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Accueil du site → Doctorat → Allemagne → 2020 → Plant nutrient mobilization and acquisition strategies : adaptation to water and nutrient availability — Three levels of aridity along the Chilean Coastal Cordillera : arid, Mediterranean, and humid-temperate

Georg-August Universität zu Göttingen (2020)

Plant nutrient mobilization and acquisition strategies : adaptation to water and nutrient availability — Three levels of aridity along the Chilean Coastal Cordillera : arid, Mediterranean, and humid-temperate

Svenja Stock

Titre : Plant nutrient mobilization and acquisition strategies : adaptation to water and nutrient availability — Three levels of aridity along the Chilean Coastal Cordillera : arid, Mediterranean, and humid-temperate

Auteur : Svenja Stock

Université de soutenance : Georg-August Universität zu Göttingen

Grade : Doctor rerum naturalium 2020

Résumé partiel
Distribution and variability of precipitation are predicted to shift in Chile and are expected to lead to increases in frequency and duration of droughts. These developments can lead to a cascade of environmental changes that are likely to alter biogeochemical cycles and ecosystem functioning. The ability of vegetation to adapt to changing conditions affects the response of natural ecosystems to predicted precipitation changes. The strategy to acquire and the ability to retain resources can be an important factor for determining the adaptation ability of plants. Thus, to assess the potential for adaptation, it is crucial to understand plant nutrient acquisition strategies under current climatic settings. Aim of this research project was, therefore, to identify plant nutrient acquisition strategies of natural perennial woody vegetation under three levels of aridity along the Chilean Coastal Cordillera : arid, Mediterranean, and humid-temperate. Nutrient availability can have a critical role on plant drought sensitivity. Therefore, the first objective was to determine the nutrient availability at the site of each aridity level. As second objective we assessed plant nutrient recycling and uplift at each aridity level as well as root traits that are indicative for the plant nutrient uptake capacity. The third objective was to determine the importance and function of recycling and weathering agents as well as plant symbionts for plants’ nutrient acquisition. Sites with similar granitoid parent material but contrasting climatic conditions were selected for this study across a >900 km long precipitation gradient in the Chilean Coastal Cordillera. From north to south, the mean annual precipitation (MAP) increased from 80 to >1500 mm a 1, accompanied by an increase of soil thickness. Carbon (C), nitrogen (N), phosphorus (P), and potassium (K) contents in soil and plants were measured. N stocks in soil increased with increasing precipitation, but N availability declined, which was indicated by the highest C:N ratios in soil under humid conditions. While plant available P increased with decreasing precipitation, water shortage in the semiarid and arid ecosystems likely restricts P mobility and accessibility. Following a soil labeling experiment with 15N as N tracer and rubidium (Rb) and cesium (Cs) as K tracers, short term (<1 year) N and K plant acquisition from topsoil, subsoil, and saprolite was determined. Additionally, the vertical distribution of exchangeable K and the natural 15N abundance of plants and topsoil was assessed to evaluate long-term (>decades) N and K uplift and recycling. Further, the P speciation and contents of low molecular weight organic acids (LMWOA) were measured in rhizosphere soil from topsoil, subsoil, and saprolite. Under arid conditions, N was not only strongly reutilized (short- and long-term) from topsoil but also from subsoil and saprolite. Similarly, the rock-born nutrient K was reutilized equally from topsoil and uplifted from subsoil and saprolite. Increasing LMWOA per microbial biomass carbon (MBC) with increasing depth, pointed to an intended LMWOA exudation by plants for biological weathering of minerals to cover their P demand. Under Mediterranean conditions, high denudation rates likely reduced long-term N recycling but induced intensive short-term reutilization of N as well as K from topsoil. This was indicated by a higher N (9 times) and K (7 times) tracer recovery in shoots from topsoil than from subsoil. Plant P acquisition seemed to rely on, both, recycling of organic P from topsoil as well as biological weathering and uplift of inorganic P from subsoil. Under humid conditions, N was strongly reutilized from topsoil (short- and long-term) as well as recaptured from subsoil and saprolite. Similarly, K was reutilized from topsoil and uplifted from saprolite. Short-term uplift of both nutrients, however, was lower than under arid conditions

Mots clés  : Nutrient acquisition strategies ; Arbuscular mycorrhizal fungi ; Extracellular enzyme activities ; Diazotrophs ; Low molecular weight organic acids ; Chilean Coastal Cordillera ; Natural ecosystems

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Page publiée le 18 novembre 2021