Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Fully exposed canopy tree and liana branches in a tropical forest differ in mechanical traits but are similar in hydraulic traits
Zhang, Lan ; Chen, Yajun ; Ma, Keping ; Bongers, Frans ; Sterck, Frank J. - \ 2019
Tree Physiology 39 (2019)10. - ISSN 0829-318X - p. 1713 - 1724.
anatomy - canopy - hydraulic conductivity - hydraulic safety - mechanical safety - trade-off

Large lianas and trees in the forest canopy are challenged by hydraulic and mechanical failures and need to balance hydraulic conductivity, hydraulic safety and mechanical safety. Our study integrates these functions in canopy branches to understand the performance of canopy trees and lianas, and their difference. We sampled and measured branches from 22 species at a canopy crane in the tropical forest at Xishuangbanna, SW China. We quantified the hydraulic conductivity from the xylem-specific hydraulic conductivity (KS), hydraulic safety from the cavitation resistance (P50) and mechanical safety from the modulus of rupture (MOR) to evaluate trade-offs and differences between lianas and trees. We also measured a number of anatomical features that may influence these three functional traits. Our results suggest the following: trade-offs between hydraulic conductivity, hydraulic safety and mechanical safety are weak or absent; liana branches better resist external mechanical forces (higher MOR) than tree branches; and liana and tree branches were similar in hydraulic performance (KS and P50). The anatomical features underlying KS, P50 and MOR may differ between lianas and trees. We conclude that canopy branches of lianas and trees diverged in mechanical design due to fundamental differences in wood formation, but converged in hydraulic design.

Data from: The hydraulic efficiency–safety trade-off differs between lianas and trees
Sande, M.T. van der; Poorter, L. ; Schnitzer, S.A. ; Engelbrecht, B.M.J. ; Markesteijn, L. - \ 2019
drought tolerance - functional traits - hydraulic conductivity - hydraulic architecture - plant-water relations - lianas - Panama - P50 - specia abundance - tropical forest
Hydraulic traits are important for woody plant functioning and distribution. Associations among hydraulic traits, other leaf and stem traits, and species’ performance are relatively well understood for trees, but remain poorly studied for lianas. We evaluated the coordination among hydraulic efficiency (i.e. maximum hydraulic conductivity), hydraulic safety (i.e. cavitation resistance), a suite of 8 morphological and physiological traits, and species’ abundances for saplings of 24 liana species and 27 tree species in wet tropical forests in Panama.
Can pore-clogging by ash explain post-fire runoff?
Stoof, Cathelijne R. ; Gevaert, Anouk I. ; Baver, Christine ; Hassanpour, Bahareh ; Morales, Verónica L. ; Zhang, Wei ; Martin, Deborah ; Giri, Shree K. ; Steenhuis, Tammo S. - \ 2016
International Journal of Wildland Fire 25 (2016)3. - ISSN 1049-8001 - p. 294 - 305.
hydraulic conductivity - infiltration - wildland fire ash

Ash plays an important role in controlling runoff and erosion processes after wildfire and has frequently been hypothesised to clog soil pores and reduce infiltration. Yet evidence for clogging is incomplete, as research has focussed on identifying the presence of ash in soil; the actual flow processes remain unknown. We conducted laboratory infiltration experiments coupled with microscope observations in pure sands, saturated hydraulic conductivity analysis, and interaction energy calculations, to test whether ash can clog pores (i.e. block pores such that infiltration is hampered and ponding occurs). Although results confirmed previous observations of ash washing into pores, clogging was not observed in the pure sands tested, nor were conditions found for which this does occur. Clogging by means of strong attachment of ash to sand was deemed unlikely given the negative surface charge of the two materials. Ponding due to washing in of ash was also considered improbable given the high saturated conductivity of pure ash and ash-sand mixtures. This first mechanistic step towards analysing ash transport and attachment processes in field soils therefore suggests that pore clogging by ash is unlikely to occur in sands. Discussion is provided on other mechanisms by which ash can affect post-fire hydrology. Journal compilation

Different biomechanical design and ecophysiological strategies in juveniles of two liana species with contrasting growth habit
Chen, Y.J. ; Bongers, F. ; Zhang, J.L. ; Liu, J.Y. ; Cao, K.F. - \ 2014
American Journal of Botany 101 (2014)6. - ISSN 0002-9122 - p. 925 - 934.
