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

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

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

Carbon Dioxide (CO2) Sequestration and Air Temperature Amelioration Provided by Urban Parks in Rome

Abstract Urban landscapes are rapidly expanding globally and transforming the structure and function of urban areas, thereby influencing the quality of life. Cities account for more than 70% of the energy related to global greenhouse gases, which is expected to rise up to 76% by 2030. Taking into account that over 50% of the world's population lives in cities and more than two thirds are expected by 2050, the problem of mitigating the atmospheric CO 2 concentration is considerable. The urban areas covered by parks, gardens, tree-lined avenues, sport fields, and hedges are important sinks for carbon dioxide (CO 2 ) by storing carbon through photosynthesis to form plant biomass. Despite plant CO 2 sequestration is an important ecosystem service, the relationship between urban park vegetation and CO 2 emission reduction is not completely clarified. In this context, the main objective of our research was to evaluate the role of urban park vegetation in improving air quality in Rome in terms of CO 2 concentration and air temperature. In particular, we analyzed the relationship among the different vegetation types, size and position of an historical urban park in Rome. Moreover, since the presence of buildings within urban parks determines CO 2 emissions closely related to their purpose of use, it is important to evaluate their impact in order to set instruments for their retrofit, considering the necessity of a compromise among the energy audit, the use of renewable energy systems and preservation of cultural heritage

Accumulation of neutral lipids in peripheral blood mononuclear cells as a distinctive trait of Alzheimer patients and asymptomatic subjects at risk of disease

<p>Abstract</p> <p>Background</p> <p>Alzheimer's disease is the most common progressive neurodegenerative disease. In recent years, numerous progresses in the discovery of novel Alzheimer's disease molecular biomarkers in brain as well as in biological fluids have been made. Among them, those involving lipid metabolism are emerging as potential candidates. In particular, an accumulation of neutral lipids was recently found by us in skin fibroblasts from Alzheimer's disease patients. Therefore, with the aim to assess whether peripheral alterations in cholesterol homeostasis might be relevant in Alzheimer's disease development and progression, in the present study we analyzed lipid metabolism in plasma and peripheral blood mononuclear cells from Alzheimer's disease patients and from their first-degree relatives.</p> <p>Methods</p> <p>Blood samples were obtained from 93 patients with probable Alzheimer's disease and from 91 of their first-degree relatives. As controls we utilized 57, cognitively normal, over-65 year-old volunteers and 113 blood donors aged 21-66 years, respectively. Data are reported as mean ± standard error. Statistical calculations were performed using the statistical analysis software Origin 8.0 version. Data analysis was done using the Student t-test and the Pearson test.</p> <p>Results</p> <p>Data reported here show high neutral lipid levels and increased ACAT-1 protein in about 85% of peripheral blood mononuclear cells freshly isolated (<it>ex vivo</it>) from patients with probable sporadic Alzheimer's disease compared to about 7% of cognitively normal age-matched controls. A significant reduction in high density lipoprotein-cholesterol levels in plasma from Alzheimer's disease blood samples was also observed. Additionally, correlation analyses reveal a negative correlation between high density lipoprotein-cholesterol and cognitive capacity, as determined by Mini Mental State Examination, as well as between high density lipoprotein-cholesterol and neutral lipid accumulation. We observed great variability in the neutral lipid-peripheral blood mononuclear cells data and in plasma lipid analysis of the subjects enrolled as Alzheimer's disease-first-degree relatives. However, about 30% of them tend to display a peripheral metabolic cholesterol pattern similar to that exhibited by Alzheimer's disease patients.</p> <p>Conclusion</p> <p>We suggest that neutral lipid-peripheral blood mononuclear cells and plasma high density lipoprotein-cholesterol determinations might be of interest to outline a distinctive metabolic profile applying to both Alzheimer's disease patients and asymptomatic subjects at higher risk of disease.</p

Intraspecific variability of leaf form and function across habitat types

: Trait-based ecology has already revealed main independent axes of trait variation defining trait spaces that summarize plant adaptive strategies, but often ignoring intraspecific trait variability (ITV). By using empirical ITV-level data for two independent dimensions of leaf form and function and 167 species across five habitat types (coastal dunes, forests, grasslands, heathlands, wetlands) in the Italian peninsula, we found that ITV: (i) rotated the axes of trait variation that define the trait space; (ii) increased the variance explained by these axes and (iii) affected the functional structure of the target trait space. However, the magnitude of these effects was rather small and depended on the trait and habitat type. Our results reinforce the idea that ITV is context-dependent, calling for careful extrapolations of ITV patterns across traits and spatial scales. Importantly, our study provides a framework that can be used to start integrating ITV into trait space analyses

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

Plant–environment interactions through a functional traits perspective: a review of Italian studies

Italy is among the European countries with the greatest plant diversity due to both a great environmental heterogeneity and a long history of man–environment interactions. Trait-based approaches to ecological studies have developed greatly over recent decades worldwide, although several issues concerning the relationships between plant functional traits and the environment still lack sufficient empirical evaluation. To draw insights on the association between plant functional traits and direct and indirect human and natural pressures on the environmental drivers, this article summarizes the existing knowledge on this topic by reviewing the results of studies performed in Italy adopting a functional trait approach on vascular plants, bryophytes and lichens. Although we recorded trait measurements for 1418 taxa, our review highlighted some major gaps in plant traits knowledge: Mediterranean ecosystems are poorly represented; traits related to belowground organs are still overlooked; traits measurements for bryophytes and lichens are lacking. Finally, intraspecific variation has been little studied at community level so far. We conclude by highlighting the need for approaches evaluating trait–environment relationship at large spatial and temporal scales and the need of a more effective contribution to online databases to tie more firmly Italian researchers to international scientific networks on plant traits