The Cu-triethylenetetramine-complex (Cutrien) is one of the commonly used index cations for CEC determination in clay science. Cutrien-exchanged smectites show basal spacings between 13.0 and 13.5 Å after correction for the Lorentz and polarization factors. The full width at half maximum (FWHM) of the d001 reflection is today related to the percentage of tetrahedral charge (beidellitic character) and/or to the Fe content of the smectites. The structural Fe content and the tetrahedral charge correlate, so their individual influence on d001 cannot be resolved. Nevertheless, the FWHM of Cutrien smectites should depend on the charge distribution rather than the Fe content.

X-ray diffraction (XRD) and water uptake capacity measurements showed that the interlayer of Cutrien-exchanged smectites does not swell any more, but can take up a few water molecules. Accordingly, the water uptake capacity of the external surface area can be determined independently from the interlayer water uptake capacity. Adjusting the pH of Cutrien-bentonite dispersion to different values allows for the determination of the variable charge.

In conclusion, Cutrien exchange of smectites appears to be suitable for the study of external surfaces area related phenomena (e.g. edge adsorption processes) without any influence of the interlayer region.

Plans to close a German radioactive waste repository in rock salt include as one alternative the construction of a ‘Cross Section Closure (CSC)’ sealing barrier. The proposed material for the sealing barrier is highly compacted bentonite. To investigate the swelling behaviour of a highly compacted bentonite, a large number of laboratory tests were performed. In addition, large scale model tests were carried out to demonstrate the development of a nearly homogeneous and isotropic swelling pressure. The results of the large scale model tests were interpreted numerically based on the models for stress-strain behaviour and water uptake which are implemented in the finite element computer codes FEST03 and HYDOPO. The investigations show good agreement between the results of the model tests and the corresponding analyses and show that the theoretical models are capable of describing the behaviour of sealing structures based on highly compacted bentonite.

Two field experiments were conducted in 1984 and 1985 to determine the effects of fluazifop, haloxyfop, and sethoxydim on the suppression of water uptake and competition of wheat to seedling alfalfa. In all cases, suppression of wheat growth and stand led to significant reduction in soil water use. The amounts of conserved soil water significantly correlated with increased numbers of alfalfa plants; the correlation coefficients, respectively, for mid- and late-summer plantings were 0.47 and 0.41 in 1984 and 0.90 and 0.86 in 1985. Conservation of soil water was attributed to growth reduction or cessation of wheat growth by the herbicides and, to some extent, suppression of wheat leaf transpiration. All of the three herbicides would be effective in controlling volunteer wheat in a new alfalfa planting.

Seeds (achenes) of fringed sage were collected in central Saskatchewan in 1987, 1990, and 1991, and studies were conducted to determine the effects of imbibition time before brief or prolonged exposure to red (R) and far-red (FR) light on germination. A majority of the seeds required light for germination, but a substantial proportion germinated in darkness. Phytochrome controlled germination, and its activity was influenced by the duration of imbibition and by seed collections. At least 8 h of imbibition were required before phytochrome was activated by R light. The stimulation of germination could be reversed by FR light, and this suppression subsequently could be reversed by exposure to R light. Variable light requirements for germination of fringed sage can be met following large- or small-scale disturbances or in relatively undisturbed conditions.

Laboratory water uptake tests are performed at the Belgian Nuclear Research Centre SCK•CEN to obtain insight into the hydromechanical behavior of Eurobitum bituminized radioactive waste under geological disposal conditions. Small nonradioactive and radioactive Eurobitum samples are hydrated in restricted swelling conditions (i.e., nearly constant volume conditions and constant stress conditions). Microfocus X-ray computer tomography (μCT) proves to be a very suitable technique to follow up the ingress of water in the samples. μCT analyses demonstrate that, under the studied hydration conditions, the water uptake by Eurobitum samples is a diffusion controlled process. A characterization of the partially leached samples with environmental scanning electron microscopy (ESEM) shows that the hydration of salt crystals and the subsequent dilution of the salt solution result in an increase in pore size that is limited to a few tens of μm in restricted swelling conditions. The μCT and ESEM analyses allow improvement in the understanding of water uptake by Eurobitum in restricted swelling conditions. In this article we discuss the μCT and ESEM analyses of nonradioactive Eurobitum samples that were hydrated for 2 to 4 years at a constant stress of 1, 22, 33, and 44 bar or in nearly constant volume conditions.