vine ipomoea-purpurea - seasonal rain-forest - support availability - tropical forest - hydraulic conductivity - phenotypic responses - aboveground biomass - light interception - climbing plants - wood density
Premise of the study: Lianas constitute a major functional type in tropical zones. While some liana species start climbing immediately after germination (shade-avoidance), others have a long self-supporting phase (shade-tolerance). The morphophysiological characteristics of these two growth habits are unknown. Methods: We quantified growth traits, biomass allocation, mechanics, anatomy, and hydraulics for saplings of Ventilago calyculata (an immediate obligate climber) and Ziziphus attopensis (having a long self-supporting phase), both in the family Rhamnaceae. The mechanics, anatomy, and hydraulics for the mature individuals of the two species were also evaluated. Key results: In the juvenile stage, V. calyculata had a higher slenderness ratio, height growth rate, and photosynthetic rate but similar biomass growth rate compared with Z. attopensis. In contrast, Z. attopensis had a higher leaf area growth rate, specific leaf area, and leaf mass fraction. Ziziphus attopensis had stiffer, but less conductive stems than V. calyculata. Stem rigidity of saplings decreased from base to apex in Z. attopensis, but increased in V. calyculata. Both species had similar resistance to xylem embolism. However, the leaves of V. calyculata were able to resist greater water deficits. At the mature stage, wider and longer vessels emerged in the xylem, and both species increased stem specific conductivity and drought resistance in stems and leaves. Ventilago calyculata had significantly higher specific conductivity and was more drought tolerant than Z. attopensis. Conclusions: The two lianas differed significantly in growth, biomass allocation, anatomy, mechanics, ecophysiology, and hydraulic properties in line with their growth habits and shade adaptation strategies.
Determining the saturated vertical hydraulic conductivity of retention basins in the Oum Zessar watershed, Soutern Tunisia
Bosch, S. van den; Hessel, R. ; Ouessar, M. ; Zerrim, A. ; Ritsema, C.J. - \ 2014
Wageningen/Médenine : Alterra, Wageningen/Institut des Régions Arides, Tunisia (Report / WAHARA number 22) - 136
waterbeheer - stroomgebieden - hydraulisch geleidingsvermogen - tunesië - water management - watersheds - hydraulic conductivity - tunisia
Biochar increases plant-available water in a sandy loam soil under an aerobic rice crop system
Melo Carvalho, M.T. de; Holanda Nunes Maia, A. de; Madari, B.E. ; Bastiaans, L. ; Oort, P.A.J. van; Heinemann, A.B. ; Soler da Silva, M.A. ; Petter, F.A. ; Marimon-Junior, B.H. ; Meinke, H.B. - \ 2014
Solid Earth 5 (2014). - ISSN 1869-9510 - p. 939 - 952.
upland rice - hydraulic conductivity - management - productivity - temperatures - fertility - retention - tropics - model
The main objective of this study was to assess the impact of biochar rate (0, 8, 16 and 32 Mg ha-1) on the water retention capacity (WRC) of a sandy loam Dystric Plinthosol. The applied biochar was a by-product of slow pyrolysis (~450 °C) of eucalyptus wood, milled to pass through a 2000 µm sieve that resulted in a material with an intrinsic porosity =10 µm and a specific surface area of ~3.2 m2 g-1. The biochar was incorporated into the top 15 cm of the soil under an aerobic rice system. Our study focused on both the effects on WRC and rice yields 2 and 3 years after its application. Undisturbed soil samples were collected from 16 plots in two soil layers (5–10 and 15–20 cm). Soil water retention curves were modelled using a nonlinear mixed model which appropriately accounts for uncertainties inherent of spatial variability and repeated measurements taken within a specific soil sample. We found an increase in plant-available water in the upper soil layer proportional to the rate of biochar, with about 0.8% for each Mg ha-1 biochar amendment 2 and 3 years after its application. The impact of biochar on soil WRC was most likely related to an effect in overall porosity of the sandy loam soil, which was evident from an increase in saturated soil moisture and macro porosity with 0.5 and 1.6% for each Mg ha-1 of biochar applied, respectively. The increment in soil WRC did not translate into an increase in rice yield, essentially because in both seasons the amount of rainfall during the critical period for rice production exceeded 650 mm. The use of biochar as a soil amendment can be a worthy strategy to guarantee yield stability under short-term water-limited conditions. Our findings raise the importance of assessing the feasibility of very high application rates of biochar and the inclusion of a detailed analysis of its physical and chemical properties as part of future investigations.
