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Functional characterization of iron transporters Nramp1 and Nramp2 from Dictyostelium discoideum: a model of cellular iron homeostasis.
Full text linkBackground: Iron is an element necessary for all the organisms; its role in essential metabolism and cellular processes is fundamental for life. Studies on iron homeostasis, regulation and transport could be also done with a simplified model of professional phagocyte and pathogen host, Dyctiostelium discoideum (Dd).
Aim: Characterize the different metal transport specificity and regulation of the two iron transporters of Dd, ddNramp1 and ddNramp2.
Methods: Electrophysiological experiments with Two Electrode Voltage Clamp, X. laevis oocytes smoothies (XLOs) and immunolocalization experiments were performed to characterize these two divalent metal transporters and started with the synthesis of the two chimeric protein c-Nramp1 and c-Nramp2.
Results: We demonstrated that c-Nramp1 is a sodium independent transporter with specificity for divalent transition metals, as mammal orthologs of SLC11 family, with maximal inward currents at acidic pH and a high affinity for substrate. We also detected a peculiar sodium leak current, mainly at neutral pH, that suggest the presence of a strong interaction in the binding site.
We found that c-Nramp2 is electroneutral and transports divalent metal ions at all pH. Site directed mutagenesis on TMD6 restore the electrogenicity with small inward currents; XLOs analysis confirmed the electrophysiological results, these mutants are more functional than wild type c-Nramp2.
Conclusions: Our findings on ddNramp1 contributed with novel insights on the mechanism of action of the mammalian ortholog, whereas similar studies on ddNramp2 suggested a role of the homologous proteins in protists, and helped to clarify the possible function of the contractile vacuole in divalent metal homeostasis
Colour gradients in cluster ellipticals at z ∼ 1.4: the hidden content of the galaxy central regions
Full text linkThe main aim of my Ph.D. thesis is to study how the colour of a sample of cluster ellipticals radially changes and to study its origin in term of variation of the stellar population properties in order to put constraints on the mechanisms of the stellar mass assembly in elliptical galaxies. To this aim, I jointly studied the rest-frame UV-U and UR colour gradients for a sample of 17 elliptical galaxies morphologically selected in the cluster XMMU J2235.3-2557 at z=1.39. The analysis shows that the U-R colour gradients are systematically negative (∼70%) or null (~30%), never positive. On the other hand, the UV-U gradients are systematically positive (∼80%) or null (~20%), never negative. Using stellar population synthesis models, we found that the behavior of the two colour gradients cannot be simultaneously explained by a radial variation of age, metallicity and/or dust. In particular, the negative observed U-R gradients can be produced by an age/metallicity gradient. On the contrary, the positive UV-U gradients cannot be explained with age or metallicity variations and imply an excess of UV emission towards the galaxies’ central regions. This excess calls into question mechanisms able to efficiently produce UV emission without altering the spectrum at longer wavelengths. The data require either steady weak star formation (< 1 M⊙ yr−1) or an He-rich population in the cores of these galaxies in order to simultaneously reproduce both the colour gradients. We have then investigated whether colour gradients depend on the environment, comparing our results with colour gradients in field ellipticals at a comparable redshift present in literature. We found that both cluster and field ellipticals present negative U-R gradients mutually consistent. Conversely to cluster ellipticals, field ellipticals show both positive and negative UV-U gradients.
Although the small statistic, this could suggest that the environment could have influenced the evolution of elliptical galaxies. Finally, through the evolution of colour gradients, we investigated how these cluster ellipticals have evolved from z=1.39 to z=0.
We found that the evolution of the studied galaxies is consistent with a passive evolution
Fine and ultrafine particulate: sampling, analysis and metal characterization for a risk assessment on human health.
