1,721,033 research outputs found
Variazioni stagionali dell’attività fotosintetica di tre specie della macchia mediterranea
No full textPer valutare come le condizioni climatiche influenzano la ripartizione dell’energia luminosa assorbita tra fotosintesi e processi dissipativi, misure di scambi gassosi e fluorescenza sono state effettuate su foglie di Quercus ilex L., Phillyrea angustifolia L. e Laurus nobilis L. in inverno ed in primavera. I risultati ottenuti hanno mostrato, per tutte le specie indagate, valori più elevati di fotosintesi e di efficienza fotochimica in primavera rispetto all’inverno facendo registrare per Q. ilex i valori più alti. In primavera, inoltre, per tutte le specie è stato evidenziato un minor contributo dei processi di dissipazione termica e fotochimica dell’energia luminosa assorbita rispetto all’inverno. Durante l’inverno il contributo significativamente più elevato dei processi di dissipazione termica e fotochimica, ha permesso, nonostante la forte riduzione della fotosintesi, di mantenere in tutte le specie una elevata efficienza fotochimica
Influenza dell'irradianza sull'attività fotosintetica di piante di Q. ilex L. cresciute su compost verde ed esposte ad elevata concentrazione di CO2
No full textMisure di scambi gassosi ed emissione di fluorescenza sono state effettuate su piante di Quercus ilex L. impiantate su terreno sabbioso (controllo) e su una miscela di compost verde 65% ed argilla espansa 35% (CV) per valutare l’influenza del substrato di crescita sulla fotosintesi all’aumentare dell’irradianza a 390 e a 800 ppm di CO2. A 800 ppm di CO2 le piante hanno mostrato rispetto a 390 ppm, un incremento significativo della fotosintesi e dell’attività di trasporto elettronico ed una diminuzione della foto-assimilazione fogliare di nitrati e dei processi di dissipazione termica e fotochimica dell’energia luminosa su entrambi i substrati di crescita. Inoltre, poiché sia a 390 che a 800 ppm di CO2 l’impianto sulla miscela di compost verde ha determinato una fissazione di carbonio ed un’attività di trasporto elettronico significativamente più elevate rispetto alle piante controllo, in tutto l’intervallo di intensità luminose, si può concludere che non solo l’esposizione ad elevate concentrazioni di CO2, ma anche il substrato di crescita influenza notevolmente la risposta fotosintetica di Q. ilex all’aumentare dell’irradianza
Morphological and physiological modifications of Cistus salvifolius L. winter leaves to rise of winter temperatures
No full textThe global climate is predicted to change in the next century; for the Mediterranean Basin, an increase in air temperature more than 4°C and a higher frequency of extreme climatic events such as drought and heat waves are expected. In this work, the response of Cistus salvifolius L. to the rise in winter temperature has been studied. Plants acclimated to winter conditions [outdoor (OUT)] were moved into a greenhouse [indoor (IND)] at higher temperature and eco-physiological behaviour was analysed on leaves after 15 days from plant transferring (IND15d) and on leaves developed IND. IND leaves were characterized by reduced thickness, higher specific leaf area, higher CO2 mesophyll conductance and photosynthetic rate, and lower respiratory rate than leaves grown OUT upon current winter conditions. In IND15d leaves, no improvement of photochemical activity was found. When IND leaves were subjected to a rapid increase in air temperature, the CO2 fixation was not limited indicating a high thermotolerance of photosynthetic machinery. The results for IND leaves indicate the occurrence of a strategy that merging changes in leaf structure as well as in photosynthetic regulation allow C. salvifolius to maintain an elevated carbon gain in response to temperature increase
Physiological and morphological acclimation of Cistus salvifolius L. winter leaves to elevated temperatures.
No full textAnnual dynamics of photosynthetic activity and photoprotective strategies in seedlings of Phillyrea angustifolia L.
No full textPlants of Mediterranean Basin are adapted to cope with wide thermal excursion over the year in order to maintain an optimal photosynthetic performance. In this study the annual dynamics of photosynthetic activity and photoprotective strategies were investigated in P. angustifolia, one of the most common species of Mediterranean maquis. To evaluate the contribute of photochemical and thermal dissipation in PSII photoprotection, gas exchange and chlorophyll fluorescence measurements were performed at saturating irradiance on two-years-old seedlings grown outdoor. The lowest values of net photosynthesis, stomatal conductance and apparent carboxylation efficiency were found in July and February; in these months the Ci/Ca ratio was the lowest and the highest, respectively. No difference was observed in quantum yield of PSII electron transport and maximal PSII photochemical efficiency throughout the year, except for the strong decrease in February. Non-photochemical quenching peaked in July and February, when the highest and the lowest ETR/AN ratio, respectively, occurred. Data suggest that in July, photochemical sinks other than CO2 fixation and thermal dissipation are able to dissipate safely the excess of energy to reaction centres. In February thermal dissipation becomes the most important safety valve for photosynthetic apparatus, but is unable to prevent efficiently photoinhibition as indicated by the maximal PSII photochemical efficiency decrease
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
The response of ecosystem carbon fluxes to LAI and environmental drivers in a maize crop grown in two contrasting seasons
No full textThe eddy correlation technique was used to investigate the influence of biophysical variables and crop phenological phases on the behaviour of ecosystem carbon fluxes of a maize crop, in two contrasting growing seasons. In 2009, the reduced water supply during the early growing stage limited leaf area expansion, thus negatively affecting canopy photosynthesis. The variability of gross primary production (GPP) and ecosystem respiration (Reco) was mainly explained by seasonal variation of leaf area index (LAI). The seasonal variation of Reco was positively influenced by soil temperatures (Tsoil) in 2008 but not in 2009. In 2008, a contribution of both autotrophic and heterotrophic components to total Reco could be hypothesized, while during 2009, autotrophic respiration is supposed to be the most important component. Crop phenological phases affected the response of ecosystem fluxes to biophysical driver
- …
