Добірка наукової літератури з теми "Unsaturated hydraulic conductivity ; plant available water ; plant response"

As a result of the lack of quantitative data regarding specific water requirements of ornamental species, precision irrigation can be a difficult task for nursery growers. One challenge for growers is that it is not clear how much of the water in soilless substrates is actually available for plant uptake. Substrate moisture release curves (MRC) have been used to predict the amount of plant-available water in soilless substrates, yet there is little information about whether there are differences among species in their ability to extract water from substrates. The objectives of this study were to determine 1) the hydraulic properties of a composted pine bark substrate; and 2) how water uptake in Hydrangea macrophylla and Gardenia jasminoides was affected by decreasing substrate volumetric water content (VWC). As the substrate VWC decreased from 0.38 to 0.17 m3·m−3, substrate matric potential decreased from –4.0 to –69 kPa, whereas hydraulic conductivity decreased from 0.115 to 0.000069 cm·d−1. To measure plant water uptake in a drying substrate, growth chambers were used to provide stable environmental conditions that included continuous lighting to prevent diurnal fluctuations in water use. Water use by H. macrophylla ‘Fasan’ started to decrease at a higher VWC (0.28 m3·m−3) than G. jasminoides ‘Radicans’ (0.20 m3·m−3). Plant water uptake stopped at a VWC of 0.16 m3·m−3 in H. macrophylla and 0.12 m3·m−3 in G. jasminoides. The results show that H. macrophylla is less adept at extracting water from a drying substrate than G. jasminoides. Traditionally, plant-available water in soilless substrates has been studied using substrate MRCs. Our data suggest that substrate hydraulic conductivity may be an important factor controlling water availability to the plants. In addition, there are important differences among species that cannot be detected by only looking at substrate hydraulic properties.

Hydrophilic polymers or hydrogels have shown potential to increase water retention of media and to reduce irrigation frequency. This property would be particularly useful in the production of fast growing species in which large amounts of water are needed. This study evaluated the effect of two acrylic-based hydrogels on water desorption curve and hydraulic conductivity of substrates and on plant growth. The duration of their effects was also investigated. Rooted cuttings of Surfinia (Petunia ×hybrida `Brilliant Pink') were transplanted into 30-cm pots containing one of three different substrates amended with one of two types of hydrogels, a commercial acrylic polymer, and a commercial acrylic-acrylamide copolymer, and grown for 9 weeks under well watered conditions and then imposed with a drought. Results indicated that both polymer types gave similar results. The substrates' physical properties (air-filled porosity, available water) at potting time were significantly affected by hydrogel addition, but differences vanished within 9 weeks of growth. Hydrogels had no significant effect on the point at which plant wilted and on the substrate's unsaturated hydraulic conductivity. Shoot dry weight was affected by substrate and hydrogel and was positively correlated to water content between container capacity and -10 kPa of water potential, or between container capacity and the soil water potential at plant turgor loss.

Static hydrological properties [aeration capacity, easily available water, reserve water, water release curves: θv(Ψm), and specific humidity curves] and dynamic hydrological properties (saturated and unsaturated hydraulic conductivity) of sub strates based on industrial cork residue (the bark of Quercus suber L.) and cork compost were studied. Samples of similar granulometry have been used to establish the effect of cork composting on the afore mentioned physical properties. Different models were tested to describe the mechanism of water release from these materials. Van Genuchtens model (Van Genuchten, 1978) was the best fit and produced specific humidity curves that revealed slight differences in the ratio of water capacity function. When cork residues were composted for 7 months, important changes occurred in hydrological properties of the material as it became more wettable. Water retention significantly increased from 45% to 54%, at a potential of 5 kPa, although this did not necessarily result in increased water available to plants. A study of the unsaturated hydraulic conductivity (Kunsat) of these materials revealed a significant de crease in the Kunsat water potential at 0-5 kPa, which corresponds to the range in which the irrigation with these substrates was usually carried out. The long composting process resulted in increased Kunsat between 4 and 5 times that of uncomposted material, which would improve the water supply to the plant.