Full text linkInformation about the size-distribution of airborne particulate matter (PM) and PM-bound toxic metals is a key knowledge in terms of health concern. The global aim of the project was to characterize the mass concentration, size-distribution and metal composition in different PM2.5 size ranges. The experimental design involved the collection of size-segregated particles at an outdoor urban background site in Como during a long-term monitoring campaign by means of a multistage low pressure impactor. The highest PM concentration levels were found during the heating period because of a joint influence of meteorological factors and variations in type and number of emission sources. In particular, the greatest and significant increase effect was registered for particles between 0.15 and 1.60 μm. For chemical analysis purposes, a novel and reliable Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) measurement protocol was properly developed and optimized, providing precise and accurate results. The proposed LA-ICP-MS method was then applied for the analysis of selected trace metals (Cr, Mn, Fe, Ni, Cu, Zn, Ba and Pb) on the extended set of size-segregated PM samples. Obtained findings revealed different and characteristic metal size-distributions in the fine, submicrometer and ultrafine fractions. The studied elements were variously enriched in the particulate sizes, suggesting that local emission sources may exist for these chemical species. Moreover, from a health and sanitary perspective, the estimated hazard quotient and index values suggested no non-carcinogenic health risks via the inhalation exposure route. Also the carcinogenic risks of Cr and Ni were within the acceptability range
Anatomical and functional custom made restoration techniques with Direct Metal Laser Forming technology: systematic workflow and CAD-CAM
Full text linkIntroduction
Bone defects are usually repaired by the body’s healing process itself. If severe fracture, tumor or infection occur on large bones, it poses a serious challenge to the regeneration ability of the bones. One of the latest advancement in medical science is the rapid prototyping technologies. Therefore, the aim of the present study was the developing and testing of a reliable workflow to fabricate custom-made grafts in the field craniofacial surgery.
Material and Methods
In this study 14 patients with different cranio-facial bone defects were enrolled. Two evaluation methods were associated to test the results of the workflow. Surveys were given to patients undergone surgery and their surgeons to have a subjective analysis of the workflow. For each patient the produced prosthesis was superimposed on the original prosthesis design, the displacement between was evaluated.
Results
Significant level of discomfort at 4 weeks after surgery compared to 2 days after surgery, aesthetic improvement significant improved 1 year after surgery compared to 4 weeks after surgery. Aesthetic improvement 1 year after surgery and aesthetic improvement according to expectations showed correlation, aesthetic improvement 1 year after surgery and aesthetic improvement according to expectations showed correlation. The mean distance of the printed model was significant smaller than the virtual model, with a mean difference of -0.075 mm.
Conclusion
According to the results of the present study custom made bone graft made with laser sintering technique represents a valid alternative to traditional bone grafts with high clinical accuracy and the advantage to avoid morbidity of the donor site or of the patient due to animal grafting
Probabilistic Semantics: Metric and Logical Character¨ations for Nondeterministic Probabilistic Processes
Full text linkIn this thesis we focus on processes with nondeterminism and probability in the PTS model, and we propose novel techniques to study their semantics, in terms of both classic behavioral relations and the more recent behavioral metrics.
Firstly, we propose a method for decomposing modal formulae in a probabilistic extension of the Hennessy-Milner logic. This decomposition method allows us to derive the compositional properties of probabilistic (bi)simulations.
Then, we propose original notions of metrics measuring the disparities in the behavior of processes with respect to (decorated) trace and testing semantics.
To capture the differences in the expressive power of the metrics we order them by the relation `makes processes further than'.
Thus, we obtain the first spectrum of behavioral metrics on the PTS model.
From this spectrum we derive an analogous one for the kernels of the metrics, ordered by the relation `makes strictly less identification than'.
Finally, we introduce a novel technique for the logical characterization of both behavioral metrics and their kernels, based on the notions of mimicking formula and distance on formulae.
This kind of characterization allows us to obtain the first example of a spectrum of distances on processes obtained directly from logics.
Moreover, we show that the kernels of the metrics can be characterized by simply comparing the mimicking formulae of processes
An integrative framework for cooperative production resources in smart manufacturing
Full text linkUnder the push of Industry 4.0 paradigm modern manufacturing companies are dealing with a significant digital transition, with the aim to better address the challenges posed by the growing complexity of globalized businesses (Hermann, Pentek, & Otto, Design principles for industrie 4.0 scenarios, 2016). One basic principle of this paradigm is that products, machines, systems and business are always connected to create an intelligent network along the entire factory’s value chain. According to this vision, manufacturing resources are being transformed from monolithic entities into distributed components, which are loosely coupled and autonomous but nevertheless provided of the networking and connectivity capabilities enabled by the increasingly widespread Industrial Internet of Things technology. Under these conditions, they become capable of working together in a reliable and predictable manner, collaborating among themselves in a highly efficient way. Such a mechanism of synergistic collaboration is crucial for the correct evolution of any organization ranging from a multi-cellular organism to a complex modern manufacturing system (Moghaddam & Nof, 2017). Specifically of the last scenario, which is the field of our study, collaboration enables involved resources to exchange relevant information about the evolution of their context. These information can be in turn elaborated to make some decisions, and trigger some actions. In this way connected resources can modify their structure and configuration in response to specific business or operational variations (Alexopoulos, Makris, Xanthakis, Sipsas, & Chryssolouris, 2016). Such a model of “social” and context-aware resources can contribute to the realization of a highly flexible, robust and responsive manufacturing system, which is an objective particularly relevant in the modern factories, as its inclusion in the scope of the priority research lines for the H2020 three-year period 2018-2020 can demonstrate (EFFRA, 2016). Interesting examples of these resources are self-organized logistics which can react to unexpected changes occurred in production or machines capable to predict failures on the basis of the contextual information and then trigger adjustments processes autonomously.
