Plant co-existence mechanisms related to stress and disturbance intensities in sub-Mediterranean and sub-desertic grassland systems

Plant species co-existence may depend upon a complex chain of events involving competitive ability, complementarity and facilitation between plants and numerous interactions with herbivores, pathogens, soil features, fauna and micro-organisms. The co-existence of species in herbaceous vegetation is possible by the presence of factors that limit the expression of the dominance of plants. This limitation may operate through stress or disturbance or by a combination of the two, and its effect is usually to debilitate the potential dominants and to allow plants of smaller stature to regenerate and to co-exist with them. Species co-existence can reflect niche partitioning at several spatial and temporal scales. The functional strategies avoiding the temporal and/or spatial overlapping of the neighbouring individuals are key factors in the niche partitioning inside the plant community, so that species do not exclude each other by competition. Stress and disturbance are the two external factors affecting the vegetation. Their effects on the system change according their intensity. Stress includes factors which restrict the photosynthetic activity. In fact, plant biomass production in vegetation is subjected to a variety of environmental constraints, the most frequent of which are related to shortages and excesses in the supply of solar energy, water, and mineral nutrients. Disturbance includes mechanisms which limit the plant biomass by causing its partial or total destruction (grazing, mowing, forest cutting, soil erosion, and fire). Vegetation composition and species distribution may be influenced by negative processes (competition) and positive interactions (facilitation). Competition shows a maximal intensity in habitats with high productivity and low disturbance, while this phenomenon disappears under conditions of low productivity or intense disturbance. In order to obtain a more complete assessment of the role of these factors upon species density it is necessary to consider the rather different circumstances which arise when the intensities of stress and/or disturbance become severe.\ud In harsh habitats plants are subjected to extreme stress or disturbance conditions, thus seedling establishment is promoted under the canopies of established vegetation. In this positive interaction, known as facilitation, some plants benefit from closely associated neighbours. The intensities of stress and/or disturbance experienced by herbaceous vegetation are sufficient, not only to eliminate potential dominants but also to produce local environments which are inhospitable to all, except a few specialised plants. Facilitation occurs widely but is more frequently documented in unproductive habitats and dominates under harsh conditions. \ud Stress and disturbance involve functional responses by plants; thus, the analysis of plant functional traits (biological characteristics of plants responding to the dominant processes in an ecosystem) is a useful tool for the understanding of plant community assemblage.\ud Grazing is a major disturbance which often causes extensive changes in plant richness and composition. However, pasture plants do not undergo herbivory passively, but react to defend themselves against grazers by means avoidance and tolerance strategies that enable them to survive and grow in grazed systems. Grazing avoidance involves mechanisms that reduce the probability and severity of grazing (mechanical and chemical defence or escape strategy), while grazing tolerance consists of mechanisms that promote growth following defoliation.\ud The research aim was to assess how different types and intensity of disturbance affect species and functional composition of sub-Mediterranean and sub-desertic grassland systems, also in relation with environmental stress. Consequently, the specific research goals were to: i) identify changes in species and functional trait composition and in diversity of plant communities, under different disturbance types (grazing vs. mowing; mown vs. unmown meadows; grazed vs. ungrazed pastures; sheep grazing vs. horse grazing); ii) identify coenological and functional responses of grassland to intensity of stress and intensity and timing of disturbance, by analysing the plant functional traits, that are expression of competitive ability, facilitation, co-existence, avoidance and tolerance strategies; iii) identify plant-plant spatial interactions, i.e. whether species have species-specific spatial associations, especially in harsh environments, and understand how disturbance intensity affect species co-occurrence.\ud Two study areas were considered: sub-Mediterranean grasslands of Umbria-Marches Apennine (central Italy) and the sub-desertic rangelands of southern Peruvian Andes (Peru).