Knowledge of hydro-physical properties is an essential prerequisite for assessing the suitability and quality of growing media. The method used for sample preparation is important for the measurement results. Three different sample preparation methods were compared. The methods differed in terms of the way the 250°cm3 steel cylinder was filled and the height of preloading. Measurements on loosely filled cylinders were included. The comparison was carried out on 15 growing media using the HYPROP device. HYPROP enables a complex analysis of the hydro-physical properties with high accuracy and reproducibility. The water retention curve, the unsaturated hydraulic conductivity function, the dry bulk density, the shrinkage and the rewetting properties can be measured simultaneously. The air capacity and the amount of plant-available water in pots depend on the height of the pot. In the field, it is related to the field capacity. The quality assessment was carried out both for flowerpots of different height and for field conditions with free drainage. Loosely filled samples consolidated hydraulically shortly after the start of the measurement. These geometric changes can be taken into account with the HYPROP. The sample preparation method - preloading or loose filling - yielded significantly different results for the pore volume, dry bulk density, plant available water and air capacity. The total pore volume of the loosely filled cylinders varied between 86.8 and 95.2°% by vol. (preloaded 81.3 and 87.7°% by vol.). The most critical factor was the air capacity. Loosely filled substrate samples achieved the highest air capacities, but also did not reach the critical value of 10°% by volume in shallow flowerpots, e.g. in 10 cm pots with 5.8°% by volume. The sample preparation method, measurement and quality assessment of the hydro-physical properties of growing media should be adapted to the conditions of use - whether they are used in a field with free drainage or in pots or containers in greenhouses.

Vapor pressure deficit (VPD) is the driving force for plant water loss. However, air relative humidity (RH) can be used as a surrogate for VPD. While plants can adapt to environments with varying RH, little is known about how they respond to sudden shifts in RH. Areas of Southern California can experience drastic shifts in RH, from 60% or greater to less than 20% in just a few hours. The effect of these shifts on avocado (Persea americana Mill.) tree productivity is a major concern to growers. We studied the effect of shifts in RH on `Hass' avocado leaf stomatal conductance (gs) and branch sap flow in trees grafted on Duke 7 clonal rootstock. Under many conditions, the avocado assimilation rate is governed by gs. When gs is high in morning (>150 mmol·m-2·s-1), the water loss generally leads to some stomatal closure in the afternoon (50% or more). Conversely, low morning gs results in a higher gs rate in the afternoon (10% to 20% stomatal closure). This relationship between morning and afternoon gs is intensified by a shift from high to low RH in the afternoon. Therefore, in a drier atmosphere in the afternoon, the afternoon depression in gs is greater, leading to an impaired assimilation capacity. We hypothesize that the afternoon decrease in gs is due to low root/shoot hydraulic conductivity since soil water is readily available. While it is possible that low hydraulic conductivity on gs is exacerbated at the graft union, sap flow of grafted trees in greenhouse studies was nearly equal to trees on their own roots (ungrafted); in fact, often the depression in the afternoon was less on grafted trees. This suggests that while avocado is not suited to areas with low RH, water flow through the roots could be an additional criterion in selecting improved rootstocks.

