratory apparatus [R = 0.23 +/- 0.08 mu mol (CO2) m(-2) s(-1)] while the low PNUE [3.5 +/- 0.2 mu mol (CO2) g(-1) (N) s(-1)] suggests that low temperatures additionally limit plant production. The experiment of the imposed water stress confirms that the C gymnocaipa growth capability is in conformity with the severe conditions of its natural habitat, likewise as it may be the case with others narrow endemic species that have occupied niches with similar extreme conditions
Effect of calcite on the soil porous structure: natural and experimental conditions
No full textTo evaluate the infilling of pores during calcification, we studied the pore size distribution of a sandy Calcisol by N2 adsorption and Hg porosimetry. Carbonates were removed and the data compared with those from a Haplic Arenosolbefore and after addition of calcite. Calcite addition induced variations in the pore volumes, which were purely addictive and depended on the porosity characteristics of the silicate plus organic fraction and CaCO3. I n the Calcisol samples, the removal of carbonates increased the pore volumes, but the mechanism cannot be explained by a simple additive effect. The < 2 nm pores were affected by the non-carbonate soil fraction, the 2-50 nm size class was the most affected by calcification, while the infilling of the larger pores depended on the size and on carbonate contents. T he largest pores are infilled only when CaCO3 concentration is around 30%, while the smallest class determined with Hg intrusion is affected at about 15% of carbonates
Analysis of mesophyll conductance in five understory herbaceous species
No full textMesophyll conductance (gm) has received over time much less attention than stomatal conductance (gs), although it affects leaf photosynthesis to about the same extent as stomatal conductance does. The objective of this study was to analyze the gm trend in five understory herbaceous species growing in a close-canopy forest in the north-west of Italy. In particular, three of analyzed species were monocots: Carex brizoides Lam., Carex pilosa Scop., and Oplismenus undulatifolius P. Beauv and the others dicots species: Circaea lutetiana L., and Pulmonaria officinalis Ced. The results showed, on one hand, the absence of correlation between gm and the considered environmental variables in the forest understory (i.e. air temperature, photosynthetic photon flux density and carbon dioxide concentration). Moreover, we carried out a principal component analysis considering all the analyzed morphological and physiological variables for the five species. The following correlation between the first component, related to the leaf mass per unit of leaf area and the leaf tissue density, and gm seem to suggest a key role of the leaf structural features in determining gm variations across the five specie
Carbon Stock Estimation in an Unmanaged Old-Growth Forest: A Case Study from a Broad-Leaf Deciduous Forest in the Northwest of Italy
No full textThe aim of the study was to evaluate the carbon storage capability of an unmanaged old-growth deciduous forest developing inside a Natural
Reserve. Our research aims to emphasize how the conservative management, by determining the actual structure and species composition,
resulted in a high carbon storage capability. The results highlight that the forest stores a large carbon amount (CTot = 418 Mg C ha–1) with the
greater pool in the aboveground biomass and in the soil (42%). In particular, among the most abundant species, Populus spp. and Quercus robur
are the major carbon sink of the forest, accounting for 31% and 63% of the forest aboveground biomass. In addition, the total economic benefits
from carbon storage of the forest of 11 209 $ ha−1 was estimated. Thus, preserving this type of forest structure and tree species composition can
ensure in the future the same forest contribution to the local carbon stock
Humus forms as a synthetic parameter for ecological investigations. Some examples in the Ligurian Alps (North–Western Italy)
No full textIn the Ligurian Alps, a wide range of site conditions that influence soil development and may affect humus variability is present. In this work, we wanted to evaluate the potentialities of humus forms as a synthetic indicator of both chemical properties of the humic episola and site conditions in the upper Tanaro Valley (NW Italy). Vegetation affected the C/N ratio of the least transformed organic horizons, but the effect disappeared in mineral ones, where soil pH was related to the parent material. All terrestrial humus forms were found in the area and their distribution well reflected the interactions between vegetation, lithology, elevation that shaped soil properties and affected the degradability of litter and its actual degradation by microorganisms and soil fauna. Humus forms were thus able to capture the ecological conditions, integrating the information provided by soil classifications
