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sur le développement des zones arides et semi-arides

Titre : Investigation of plant water uptake and transpiration fluxes using stable isotopes in the semi-arid Hailiutu catchment, northwest China

Auteur : Jimenez Rodriguez C.D.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science 2012

Résumé
Deuterium and oxygen-18 composition of sap water, soil water, precipitation, and groundwater was analysed to determine the relative water source contributions to sap flow in two plant species utilized in sand dunes in Shaanxi province, northwest China. Two experimental plots established at the Hailiutu catchment were utilised to gather water samples and monitor groundwater levels, soil water contents, precipitation, and temperature through the period : September-October 2010. One plot is dominated by Salix shrubs (Salix psammophila C. Wang & Chang Y. Yang) ; while the second one by the tree species Willow (Salix matsudana Koidz.) and Poplar (Populus simonii Carr.). For the study only Salix and Willow plants were monitored. The total precipitation at the experimental site was 401 mm a-1 during 2010, while 88.7 mm was collected in total for the period September to October. The Salix stand is characterized by a higher water content (11.5 ± 4.4%) in respect to Willow (10.4 ± 2.4%) keeping on average 37.7 mm and 30.1 mm of available water content through the first 100 cm of the soil profile, respectively. In addition, to this high soil water availability in both species and shallow groundwater levels (Salix depth : 144.6 ± 1.6 cm ; Willow depth : 164.9 ± 1.8 cm), it was found that Salix transpires more water than Willow (1094.1 ± 503.2 g d-1 branch-1 and 641.9 ± 354.7 g d-1 branch-1, respectively). The isotopic analysis shows high fractionation in the soil water at a depth of 40 cm beneath Willow and the absence of the evaporation front in Salix. Multisource software application to process the sap water isotope composition, determined that the Salix is highly dependent on the groundwater and the available soil water in deeper layers, which is 37.2 ± 7.2% of the sap water from soil layers beneath 70 cm, whilst Willow extracts more water from the shallow soil layers with only 5.0 ± 2.1% from this source of water.

Mots clés : isotopes ; plants ; transpiration ; semi-arid areas ; China

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