10,891 research outputs found

    Modelling Water Flow and Solute Transport for Horticultural and Environmental Management

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    During the past 10 years, the simulation model SWAP (Soil, Water, Atmosphere, Plant) was developed by the Sub-Department Water Resources of Wageningen University jointly with the Department Water and Environment of Alterra Green World Research. SWAP simulates vertical transport of water, solutes and heat in variably saturated, cultivated soils at field scale level and during whole growing seasons. Different versions of the model have been applied worldwide in research, education and as a decision support tool in the management of agricultural, horticultural and natural systems water flow in homogeneous and heterogeneous soils with or without the influence of groundwater. The main features of and theoretical concepts behind SWAP are described, in particular soil water flow, solute transport and crop growth

    Spring water stress in Scots pine

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    Water use and net carbon assimilation during spring was examined on Scots pine trees exposed to different soil warming dynamics in the field. Sap flow, needle water potential and net carbon assimilation were measured on trees that were exposed to a wide range of soil temperature regimes caused by manipulating the snow cover on tree-scale soil plots. This made it possible to quantify the sensitivity of water uptake and recovery of gas exchange by Scots pine in the critical transition from winter dormancy to the growing season, which can be influenced by silvicultural practices. A part of the study was to find a tool for estimating the coupled effect of belowground and aboveground climate on transpiration, as well as to adapt this tool to the harsh climate of the boreal forest. Combining the results of field experiments on tree susceptibility to water stress with a physically based SVAT model as well as a model for estimating the recovery of photosynthesis helped to predict spatial and inter-annual variability of snow depths, soil warming, water uptake and net primary productivity during spring within different Scots pine stands across the landscape. This could provide a better basis for a more frostconscious forest management. The studies have confirmed the importance of low soil temperatures in combination with aboveground climate for root water uptake and net carbon assimilation during spring, when soil warming occurs after the start of the growing season. The studies have also confirmed that earlier, controlled laboratory studies on the inhibiting effects of low soil temperature on water relations and gas exchange for seedlings or saplings also hold true on mature trees in the field. The experimental data served well as the basis for model analyses of the interaction between belowground and aboveground conditions on water use and net photosynthesis. The results of the field studies and model analyses suggest that the effect of soil temperature on tree water uptake and net photosynthesis during spring, in conjunction with aboveground conditions, are factors that need to be considered in forest management in areas susceptible to soil frost and low soil temperatures

    SWAP Version 3.2. Theory description and user manual

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    SWAP 3.2 simulates transport of water, solutes and heat in the vadose zone. It describes a domain from the top of canopy into the groundwater which may be in interaction with a surface water system. The program has been developed by Alterra and Wageningen University, and is designed to simulate transport processes at field scale and during whole growing seasons. This is a new release with special emphasis on numerical stability, macro pore flow, and options for detailed meteorological input and linkage to other models. This manual describes the theoretical background, model use, input requirements and output tables

    Integrated basin modeling

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    Simulation models / Irrigation management / Water balance / Groundwater / River basins / Hydrology / Flow / Evapotranspiration / Precipitation / Soils / Turkey / Gediz Basin

    Physical and biological controls on fine sediment transport and storage in rivers

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    Excess fine sediment, comprising particles <2 mm in diameter, is a major cause of ecological degradation in rivers. The erosion of fine sediment from terrestrial or aquatic sources, its delivery to the river, and its storage and transport in the fluvial environment are controlled by a complex interplay of physical, biological and anthropogenic factors. Whilst the physical controls exerted on fine sediment dynamics are relatively well-documented, the role of biological processes and their interactions with hydraulic and physico-chemical phenomena has been largely overlooked. The activities of biota, from primary producers to predators, exert strong controls on fine sediment deposition, infiltration and resuspension. For example, extracellular polymeric substances (EPS) associated with biofilms increase deposition and decrease resuspension. In lower energy rivers, aquatic macrophyte growth and senescence are intimately linked to sediment retention and loss, whereas riparian trees are dominant ecosystem engineers in high energy systems. Fish and invertebrates also have profound effects on fine sediment dynamics through activities that drive both particle deposition and erosion depending on species composition and abiotic conditions. The functional traits of species present will determine not only these biotic effects but also the responses of river ecosystems to excess fine sediment. We discuss which traits are involved and put them into context with spatial processes that occur throughout the river network. Whilst strides towards better understanding of the impacts of excess fine sediment have been made, further progress to identify the most effective management approaches is urgently required through close communication between authorities and scientists