Correction of the Vimoke–Taylor Concept Representing Drains in a Numerical Simulation Model
Heinen, M. - \ 2014
Vadose Zone Journal 13 (2014)10. - ISSN 1539-1663 - 9 p.
flood-irrigated field - hydraulic conductivity - water-flow - subsurface drains - preferential flow - soil - transport - equation - nitrate
Proper prediction of drain discharge using the single node Vimoke and Taylor approach in a numerical simulation model requires an additional correction factor. This correction factor was calibrated and dependent on node size, drain radius and the way of averaging the hydraulic conductivity. For a transient situation the additional correction factor resulted in higher groundwater levels and lower drain discharges. Drains are special internal or boundary conditions in numerical simulation models. Instead of approximating them by a hole surrounded by a very dense grid of finite elements, the single node or single element approach based on the theory of Vimoke and Taylor proposed in 1962 offers a good alternative. Several authors have suggested that the Vimoke and Taylor constant to adapt the hydraulic conductivity of the element representing the drain should be changed by a certain factor. However, different correction factors have been given. Here this correction factor is derived for a control volume finite element numerical simulation model for different ratios of the size of the control volume representing the drain and the effective drain radius. It is shown that this relationship is dependent on the way the hydraulic conductivity is averaged at the interfaces between the neighboring control volumes. The relationships were obtained by optimization against an analytical solution for a steady-state, saturated situation. By applying the additional correction to a hypothetical transient situation for four soil types it was shown that the application of the additional correction factor resulted in 3 to 13% lower drain discharges compared to uncorrected simulations. Consequently, higher groundwater levels of on average 2 to 4 cm were obtained when applying the additional correction. For situations where exact predictions of drain discharge are needed, typically when solute transport is considered, it is advised to make use of the additional correction. Model specific correction factors may be required.
Unsaturated hydraulic properties of xerophilous mosses: towards implementation of moss covered soils in hydrological models
Voortman, B.R. ; Bartholomeus, R.P. ; Bodegom, P.M. van; Gooren, H.P.A. ; Zee, S.E.A.T.M. van der; Witte, J.P.M. - \ 2014
Hydrological Processes 28 (2014)26. - ISSN 0885-6087 - p. 6251 - 6264.
evaporatie - bryophyta - hydraulisch geleidingsvermogen - korstmossen - mossen - hydrologie - waterbalans - bodemwaterretentie - modelleren - evaporation - bryophyta - hydraulic conductivity - lichens - mosses - hydrology - water balance - soil water retention - modeling - sphagnum moss - water - conductivity - bryophytes - desiccation - ecosystems - tolerance
Evaporation from mosses and lichens can form a major component of the water balance, especially in ecosystems where mosses and lichens often grow abundantly, such as tundra, deserts and bogs. To facilitate moss representation in hydrological models, we parameterized the unsaturated hydraulic properties of mosses and lichens such that the capillary water flow through moss and lichen material during evaporation could be assessed. We derived the Mualem-van Genuchten parameters of the drying retention and the hydraulic conductivity functions of four xerophilous moss species and one lichen species. The shape parameters of the retention functions (2.17¿
The impact of aquifer heterogeneity on the performance of aquifer thermal energy storage
Sommer, W.T. ; Valstar, J.R. ; Gaans, P. van; Grotenhuis, J.T.C. ; Rijnaarts, H. - \ 2013
Water Resources Research 49 (2013)12. - ISSN 0043-1397 - p. 8128 - 8138.
