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Politecnico di Milano (2016)

Ecohydrological modelling of soil water and nuntrients dynamics in tropical and subtropical biomes

DONZELLI, DAVIDE

Titre : Ecohydrological modelling of soil water and nuntrients dynamics in tropical and subtropical biomes

Auteur : DONZELLI, DAVIDE

Université de soutenance : Politecnico di Milano

Grade : Ph.D. in Hydraulics Engineering 2012

Résumé
The present work describes an eco-hydrological approach in order to analyze the interaction between hydrological and biogeochemical cycles in tropical and sub-tropical biomes, seen as ecosystems shaped by resources limitation and competitition between the two dominating plant functional types of trees and grasses. A first model investigates the tree-grass competition for multiple resources, representing the characteristics biomes succession mainly as the results of the dynamical behavior of tree and grasses competing for water and mineral in a shared volume of soil. We use a simple dynamical resource-competition model considering two contrasting hypotheses about the behavior of tree and grasses respect to the resources : 1) tree is the superior competitor for nitrogen and grass is the superior competitor for water, and 2) tree is the superior competitor for water, and grass for nitrogen. We study the model’s properties in both the two different hypotheses, calculating steady states and bifurcations. We use data of some african savanna and a statistical analysis to select the hypothesis which better represent the data. In addition we compare the model’s results with a global simulated database finding an agreement of about 72%. Finally we study patterns of vegetation along two gradients of resources in order to investigate the potential changes of vegetation under climate variability, and patchiness of soil properties. We develop a second model which focuses on nitrogen and phosporous limitation in the same latitudinal range. We start from a minimal description of the dynamics of soil moisture and its interaction with the cycling of nutrients in soil, and in particular with the mineralizationimmobilization turnover. We shows that, despite its parsimonius parameterization, this model is able to capture relevant characteristics of the observed patterns of nutrient limitation, in particular those obtained in nutrient enrichment experiments.

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