Assessing the origin of carbonates in a complex soil with a suite of analytical methods
No full textStable isotope C analysis is the most reliable method used for the distinction and understanding of soil carbonates origin. However, in soils with a complex geological setting the carbonate δ13C signature could lead to incorrect interpretations if used alone. Thus coupling this technique to other methods may be necessary. In this work we evaluated advantages and disadvantages of several methods, some of which are well known while others are still unused, to distinguish among carbonates of different origins in a soil developed on “Valle Versa Chaotic Complex”, a marly geological formation in North-western Italy. For a better evaluation of their potentialities the methods were also applied to simpler situations used as a reference for carbonate of pedogenic and lithogenic origins. Thin sections analysis revealed the presence of three kinds of carbonates in the investigated complex soil: one was pedogenic, while two showed clear lithogenic origin. The lithogenic carbonate that showed a low δ13C (about −9‰) was interpreted as freshwater while isotopic signature increased up to −4‰ with the presence of marls, thus no evidence of pedogenic precipitations could be obtained with isotopic analysis. The mean crystallite domain (L104) was highly variable and related to the amounts of co-precipitated impurities in the carbonates. Thus these methods provided important information about the formation environment. These rarely used techniques permitted to distinguish between pedogenic and lithogenic material in simple systems, but did not adequately support the presence of pedogenic carbonates in the complex soil. Surface areas and porosity evaluated by N2 adsorption are particularly influenced by the processes occurring during calcification such as the development of coatings and pore infillings. The comparison between additive models and measured specific surface area, indeed allowed us to observe the effect of pedogenic carbonate on the physical properties, although it did not permit any quantification. These results indicated that, although all the methods were able to distinguish between pedogenic and lithogenic origins in simple systems, only micromorphology and N2 adsorption techniques allowed for the identification of pedogenic carbonate in a more complex soil system
Contrasting environmental memories by ancient soils on different parent rocks in the South-western Italian Alps
No full textAncient soils (pre-Holocenic paleosols and vetusols) are uncommon on the Alps, because of the extensive
Pleistocenic glaciations which erased most of the previously existing soils, the slope steepness and climatic
conditions favoring soil erosion. However, in few sites, particularly in the outermost sections of the Alpine range,
Pleistocene glaciers covered only small and scattered surfaces because of the low altitude reached in the basins,
and ancient soils could be preserved for long periods of time on particularly stable surfaces.
We described and sampled soils on 11 stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern
Piemonte, Italy). The sampling sites were characterized by low steepness and elevation between 600 to 1600
m, under present day lower montane Castanea sativa/Ostrya carpinifolia forests, montane Fagus sylvatica and
Pinus uncinata forests or montane heath/grazed grassland, on different substrata. In particular, we sampled soils
developed on dolomite, limestone, quartzite, gneiss and shales.
The soils were always well representative of the pedogenic trends active on the respective parent materials, i.e.
the skeletal fraction in each soil was always composed of just one rock type, despite the proximity of lithological
boundaries and the small dimensions of the different outcrops, often coexisting on the same stable surface.
All the considered profiles showed signs of extremely long pedogenesis and/or different phases of intense
pedogenesis interrupted by the deposition of periglacial cover beds in the steepest sites. Up to four phases of
intense pedogenesis were recognized where cover beds were developed, presumably during cold Pleistocene
phases, as present-day climate is not cold enough to create such periglacial morphologies. In such cases, each
cover bed underwent similar pedogenesis, strongly dependent on the parent material: on quartzite, podzols with
thick E horizons and well developed placic ones were formed in all phases except the most superficial one (i.e.
Holocene phase), where non cemented spodic horizons or weakly cemented ortstein were formed; placic horizons
were never found in Holocene soils. On limestone, each cover bed separated soils with extremely hard petrocalcic
horizons overlaid by argillic ones.
