108 research outputs found
El concepto de progreso en el pensamiento de Juan Andrés
No full text[ES] El artículo analiza el desarrollo de la idea de progreso en el siglo XVIII, comparando la teoría del abate Juan Andrés con la filosofía del Siglo de las Luces y centrando la atención en la relación con la historia.[EN] The article examines the relationship between literature, history and science with the «idea» of progress in Juan Andrés’ works. The author explores the philosophy of progress in the human civilization through Juan Andrés’ thought
Advancements in the study of the grapevine hydraulic strategy under water deficit in relation to the formation of embolism
No full textIn recent years, the validity of embolism quantification methods has been questioned, especially for long-vesseled plants, as some studies have suggested that cutting xylem while under tension (even under water) might generate artificial cavitation. Accordingly, a rehydration procedure prior to hydraulic measurements has been recommended to avoid this artefact. On the other hand, concerns have been raised that xylem refilling might occur when samples are rehydrated. Recently we have proposed an improved method for reliable quantification of this phenomenon in grapevine petioles in which the inclusion of a short-time (20 min) xylem tension relaxation prior to the hydraulic measurement resulted in reliable quantification of native embolism. Much longer periods of hydration (overnight) were required before xylem refilling was observed to occur. This method yielded xylem vulnerability curves similar to the ones obtained using direct microCT visualization and the values were lower than the ones found in samples harvested under native tensions. The new protocol revealed cavitation in grapevine petioles occurs only after significant stomatal conductance reduction, contrary to what was previously hypothesized. In field-grown vines, over 85% of stomatal closure occurred at less negative xylem tension than that required to induce 12% loss of conductivity (PLC). These findings indicate that grapevines regulate their stomata to prevent xylem embolism and would even shed a large proportion of their leaves in order to avoid cavitation tensions. This pattern of stomatal behavior is more consistent with a strategy of cavitation resistance and avoidance, rather than a paradigm of tolerance featuring diurnal cycles of cavitation accumulation and repair
I paesaggi dell’Olivo. Una metodica per il loro riconoscimento applicata in Sardegna
No full textIntroduzione. Il Piano Paesaggistico della Sardegna (2006) ha, sinora, interessato la sola fascia costiera, articolata in 27 Ambiti di paesaggio cui si aggiungono nelle aree interne ulteriori 24 Ambiti che attendono di essere descritti e normati.
Materiali e metodi. Il riconoscimento, nei 24mila Km2 del territorio regionale, di tessere elementari subordinate agli ambiti del PPR è stato realizzato, in ambiente GIS, stratificando all’Uso del Suolo della regione Sardegna (2008), gli shape della Carta Pedologica (con substrato litologico), ricorrendo, per i casi dubbi, a verifiche in loco. L’analisi ha delimitato unità omogenee per tipologia di copertura spingendosi sino al quinto livello dell’UDS RAS. Il successivo arricchimento in conoscenze del singolo paesaggio agrario locale (PAL) è ottenuto sovrapponendo ulteriori db.
Risultati. L’analisi ha individuato 258 PAL con superfici comprese tra 118÷48.662 ettari, in funzione dell’uniformità o eterogeneità dell’uso del suolo e del substrato litologico. I PAL caratterizzati dalla prevalente presenza dell’oliveto sono 11, in 7 l’oliveto è la seconda classe UDS più rappresentata e in 15 la terza.
