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Accueil du site → Doctorat → Australie → Application of stable isotope analyses to examine patterns of water uptake, water use strategies and water-use-efficiency of contrasting ecosystems in Australia

University of Technology Sydney (2016)

Application of stable isotope analyses to examine patterns of water uptake, water use strategies and water-use-efficiency of contrasting ecosystems in Australia

Rumman, Rizwana

Titre : Application of stable isotope analyses to examine patterns of water uptake, water use strategies and water-use-efficiency of contrasting ecosystems in Australia

Auteur : Rumman, Rizwana

Université de soutenance : University of Technology Sydney

Grade : Doctor of Philosophy (PhD) 2016

Résumé partiel
Spatial differences and temporal variation in the availability of water accessible by plants have significant influences on a range of plant functions, including photosynthesis, transpiration, growth and yield. Coexisting plant species often adopt contrasting water use strategies to reduce inter-species competition for water and to cope with seasonal and/or geographical differences in water availability. The work described in this thesis aimed to analyse the variations in sources of water uptake by vegetation as well as contrasting water use strategies across spatial and temporal scales in a range of sites across Australia. In particular, it employs stable hydrogen, oxygen and carbon isotopes to investigate variations in sources of water uptake by vegetation and discrimination against carbon-13 and water-use-efficiency at a range of spatial scales (from 10s of metres to thousands of kilometres) across a range of sites located along gradients of water availability. The generality of the trends found within smaller spatial scales in contrasting mesic and semi-arid ecosystems across water availability gradients are compared with trends obtained from different sites at a continental scale across a climate gradient (with mean annual precipitation ranging from 255 mm to 2140 mm). At smaller spatial scales, analyses were performed along two naturally occurring depth-to-groundwater gradients in contrasting mesic and arid ecosystems. Results from stable deuterium and ¹⁸O analysis revealed that, even in the mesic site that received >1000 mm rainfall for two consecutive years prior to sampling, increased water availability (via access to groundwater) still exerted some influence on sources of water uptake by dominant vegetation. However, stable isotope analysis more consistently and reliably identified access to groundwater by deep-rooted vegetation in the semi-arid sites that receives rainfall < 350 mm year⁻¹. A key result identified in this research was that discrimination against stable ¹³C isotopes (Δ¹³C) and leaf intrinsic water-use-efficiency (WUEᵢ) calculated from ¹³C at the leaf-level accurately identified water availability, specifically, groundwater use and spatial and/or seasonal patterns of groundwater use especially in water-limited regions. Consistent with the results of (branch water) deuterium and ¹⁸O analysis, discrimination against ¹³C and WUEᵢ (leaf-level) did not vary significantly with depth-to-groundwater in shallower rooted (Acacia) species but showed significant trends up to a threshold value of depth-to-groundwater of 13.9 m in the deep-rooted (Eucalyptus and Corymbia) species, indicating possible access to groundwater. A strong positive correlation of bulk-leaf Δ¹³C (strong negative correlation with WUEᵢ) of the dominant overstorey species with MAP and moisture index was observed during both dry- and wet-season across an eight-fold increase in mean annual precipitation (MAP) along a continental-scale climate gradient

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