\ud In the studied sub-Mediterranean grasslands the competition for light and soil resources may be extremely intense among species. In fact, competition plays a key role, especially in dense and more productive grasslands, where the co-existence of plants is mainly linked to the competitive exclusion. For this reason, in these plant communities the species co-existence is driven by a specific pattern of functional plant traits that ensures foliage expansion affording a competitive advantage. Furthermore, clonal growth forms and vegetative propagation modes that imply horizontal space occupation, can be interpreted as a strategy aimed at maximizing the species competitive ability when there is higher exploitation of soil resources, allowing individuals to explore the neighbouring areas and find unexploited soil niches. This helps to avoid competition for soil resources with the dominant species. Accordingly, the plant functional composition also affects the competitive ability in relation to the stress and the disturbance intensity. \ud In terms of biodiversity conservation, the research outputs represent an advance in the understanding of the ecological processes involved at plant community level, as well as at landscape scale. Some plant traits may reflect selection by herbivores, while others are likely to be by-products of selection for other ecological functions. Moreover, several plant traits may have a dual role. The study findings allow to highlight a general scheme, in which the stress intensity filters the pool of traits at landscape scale, while the disturbance intensity leads to the distribution, occurrence and abundance of single traits at plant community level.\ud Stress intensity (drought stress) selects the trait composition of the plant community at a landscape scale. Thus, traits and associated plant species are distributed at landscape scale depending on stress intensity. In xeric grassland, stress tolerance and avoidance strategies by hairs and leaf texture, determining low evapotranspiration and low palatability, are widespread. Therophyte and chamaephyte life forms are fostered. In semimesic condition either avoidance mechanisms (rosette form, chemical substances, spines and prostrate form) or tolerance strategies (re-growth capacity) occur, as well as late flowering and tall species (upright forbs, tall tussock grasses). More productive environments develop numerous functional types and a higher floristic richness.\ud Disturbance intensity (number of herbivores), type (mowing or grazing, and the different livestock type) and timing act as driving forces in promoting or suppressing the plant functional traits expression. The pool of traits is filtered in different ways by the system. High intensity of disturbance favours avoidance strategies (i.e. prostrate form, rosette forbs, hairs) and vegetative reproduction (clonal ability). The intermediate disturbance condition leads to the largest pool of traits that allows maximum floristic richness. The co-existence of species is promoted by the co-existence of avoidance and tolerance strategies, due to the possibility to use the maximum number of spatial (micro-scale) and temporal niches (change in sward structure during the growing season).\ud In low intensity of disturbance and abandonment conditions, tolerance strategies and dominant species are promoted; on the contrary, the low statured (rosette and prostrate form), accidental and subordinate species are disadvantaged. \ud Large herbivores like horses cause the increase of short grasses, sedges, rosette forbs and annuals (growth forms with poor root systems). These plants do not ensure the maintenance of soil on steep slopes.\ud Upright forbs, dominant unpalatable tall grasses (Brachypodium rupestre) and chamaephyte species are promoted by selective defoliation of small herbivores like sheep. Facilitative interactions between palatable and unpalatable species were observed. Grazing in springtime negatively affects the early spring flowering species of mid/tall dimensions and relevant species such as orchids. This is an issue for biodiversity conservation.\ud The research findings highlight the strong importance of plant–plant spatial interactions in the Peruvian dry Puna. In this harsh environment many species need some kind of facilitative interaction with nurses (mainly with tall grasses, shrubs or cushion plants). Tall grasses (mainly Festuca orthophylla) are the most important nurse species because they have the highest number of spatially associated plants. Thus, the management of this species should be viewed as a key factor for dry Puna biodiversity conservation. In fact, as camelids prefer the fresh, regrown leaves of F. orthophylla that resprout after burning throughout the Peruvian dry Puna, there is the widespread practice of burning these plant communities to renew forage for livestock. Subsequent to burning, shelter and regenerative niches are probably few and small for some years. Because of this, species with strong spatial relationship with F. orthophylla could be threatened with local extinction, especially in conditions of overgrazing. The effects of combined overgrazing and fire lead to the decrease of tall species F. orthophylla and to an increase of the dwarf and spiny shrub Tetraglochin cristatum. The reduction of nurse cover value leads to the decrease of facilitative interactions and consequently to a reduction of species richness. Thus, inappropriate land use practices (e.g. excessive grazing and uncontrolled fire) are the fundamental causes of land degradation. The abundance of tall grasses and shrubs counters soil erosion by wind, and reduction of their cover value could lead to increased soil loss. This could contribute to desertification more than climatic change, or contribute to a cumulative process that amplifies the impact of climatic change. \ud \ud Key words: Avoidance and tolerance strategies, Competition, Facilitation, Plant functional traits, Plant-plant spatial interactions.\u