This vision of collaborative and cooperative resources can be realized with the support of several studies in various fields ranging from information and communication technologies to artificial intelligence. An update state of the art highlights significant recent achievements that have been making these resources more intelligent and closer to the user needs. However, we are still far from an overall implementation of the vision, which is hindered by three major issues. The first one is the limited capability of a large part of the resources distributed within the shop floor to automatically interpret the exchanged information in a meaningful manner (semantic interoperability) (Atzori, Iera, & Morabito, 2010). This issue is mainly due to the high heterogeneity of data model formats adopted by the different resources used within the shop floor (Modoni, Doukas, Terkaj, Sacco, & Mourtzis, 2016). Another open issue is the lack of efficient methods to fully virtualize the physical resources (Rosen, von Wichert, Lo, & Bettenhausen, 2015), since only pairing physical resource with its digital counterpart that abstracts the complexity of the real world, it is possible to augment communication and collaboration capabilities of the physical component. The third issue is a side effect of the ongoing technological ICT evolutions affecting all the manufacturing companies and consists in the continuous growth of the number of threats and vulnerabilities, which can both jeopardize the cybersecurity of the overall manufacturing system (Wells, Camelio, Williams, & White, 2014). For this reason, aspects related with cyber-security should be considered at the early stage of the design of any ICT solution, in order to prevent potential threats and vulnerabilities. All three of the above mentioned open issues have been addressed in this research work with the aim to explore and identify a precise, secure and efficient model of collaboration among the production resources distributed within the shop floor.
This document illustrates main outcomes of the research, focusing mainly on the Virtual Integrative Manufacturing Framework for resources Interaction (VICKI), a potential reference architecture for a middleware application enabling semantic-based cooperation among manufacturing resources. Specifically, this framework provides a technological and service-oriented infrastructure offering an event-driven mechanism that dynamically propagates the changing factors to the interested devices. The proposed system supports the coexistence and combination of physical components and their virtual counterparts in a network of interacting collaborative elements in constant connection, thus allowing to bring back the manufacturing system to a cooperative Cyber-physical Production System (CPPS) (Monostori, 2014). Within this network, the information coming from the productive chain can be promptly and seamlessly shared, distributed and understood by any actor operating in such a context. In order to overcome the problem of the limited interoperability among the connected resources, the framework leverages a common data model based on the Semantic Web technologies (SWT) (Berners-Lee, Hendler, & Lassila, 2001). The model provides a shared understanding on the vocabulary adopted by the distributed resources during their knowledge exchange. In this way, this model allows to integrate heterogeneous data streams into a coherent semantically enriched scheme that represents the evolution of the factory objects, their context and their smart reactions to all kind of situations. The semantic model is also machine-interpretable and re-usable. In addition to modeling, the virtualization of the overall manufacturing system is empowered by the adoption of an agent-based modeling, which contributes to hide and abstract the control functions complexity of the cooperating entities, thus providing the foundations to achieve a flexible and reconfigurable system. Finally, in order to mitigate the risk of internal and external attacks against the proposed infrastructure, it is explored the potential of a strategy based on the analysis and assessment of the manufacturing systems cyber-security aspects integrated into the context of the organization’s business model.