Conservation tillage practices such as no-till (NT) and conventional tillage (CT) with a heavy-duty cultivator can influence the physical properties of soils. This study was conducted to determine the effect of 24 yr of NT versus CT on the physical properties of a clay loam soil in southern Alberta. Physical properties quantified were bulk density (BD), mean weight diameter (MWD), plant-available water-holding capacity (PAWHC), saturated hydraulic conductivity (Ksat), soil water characteristic [θ(ψ)] and unsaturated hydraulic conductivity [K(ψ)] relationships, and pore-size distribution (PSD). Bulk soil samples and small soil cores (5-cm depth increments to 20 cm) were taken from CT and NT fields in 1992, and tension infiltrometer measurements were made in 1994. The results from this study are reported as general trends for the tillage fields. Statistical probability levels are not reported because of the unreplicated nature of the experiment, the limited number of sampling locations within each tillage field, and to a lesser extent, the different sampling times for CT and NT in 1992. Plant-available water-holding capacity was higher for the CT field (14.3%) than the NT field (10.8%), and a greater amount of water was held at a given water potential (−1500 to −1.5 kPa) for the former, indicating a higher potential for soil water conservation under conventional tillage. Geometric mean Ksat values (small soil cores) were higher for the NT field (18.20 × 10−6 m s−1) than the CT field (1.74 × 10−6 m s−1). The K(ψ) values (small soil cores) between −10 and −2 kPa were higher for the CT field than the NT field at the 0- to 5-cm, 10- to 15-cm and 15- to 20-cm depths, but values were higher for the NT field at the 5- to 10-cm depth. Near-saturated K(ψ) values (−1.5 to −0.3 kPa) of the surface soil, as derived from tension infiltration measurements in 1994, were higher for the CT field (2.43 × 10−7 m s−1) than for the NT field (6.09 × 10−8 m s−1). There was a greater percentage volume of larger pores (30–40, 40–67, 67–200, >200 µm) for the NT field than for the CT field, and there was a lower percentage volume of smaller pores (0.2–0.6, 0.6–4 µm) for the CT field than for the NT field. Differences in certain soil physical properties between CT and NT fields may be related to the lag time between the most recent tillage event and sampling for the CT field. Key words: Conservation tillage, heavy-duty cultivator, physical attributes, soil water, hydraulic conductivity, porosity

Abstract This study was performed to measure changes in soil properties due to cable yarding and to estimate the resulting changes in hydrologic response. Soils were sampled before and after a commercial logging operation in the northern Cascade Mountains of Washington. The samples were analyzed for saturated hydraulic conductivity (Ks), moisture release characteristics, and bulk density (BD). Postlogging Ks values ranged from 1.08 to 497 cm/h and were significantly less than prelogging values, which ranged from 10.8 to 623 cm/h. Postlogging bulk densities ranged from 0.34 to 1.13 g/cm³ and were significantly greater than prelogging values, which ranged from 0.10 to 0.95 g/cm³. Because of the high Ks values it was concluded that Horton overland flow is not a dominant process even after disturbance. A 32.7% reduction in available water storage was found due to decreases in noncapillary porosity and surface horizon thickness. From this, increases in saturation overland flow and/or subsurface flow are predicted on skid trails. Overall impacts on the cutting unit however are considered small. West. J. Appl. For. 7(2):36-39.

Riparian phreatophytes in hyperarid areas face selection pressure from limiting groundwater availability and high transpiration demand. We examined whole-plant water use and hydraulic traits in Populus euphratica and Tamarix ramosissima seedlings to understand how they adapt to groundwater variations. These species coexist in the Tarim River floodplain of western China. Measurements were performed on 3-year-old seedlings grown in lysimeters simulating various groundwater depths. P. euphratica had relatively greater leaf area-specific water use due to its comparatively higher sapwood area to leaf area ratio (Hv). A high Hv indicates that its sapwood has a limited capacity to support its leaf area. P. euphratica also showed significantly higher leaf-specific conductivity (ksl) than T. ramosissima but both had similar sapwood-specific conductivities (kss). Therefore, it was Hv rather than kss which accounted for the interspecific difference in ksl. When groundwater was not directly available, ksl and Hv in P. euphratica were increased. This response favors water loss control, but limits plant growth. In contrast, T. ramosissima is more capable of using deep groundwater. Stomatal sensitivity to increasing leaf-to-area vapor pressure deficit was also higher in P. euphratica. Overall, P. euphratica is less effective than T. ramosissima at compensating for transpirational water loss at a whole-plant level. For this reason, P. euphratica is restricted to riverbanks, whereas T. ramosissima occurs over a wide range of groundwater depths.