heat-transport - solute transport - porous-media - hydraulic conductivity - geothermal systems - field - simulation - flow - macrodispersion - dispersion
Heterogeneity in hydraulic properties of the subsurface is not accounted for in current design calculations of aquifer thermal energy storage (ATES). However, the subsurface is heterogeneous and thus affects the heat distribution around ATES wells. In this paper, the influence of heterogeneity on the performance of a doublet well system is quantified using stochastic heat transport modeling. The results show that on average, thermal recovery decreases with increasing heterogeneity, expressed as the lognormal standard deviation of the hydraulic conductivity field around the doublet. Furthermore, heterogeneity at the scale of a doublet ATES system introduces an uncertainty in the amount of expected thermal interference between the warm and cold storage. This results in an uncertainty in thermal recovery that also increases with heterogeneity and decreases with increasing distance between ATES wells. The uncertainty in thermal balance due to heterogeneity can reach values near 50 percent points in case of regional groundwater flow in excess of 200 m/yr. To account for heterogeneity whilst using homogeneous models, an attempt was made to express the effect of heterogeneity by an apparent macrodispersivity. As expected, apparent macrodispersivity increases with increasing heterogeneity. However, it also depends on well-to-well distance and regional groundwater velocity. Again, the uncertainty in thermal recovery is reflected in a range in the apparent macrodispersivity values. Considering the increasing density of ATES systems, we conclude that thermal interference limits the number of ATES systems that can be implemented in a specific area, and the uncertainty in the hydraulic conductivity field related to heterogeneity should be accounted for when optimizing well-to-well distances.
Modelling diffusive Cd and Zn contaminant emissions from soils to surface waters
Bonten, L.T.C. ; Kroes, J.G. ; Groenendijk, P. ; Grift, B. van der - \ 2012
Journal of Contaminant Hydrology 138-139 (2012). - ISSN 0169-7722 - p. 113 - 122.
hydraulic conductivity - automatic calibration - groundwater - catchment - flow - cadmium - netherlands - zinc - quality - copper
Modeling contaminant transport of diffusive contaminants is generally difficult, as most contaminants are located in the top soil where soil properties will vary strongly with depth and often a strong gradient in contaminant concentrations exists. When groundwater periodically penetrates the contaminated layers, stationary models (like most 3D models) cannot adequately describe contaminant transport. Therefore we have combined a hydrological instationary model using a 1D distributed column approach with a simple geochemical model to describe contaminant transport in the soil. Special to this model is that it includes lateral drainage from the soil column to different types of surface waters, which makes it possible to calculate surface water emissions especially for fluctuating groundwater tables. To test this model approach, we used it to quantify surface water emissions from soils in a catchment in the Kempen area which has been diffusively contaminated with Cd and Zn by zinc smelters. We ran the model for the period 1880–2000, starting with an uncontaminated soil in 1880. The model could describe both water discharge, surface water concentrations and current soil contents of Cd and Zn well. Further the model calculations showed that a stationary approach would underestimate leaching to surface waters considerably.
A spatially distributed model of pesticide movement in Dutch macroporous soils
Tiktak, A. ; Hendriks, R.F.A. ; Boesten, J.J.T.I. ; Linden, A.M.A. van der - \ 2012
Journal of Hydrology 470-471 (2012)november. - ISSN 0022-1694 - p. 316 - 327.
clay soil - preferential flow - solute transport - hydraulic conductivity - unsaturated soils - water-flow - infiltration - simulation - rainfall - bromide
In the Netherlands, a spatially distributed version of the pesticide fate model PEARL is routinely used to assess the leaching potential of pesticides to groundwater. Recently, the model was modified to simulate the movement of pesticides to surface water. The peak concentration is considered to be the most important exposure endpoint for the ecotoxicological effect assessment for aquatic organisms. Macropore flow is an important driver for the peak concentration, so the leaching model PEARL was extended with a macropore module. Macropore parameters were derived from generally available soil data such as organic matter content and clay content using newly developed pedotransfer functions. These pedotransfer functions were constructed using a wide range of Dutch clayey soils. Results indicate a good correlation between these variables and soil structural parameters, which is due to the homogeneous mineralogical composition of Dutch clayey soils. Results of the spatially distributed modelling indicate that due to rapid transport through macropores, the concentration of pesticides in drainage water is generally higher in clayey soils than in light textured soils. In clayey soils, the boundary hydraulic conductivity and organic matter content were the most important drivers for the concentration in drainage water. Results further indicate that the concentration of pesticide in drainage water increases with increasing half-life and decreases with increasing sorption coefficient. However, the effect of these parameters is much less than obtained with the convection–dispersion equation because due to preferential flow most of the reactive part of the soil profile is bypassed.
