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Accueil du site → Doctorat → Israel → Reorganization and functioning of vegetation in a water limited environment

Ben-Gurion University of the Negev (2014)

Reorganization and functioning of vegetation in a water limited environment

Dovrat Guy

Titre : Reorganization and functioning of vegetation in a water limited environment

התארגנות מחדש ותפקוד צומח בסביבה מוגבלת מים : תכונות גודל וחלוקת משאבים בהשפעת זמינות מים

Auteur : Dovrat Guy

Etablissement de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2014

Descriptif partiel (à la fin de la version intégrale)
Background : Recently there is a gradual increase in the use of plant "functional traits" as a tool for characterizing species and communities and linking environmental conditions, community structure, and ecosystem functions. Plant size and resource partitioning patterns are quantitative functional traits that are especially suitable for these aims. By observing the community "functional structure" through size and resource partitioning traits, we can achieve a better understanding of the ways by which plant communities reorganize in response to environmental changes, and the effects of these changes on ecosystem functions, such as resources capture and biomass production. A quantitative assessment of community functional structure can be done through indexes of "functional identity", which represent the community’s trait values, and/or "functional diversity", which represent the range and variations of the community’s trait values. However, in natural plant communities subject to environmental heterogeneity, it is difficult to distinguish between the contribution of changes occurring at the individual plant level (i.e. phenotypic plasticity) and those that are occurring at the community level (i.e. species composition shifts) in shaping the community’s functional structure. Moreover, it is difficult to assess the direct effect of community’s functional structure on ecosystem function, as both the structure and function are affected by environmental variation. Additionally, in natural plant communities there is an inherent relationship between the functional diversity and the functional identity, and the understanding with regard to the distinct role of each of these community properties in determining ecosystem function and reorganization capacity is still lacking. The aim of this research was to achieve better understanding of the relationships between resources availability, community structure and reorganization and ecosystem function of plant communities in water-limited environments. The following thesis was examined : in water limited environments, plant growth rate and biomass partitioning among the plant organs (resource partitioning) are functional traits related to soil resources availability. Therefore, plant community reorganization in response to variations in soil resources availability will be expressed through changes in the diversity and identity of these functional traits (community functional structure). Changes in community functional structure are a result of processes that occur both at the individual level, through phenotypic plasticity, and at the community level through species composition shifts. Both of these mechanisms operate according to the same principle exhibiting a trade-off between the ability to utilize resources at high rate vs. the capacity to cope with resource stress. Hence, an increase of soil resources availability is expected to bring about an increase in the relative abundance of traits related to rapid resource capture and competitive ability, while a decrease in soil resources availability is expected to cause an increase in the relative abundance of traits related to the capacity to cope with resource stress. These variations in community functional structure reflect reorganization to maximize utilization of available resources.

Research approach : The research focuses on an annual plant community of the Northern Negev Desert in Israel. In annual plants, the size of the whole plant and the biomass partitioning among its organs at the end of the growing season are directly related to its function (biomass production rate) and reorganization (resource partitioning) during a specified period of time (the growing season). Community functional structure at the end of the growing season, which includes the distribution of plant sizes due to variation in biomass production among individuals, represents the community’s ecosystem function (productivity). Therefore, temporal and spatial variation in community functional structure can express community reorganization in response to changes in resource availability. Annual plant communities composed of individual plants of varying sizes present functional diversity. The diversity of sizes in a community is a product of both interspecific variations in inherent growth rate, as well as phenotypic plasticity within species. The diversity and identity of sizes in a community reflects community "functional structure". Functional structure defined by the inherent traits of the species that compose the community was defined in this work as : "community inherent functional structure". Yet, the actual functional structure found in a community as a result of the combination between species inherent traits and phenotypic plasticity was defined as : "real functional structure". The real functional structure determines community total biomass and therefore represents community function at the ecosystem level. The research, which is summarized in four chapters, was conducted in the field and in the laboratory, on an annual plant community growing in a water limited environment (Northern Negev Desert). In chapters 1 and 2, which are based on a reanalysis of field data, we examined the variation patterns of community real functional structure under temporal and spatial heterogeneity in resources availability. We examined the variation in the diversity and identity of plant sizes in the community, in response to changes in resource availability, and the relationship between functional structure and community’s ecosystem function (annual biomass production). In chapters 3 and 4, we examined, under laboratory conditions, the effects of soil resource availability on the productivity and resource partitioning at the individual plant level and at the community level, and the relationships between community functional structure and its ecosystem function (productivity).

Mots clés : functional structure, functional diversity, functional identity, functional traits, biodiversity, ecosystem function, annual plants, growth rate, root to shoot ratio.

Présentation et version intégrale (PRIMO)

Page publiée le 12 janvier 2023