In urban environments, newly planted street trees suffer from poor site conditions and limited water availability. It is challenging to provide site conditions that allow the trees to thrive in the long term, particularly under climate change. Knowledge about the hydrological properties of artificial urban planting soils related to the response of tree species-specific growth is crucial, but still lacking. Therefore, we established a three-year experimental field setup to investigate the response of nine tree species (135 individuals) to two common urban planting soils and a loamy silt reference. We determined and measured soil hydrological parameters and monitored tree growth. Our results revealed low plant available water capacities (6% and 10% v/v) and hydraulic conductivity restrictions with the drying of the sandy-textured urban planting soils. Therefore, tree species that are investing in fine root growth to extract water from dry soils might be more successful than trees that are lowering their water potential. Tree growth was overall evidently lower in the urban planting soils compared with the reference and differed between and within the species. We showed that using unfavorable planting soils causes severe, species-specific growth deficits reflecting limited above-ground carbon uptake as a consequence of low water availability.

Low water retention in hanging baskets is a constraint in urban floriculture and hydrogel addition is an alternative. However, growth may be reduced with such a product depending on the substrate used. This study was conducted to determine the combined effects of substrate and type of hydrogel on the growth of Surfinia plants produced in hanging baskets. During Spring 1998, three rooted cuttings of Surfinia (Petunia × hybrida `Brilliant Pink') were transplanted into 30-cm hanging baskets. Plants were transplanted into one of the following substrates: 1) Pro-Mix BX, 2) a blend of 4/5 Pro-Mix BX and 1/5 compost, or 3) 1/3 perlite 1/3 vermiculite and 1/3 compost (v/v). These three substrates were amended with two types of hydrogels. The first type, Soil Moist, is an acrylic-acrylamide copolymer and the second type is Aqua-Mend, an acrylic polymer. Plants were grown for 8 weeks under standard irrigation and fertilization practices. Plant growth characteristics, percent dry weight, mineral nutrition, and growth index were determined. Substrate physical properties such as available water content, unsaturated hydraulic conductivity and total porosity were measured. The dry weight and growth index of plants in Pro-Mix BX amended with both types of hydrogels were greater than those plants growing in Pro-Mix BX without hydrogel. Plants growing in substrates 2 and 3 with hydrogels were smaller or similar respectively than those plants growing in substrates without hydrogel. Their effects on physical properties of substrates and plant growth will be discussed.

