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  • 1
    Language: English
    In: Plant and Soil, 2011, Vol.341(1), pp.233-256
    Description: The estimation of root water uptake and water flow in plants is crucial to quantify transpiration and hence the water exchange between land surface and atmosphere. In particular the soil water extraction by plant roots which provides the water supply of plants is a highly dynamic and non-linear process interacting with soil transport processes that are mainly determined by the natural soil variability at different scales. To better consider this root-soil interaction we extended and further developed a finite element tree hydro-dynamics model based on the one-dimensional (1D) porous media equation. This is achieved by including in addition to the explicit three-dimensional (3D) architectural representation of the tree crown a corresponding 3D characterisation of the root system. This 1D xylem water flow model was then coupled to a soil water flow model derived also from the 1D porous media equation. We apply the new model to conduct sensitivity analysis of root water uptake and transpiration dynamics and compare the results to simulation results obtained by using a 3D model of soil water flow and root water uptake. Based on data from lysimeter experiments with young European beech trees ( Fagus silvatica L.) is shown, that the model is able to correctly describe transpiration and soil water flow. In conclusion, compared to a fully 3D model the 1D porous media approach provides a computationally efficient alternative, able to reproduce the main mechanisms of plant hydro-dynamics including root water uptake from soil.
    Keywords: Transpiration ; Plant hydro-dynamics model ; Root water uptake ; European beech ; Porous media equation
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 2
    Article
    Article
    Universitätsbibliothek Tübingen
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  • 3
    Language: English
    In: Ecological Modelling, 24 July 2017, Vol.356, pp.14-24
    Description: Water is one of the major drivers determining distribution and abundance of plant species. Namely, plant species’ presence and location in the landscape can be explained using metrics of soil water because plant species are restricted to a species-specific range of soil water conditions, i.e. their hydrological niche. However, little is known about the specific traits that determine the hydrological niche of a plant species. To investigate the relationship between plant functional traits, community structure and hydrological niche segregation, we developed a new generic individual-based model PLANTHeR which describes plant functional trait abundance as a function solely of soil water potentials and individual behavior. An important innovation is that there are no defined trade-offs so that the model is neither restricted to a certain set of species nor scaled to a specific ecosystem. We show that PLANTHeR is able to reproduce well-known ecological rules such as the self-thinning law. We found that plant functional traits and their combinations (plant functional types − PFTs) were restricted to specific ranges of soil water potentials. Furthermore, the existence of functional trait trade-offs and correlations was determined by environmental conditions. Most interestingly, the correlation intensity between traits representing competitive ability and traits promoting colonization ability changed with water stress intensities in a unimodal fashion. Our results suggest that soil water largely governs the functional composition, diversity and structure of plant communities. This has consequences for predicting plant species’ response to changes in the hydrological cycle due to global change. We suggest that PLANTHeR is a flexible tool that can be easily adapted for further ecological-modelling studies.
    Keywords: Hydrological Niche ; Functional Traits ; Trade-Offs ; Self-Thinning ; Individual-Based Modelling ; Environmental Sciences ; Ecology
    ISSN: 0304-3800
    E-ISSN: 1872-7026
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  • 4
    Language: English
    In: European Journal of Agronomy, 2011, Vol.35(2), pp.71-82
    Description: ► Crop models were tested against complete data sets with different CO and H O regimes. ► The crop models adequately simulated the open-top chamber experimental conditions. ► Dynamic interplay was simulated best using the Farquhar photosynthesis sub-model. ► Simple photosynthesis models increased specific assimilation rates under elevated CO . We used the modeling package Expert-N to investigate the ability of four generic-mechanistic crop models that were originally developed under field conditions to simulate the plant growth of spring wheat grown in open-top chambers (OTC) under different environmental conditions. We focus on the impacts of water limitation and elevated atmospheric CO concentration on biomass production. Expert-N facilitates the comparison of the components of agro-ecosystem models because it allows the exchange of single modules while leaving the rest of the model unchanged. The crop growth part of the models SPASS, CERES-Wheat, SUCROS and GECROS were combined with the Penman–Monteith equation for potential evapotranspiration, the HYDRUS-1D model for water transport and the LEACHN model for nitrogen transport and turnover simulation. The models were applied to a data set provided by OTC experiments with spring wheat ( L. cv. ‘Minaret’) that was grown under two atmospheric CO concentrations (ambient/elevated), two irrigation schemes (non-limited water supply/water limitation) and two soil types (Cambisol/Chernosem) in two subsequent vegetation periods (1998/1999). Based on the model calibration using experimental and literature data, the best simulation results describing the impact of the considered environmental conditions were obtained using the SUCROS model followed by the SPASS, GECROS and CERES models. The study depicts the shortcomings of the underlying processes in all of the models. These shortcomings need to be addressed when models are applied on regional scales or for prediction under climate change conditions.