Root water uptake as simulated by three water flow models
Willigen, P. de; Dam, J.C. van; Javaux, M. ; Heinen, M. - \ 2012
Vadose Zone Journal 11 (2012)3. - ISSN 1539-1663 - 14 p.
flux potential approach - hydraulic conductivity - integrated approach - nutrient-uptake - architecture - system - absorption - scales - maize
The objective of our study was to determine to what extent four root water uptake (RWU) models differed when tested under extreme conditions. Cumulative transpiration patterns were similar, contrary to the spatial extraction patterns. The analysis showed that both soil physical and root physiological factors are important for proper deterministic modeling of RWU. We compared four root water uptake (RWU) models of different complexity that are all embedded in greater soil water flow models. The soil models used were SWAP (one-dimensional), FUSSIM2 (two-dimensional), and RSWMS (three-dimensional). Within SWAP, two RWU functions were utilized (SWAP-macro and SWAP-micro). The complexity of the processes considered in RWU increases from SWAP-macro, to SWAP-micro, to FUSSIM2, to RSWMS. The objective of our study was to determine to what extent the RWU models differed when tested under extreme conditions: low root length density, high transpiration rate, and low water content. Comparison 1 looked at the results of the models for a scenario of transpiration and uptake and Comparison 2 studied compensation mechanisms of water uptake. The uptake scenario pertained to a long dry period with constant transpiration and a single rainfall event. As could be expected, the models yielded different results in Comparison 1, but the differences in cumulative transpiration were modest due to various feedback mechanisms. In Comparison 2, the cumulative effect of different feedback processes were studied. Redistribution of water due to soil pressure head gradients generated by water uptake led to an increase in cumulative transpiration of 32%, and the inclusion of compensation in uptake by the roots resulted in a further increase of 10%. Going from one- to three-dimensional modeling, the horizontal gradients in the soil and root system increased, which reduced the actual transpiration. The analysis showed that both soil physical and root physiological factors are important for proper deterministic modeling of RWU
Microtopography as a driving mechnism for ecohydrological processes in shallow groundwater systems
Ploeg, M.J. van der; Appels, W.M. ; Cirkel, D.G. ; Oosterwoud, M.R. ; Witte, J.P.M. ; Zee, S.E.A.T.M. van der - \ 2012
Vadose Zone Journal 11 (2012)3. - ISSN 1539-1663
acrotelm-catotelm model - peat bog growth - hydraulic conductivity - blanket peat - surface-water - micro-topography - flow - vegetation - runoff - infiltration
Microtopography can have a large effect on flow processes at the soil surface and the composition of soil water. Microtopography is often represented by a roughness parameter in hydrological models. In areas without a strong topographical gradient, microtopography may be underestimated when accumulated in a single parameter, especially in shallow groundwater systems. This study reviews the intricate relationships between microtopography, surface runoff, and ecohydrology in systems featuring shallow water tables. We specifically focus on relations between microtopography and runoff, impact of microtopography on response times of shallow groundwater ecosystems, and microtopography and spatial distribution of groundwater quality parameters and site factors. We advocate the use of microtopography in modeling approaches by examples that feature typical ecosystems with shallow groundwater under influence of microtopography. With a simple modeling approach, we show how microtopography could add flexibility to the acrotelm–catotelm concept in raised bog hydrology. The classic acrotelm–catotelm concept hinders progress in understanding small scale hydrological variations and other ecohydrological relations. Furthermore, we illustrate possible self-organization properties of wetlands. Finally, we show how microtopography and surface runoff affect the mixing of water with different chemical signatures, resulting in variations of the occurrence of plant species.
Experiments on the movement of pesticides in sandy soils to groundwater : prospects of testing preferential transport models
Leistra, M. ; Boesten, J.J.T.I. - \ 2012
Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2291) - 60
zandgronden - hydraulisch geleidingsvermogen - pesticiden - bodemwaterbeweging - waterverontreiniging - experimenteel veldonderzoek - sandy soils - hydraulic conductivity - pesticides - soil water movement - water pollution - field experimentation
Many agricultural areas with humic-sandy and loamy-sandy soils are used also for the extraction of water for drinking-water supply. Model concepts have been developed for the fast preferential transport of plant protection products (pesticides) in such soils, e.g. by fingered and funneled flow. An inventory is given of experiments that may be suitable for the testing of preferential transport models for cultivated sandy soils (without macropores). The pesticide concentrations per depth in soil are highly variable, due to local differences in transport, adsorption and transformation. Measurements in both the subsoil and in the upper groundwater are scarce, also due to sampling problems. Suggestions are given to improve the characterisation of soil profiles and weather conditions. Sampling methods for soil and soil solution can easily miss the preferential transport pathways. The methods of pesticide analysis in soils samples are often not sensitive enough to measure concentrations relevant for groundwater quality. The present study serves as the starting point for selecting the most suitable data sets for model testing and for the design of more complete and detailed data sets in the future.