Chapters 1 and 2 identify the aims and objectives of the study, as well as the hypotheses and assumptions required. The relevant literature on soil water availability and plant response to water stress is explored. In particular these two chapters explain that plants extract water from soils by regulating a host of physiological mechanisms at their disposal – some plants are more efficient than others at doing this. As soil dries out, plants must ‘sense’ and gradually integrate the net effect of many soil conditions including: increasing soil aeration, as well as matric and osmotic suctions and soil strength, but also diminishing soil hydraulic conductivity. Plants, therefore, gradually take up water more slowly as the soil dries, depending on environmental conditions and other factors, all of which vary enormously on an hourly basis and which are difficult to predict let alone measure. Groenevelt et al. (2001; 2004) proposed a model, the Integral Water Capacity (IWC) to predict the effects of soil physical and chemical restrictions on water availability, but this model has not yet been tested against the performance of realplants. Evaluation of this model forms the primary focus of this study. The IWC uses the soil water retention curve, θ(h), to produce a differential water capacity, C(h)= dθ/dh, which is then reduced using various weighting functions, ω(h),to account for the above limiting physical and chemical properties, then integrated to produce a total amount of water that can be extracted from the soil by plants. The key, of course, is to identify robust weighting functions for each of the limiting soilconditions, yet this is no easy task because the limiting soil conditions often interact.For example, as the soil dries out, the hydraulic conductivity drops while aeration,strength and salinity all increase to varying extents – this makes it difficult to quantify the effect of any one limitation. In the present study it was therefore decided to focus solely on the unsaturated soil hydraulic conductivity as the major limiting soil condition. A significant drop in the soil hydraulic conductivity during a dry period after rainfall or irrigation can make the difference between crop success and failure, particularly in Mediterranean and arid environments. The aims of the study were to: 1) Evaluate the effect of declining soil hydraulic conductivity on soil water availability in the absence of all other known soil physical limitations. 2) Evaluate the link between real plant response to water stress and that predicted using the IWC model of Groenevelt et al. (2001) for a range of different plant species, planting densities, soil types and environmental conditions. 3) Evaluate the utility of the hydraulic conductivity function of Grant et al. (2010) in weighting the water capacity. Chapter 3 identifies the main methods used in the study. It explains that two different, light-textured soils were selected (Very fine sand and Loamy sand), for some pot experiments designed to compare the predicted and measured amounts of water that two contrasting plants (maize v. sorghum) could extract from the soil under different environmental conditions (low and high evaporative demand). In the first instance, the water retention curves were measured on soil samples packed to the same bulk densities used in the plant experiments. The water retention curves were then modelled to produce the differential water capacities and the relative hydraulic conductivities for the two soils. The IWC was then calculated based upon experimental data describing plant responses to environmental conditions (see below). A large number of pots holding 5 kg soil and different numbers of maize or sorghum seeds were well watered until plants reached a critical stage, after which half the pots were no longer supplied with water while the other half were maintained at ideal water contents. An identical set of control pots containing no plants was monitored to separate evaporation from plant transpiration, and to thus determine the soil matric suction at which the rate of water loss from the planted pots declined to the rate of natural evaporation – indicating the point at which transpiration effectively stopped. Stomatal conductance, g (mmol m⁻² s⁻¹), and soil water content, θ (m³ /m³ ) were measured first thing each morning every day until this was no longer possible. When stomatal conductance on the stressed plants could no longer be measured (ranging between 5 and 21 days depending on conditions) the experiments were terminated and the fresh weights of roots and shoots measured. Chapter 4 describes how the stomatal conductance of the stressed plants, g, was expressed as a fraction of that for the well-watered control plants, g[subscript]c, and plotted as afunction of the soil water suction, h (cm). At a certain stage the decline in relative stomatal conductance, g/g[subscript]c, changed from a curved to a linear form and continued in thisway until it was no longer possible to take measurements, at which point g/g[subscript]c wasjudged to be zero. The transition between the curved and linear decline in g/g[subscript]c was considered to mark the soil matric suction, h[subscript]t, at which plants began to experienceterminal water stress. When plants finally stopped transpiring, the soil matric suction, hw, was noted as the end point of the experiments. The stressed plants stopped transpiring across a large range of soil matric suctions, demonstrating that plant-response is strongly influenced by soil texture, plant species, root-length density, and environmental conditions. By far the most important factor, however, was soil texture; plants grown in the Very fine sand (coarser-textured) perished at suctions much smaller than the classical wilting point of 15,000 cm, while plants grown in the finer Loamy sand persisted to matric suctions of nearly 27,000 cm in some cases. The other variables appeared to be less important and somewhat complicated by interactions. For example, when averaged across soil texture (and in most cases, regardless), sorghum extracted water to greater matric suctions at all planting densities than did maize; however at higher planting densities and under higher evaporative demand, maize extracted water to greater matric suctions than sorghum. The large difference in behaviour of plants between the two soils demonstrated that a primary cause of water stress was a limitation in the unsaturated hydraulic conductivity. This highlighted the importance of hydrodynamics in controlling water-availability to plants and indicated the potential usefulness of the unsaturated hydraulic conductivity function in weighting the differential water capacity. Chapter 5 explores the extent to which dynamic plant responses to water stress can be used to calculate the IWC. The best function for weighting the soil water capacity was found to be a modified quadratic relation that incorporated the critical soil matric suctions at the onset and end of hydraulic stress, as well as the root-length density. The onset of hydraulic stress shifted toward lower matric suctions as temperature and evaporative demand increased, and transpiration stopped at lower matric suctions as well – particularly in the Very fine sand (well before the classical permanent wilting point of 15,000 cm). The effects were more modest in Loamy sand where plants (particularly sorghum) survived well beyond the classical wilting point. Both sorghum and maize extracted greater amounts of water from the Loamy sand than from the Very fine sand, and sorghum extracted more water from both soil types than did maize.Chapter 6 explores how soil properties combined with plant response can be used to calculate the IWC. In the first instance, the model of Grant et al. (2010) was applied to obtain the relative hydraulic conductivity of the two soils, which provided useful parameters to develop a simple weighting function for the water capacity. The functional form was based on two factors: the shape of the unsaturated hydraulic conductivity and the soil matric suctions at which plants experienced the onset of water stress and then cessation of transpiration. The IWC’s predicted by applying this weighting function were closer to the actual amounts of water extracted by the plants than were the IWC’s produced in Chapter 5, and were more accurate in the coarser of the two soils, the Very fine sand. The combination of soil and plant factors in predicting IWC appears to produce superior estimates than either soil or plant factors alone. Chapter 7 draws some general conclusions, highlights the implications of the work conducted in this study and identifies potentially fruitful lines of future research.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2010