To test and validate the proposed framework, a demonstration scenarios has been identified, which are thought to represent different significant case studies of the factory’s life cycle. To prove the correctness of the approach, the validation of an instance of the framework is carried out within a real case study. Moreover, as for data intensive systems such as the manufacturing system, the quality of service (QoS) requirements in terms of latency, efficiency, and scalability are stringent, an evaluation of these requirements is needed in a real case study by means of a defined benchmark, thus showing the impact of the data storage, of the connected resources and of their requests
CIITA-induced MHC class II expression in tumor cells: a novel universal strategy of anti-tumor vaccination.
Full text linkPriming and activation of CD4+ T helper (TH) cells against tumor associated antigens can be achieved after their recognition on antigen presenting cells (APC) only within the context of MHC class II (MHC-II) molecules. We previously reported successful triggering of TH-specific long lasting anti-tumor immune response in H-2d haplotype BALB/c mice using tumor cells genetically modified to express endogenous MHC-II genes (I-A and I-E) after transfection with CIITA (MHC-II transactivator). Now, we investigated the pertinence of this approach in H-2b haplotype C57BL/6 mice that only express I-A molecules due to a defect in their I-Eα gene.
MC38 colon carcinoma cells of the H-2b haplotype were stably transfected with CIITA. Selected MHC-II positive clones were injected into C57BL/6 mice. Complete rejection or significant growth retardation as compared to MHC-II negative parental tumor was obtained. Subsequent challenge of the protected mice with parental tumor proved that the CIITA-transfected tumor engendered efficient anti-tumor vaccination. Then, adoptive cell transfer from the vaccinated mice to naïve recipients demonstrated that CD4+ TH cells orchestrate the anti-tumor protection.
Finally, the use of CD11c.DTR transgenic mice in which conditional deletion of dendritic cells (DC) can be performed, and the use of Liposomal Clodronate as a depletion agent for macrophages, proved that CIITA-driven MHC-II positive tumor cells act as surrogate APC for priming and activating CD4+ TH cells, without the need of either DC or macrophages.
These results demonstrate the validity of CIITA-driven MHC-II+ tumor cells as anti-tumor vaccination tool in mouse models of different haplotypes. Moreover, they prove that expression of a single MHC-II restriction element in tumor cells is sufficient to trigger anti-tumor CD4+ TH cells and, more importantly, demonstrate for the first time that CIITA-driven MHC-II expressing tumor cells can act as professional APCs in vivo to prime naïve tumor-specific CD4+ TH cells
Study of the molecular mechanism(s) underlying the antitumoral and highly pleiotropic functions of the human RNASET2 protein, a phylogenetically conserved extracellular RNase.
Full text linkThe RNASET2 gene encodes for the only human secreted acid ribonuclease of the T2 family. This gene maps in 6q27, a region that is consistently found rearranged in many solid and hematological tumors. Experimental data gathered in our laboratory have demonstrated the role of RNASET2 as a tumor suppressor gene which is endowed with several functions including chemotactic and possibly activating activities toward the monocyte/macrophage population. In a mouse xenograft model, we have recently reported that inoculation of human ovarian cancer-derived cells forced to overexpress RNASET2 led to the development of small, growth-suppressed tumors, characterized by a strong infiltrate of host-derived innate immunity cells, which have been identified as mainly M1 polarized macrophages. By contrast, control cells not expressing RNASET2, developed large, fast-growing tumors with no sign of macrophage infiltration.
Further investigations proved that recombinant RNASET2 (produced in either baculovirus or Pichia pastoris expression system) displayed a marked chemotactic activity in vitro, most likely dependent on a subfamily of G-protein Coupled Receptors associated with inhibitory G protein.
Taken together, these results led us to suggest that RNASET2-mediated in vivo tumor suppression is a non-cell-autonomous process which result in the recruitment of macrophages into the tumor mass.
Based on such evidences, we decided to further investigate the relation between RNASET2 and cells belonging to the monocyte-macrophages lineage.
Most of the experiments we planned to carry out involved the use of purified recombinant human RNASET2, hence, the first step of the project was the development of a reliable supply system.
Two different sources of production and purification of human RNASET2 protein were already available in our lab (P. pastoris and BEVS), however, a full exploitation of these reagents was precluded by several limitations inherent to both systems.
To overcome these limitation, we decided to focus our efforts on improving the P. pastoris expression system, which was more cost-effective and easier to handle in term of available facilities.
To solve the problem, we added another 6XHis tag to the construct coding for the human RNASET2 and managed to significantly improve the recovery of the input protein.