    Keywords: Triticum Aestivum L ; Wheat ; Elevated CO 2 ; Crop Growth Simulation ; Crop Model ; Agriculture
    ISSN: 1161-0301
    E-ISSN: 1873-7331
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  • 5
    Language: English
    In: Journal of Hydrology, 2007, Vol.335(3), pp.259-270
    Description: A challenge of soil water transport modelling is the assessment of various uncertainties resulting from input data, from parameterisation of soil hydraulic characteristics and from estimation of sink terms like plant water uptake and soil evaporation. The objective of this study is to evaluate different modelling approaches for the estimation of soil hydraulic characteristics and evapotranspiration. A dataset from a lysimeter study in South-Germany with rotative crop vegetations over 5 years was used to perform the analysis. The pedotransfer functions that were used to estimate parameters for the representation of soil water retention and hydraulic conductivity have shown to be appropriate for water flow simulations. Although the simulated annual percolation amount is not very sensitive to the used soil hydraulic characteristics for the chosen boundary conditions, the diurnal percolation dynamics are highly sensitive to the soil hydraulic characteristics. The results show a strong dependence of simulated percolation on the used potential evpotranspiration (ET ) model. The Penman, Penman–Monteith and Haude approach overestimate the measured cumulative actual evapotranspiration in the present study. The measured outflow from the lysimeters can be correctly simulated, if a modified Haude approach is used. However, in the simulation of daily evapotranspiration fluxes the physically based Penman–Monteith approach has higher correlation with measurements than the empirical approach of Haude. For the tested lysimeter data we show that depending on ET model choice the simulated percolation amounts vary between 52% and 126% of the measured amounts. Compared to this, the influence of the parameterisation of the soil hydraulic characteristics is small with a variation of up to 5% of the measured outflow.
    Keywords: Water Transport Modelling ; Soil Hydraulic Characteristics ; Potential Evapotranspiration Models ; Field Lysimeter ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Trees, 2013, Vol.27(6), pp.1763-1773
    Description: KEY MESSAGE : Our study provides evidence that neither elevated CO ₂ nor elevated O ₃ alters the positive asymmetric competition for light and the symmetric competition for water among beech and spruce individuals grown in monoculture. We conclude that the mechanism of competition (i.e. symmetric/asymmetric) above (e.g shading or overtopping effect) and belowground (e.g. non-preemption or foraging) rather than abiotic treatments such as elevated CO ₂ , O ₃ and CO ₂ /O ₃ regimes, plays a dominant role for ensuring competitive success among tree saplings. Despite numerous studies conducted on plant responses to increasing CO₂ and O₃ concentrations, there is still a gap in understanding on how these gasses would affect the mode of competition (e.g., the ability by which larger and smaller plants capture resources) at the individual level of intra-specific beech and spruce saplings. Using empirical data and simulations from the plant-growth model PLATHO, we analyzed underlying mechanisms of competition and extrapolated effects beyond the time span of the experiment. We hypothesized that among juvenile beech and spruce trees planted in monoculture, +CO₂ would diminish the positive asymmetric competition for light. Conversely, +O₃ would enhance this outcome. In addition, we hypothesized that the symmetric mode of competition belowground for water would remain unchanged, irrespective of +CO₂ and/or +O₃ treatments. Our results showed that +CO₂ and/or +O₃ treatments did not alter the mode of competition aboveground for light. Conversely, we accepted our hypothesis that the mode of competition for water would remain unchanged under both treatments. Overall, we conclude that neither +CO₂ nor +O₃ alters the positive asymmetric competition for light and the symmetric competition for water among beech and spruce individuals grown in monoculture. We further conclude that competitive mechanism above (e.g., shading or overtopping effect) and belowground (e.g., non-preemption or foraging) rather than abiotic treatments, such as elevated CO₂, O₃ and CO₂/O₃ regimes, plays a dominant role for ensuring competitive success among tree saplings. ; p. 1763-1773.
    Keywords: CO ; O ; Mode of competition ; Light ; Water ; Beech and spruce saplings
    ISSN: 0931-1890
    E-ISSN: 1432-2285
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  • 7
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  • 8
    Article
    Article
    Universitätsbibliothek Tübingen
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  • 9
    In: Water Resources Research, April 2015, Vol.51(4), pp.2825-2846
    Description: A Bayesian model averaging (BMA) framework is presented to evaluate the worth of different observation types and experimental design options for (1) more confidence in model selection and (2) for increased predictive reliability. These two modeling tasks are handled separately because model selection aims at identifying the most appropriate model with respect to a given calibration data set, while predictive reliability aims at reducing uncertainty in model predictions through constraining the plausible range of both models and model parameters. For that purpose, we pursue an optimal design of measurement framework that is based on BMA and that considers uncertainty in parameters, measurements, and model structures. We apply this framework to select between four crop models (the vegetation components of CERES, SUCROS, GECROS, and SPASS), which are coupled to identical routines for simulating soil carbon and nitrogen turnover, soil heat and nitrogen transport, and soil water movement. An ensemble of parameter realizations was generated for each model using Monte‐Carlo simulation. We assess each model's plausibility by determining its posterior weight, which signifies the probability to have generated a given experimental data set. Several BMA analyses were conducted for different data packages with measurements of soil moisture, evapotranspiration (), and leaf area index (LAI). The posterior weights resulting from the different BMA runs were compared to the weight distribution of a reference run with all data types to investigate the utility of different data packages and monitoring design options in identifying the most appropriate model in the ensemble. We found that different (combinations of) data types support different models and none of the four crop models outperforms all others under all data scenarios. The best model discrimination was observed for those data where the competing models disagree the most. The data worth for reducing prediction uncertainty depends on the prediction to be made. LAI data have the highest utility for predicting , while soil moisture data are better for predicting soil water drainage. Our study illustrates, that BMA provides an objective framework for data worth analysis with respect to both model discrimination and model calibration for a wide range of applications. BMA provides a data worth analysis framework for model selection and calibration BMA does not converge to the “true” model Different data types support different models and none outperforms all others
    Keywords: Bayesian Model Averaging ; Data Worth ; Model Selection ; Soil‐Plant Modeling
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 10
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