    WHY DOES DROUGHT KILL TREES? INTERACTIONS BETWEEN WATER, CARBON, AND FUNGAL SYMBIONTS

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    One of the global causes of forest die-off is climate-change induced drought. Drought kills trees by reducing water supply and non-structural carbohydrate (NSC) availability and by increasing susceptibility to negative biotic interactions. However, we lack an understanding of how water, NSC, and biotic agents interact. As a result, we still cannot accurately predict drought-induced mortality. The overarching goal of my dissertation is to increase our understanding of the interacting mechanisms leading to drought-induced mortality (DIM) and to identify physiological variables that accurately predict risk of DIM. Via greenhouse experiments with Pinus ponderosa (ponderosa pine) seedlings, I addressed three overarching research questions: (1) which physiological variables are good predictors of DIM?, (2) What is the role of NSC on plant water relations and DIM?, and (3) Do fungal symbionts affect plant water relations by altering host NSC during periods of carbon deficit? I first show that plant water content integrates the negative effects of reduced water supply and NSC availability under drought and it accurately predicts DIM risk. Further, plant water content shows a threshold at which DIM risk increases. I also provide evidence that plants use NSC to retain water in living tissues and maintain plant water content above critical mortality thresholds. Next, I show that plant water content is a good predictor of DIM risk across populations of ponderosa pine despite differences in morphology, physiology, and drought strategies. The integrative nature of plant water content is relevant because it can be detected remotely, which may allow large-scale assessments of mortality risk. Lastly, I show that fungal symbionts connecting multiple plant hosts can become parasitic and deplete NSC in some hosts. Such a depletion impairs plant water relations, which could increase host vulnerability to drought. My dissertation provides insight on physiological mechanisms leading to DIM and identifies simple physiological variables useful for monitoring DIM risk

    Dynamic Energy Budget models: fertile ground for understanding resource allocation in plants in a changing world

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    Climate change is having dramatic effects on the diversity and distribution of species. Many of these effects are mediated by how an organism’s physiological patterns of resource allocation translate into fitness through effects on growth, survival and reproduction. Empirically, resource allocation is challenging to measure directly and so has often been approached using mathematical models, such as Dynamic Energy Budget (DEB) models. The fact that all plants require a very similar set of exogenous resources, namely light, water and nutrients, integrates well with the DEB framework in which a small number of variables and processes linked through pathways represent an organism’s state as it changes through time. Most DEB theory has been developed in reference to animals and microorganisms. However, terrestrial vascular plants differ from these organisms in fundamental ways that make resource allocation, and the trade-offs and feedbacks arising from it, particularly fundamental to their life histories, but also challenging to represent using existing DEB theory. Here, we describe key features of the anatomy, morphology, physiology, biochemistry, and ecology of terrestrial vascular plants that should be considered in the development of a generic DEB model for plants. We then describe possible approaches to doing so using existing DEB theory and point out features that may require significant development for DEB theory to accommodate them. We end by presenting a generic DEB model for plants that accounts for many of these key features and describing gaps that would need to be addressed for DEB theory to predict the responses of plants to climate change. DEB models offer a powerful and generalizable framework for modelling resource allocation in terrestrial vascular plants, and our review contributes a framework for expansion and development of DEB theory to address how plants respond to anthropogenic change

    Electrophysiology of Woody Plants

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