Considering the downstream applications of the purified human RNASET2, contamination of the preparation by metals (especially Ni, Cd, Zn) and endotoxin are important factor to control in order to properly assess a relationship between a specific treatment (in our case the addition of recombinant human RNASET2) and immune cell response. Applying the proper care in the preparation of the buffers and the handling of the sample we manage to achieve a low endotoxin content and an undetectable level of contamination by metals (Ni, Cd, Zn).
As previously mentioned, several studies have reported the consistent tumor suppressive role for several members of the T2 RNase protein family and the recruitment of immune cells seems to be involved in this suppression. In order to improve our knowledge of these functional features of T2 RNases and at the same time to evaluate their evolutionary conservation, we tested the role of human recombinant RNASET2 in the activation and recruitment of immune cells by injecting recombinant human RNASET2 in the body wall of Hirudo verbena a useful model system for our purposes.
After rRNASET2 injection, a significant increase in the production of collagen fibrils and a consequent remodeling of the muscle layers was observed. The resulting massive production of connective tissues is then used as a scaffold for immune cells migration and for proper orientation of growth of new vessels.
Injection of human recombinant RNASET2 was also shown to induce a massive migration of cells belonging to the macrophages lineage (characterized as HmAIF-1+ and CD68+ cells) within 24 h, coupled to the formation of new blood vessels.
The observed inflammatory response was specifically dependent of recombinant RNASET2 injection, since infiltrating macrophages and neo-vessel formation were not observed following injection of either PBS or rRNASET2 protein that was pre-incubated with a neutralizing anti-RNASET2 antibody.
Taken together, these data strongly suggest that rRNASET2 injection in leeches induces a marked inflammatory response characterized by macrophage recruitment.
The data gathered in our lab in several in vitro and in vivo experimental systems strongly suggest the occurrence of an RNASET2-based intercellular cross-talk, whose molecular mechanisms are nevertheless largely unknown.
As a first step in the logical sequence of events culminating in the above mentioned RNASET2 biological activities, we hypothesized the occurrence of a putative receptor for RNASET2.
The common idea behind all our approaches was to covalently link RNASET2 (either the endogenous protein or the human recombinant protein) to any interactor and, after purification of the complex, to perform a MS analysis to characterize the interactants.
As a first approach, we carried out chemical modification of purified recombinant RNASET2 with different compounds (SDA, LC-SDA, Sulfo SDA, Sulfo LC-SDA) in order to add a diazirine ring to all primary ammines of the target protein. The resulting modified RNASET2 protein could then, in principle, be crosslinked to all electron donors available following UV light activation. The modified protein was then incubated with RNASET2-silenced OVCAR3 cells and analyzed by western blot following UV exposure. Despite several attempts with this approach, we could not observe any shift in the molecular weight of RNASET2.
Considering that most of the result obtained show evidence of a tropism of RNASET2 for cells belonging to the monocyte/macrophage lineage, with our last approach we tested a promyelocytic cell line. We exposed the U937 cells preincubated with rRNASET2 to a chemical crosslinkers (BS3) able to covalently link two or more proteins in close proximity. By this approach we managed to see a shift in the molecular weight of the RNASET2, but unfortunately in the next step we couldn't purify any detectable complex.
Considering that TAMs are usually forced by the tumor cells to acquire an M2-polarized pro-tumorigenic phenotype, a key finding of our research group is that tumor xenografts that are suppressed in their growth following RNASET2 overexpression display a strong infiltration of M1-polarized macrophages which are known to show anti-tumorigenic properties. Therefore, the last part of this PhD program was dedicated to investigate the molecular/cellular bases of the interaction between RNASET2 and immune cells, in particular to describe a possible involvement of this protein in driving macrophages polarization.
The main idea was to develop a system to reliably produce M0, M1 and M2 macrophages that could then be used to test the effect of RNASET2 looking at their transcriptional profile.
To this end, we chose a well-known cellular model (THP-1 cell line) and, in order to remove any bias from future analysis, we selected a pool of cells silenced for the expression of RNASET2.
THP-1 is a promyelocytic cell line therefore in order to effectively produce polarized cells we needed to differentiate it into macrophages. Using the guidelines found in the literature we managed, by treating THP-1 cells with PMA 5 ng/ml for 48 h, to produce M0 macrophages.