Hydrological effects of buried palaeosols in eroding landscapes: A case study in South Africa
Temme, A.J.A.M. ; Schaap, J.D. ; Sonneveld, M.P.W. ; Botha, G.A. - \ 2012
Quaternary International 265 (2012). - ISSN 1040-6182 - p. 32 - 42.
pleistocene-holocene transition - hydraulic conductivity - pedotransfer functions - retention characteristics - porous-media - northern - climate - evolution - soils - flow
Palaeosols have long been studied as valuable records of past climate and landscape changes. The influence of palaeosols on the functioning of present-day landscapes is receiving closer attention due to the relevance of palaeosols on long-term hydrological processes and the future hydrological and erosive response of catchments. This study describes a sequence of interbedded colluvial sedimentary deposits and buried palaeosols exposed by gully erosion in the Drakensberg escarpment foothills in KwaZulu-Natal province, South Africa. Model simulations are then presented that explore present-day hydrological effects of pedogenetic and textural differentiation under conditions of groundwater lowering caused by gully erosion at 14 sites. The results suggest that the colluvial deposits and palaeosols cause a significant increase in total annual drainage from most of the 14 studied sites compared with similar sites without textural or structural differentiation. In the simulations, sediment deposition, not palaeosol formation, has the most profound influence on the present-day hydrological functioning of the catchment: a true deposystem service. The effects of the limited observed palaeosol development on soil water holding capacity and actual soil water storage appear to be negligible
Process-based proxy of oxygen stress surpasses indirect ones in predicting vegetation characteristics
Bartholomeus, R.P. ; Witte, J.P.M. ; Bodegom, P.M. van; Dam, J.C. van; Becker de, P. ; Aerts, R. - \ 2012
Ecohydrology 5 (2012)6. - ISSN 1936-0584 - p. 746 - 758.
vegetatietypen - ecohydrologie - klimaatverandering - vegetation types - ecohydrology - climatic change - ellenberg indicator values - climate-change - hydraulic conductivity - species richness - soil-conditions - plant-roots - moisture - temperature - models - growth
Robust relationships among soil, water, atmosphere and plants are needed to reliably forecast the plant species composition. In this paper, we show the need for, and the application of, a process-based relationship between soil moisture conditions and vegetation characteristics. We considered 366 groundwater-dependent sites, where oxygen stress, caused by a surplus of soil moisture, codetermines plant performance. We compared two existing indirect proxies for the soil oxygen status – namely mean spring groundwater level (MSL) and sum exceedence value (SEV) – with our newly developed process-based proxy, viz. root respiration stress (RS). The two indirect proxies and the process-based proxy for oxygen stress performed equally well in describing vegetation characteristics for the Netherlands under the current climate. However, relationships based on MSL and SEV appeared to produce systematic prediction errors when applied outside their calibration range, in contrast to the relationship based on RS. Hence, the two indirect proxies cannot be used in projections, such as in predicting effects of climate change on vegetation composition, all the more because they – unlike RS – do not account for essential parameters that determine oxygen stress (e.g. temperature and extreme rainfall events in the growing season). We advocate using RS for estimating vegetation impacts in climate projections to increase the reliability and effectiveness of adaptive strategies
Scales in single root water uptake models: a review, analysis and synthesis
Metselaar, K. ; Lier, Q.D. van - \ 2011
European Journal of Soil Science 62 (2011)5. - ISSN 1351-0754 - p. 657 - 665.
zea-mays l - soil-water - plant-roots - porous-media - hydraulic conductivity - computed-tomography - system architecture - nutrient-uptake - sample-size - volume
Scales in transport of water to roots are compared with the length and volume scales by using the concepts associated with the representative elementary volume (REV). The possibility of a mismatch between model scale and system scale when using a Darcy-Buckingham-based model to describe soil water transport to a single root is evaluated. In the absence of a mismatch, the replication requirements for evaluating the Darcy-Buckingham-based model near a single root are discussed by using a synthesis of the elementary scales involved, including those for soil, plant and roots, and of the measurement device. By using REV scales from lattice-Boltzmann simulations, the effective half-root mean distance and the available measurement techniques, the evaluation of Darcy-based single root uptake models is possible in roughly 50% of the combinations of soil- and root-system properties. On the basis of an assessment of the scale characterizing natural soil variability, the number of replicates required to assess the average root water uptake profile near a single root is large, and either requires miniaturization of the measurement methods for the hydraulic transport characteristics, or very homogeneous (artificial) growing media with little variability. Variability of water uptake per unit root length will increase the number of samples required.
Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherlands
Gaans, P.F.M. van; Griffioen, J. ; Mol, G. ; Klaver, G. - \ 2011
Journal of Soils and Sediments 11 (2011)2. - ISSN 1439-0108 - p. 336 - 351.
natural background levels - complex confining layer - facies-based approach - hydraulic conductivity - aquifer sediments - pyrite oxidation - organic-matter - ground-water - nw germany - heterogeneity
Geochemical reactivity of subsurface sediments as potential buffer to anthropogenic inputs: a strategy for regional characterization in the Netherlands
Hydrogel Regulation of Xylem Water Flow: An Alternative Hypothesis
Doorn, W.G. van; Hiemstra, T. ; Fanourakis, D. - \ 2011
Plant Physiology 157 (2011)4. - ISSN 0032-0889 - p. 1642 - 1649.
ion-mediated increase - induced vascular occlusions - intervessel pit membranes - hydraulic conductivity - bordered-pit - cell-walls - tracheary elements - angiosperm xylem - model films - cavitation
The concentration of cations in the xylem sap influences the rate of xylem water flow in angiosperm plants. It has been speculated that this is due to the shrinking and swelling of pectins in the pit membranes. However, there is as yet minimal evidence for the presence of pectin in pit membranes of angiosperms. The little pectin that has been found at the pit membrane edges of some species might not be adequate to explain the swelling and shrinking phenomena. The presence of hemicelluloses is also not certain. Lignin, by contrast, seems to be sometimes present, apart from cellulose, which is the main component. An alternative hypothesis is formulated, which involves the shrinking of any polyelectrolyte polymers in the pit membrane and a change in volume of the mobile phase in the pit pores. These phenomena are the result of electrostatic events. Some pit membrane polymers are negatively charged because of proton dissociation from functional groups. This charge is compensated by cations in the aqueous phase, which form a diffuse double layer (DDL). Inside the pit pores, an increase of the electrolyte concentration in the xylem sap will reduce the extent of the DDL. This will result in an increase in water flow. Additional flow enhancement, upon increase of the cation concentration, can be due to shrinkage of all membrane polymers. This contraction will also lead to an increase of the pit pore diameter. These processes will only be partly counteracted by forces that decrease the diameter of the pit pore due to relaxation.
Climate change threatens endangered plant species by stronger and interacting water-related stresses
Bartholomeus, R.P. ; Witte, J.P.M. ; Bodegom, P.M. van; Dam, J.C. van; Aerts, R. - \ 2011
Journal of Geophysical Research: Biogeosciences 116 (2011)G4. - ISSN 2169-8953
klimaatverandering - bedreigde soorten - vegetatie - bodemwater - stress omstandigheden - droogte - ecohydrologie - climatic change - endangered species - vegetation - soil water - stress conditions - drought - ecohydrology - environmental variation - terrestrial ecosystems - hydraulic conductivity - regression quantiles - indicator values - soil-conditions - oxygen stress - root-growth - diversity
Atmospheric CO2-concentration, temperature and rainfall variability are all expected to increase in the near future. The resulting increased dynamics of soil moisture contents, together with increased plant physiological demands for both oxygen and water, will lead to an increased occurrence of wet and dry extremes of plant stresses, i.e. of oxygen and drought stress, respectively, alone and in interaction. The use of indirect environmental variables of previous studies and their focus on one stress at a time has hampered understanding the causal impact of climate change on plant species composition through changes in abiotic site conditions. Here, we use process-based simulations of oxygen and drought stress and show that both stresses will increase (on average with ca. 20% at sites where both stresses occur) in a warmer and more variable future (2050) climate (applying a national downscaled version of IPCC scenarios). These stresses will increasingly coincide, i.e. both stresses will occur more often (but not at the same time) within the same vegetation plot. We further show that particularly this increased coincidence of water-related stresses will negatively affect the future occurrence of currently endangered plant species (a reduction of 16%), while such a decrease is not apparent for common species. Individual stresses did not affect the occurrence of endangered plant species. Consequently, the species that are already threatened under the current climate, will suffer most from climate change
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