Inherent variation of functional traits in winter and summer leaves of Mediterranean seasonal dimorphic species. Evidence of a 'within leaf cohort' spectrum

The covariation pattern among leaf functional traits involved in resource acquisition has been successfully provided by the leaf economic spectrum (LES). Nevertheless, some aspects such as how the leaf trait variation sources affect LES predictions are still little investigated. Accordingly, the aim of this paper was to test whether leaf trait variations within different leaf cohorts could alter LES. Improving this knowledge can extend the potential of trait-based approaches in simulating future climate effects on ecosystems. A database on leaf morphological and physiological traits from different leaf cohorts of Cistus spp. was built by collecting data from literature. These species are seasonal dimorphic shrubs with two well-defined leaf cohorts during a year: summer leaves (SL) and winter leaves (WL). Traits included: leaf mass area (LMA), leaf thickness (LT), leaf tissue density (LTD), net photosynthetic rate on area (Aa) and mass (Am) base, nitrogen content on area (Na) and mass (Nm) base. The obtained patterns were analysed by standardized major axis regression and then compared with the global spectrum of evergreens and deciduous species. Climatic variable effect on leaf traits was also tested. Winter leaves and SL showed a great inherent variability for all the considered traits. Nevertheless, some relationships differed in terms of slopes or intercepts between SL and WL and between leaf cohorts and the global spectrum of evergreens and deciduous. Moreover, climatic variables differently affected leaf traits in SL and WL. The results show the existence of a 'within leaf cohort' spectrum, providing the first evidence on the role of leaf cohorts as LES source of variation. In fact, WL showed a high return strategy as they tended to maximize, in a short time, resource acquisition with a lower dry mass investment, while SL were characterized by a low return strategy

Short-term physiological plasticity.Trade-off between drought and recovery responses in three Mediterranean cistus species

Short-term physiological plasticity allows plants to thrive in highly variable environments such as the Mediterranean ecosystems. In such context, plants that maximize physiological performance under favorable conditions, such as Cistus spp., are generally reported to have a great cost in terms of plasticity (i.e., a high short-term physiological plasticity) due to the severe reduction of physiological performance when stress factors occur. However, Cistus spp. also show a noticeable resilience ability in response to stress factors. We hypothesized that in Cistus species the short-term physiological response to stress and that to subsequent recovery can show a positive trade-off to offset the costs of the photosynthetic decline under drought. Gas exchange, chlorophyll fluorescence, and water relations were measured in C. salvifolius, C. monspeliensis, and C. creticus subsp. eriocephalus during an imposed experimental drought and subsequent recovery. Plants were grown outdoor in common garden conditions from seeds of different provenances. The short-term physiological response to stress and that to recovery were quantified via phenotypic plasticity index (PIstress and PIrecovery, respectively). A linear regression analysis was used to identify the hypothesized trade-off PIstress-PIrecovery. Accordingly, we found a positive trade-off between PIstress and PIrecovery, which was consistent across species and provenances. This result contributes in explaining the profit, more than the cost, of a higher physiological plasticity in response to short-term stress imposition for Cistus spp because the costs of a higher PIstress are payed back by an as much higher PIrecovery. The absence of leaf shedding during short-term drought supports this view. The trade-off well described the relative variations of gas exchange and water relation parameters. Moreover, the results were in accordance with the ecology of this species and provide the first evidence of a consistent trade-off between the short-term physiological responses to drought and recovery phases in Mediterranean species

Leaf rolling as indicator of water stress in Cistus incanus from different provenances

Leaf movements such as leaf rolling affect plant physiological performance by reducing light capture. The relationship between leaf rolling and physiological traits under imposed water stress conditions was analyzed in two population of Cistus incanus. We tested the hypothesis that leaf rolling reflected physiological changes occurring during water stress irrespective of the different acclimation in order to cope with water stress. On the whole, our results confirmed our hypothesis since leaf rolling significantly reflected physiological activity changes. Moreover, leaf rolling might be involved in protecting the PSII complex under water stress during the progressive inhibition of photosynthetic metabolism. Thus, leaf rolling could be part of C. incanus adaptive strategy to cope with water stress by sustaining leaf turgor. As such, leaf rolling may be used as a morphological index to evaluate the progressive inhibition of photosynthesis irrespective of the different acclimation to cope with water stress