Subsequently, we developed a protocol to effectively drive naive macrophages to either M1 or M2 phenotype. We followed the suggested guidelines and assessed the efficacy of our system by testing a small panel of known marker of polarization (TNF, CXCL10, CCL19 for M1 polarization and CCL22, MRC1, MSR1 for M2 polarization).
Considering the final aim of the developed assay, we tested whether our macrophages, especially M1 and M2, still retained the plasticity to change their profile according to external stimuli. M0 cells were exposed to both M1 and M2 stimuli; the resulting profile was neither M1 nor M2, suggesting that the cells prepared with our system still retained the characteristic/desired plasticity to properly respond to external signals.
The data gathered so far support the idea that the system developed might be useful to study the involvement of RNASET2 in macrophages polarization.
To summarize, during these three years of my PhD program I was involved in many different parts of a project aimed at deepen our understanding of the mechanism underlying RNASET2 tumor suppression. Although I wasn't able to identify any putative receptor for RNASET2 experimental evidence suggests the existence of a molecular mechanism involved in the “sensing” of the RNASET2 protein. Further studies are clearly needed in order to clarify this issue and the recent finding of RNASET2-containing exosomes is a promising avenue of investigation.
The data collected in Hirudo strengthen our hypothesis of a close relationship between Immune cells (in particular cells belonging to monocyte/macrophages lineage) and RNASET2 but, more importantly these
results open new research opportunities to study the involvement of T2 ribonucleases in inflammation. From a strictly technical point of view, I was able to improve the system of production and purification of the recombinant human protein, making it possible the use of RNASET2 in conditions previously inaccessible (interaction with immune cells/injection in organism).
To conclude I contributed to laid the bases for future studies aiming at dissecting the involvement of RNASET2 in macrophages polarization and I did it by developing a simple assay that might test the "polarizing potential" of RNASET2 (but potentially of any compound)
Il ruolo dell'arte nella società post moderna. Sentimenti identitari, coesione sociale e spirito critico.
Full text linkAware of being part of an increasingly individualistic society where social cohesion and the struggle for shared ideals now seem to be a thing of the past, we see a possible cure for this spiritual squalor in contemporary art as a means of communication to create new symbolic paths which are understood and shared. The research focuses on the analysis of not only those artistic projects whose audience is art experts and the art market but on projects that target a wider audience. Works with a strong communicative purpose which, through the artist’s direction, intend to transmit a symbolic and participated meaning within the reality in which they come to life. The research essentially has the following objectives: in-depth analysis of the artist’s role in post-modern society in the light of the changes that this entails; understanding the direction in which art is evolving and seeing if its conception aimed at the sole purpose of exhibitions and museums can still exist.
The study was carried out mainly through an in-depth and targeted bibliographic study; the texts used were chosen according to a precise and multi-disciplinary method bearing in mind economic, managerial, artistic, social and psychological aspects. A number of Italian cases considered useful for understanding the theoretical part of the research are also presented and analyzed. During the preparation of the research work it was not considered important to focus our study on the current changes to artistic practices. Instead, we want to demonstrate how contemporary art is to all purposes a highly effective means of communication for creating shared feelings of identity and for increasing the level of social cohesion above all in communities where the artistic projects have a high level of visibility and credibility and are developed respecting precise parameters. We are also sure, today more than ever, that the artist has to take back a precise social role, a role which is more credible in the eyes of the public which must see in him a means to understanding society. Indeed, even if there can no longer be and there is no longer any sense in having a nostalgic vision of the artist since each one is called on to live their own times, speak to a contemporary public and do this with the means available, art must however be seen as a vocation just like a religion because, if practiced correctly, it holds and can hold an important and delicate role in society. Aware that the results obtained cannot be measured in absolute terms, we are however convinced that a good artistic production able to gain ground also outside the institutional places of art and to favor open and positive dialogue between artists, institutions and communities is a sign of an active and lively society, driver of a dynamic community able to reflect on itself
Monitoring and analysis of the impacts of climate change on plant biodiversity and terrestrial ecosystems in alpine and polar environment.
Full text linkHigh altitude and latitude environments are among those areas of the Planet that are experiencing the most significant changes of the climatic conditions due to the recent global change. Terrestrial ecosystems in these regions are extremely sensitive to climate, and for this reason, well suited for the comprehension, evaluation and monitoring of their responses, and their modelling under different climate change scenarios.