Conclusioni. La metodologia ha consentito di riconoscere undici ambiti elementari di paesaggio caratterizzati dalla coltivazione dell’olivo per una superficie complessiva di 17.306 ha su una superficie totale di 48.778 presenti sull’intera Isola secondo l’UDS 2008 e rispetto ai 36.468 attribuiti dall’Istat (2010) alla coltura. La progettazione di interventi di valorizzazione sarà facilitata dalla possibilità di poter calare speditamente sui poligoni ulteriori strati informativi
L’esperienza della città-giardino a Roma: Montesacro, San Saba, Garbatella
No full textThis proposal will illustrate several architectural experiences realized in Rome, during the first twenty years of the XX century, which are connected to the English Garden city model. The exposition will particularly focus on the Aniene and Montesacro examples, on the San Saba all’Aventino neighbourhood and also on the Garbatella garden suburb, which all constitute the most representative interventions related to the political decentralization supported by Gustavo Giovannoni and promoted by the Istituto per le Case Popolari of Rome. The comparison between these different interventions, in relation to the urban growth and the typological and stylistic development, will enlighten the particular features that define the Garden city model based on the necessity to combine the morphological characters of the historical city to the modern housing demands of the new city. These aspects have strongly contributed to the preserve and enhance the value of the garden suburbs, which are considered nowadays deeply embedded within the Rome historical urban fabric
Morpho-anatomical adaptations of Callistemon citrinus to CaCl2 and NaCl solutions
No full textAbiotic stress such as salinity is the major abiotic stress that reduce plant growth worldwide, especially in semi-arid regions. Ornamental plants are classified as tolerant species due to their ability to adapt under salt stress conditions. However, most studies concerning the salt tolerance of ornamental species have been based on studies in which NaCl is the predominant salt, whereas information is lacking concerning the CaCl2 effects on morphological, physiological and anatomical adaptations of ornamentals. The aim of this study was to assess the adaptation/tolerance of green house grown Callistemon citrinus an important potted flowering shrub in terms of plant growth, leaf water potential, leaf gas exchange, leaf anatomy and mineral composition, to two chloride salts NaCl and CaCl2. The experiment was performed in terms of equimolar concentrations in order to assess the ion effects of the two salinity sources. Plant growth parameters such as leaf area, leaf number, shoot and root dry weight were negatively affected by salinity, with more pronounced effects recorded under CaCl2 irrigation. The growth reduction was related to a significant decrease of the photosynthetic rate and stomatal conductance. A reduction of stomata size and palisade tissue size was also observed under NaCl irrigation. The differential responses of Callistemon citrinus plants to water salinity by CaCl2 or NaCl elicited several considerations. Other than the ion imbalance, in the CaCl2 treatment ion toxicity might have played a major role on the growth and Pn rate, since the amount of Cl ions accumulated in the leaves of these plants was doubled compared to NaCl treated ones. The adaptation mechanisms developed by the plant to cope with the salinity stress conditions are more effective under NaCl, such as the increased density of glands and trichomes
Componenti della produttività ed effetto del-l’irrigazione sulla cascola pre-raccolta dei frutti in olivi della cultivar Frantoio
No full textGli effetti dell’irrigazione sulla cascola pre-raccolta dei frutti e sulle componenti produttive dell’olivo sono stati valutati in un esperimento condotto in un oliveto (Olea europaea L., cv Frantoio) intensivo di 6 anni di età. La piena restituzione del fabbisogno idrico dell’albero (PI) durante tutto il periodo irriguo è stata confrontata con un’ir-rigazione di soccorso (IS). Settimanalmente è stato misurato il peso fresco del frutto, l’indice di maturazione e il conte-nuto in olio nella polpa. La raccolta è stata effettuata 142 giorni dopo la piena fioritura (GDPF), ad eccezione di 3 alberi per tesi raccolti 185 GDPF. A partire da 106 GDPF, e per ogni settimana fino a 185 GDPF, sugli alberi selezionati per una raccolta tardiva è stata misurata la cascola dei frutti, distinta tra cascola fisiologica e causata da B. oleae. I frutti degli alberi IS hanno mostrato un minor peso fresco durante tutto il periodo irriguo (-24%) e un maggior indice di matu-razione alla raccolta di ottobre (+25%) rispetto agli alberi PI. Non sono emerse differenze significative tra le tesi in merito al contenuto in olio nella