Root water uptake in anthropogenic change

Root water uptake can adapt quickly to changing environmental conditions. For example, ecosystems shift uptake downwards, when water is scarce. Here we investigste, how this capacity of the ecosystems depends on the management, changing climate conditions and especially the availability of other resouces that are also acquired by the root systems, like nitrogen. In this PhD project, we use soil moisture information in the Global Change Experimental Facility and in the Nutrient Network, with the aim to improve representation of plant resource acquisition in models.

Contact:  Sven Westermann , Anke Hildebrandt

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A Parsimonious Canopy Model (PCM)

Temperate forest ecosystems play a crucial role in governing global carbon and water cycles. The total carbon uptake of ecosystems by photosynthesis (GPP) is the largest flux between the land and the atmosphere within the carbon cycle. It is intrinsically linked to the canopy leaf production and potentially strongly affected by drought. For the water cycle, leaf area index (LAI) plays a crucial role, as it affects both the interception of rainwater and the water loss during carbon uptake. Therefore, a prognostic simulated vegetation leaf area index (LAI) would substantially improve representation of the water cycle components in hydrological models (e.g., evapotranspiration), while GPP predictions would benefit from simulated soil water storage. Those two key variables can be estimated together by incorporating a light use efficiency concept into a hydrological model. But existing LUE-modules either require external (e.g. satellite-based) LAI dynamics which are subjected to uncertainty and/or the level of the model complexity (when LAI is also simulated) prohibits their integration into hydrologic models. In this project, we develop a parsimonious forest canopy model to simulate the daily development of both GPP and LAI, while ensuring adequate level of complexity to allow coupling into hydrological models.

Model description can be found here: Bahrami et al., GMD

Contact:  Bahar Bahrami , Anke Hildebrandt

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AquaDiva

The CRC AquaDiva is a Collaborative Research Centre funded by the German Science Foundation. It deals with the coupling between surface and subsurface processes within the Earth Critical Zone. Two exploratories have been established in the first two phases of this altogether twelve year long project.

Our working group contributes understanding on how surface structure, like vegetation type, diversity and management, affect where and how water enters into the subsurface, and which part enters the deeper subsurface. We also look at how carbon and nitrogen enter the subsurface, are transformed and transported below the main rooting zone. For this, we couple the ecological model FORMIND to the hydrological model mHM and add a module that accounts for nutrient and carbon turnover in the forest soils. The models will first be adopted at the intensive monitoring sites of our project partners and than further extended to larger watersheds to allow generalization of the results.

Using the coupled model, we want to investigate, how land use management or changes in ecosystem structure due to extreme climate events, affect the input of water and matter to the deeper subsurface.

Contact:  Friedrich Bohn , Anke Hildebrandt

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