Author: Zijuan Deng
Deng, Zijuan, 2015 EXAMINATION OF HYDRODYNAMIC SOIL-PLANT WATER RELATIONS WITH A NEW SPAC MODEL AND REMOTE SENSING EXPERIMENTS, Flinders University, School of the Environment
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Understanding soil-plant water relations is important for water resources management and ecosystem conservation in a changing environment. Simulating the water transfer in the soil-plant-atmosphere continuum (SPAC) is one of the key ecohydrological subjects which illustrates land surface mass and energy exchanges and provides meaningful guidance for future scenarios. Barriers, however, exist in SPAC modelling in terms of data sharing and methodology integration among the communities of hydrology and eco-physiology.
This study focuses on developing a new SPAC model (namely v-SPAC model) to enhance the communications between the communities. Unlike hydrologic models which lack representation of key plant hydraulic processes or eco-physiological models which usually assume steady-state environment, the new model integrates both root-zone hydrological processes and vegetation controls on plant water use. For the first time, a model of such type is parameterized with reduces uncertainty in hydrologic model calibration. Testing of the v-SPAC model was conducted on two native species: Acacia pycnantha in the natural field and potted Eucalyptus crenulata saplings in a water controlled experiment. The results show that the v-SPAC model performs well in reproducing the dynamics of both plant and soil water status and water flux.
Equipped with the new model, we are able to explore several hot topics in ecohydrology. For example, nocturnal transpiration has attracted continuous attention in the eco-physiology group, which, however, is ignored in the zero flux boundary in the hydrologic models. The v-SPAC model is capable to quantify the observed hydraulic disequilibrium between soil and plant which cannot be explained with hydrologic models. The v-SPAC model is also used to evaluate the associated uncertainties in the nocturnal transpiration calculation with existing methods in the eco-physiology group.
Based on the v-SPAC modelling experiments, the robustness of a novel method (RWRC method) to depict root zone soil water retention curve is tested. With simulations under various plant, soil, atmosphere scenarios, the v-SPAC model helps to identify favourable conditions for the RWRC application. The new method provides an important complement to the tradition methods which may only capture the soil hydraulic properties at the centimetre scale. In some cases, this can be done over metre scale but with high cost. The new method characterizes the root-zone averaged hydrological properties (in metre scale) which are more appropriate for root-zone hydrologic modelling and land surface modelling.
Finally, the usefulness of thermal remote sensing technique is tested on detecting plant water stress. The v-SPAC model is indirectly applied by gap-filling the benchmark water stress time series. The work serves as an important extension to previous components as thermal remote sensing is a common up-scaling tool for land surface modelling. The experiment provides important insight into upscaling individual tree properties to ecosystem level with remote sensing technique. The results suggest that the linear upscaling scheme commonly used in remote sensing may not be valid under all atmospheric conditions.
This thesis demonstrates the great benefits of integrating knowledge, data and methodology from both hydrology and eco-physiology fields. The preliminary application of the v-SPAC model has illustrated its robust capacity in explaining some ecohydrological phenomena and is expected to continue contributing to the field.
Keywords: soil-plant water relations, soil-plant-atmosphere continuum model, plant water potential, night-time transpiration, thermal imaging,
Subject: Environmental Science thesis
Thesis type: Doctor of Philosophy
Completed: 2015
School: School of the Environment
Supervisor: Huade Guan