Mechanical stress and stress compensation in Hall sensors

Silicon magnetic sensors based on the Hall effect have proven to be an excellent sensor choice for many applications, such as position sensing, gear-tooth sensing, contact-less switching and linear sensing. Although a sensor can be trimmed over temperature before it is shipped to the customer, little can be done about the sensitivity's stability once the sensor has been installed in its final application. The goal of this project is to propose and implement mechanisms to stabilize the Hall sensor's sensitivity through the use of mechanical stress feedback and magnetic feedback.M.S.Committee Chair: Brand, Oliver; Committee Member: Hasler, Paul; Committee Member: Taylor, Willia

“A life of metal”: an ecocritical reading of Silvia Avallone’s "Acciaio"

Silvia Avallone’s acclaimed novel "Acciaio" (2010) narrates the struggling friendship, complicated existence, and coming of age of Anna and Francesca, two teenage girls who live in a working class neighborhood in the Tuscan coastal town of Piombino, near the Lucchini steel plant where most of their blue-collars older friends and relatives work. It tells the stories of human bodies who grow, love, suffer, struggle and die, but also of nonhuman matter (iron, steel) that is created, transformed and then “lives” a parallel co-existence in the same environment. More in particular, as its title and plot suggest, the novel also deals with the close relationship and reciprocal interferences between human beings and nonhuman matter, be it inorganic, like the iron ore and the machines the workers use to produce steel, or organic, like the animals, plants and shells the girls find on a beach near the plant site. Building on some of the theoretical postulates and methodological insights provided by ecocriticism’s recent “material turn”, that is, focusing on the novel’s representations of the encounters “between people-materialities and thing-materialities” (Bennett x), the aim of this paper is to suggest that Avallone’s novel not only presents a radically alternative vision of—at least a section of—Tuscany’s famed “Etruscan Coast,” but also hints at the sort of posthuman ecology that regulates this particular place. Ultimately, I argue that this text, by drawing attention to the mutual connections between “organisms, ecosystems, and humanly made substances” (Iovino 10), and between the biological, socio-economic and cultural spheres, goes way beyond the story of Anna and Francesca and the industrial area of Piombino where the Lucchini factory is situated. Taking this unusual Tuscan territory as an example, Avallone’s text provides a template for understanding ongoing dynamics in many other “Piombinos”, be they nearby in Tuscany—the Solvay soda-ash plant in Rosignano comes to mind—elsewhere in Italy, or all around the globe.La aclamada novela de Silvia Avallone, "Acciaio" (2010), narra la lucha de la amistad y la complica existencia y mayoría de edad de Anna y Francesca, dos adolescentes que viven en un barrio de clase obrera en el costero pueblo Toscano de Piombino, cerca de la acerería Lucchini, donde trabajan la mayoría de sus amigos mayores y sus parientes obreros. La novela cuenta la historia de cuerpos humanos que crecen, aman, sufren, luchan, y mueren, pero también de la materia no humana (hierro, acero) que se crea, se transforma, y después “vive” una existencia paralela en el mismo entorno. En particular, tal y como sugieren el título y la trama, la novela también trata de la cercana relación y las interferencias recíprocas entre los seres humanos y la materia no humana, sea inorgánica, como el mineral de hierro y las máquinas que los trabajadores usan para producir acero, u orgánica, como los animales, las plantas y las conchas que las chicas encuentran en una playa cerca de la acerería. Usando como base algunos postulados teoréticos y conocimientos metodológicos surgidos del reciente “giro material” de la ecocrítica, es decir, centrándose en las representaciones que la novela ofrece de los encuentros “entre materias-humanas y materias-cosas” (Bennett x), el objetivo de este ensayo es sugerir que la novela de Avallone no solo presenta una visión de la famosa “Costa Etrusca” de la Toscana (por lo menos una parte) radicalmente alternativa, sino que también insinúa el tipo de ecología posthumana que regula este lugar en concreto. Por último, argumento que este texto, al dirigir la atención a las conexiones mutuas entre “organismos, ecosistemas, y sustancias hechas por humanos” (Iovino 10), y entre las esferas biológicas, socioeconómicas, y culturales, va más allá de la historia de Anna y Francesca y del área industrial de Piombino donde se encuentra la acerería Lucchini. Tomando este insólito territorio toscano como ejemplo, el texto proporciona una plantilla para entender las continuas dinámicas en muchos otros “Piombionos”, estén cercanos a la Toscana (la planta de sosa Solvay en Rosignano viene a la mente), en otros lugares en Italia, o alrededor del mundo

“A life of metal”: an ecocritical reading of Silvia Avallone’s "Acciaio"