This thesis focuses on the impacts of climate change on terrestrial ecosystems of alpine (Foscagno valley, central Italian Alps) and Polar (both Continental Antarctica and Maritime Antarctica) tundra habitats. European Alps and Maritime Antarctica are two of the three areas of the world where have been recorded the greatest air temperature warming in the last 50 years, whereas simultaneously in Continental Antarctica, air temperature was almost stable. Due to different trends of climate and anthropogenic pressures around the world, contemporary global change is characterized by a large spatial variability that makes the planning of adaptation and mitigation strategies particularly complicate. Peculiar habitats have been protected by international, European and national programs (the Foscagno valley belongs to the Nature 2000 network, while the Antarctica ecosystems are protected under the Antarctic treaty and specially protected areas). However, analyzing the dynamics of terrestrial ecosystems in regions that are facing different climate change scenarios, as well as biological and anthropogenic constrains, could improve the knowledge of the dynamics of terrestrial ecosystems, that could be used for modelling future scenarios and to implement the adaptation plans for such protected areas.
The identification of conservation actions and monitoring plans is thus the priority for such threatened environments, to ensure a correct management of the biodiversity and of the ecosystem services that they can provide.
The alpine site is the Foscagno Valley, a high altitude site (>2500 m a.s.l.) located in the central Italian Alps, where since 2007 a field-based project of snow, ground surface temperature and plant phenology monitoring started. This PhD is part of this project, that since summer 2015 was implemented with manipulation experiments on two typical alpine vegetation communities (snowbed and grassland) to simulate potential future climate change related impacts on plant phenology and growth, including increase of nutrient availability (simulated by additions of urea, ammonium sulfate, NPK respectively), water availability (once or twice per week additions of water), lack of reproductive stages (flowers removal).
The primary aim of this PhD was to investigate alpine plant phenology and its relationships with climate change. We monitored phenology of 21 plants typical of alpine environments and representative of different growth forms types. In particular, we hypothesized that: a) the vegetative development (shoot appearance and leaf emergence) is regulated by snow melt timing, while the other phenological stages (i.e. flowering, seed development and ripening, and leaf senescence) are regulated mostly by photoperiod, which should indicate a conservative and adaptive strategy of alpine plants; b) plant phenology shows different plasticity depending on the growth form types and also on the phenological stage; c) extreme events can overwhelm the effect of photoperiod, and can lead to carry over effects in the phenological cycle and plant growth.
Our data indicated that the main predictor of the vegetative development stages was the snow melt, while the photoperiod was the best predictor of phenological stages from flowering peak up to leaf senescence. Therefore, the photoperiodic control on alpine plant phenology should be considered for the evaluation and modelling of the impacts of climate change in alpine region, not only concerning the reproductive stages, but also for the leaf senescence. This constitute a novelty concerning literature data about phenology of alpine plants (which have been always related to snow and/or temperature as triggering factors) because provides new insights on the capability of alpine plants to profit of potential future autumn warming.
Alpine plant phenology showed thus a strong conservative strategy, which differed among growth forms, according to our hypothesis. Over all the investigated phenological stages graminoids were the most plastic and responsive growth form and their higher adaptation capability could help to explain why this growth form is expanding more than forbs in alpine and Polar tundra habitats.
Extreme events showed impact on plant phenology, with differences among growth forms and phenological stage. In particular, we found the leaf senescence of herbaceous species to be highly sensitive to the combination of drought and heat, which led to an advance of almost one month in the season, while deciduous shrubs were not or less sensitive. Moreover, an extreme leaf senescence showed carry over effects on the next season growth rate.
Our results indicate also a statistically significant increase of the height of evergreen shrubs on the period 2010-2016, which was in agreement with the observed range expansion of shrubs in the Alps.
Relating to the long-term ground surface temperature (GST) monitoring, 13 temperature data loggers were installed in the Foscagno valley, under different surface types conditions, covering the most widespread growth forms of the area. In particular, we hypothesized that: a) GST was strongly influenced by the soil coverage types and snow cover, b) although the actual climatic conditions are less favorable, some vegetated soils could lead a ground cooling until to permafrost condition; c) the shrubland expansion could drive to an energetic disequilibrium of soils with thus positive feedbacks on the carbon cycle.
