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| Home > Publications database > Monitoring root water uptake of Centaurea jacea using water stable isotopes |
| Home > Publications database > Monitoring root water uptake of Centaurea jacea using water stable isotopes |
| Master Thesis | FZJ-2018-06315 |
; ; ; ;
2018
Please use a persistent id in citations: http://hdl.handle.net/2128/19997
Abstract: Root water uptake plays a crucial role in the water cycle, as it is the largest flux on land surfaces returning water to the atmosphere. Its complex dynamics and ecosystem feedbacks are however still not well understood and can therefore not be adequately accounted for in models simulating water transport in the soil-plant-atmosphere interface. Especially on short time scales, high uncertainty exists with regards to the plasticity of water uptake and its associated driving forces. In view of an increase in hydrological extremes and a changing climate, a more mechanistic understanding is however crucial.For five decades, water stable isotopes substantially improved our knowledge about this hard to observe belowground process. However, monitoring short-term variations was restricted, due to the necessity for destructive sampling and laborious sample analysis. Recent methodological advances now offer new possibilities to overcome these constraints and triggered the development of new approaches, which enable an in-situ monitoring of water stable isotopes in soil water and water taken up by plants. First combined in-situ measurements were already conducted in trees, but have not yet been applied to the examination of root water uptake in herbaceous species.In the presented work, a new method is tested that allows for long-term in-situ sampling of water stable isotopes across a soil column and in plant transpiration under controlled conditions in the laboratory, using Cavity Ring-Down Spectroscopy.For this purpose, an existing soil column setup is further developed and expanded by a plant component. Dual isotope data in daily and sub-daily temporal resolution is collected across soil isotopic profiles and transpiration of Centaurea jacea, respectively. It will be shown that measured transpiration values reflect a mixture of soil water differing in its isotopic composition across the profile throughout a period of six weeks, despite pronounced dynamic changes in both systems. Derived measurement precision is comparable to that of established and also other newly developed in-situ methods. The setup proved to be an adequate tool for capturing short-term variations in root water uptake in response to differences of water availability in daily resolution. To visualize water uptake profiles, data sets of the isotopic composition in plant transpiration and soil profiles are combined in a statistical multi-source mixing model. Observed trends can logically be interpreted with existing knowledge on water uptake dynamics and plasticity, while highlighting knowledge gaps in the mechanistic understanding of contributions of underlying processes. Prospectively, the implementation of data sets, obtained with the tested method, in mechanistic state-of-the-art models could help to further disentangle complex interactions between soils and root systems. On the other hand modeling approaches across scales that now more commonly include water stable isotopes, will potentially benefit from recorded time series. Therefore temporally highly resolved data sets should be collected for a rangeof plant species, soil types and scenarios in the future.
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