Silvia Avallone’s acclaimed novel "Acciaio" (2010) narrates the struggling friendship, complicated existence, and coming of age of Anna and Francesca, two teenage girls who live in a working class neighborhood in the Tuscan coastal town of Piombino, near the Lucchini steel plant where most of their blue-collars older friends and relatives work. It tells the stories of human bodies who grow, love, suffer, struggle and die, but also of nonhuman matter (iron, steel) that is created, transformed and then “lives” a parallel co-existence in the same environment. More in particular, as its title and plot suggest, the novel also deals with the close relationship and reciprocal interferences between human beings and nonhuman matter, be it inorganic, like the iron ore and the machines the workers use to produce steel, or organic, like the animals, plants and shells the girls find on a beach near the plant site. Building on some of the theoretical postulates and methodological insights provided by ecocriticism’s recent “material turn”, that is, focusing on the novel’s representations of the encounters “between people-materialities and thing-materialities” (Bennett x), the aim of this paper is to suggest that Avallone’s novel not only presents a radically alternative vision of—at least a section of—Tuscany’s famed “Etruscan Coast,” but also hints at the sort of posthuman ecology that regulates this particular place. Ultimately, I argue that this text, by drawing attention to the mutual connections between “organisms, ecosystems, and humanly made substances” (Iovino 10), and between the biological, socio-economic and cultural spheres, goes way beyond the story of Anna and Francesca and the industrial area of Piombino where the Lucchini factory is situated. Taking this unusual Tuscan territory as an example, Avallone’s text provides a template for understanding ongoing dynamics in many other “Piombinos”, be they nearby in Tuscany—the Solvay soda-ash plant in Rosignano comes to mind—elsewhere in Italy, or all around the globe.La aclamada novela de Silvia Avallone, "Acciaio" (2010), narra la lucha de la amistad y la complica existencia y mayoría de edad de Anna y Francesca, dos adolescentes que viven en un barrio de clase obrera en el costero pueblo Toscano de Piombino, cerca de la acerería Lucchini, donde trabajan la mayoría de sus amigos mayores y sus parientes obreros. La novela cuenta la historia de cuerpos humanos que crecen, aman, sufren, luchan, y mueren, pero también de la materia no humana (hierro, acero) que se crea, se transforma, y después “vive” una existencia paralela en el mismo entorno. En particular, tal y como sugieren el título y la trama, la novela también trata de la cercana relación y las interferencias recíprocas entre los seres humanos y la materia no humana, sea inorgánica, como el mineral de hierro y las máquinas que los trabajadores usan para producir acero, u orgánica, como los animales, las plantas y las conchas que las chicas encuentran en una playa cerca de la acerería. Usando como base algunos postulados teoréticos y conocimientos metodológicos surgidos del reciente “giro material” de la ecocrítica, es decir, centrándose en las representaciones que la novela ofrece de los encuentros “entre materias-humanas y materias-cosas” (Bennett x), el objetivo de este ensayo es sugerir que la novela de Avallone no solo presenta una visión de la famosa “Costa Etrusca” de la Toscana (por lo menos una parte) radicalmente alternativa, sino que también insinúa el tipo de ecología posthumana que regula este lugar en concreto. Por último, argumento que este texto, al dirigir la atención a las conexiones mutuas entre “organismos, ecosistemas, y sustancias hechas por humanos” (Iovino 10), y entre las esferas biológicas, socioeconómicas, y culturales, va más allá de la historia de Anna y Francesca y del área industrial de Piombino donde se encuentra la acerería Lucchini. Tomando este insólito territorio toscano como ejemplo, el texto proporciona una plantilla para entender las continuas dinámicas en muchos otros “Piombionos”, estén cercanos a la Toscana (la planta de sosa Solvay en Rosignano viene a la mente), en otros lugares en Italia, o alrededor del mundo

Between the Greater and Lesser Caucasus: An Analysis of the Belts from the Tli Burial Ground and Their Contexts (Graves 40b, 215b, 425)

This article presents a new study of three burial contexts from the important Tli graveyard located in the Southern Caucasus. The three tombs contained bronze belts with features mainly pertaining to an Assyro-Urartian tradition. An analysis of the belts’ iconographic apparatuses is given, together with a new chronological position proposed for the belts and the tombs: our idea is that a possible date for them should be within the period between the 7th and 6th centuries B.C.E. The analysis showed, moreover, that the Tli necropolis must be considered a great example of the complex contacts and cultural exchanges between multiple realities located both in the Caucasus and in the Mesopotamian region

A model of working memory for encoding multiple items and ordered sequences exploiting the theta-gamma code

Recent experimental evidence suggests that oscillatory activity plays a pivotal role in the maintenance of information in working memory, both in rodents and humans. In particular, cross-frequency coupling between theta and gamma oscillations has been suggested as a core mechanism for multi-item memory. The aim of this work is to present an original neural network model, based on oscillating neural masses, to investigate mechanisms at the basis of working memory in different conditions. We show that this model, with different synapse values, can be used to address different problems, such as the reconstruction of an item from partial information, the maintenance of multiple items simultaneously in memory, without any sequential order, and the reconstruction of an ordered sequence starting from an initial cue. The model consists of four interconnected layers; synapses are trained using Hebbian and anti-Hebbian mechanisms, in order to synchronize features in the same items, and desynchronize features in different items. Simulations show that the trained network is able to desynchronize up to nine items without a fixed order using the gamma rhythm. Moreover, the network can replicate a sequence of items using a gamma rhythm nested inside a theta rhythm. The reduction in some parameters, mainly concerning the strength of GABAergic synapses, induce memory alterations which mimic neurological deficits. Finally, the network, isolated from the external environment ("imagination phase") and stimulated with high uniform noise, can randomly recover sequences previously learned, and link them together by exploiting the similarity among items