Constraints on water resources and the environment necessitate more efficient use of water. The key to efficient management is an understanding of the physical and physiological processes occurring in the soil-root hydraulic continuum.While both soil and plant leaf water potentials are well understood, modeled and measured, the root-soil interface where actual uptake processes occur has not been sufficiently studied. The water potential at the root-soil interface (yᵣₒₒₜ), determined by environmental conditions and by soil and plant hydraulic properties, serves as a boundary value in soil and plant uptake equations. In this work, we propose to 1) refine and implement a method for measuring yᵣₒₒₜ; 2) measure yᵣₒₒₜ, water uptake and root hydraulic conductivity for wild type tomato and Arabidopsis under varied q, K⁺, Na⁺ and Cl⁻ levels in the root zone; 3) verify the role of MIPs and ion channels response to q, K⁺ and Na⁺ levels in Arabidopsis and tomato; 4) study the relationships between yᵣₒₒₜ and root hydraulic conductivity for various crops representing important botanical and agricultural species, under conditions of varying soil types, water contents and salinity; and 5) integrate the above to water uptake term(s) to be implemented in models. We have made significant progress toward establishing the efficacy of the emittensiometer and on the molecular biology studies. We have added an additional method for measuring ψᵣₒₒₜ. High-frequency water application through the water source while the plant emerges and becomes established encourages roots to develop towards and into the water source itself. The yᵣₒₒₜ and yₛₒᵢₗ values reflected wetting and drying processes in the rhizosphere and in the bulk soil. Thus, yᵣₒₒₜ can be manipulated by changing irrigation level and frequency. An important and surprising finding resulting from the current research is the obtained yᵣₒₒₜ value. The yᵣₒₒₜ measured using the three different methods: emittensiometer, micro-tensiometer and MRI imaging in both sunflower, tomato and corn plants fell in the same range and were higher by one to three orders of magnitude from the values of -600 to -15,000 cm suggested in the literature. We have added additional information on the regulation of aquaporins and transporters at the transcript and protein levels, particularly under stress. Our preliminary results show that overexpression of one aquaporin gene in tomato dramatically increases its transpiration level (unpublished results). Based on this information, we started screening mutants for other aquaporin genes. During the feasibility testing year, we identified homozygous mutants for eight aquaporin genes, including six mutants for five of the PIP2 genes. Including the homozygous mutants directly available at the ABRC seed stock center, we now have mutants for 11 of the 19 aquaporin genes of interest. Currently, we are screening mutants for other aquaporin genes and ion transporter genes. Understanding plant water uptake under stress is essential for the further advancement of molecular plant stress tolerance work as well as for efficient use of water in agriculture. Virtually all of Israel’s agriculture and about 40% of US agriculture is made possible by irrigation. Both countries face increasing risk of water shortages as urban requirements grow. Both countries will have to find methods of protecting the soil resource while conserving water resources—goals that appear to be in direct conflict. The climate-plant-soil-water system is nonlinear with many feedback mechanisms. Conceptual plant uptake and growth models and mechanism-based computer-simulation models will be valuable tools in developing irrigation regimes and methods that maximize the efficiency of agricultural water. This proposal will contribute to the development of these models by providing critical information on water extraction by the plant that will result in improved predictions of both water requirements and crop yields. Plant water use and plant response to environmental conditions cannot possibly be understood by using the tools and language of a single scientific discipline. This proposal links the disciplines of soil physics and soil physical chemistry with plant physiology and molecular biology in order to correctly treat and understand the soil-plant interface in terms of integrated comprehension. Results from the project will contribute to a mechanistic understanding of the SPAC and will inspire continued multidisciplinary research.