Adaptive strategies of Cistus species to Mediterranean stress factors

Plant functional diversity is achieved by trade-offs between physiological and morphological traits which are now widely used to define plants’ adaptive strategies to cope with environmental changes. Under Mediterranean conditions, species have to face two main stress factors, namely winter chilling and summer drought. Such factors show a great spatial variability through the Mediterranean Basin and contributed to diversify plant species adaptive strategies. Furthermore, local plant populations within the Mediterranean Basin can be exposed to different selective pressures possibly affecting their adaptive strategies in response to the same environmental cues. Common garden experiments have been proved valuable approaches to disentangle differences in leaf traits among populations of Mediterranean species, particularly in widespread ones. Among them, the genus Cistus (Cistaceae) comprises 21 species which developed with the advent of the Mediterranean climate and contributed to shape the current composition and diversity of the Mediterranean area. They are dominant elements in the Mediterranean shrub communities of European-African-Mediterranean ecosystems. In this context, the aim of the present thesis was to analyze some aspects of the adaptive strategies of the three widespread Cistus spp., namely C. monspeliensis L., C. salvifolius L. and C. creticus subsp. eriocephalus (Viv.) Greuter & Burdet) in response to the main limiting factors of the Mediterranean climate. Plants were grown from seeds of different provenances under common garden conditions. In particular, common pattern of response across species growing under the same environmental cues as well as the intraspecific variability in such responses were analyzed. From an ecological point of view, three main features make these species important to investigate: (i) they have pioneer character, making early growth a key point of their adaptive strategies; (ii) being seasonal dimorphic species they display two leaf types (winter and summer leaves) characterized by a relatively short leaf longevity and relatively low leaf construction costs during a growing season, which seems to be an advantage in habitat under intense stress; (iii) they possess a marked short-term physiological plasticity in response to environmental changes. However, within these three features, some aspects of Cistus spp. adaptive strategies have not yet been clarified. In detail: (i) the early growth of this species in relation to environmental changes has been overlooked so far; (ii) it is not yet clear if these species can actually rely on the formation of different functional leaf ‘populations’ within a single leaf type in order to face environmental changes; (iii) there is no previous study on the profits that can be achieved by adopting a marked short-term physiological plasticity in response to environmental changes. To address the broad objective and fill the highlighted gaps of knowledge, different experimental approaches were used making up a total of 3 Chapters (plus General Introduction, General Discussion and Conclusions). In Chapter 2, by fitting non-linear models on seedling height data, it was possible to analyze the relationship between early growth parameters and daily air temperature changes. A parameter that could summarize the temperature dependency of the maximum relative growth rate (RGRmax) during the early growth stages for the selected provenances was quantified. Nevertheless, a greater temperature sensitivity of RGR lead to a reduced maximum height reflecting a negative trade-off between the extent of RGR temperature responsiveness and the length of the developmental phases. The findings quantitatively defined provenance dependent strategies by which the selected species cope with daily air temperature variations during early growth. In Chapter 3 leaves produced under different climatic conditions through the winter season (i.e. chilling stress) to spring were analyzed in order to highlight the leaf traits involved in determining potential resilience of three Cistus spp. to changing environmental conditions and to what extent intraspecific differences could affect such response. The results highlighted a complex mechanism that involves diachronic leaf trait adjustments that are parameter-dependent. The findings also demonstrated the existence of different functional leaf populations in Cistus spp. which further extend the current understanding of winter leaves structuring and functioning. Such leaf functional differentiation allows the species to minimize leaf construction costs while maximizing resource acquisition and provide a less costly resilience mechanism in the transition from winter to spring season. In Chapter 4, the short-term physiological response of the considered Cistus spp. during an imposed experimental drought and subsequent recovery was analyzed. A positive trade-off between stress and recovery responses during a short-term drought experiment was found, and it was also consistent across species and provenances. The study highlighted a short-term functional strategy which involves a rapid recovery of gas exchange parameters to avoid the progression of photoinhibition. Such response was associated with the lack of leaf shedding. Such short-term strategy is advantageous by allowing the species to hold the more costly summer leaves (compared to winter leaves) in order to maintain relatively high productivity to face prolonged drought events. Overall, the results demonstrated that Cistus spp. are affected by stress imposition but they can recover as soon as favorable conditions are restored. This is achieved through their ability to respond to climate unpredictability by adjusting their photosynthetic organs, morphologically and/or physiologically, in order to enhance their performance during favorable climatic conditions. Nevertheless, such ability can constrain their response to stochastic changes in thermal amplitudes during a growing season due to climate change thus threatening their competitive ability. The characterization of plant species responses to the major targets of climate change is important in order to highlight mechanisms that can be further investigated both experimentally and in the field. The reported findings provide a conceptual framework, in terms of experimental designs, traits to be included and mechanisms, that deserve to be applied by including other Cistus spp. in the field in order to extend the results at the genus level

Educazione degli adulti e globalizzazione: la critica pedagogica di Ettore Gelpi

This paper offers an analysis of selected works by Ettore Gelpi (1933-2002) which were variously published between the last decade of the XXth century and the beginning of the XXIst. While these writings do not contain an organic analysis of the historical process started in the years 1989-1991 and known as «laissez-faire globalization», they do provide an accurate examination of globalization’s major consequences for society, the world of work and the field of adult education, especially in Western countries. In this part of the world, in fact, adult education has lost considerable ground. Once a factor in inclusion, upward social mobility, an increase in autonomous and critical public opinion, democratic development and intercultural dialogue, adult education is now being increasingly restructured around the concept of «employability», thus turning it into an instrument for competitiveness and flexible accumulation which is realised, as Gelpi demonstrates, to the detriment of human development.L’articolo propone uno studio di alcuni scritti di Ettore Gelpi (1933-2002) pubblicati tra l’ultimo decennio del XX secolo e l’alba del secolo XXI. In tali scritti non vi è un’analisi organica del processo storico schiusosi nel biennio 1989-91 e denominato «globalizzazione liberista»; vi troviamo, invece, una attenta disamina delle principali conseguenze che la globalizzazione determina nelle società, nel mondo del lavoro e nell’ambito dell’educazione degli adulti segnatamente nei paesi occidentali. In questi paesi, infatti, l’educazione degli adulti ha fatto registrare pesanti regressioni. Da fattore di inclusione, di mobilità sociale ascendente, di potenziamento di un’opinione pubblica autonoma e critica, di sviluppo democratico e del dialogo interculturale, l’educazione degli adulti tende sempre più a riorganizzarsi sulla base del paradigma della «occupabilità», trasformandosi in strumento di competitività e di sviluppo dell’accumulazione flessibile che si realizza, come Gelpi dimostra, a danno dello sviluppo umano