Where no cover beds were observed, podzols with extremely thick E horizons (up to more than 2 m thick) and a
very hard, very thick ortstein were formed on quartzite. Red Nitisols-like or reddish brown Luvisols were formed
on limestone and dolomite, while red, extremely acidic Alisols, with or without fragipan horizons were formed on
shales. Very large stone circles and other large patterned ground features, which can be interpreted as evidence of
past permafrost conditions, were preserved on coarse quartzitic conglomerate.
These soils represent excellent pedo-signatures of different specific past climatic or environmental conditions,
as a response of different lithologies to specific soil-forming environments, which range from warm and humid
climates typical of red Luvisols and Nitisols, to cool and wet climates leading to the formation of Podzols with
placic or ortstein horizons, to extremely cold and dry ones characterizing permafrost sites and often associated
with fragipan formation, to warm and dry leading to the cementation of petrocalcic horizons. The precise dating
and interpretation of these soils are intriguing
Micropore characteristics of organic matter in cemented and non-cemented spodic horizons
No full textSoils store three times as much organic carbon (OC) as is found in living plants, and most forest soils are active CO 2 sinks at present. With climate change however, the capacity of soils to preserve OC against degradation will highly depend on the presence of stabilized organic matter (OM) pools. Podzols are among the most characteristic soils in forest ecosystems and their formation is linked to OM movements through the profile and the following stabilization by metal-organic interactions (Fe-and Al-OM) in deeper soil horizons. Recently, we found that the type of metal-organic association changes with increasing intensity of podzolisation and that the variations can be followed by evaluating specific surface area (SSA) by N 2 adsorption. We hypothesised that at later stages of podzolisation stable OM is more tightly bound to metals, hence more rigid and poorer in N 2-accessible pores. In well-developed Podzols, cemented metal-rich horizons (ortsteins i.e. Bsm or Bhsm) may form in addition to non-cemented Bs or Bhs ones. In orsteins the rigidity/condensation of stabilized OM should be further enhanced both because of component ageing and of high amounts of metals. Consequently, OM in cemented podzolic horizons should have a higher amount of N 2 non-accessible pores. In this work we evaluated the specific surface area and porosity of bulk and stabilized OM in cemented and non-cemented podzolic B horizons using gas-adsorption. Thanks to the different accessibility of the probe molecules, the pores between ~<2 and 50 nm and down to less than 0.5 nm can be characterized by, respectively, N 2 (77K) and CO 2 (273K). Four Podzols were selected in Northwestern Italy and both Bs or/and Bhs and cemented horizons were sampled. The samples were treated with 6% NaClO at pH 8, to eliminate the most labile OM, and surface properties were measured before and after oxidation (UT and T samples, respectively) with both N 2 and CO 2. The Bs/Bhs horizons had around 23% of oxidation-resistant OC while orsteins generally showed a slightly higher proportion (29%). The N 2 detectable specific surface area (SSA) seemed to be strongly affected by the porosity of mineral phase, but the variation of SSA upon oxidation was linked to the horizon type. Only the OC richest horizons (Bs/Bhs and Bhsm) showed the typical increase in SSA after removal of labile OM, while in the cemented horizons the SSA decreased. This probably reflects the exposure of highly stabilized OM, richer in small micropores, in the ortsteins. Plotting the SSA measured by CO 2 vs. the amount of OC revealed that the microporosity occurrence mainly depended on the presence of OM in both UT and T samples (r 2 =0.973 and 0.918, respectively), with the exception of Bhsm horizons that, in both cases, showed a lower SSA with respect to OC content than the other samples. The anomalous behavior of Bhsm could be related to the high presence of roots, hence to the presence of chemical recalcitrance as an additional mechanism in OM stabilization. The relationships between SSA and OM in UT and T samples had equivalent intercept values (4.35 and 4.36 m 2 g-1 , respectively), pointing out that oxidation had no effect on the contribution of the mineral phase on micropore surface. The slopes instead were different, and indicated that stabilized OM increased SSA twice as much as the UT sample. Our results show that stabilized OM structure in Podzols sharply differ from that of more labile OM pools thanks to a larger presence of small micropores. The high amount of <0.5 nm pores may contribute in preserving organic matter towards degradation, thus decreasing its turnover even in a climatic change perspectiv
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