polpa. Le produzioni ad albero nella tesi PI sono state superiori di circa il 30%rispetto a quelle degli alberi IS. A partire da 163 GDPF, e fino alla seconda raccolta, le maggiori percentuali di casco-la sono state misurate sugli alberi sottoposti ad irrigazione di soccorso. Tale cascola, prevalentemente fisiologica, è imputabile al crescente livello di stress idrico subito dagli alberi in asciutto nel corso del periodo estivo. Al contrario, la piena irrigazione ha comportato un maggior livello di infestazione di B. oleae, stimata come % di frutti con foro d’uscita, sulle produzioni alla raccolta 142 GDPF. Considerando il regime irriguo e le perdite legate alla cascola, il periodo di raccolta utile per ottenere produzioni superiori al 90% della produzione massima stimata è stato compreso tra i 263 e i 298 e tra i 273 e i 295 GDPF per la tesi PI e IS, rispettivamente
Stomatal and hydraulic water transport factors in mycorrhizated olive trees
No full textWater uptake and transport are complex processes
affected by root hydraulic conductance and water utilization,
as mediated by leaf. Arbuscular mycorrhizal (AM)
fungi may colonize roots and regulate stomatal behaviour
contributing to the overall water economy of the tree.This
study test whether AM colonisation has a beneficial effect
on total root hydraulic conductance and leaf gas exchange
parameters in olive trees both well irrigated and under
drought.Approx. 20 2-year old potted olive trees were inoculated
with Glomus intraradices, 10 inoculated trees were
kept well irrigated (WI) while the remaining were allowed
to dry up (D) till a value of -2 MPa predawn leaf water
potential (Y). Additional 20 trees were not inoculated and
served as control.Hydraulic conductance (K, kg s-1 MPa-1)
was determined by a HCFM (Dynamax, Inc. USA) (0.1-
0.5 MPa of applied pressure). Leaf transpiration (E), assimilation
(A) and stomatal conductance (gs) was appraised
through the LI-6400 (Li-Cor Inc., NE, USA).Drought in
non-inoculated trees induced a decline of midday K from
1.1±0.1 (SE) to 0.9±0.1 kg s-1 MPa-1, AM fungi maintained
K stable or even higher at 1.3±0.1 kg s-1 MPa-1 (inoculated
D trees). A positive impact on hydraulic transport (~23%
increase of K) was also detected in mycorrhizated WI
trees.In WI trees, average daily A remained similar in control
and mycorrhizated trees (~ 4 mmol CO2 m-2 s-1), concomitantly
it was registered a significant reduction of E
and gs in mycorrhizated WI trees compare to non
mycorrhizated WI. In D trees, a similar response of E and
A was detected, while gs was not clearly affected by
AM.This study revealed that AM may regulate both K and
some gas exchange parameters in both WI and D olive
trees and that the fungi improved the water use efficiency
at leaf scale. It could be concluded that knowledge and
improvement of soil biodiversity level (including AM)
through sustainable practices may be in favour of an optimal
water use in agriculture
Atmospheric nitrogen fixation by gliricidia trees (Gliricidia sepium (Jacq.) Kunth ex Walp.) intercropped with cocoa (Theobroma cacao L.)
No full textAims The objective was to estimate the fixation of atmospheric nitrogen (Ndfa) by legume (Gliricidia sepium) trees for the benefit of cocoa (Theobroma cacao) trees in agroforestry systems.
Methods Four sites where cocoa and gliricidia were intercropped and one site where gliricidia, cocoa, and orange trees were grown as separate stands were selected in Ghana. Ndfa in gliricidia and cocoa leaves (from all sites) and in shoot axes (in one site only) was assessed by the 15N natural abundance technique. Cocoa trees distant (> 10 m) from the closest gliricidia were used as reference plants.
Results With few exceptions, leaves of gliricidia and cocoa trees growing in proximity had similar δ15N, whereas the foliar δ15N value of gliricidia was lower
than that of distant cocoa trees. The Ndfa in gliricidia leaves ranged from 22 to 50% of total leaf N and was 48% in the shoot axis. Root nodules, found only after the wet season, always showed the inner red color indicating effective N2 fixation and the occurrence of Rhizobium tropici and Rhizobium etli. The annually produced shoots of gliricidia, theoretically suitable to become green manure after pruning, contained 31.4 to 38.0 kg N ha−1 derived from the atmosphere.
Conclusions Gliricidia sepium trees are able to take advantage of the association with rhizobial symbionts to fulfill, at least in part, the N needs of their rapidly growing shoots. In mixed-stand agroforestry systems, with intercropped gliricidia and cocoa trees, the amount of N derived from the atmosphere that could enter the soil if the pruned shoots of gliricidia trees are used as green manure could diminish the need for N fertilizers for cocoa trees
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