Effect of long-term abandonment and spring grazing on floristic and functional composition of dry grasslands in a central Apennine farmland

Semi-natural dry grasslands host some of the most valuable habitats in Europe, due to their biodiversity heritage. Nevertheless, a strong decline in their extension, due to the cessation of traditional management, has been observed in the last decades. The aim of the study was to assess plant community changes due to abandonment and the effect of spring grazing in sub-Mediterranean dry grasslands, focusing on the plant functional traits involved in this turnover. The study area is located in the central Apennines (Italy), where grasslands were grazed by sheep in late winter and spring until 1980 and are nowadays abandoned. Relevés sampled (using the Braun-Blanquet method) in different years, namely in 1976–1980 (grazed pasture) and again in 2010 (abandoned pasture) were compared. Results indicated that abandonment leads to the increase of species richness. Traits and strategies indicator sets were: therophyte for the grazed pasture; geophytes, flower palatability, early flowering strategy, clonal ability and presence of storage organs for the abandoned ones. Traits related to low levels of stress (tolerance strategies) are heavily reduced in grazed systems, and thus the functional composition of plant community is mostly characterised by traits promoting avoidance strategies. In abandoned conditions a higher number of species can co-exist thanks to the micro-scale variation of soil features and niche diversification. The research findings also revealed grazing timing as a key factor for understanding changes of plant functional trait patterns and spring grazing as a threat for orchid species

The geosynphytosociological approach as a tool for agriculture innovation: the study case of saffron (Crocus sativus L.) cultivation suitability assessment in the Macerata district (central Italy)

The maintenance of open areas as grasslands and croplands has become a vital issue addressed to biodiversity conservation. For this purpose, innovation in agricultural activities may be a key factor. To achieve this goal, it is essential to identify the agronomic suitability and the most appropriate spatial pattern for the proposed cultivation. Therefore, the definition of land suitability classes and of their boundaries is a key step. For this purpose we used the phytosociological approach since it is based on an ecological definition and hierarchical classification of plant communities and landscapes and can be considered as an indirect way to assess the variation of the environmental conditions. Starting from the Marche Region vegetation geo-database, for each vegetation series a draft of the main ecological factors matching with the ecological needs of Crocus sativus L. was carried out. Afterwards, two intermediate maps were drawn: the “Climatic suitability map” and the “Soil suitability map”. Finally, the “Crocus sativus cultivation suitability map” was drawn by overlapping these two maps. Results were tested by agronomic experimentations. The synphytosociological approach proved to be a very valuable method. In fact, the areas belonging to the highlighted different suitability classes (that is the different vegetation series) showed substantial differences in the saffron productivity. Moreover using the vegetation mapping procedures also the definition of the borders of each suitability class has been easily solved at the landscape scale

Confocal Laser Scanning Microscopy Applied to a New Species Helps Understand the Functioning of the Reproductive Apparatus in Stylet-Bearing Urodasys (Gastrotricha: Macrodasyida)

Gastrotrichs are highly diverse and abundant in all aquatic ecosystems; however, they are often overlooked. During a biodiversity survey in Sardinia (Italy), a new species of gastrotrich herein described was discovered. Specimens of Urodasys bifidostylis sp. nov. were found in sandy sediments from two submarine caves. Using an integrative approach of traditional light (DIC) and high-resolution (CLSM) microscopies, we herein reveal, for the first time, the fine structure and function of the reproductive organ in an Urodasys representative. This is particularly relevant considering the complex reproductive organs and strategies of this group. Results allow comparisons between the reproductive apparatus and sperm transfer modalities in Urodasys and the closely related genus Macrodasys. One similarity is that both groups transfer male gametes in packets, suggesting the production of spermatophores to be a common phenomenon in Gastrotricha. Unique to Urodasys is the ability of multiple and consecutive copulations and sperm transfers and, differently than Macrodasys, the transfer of sperms unlikely occurs simultaneously between the two hermaphroditic partners. These findings provide new insights into the reproductive strategies of Urodasys and are expected to advance future studies on the evolution of reproductive strategies and the rise of interspecific reproductive barriers in interstitial meiofauna