Our data confirmed that the snow cover duration was the main driver of the mean annual ground surface temperature, while the beginning of snow cover deeper than 80 cm influenced the freezing state of the soils during winter, and the timing of snow melt was related to the thawing degree days of the snow free period. Vegetated soils (shrublands and grasslands surface types) were warmer compared to bare ground, except for pioneer species (i.e. Cerastium uniflorum), that involved a cooling on soils leading to permafrost condition. Therefore, future changes in vegetation cover can lead to different soil thermal regimes and different spatial distribution of temperatures in alpine terrains. Potentially, the expansion of pioneer species could be related to longer persistence of permafrost conditions; on the contrary, if the shrublands expansion that we are facing in the Alps will continue in the future, soil temperatures will be warmer, which imply positive feedbacks to the carbon cycle.
The main purpose of the manipulation experiments started at the Foscagno Valley in 2015 was to investigate the responses of phenology and plant growth under different simulations of climate change. As many phenophases exhibited a strong photoperiodic control, we aimed to assess and quantify the eventual effects of the different manipulation treatments and identify the most responsive phenophases and communities types. Concerning the quantitative development, we hypothesized that: a) the vegetative development (shoot length, leaf length, maximum plant height) would be influenced by manipulations, with nutrients exerting the higher impacts, compared to flower removal and water addition (since terrestrial ecosystems are N and P limited); b) the above ground biomass (ABG) would be strongly influenced by the addition of nutrients, more than flowers removal or water addition.
Our data showed that manipulation experiments (in particular nutrient additions) involved strong impacts on plant phenology and growth, lengthening (with xNPK) or shortening (with ammonium sulfate) the duration of flowering and leaf senescence, and enhancing the vegetative quantitative phenology of alpine plants (with xNPK). One of the most important findings is that the photoperiodic limitation observed at the long-term phenology monitoring, could be overcome under future climate changes, with potentially consequences on niche competition within communities.
Above all the manipulation we found a strong N and P limitation, in particular concerning the vegetative development, which thus will imply strong consequences also on the carbon budget. Also the flower removal exerted visible effects especially on the quantitative growth, highlighting differences among the vegetation communities, with higher capability for snowbeds species to remobilize nutrients than grasslands species.
Another feedback of the manipulations experiments concerned the occurrence of carry over effects on the quantitative growth of the first shooting stage at the beginning of the season, provided by the enhanced nutrient availability from the previous year.
While in the alpine tundra vascular plants are dominant, in high latitude ecosystems, cryptogams (mosses and lichens) are the major components of terrestrial ecosystems. In particular, in Antarctica only few long-term data are available on the responses of mosses and lichens to climate change.
Comparable to Alps, the Maritime Antarctica is one of the regions of the planet recording the most rapid air warming, and Signy Island (South Orkney Islands) has been identified as a suitable context for the monitoring of biological changes. Here we analyzed the contemporary abundance and distribution of moss banks on the entire island, assessing their ecological requirements, and providing thus a baseline for future monitoring.
Thanks to the availability of previous field-based studies on the spatial distribution of moss banks carried out in the 1960s and 1970s, we assessed long-term and large-scale moss responses to climate change underlying the related ecological processes.
Differently to Alps and Maritime Antarctica, Continental Antarctica in the last 50 years showed a stable air temperature trend. This region is the last pristine environment on Earth, which provides a unique opportunity to assess the natural dynamics and responses to climate. In Victoria Land, in 2002 started a long-term monitoring project of the climate, permafrost and vegetation, of which we present here the results after 10 years of monitoring. Concerning this activity, we aim to: a) identify the patterns of spatial and temporal active layer variability; b) analyze the changes of the associated vegetation; c) identify the climatic forcing of active layer and vegetation changes.
In the Antarctic summer 2014/2015, we installed over a latitudinal gradient (73-77°S) in Victoria Land, some manipulation experiments (additions of snow, water, urea, ammonium sulfate, NPK, guano respectively) coupled with the manipulation of snow accumulation, soil temperature and precipitation (installing respectively snow fences, open top chambers and snow shield) for the simulation of potential future climate change impacts. We thus briefly evaluated the effects on soil temperatures after the first year of the experiments, providing thus the start point for future further monitoring.
Among all the experiments, we found that the snow cover exerted the largest effect on the GST, thus highlighting its main role in regulating soil temperatures, which effects overcome the influence of air temperature, leading also to changes of soil moisture and water regim