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK) membranes annealed at 180 °C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications.

Physical dormancy refers to seeds that are water impermeable. Within the Fabaceae, the structure associated with the breaking of dormancy is usually the lens. This study verified the role of the lens in physical dormancy of seeds of Schizolobium parahyba, a gap species of Fabaceae from the Atlantic Forest of Brazil. The lens in S. parahyba seeds appeared as a subtle depression near the hilum and opposite the micropyle. After treatment of the seeds with hot water, the lens detached from the coat. Blocking water from contacting the lens inhibited water absorption in hot-water-treated seeds. High constant (30°C) and alternating (20/30°C) temperatures promoted the breaking of physical dormancy and germination in non-scarified seeds. Maximum percentage of germination occurred earlier for seeds incubated at 20/30°C than for those incubated at 30°C. Seeds with a blocked lens did not germinate at alternating or high temperatures. This study suggests that alternating temperatures are probably the cause of physical dormancy break of seeds of S. parahyba in gaps in the forest.

Dormancy and germination ecology of two Harpagophytum species (Pedaliaceae) from an open Acacia savanna in Botswana were investigated. The maintenance of dormancy is governed partly by the seed coat but mainly by the endosperm and the embryo itself, as demonstrated by removal of the endosperm. Dissemination of the seed from the fruit can be delayed for several years without affecting the viability of the embryo, due to very low respiration rates.

Germination can be enhanced slightly by high temperatures under natural conditions, and by gibberellic acid or removal of the endosperm under laboratory conditions. Relative growth rates for both Harpagophytum species are lower than for subtropical grasses and legumes, due to a strong investment in root and tuber biomass. Germination and seedling growth is discussed in relation to the drought avoidance syndrome and the animal disperser syndrome.

Although many studies have been conducted on seeds with a water-impermeable seed or fruit coat (physical dormancy), the primary site of water entry into these seeds after dormancy-breaking treatments is still controversial. Thus, the role of lens, hilum, micropyle and extrahilar regions in water uptake of seeds treated to break physical dormancy was examined in Vigna oblongifolia and Sesbania sesban (Fabaceae) following pretreatment with sulphuric acid and hot water. Morphology of seed surfaces in treated versus non-treated seeds of both species was examined with scanning electron microscopy. Most seeds of V. oblongifolia first cracked in the hilum when pretreated with sulphuric acid, but they cracked in both the hilum and extrahilar regions when pretreated with hot water. However, in S. sesban seeds, a crack formed only in the lens following either acid scarification or hot-water treatments, and the seeds imbibed water only through the lens. These results indicate that the primary site of water entry into seeds following physical dormancy break can vary with species and treatments. Slow, early imbibition via the hilum, and subsequent rapid imbibition via the lens, may not be detected unless seeds are monitored for several days. Time allowed for imbibition studies may, at least in part, explain various interpretations about the role of the lens in physical dormancy reported in the literature.

The heat production of seeds during germination comes from metabolism as well as hydration. Previous studies either lack continuous measurements, or are based on samples composed of more than one seed, thus failing to characterize differences among the critical phases of germination. This study examines the potential of isothermal calorimetry to characterize water uptake and metabolism in single seeds. Seeds of malting barley (Hordeum vulgare L.) and winterfat [Krascheninnikovia lanata (Pursh) A.D.J. Meeuse & Smit], two species with contrasting seed size, structure, composition and selection history, were used to determine patterns of heat production rate by isothermal calorimetry during water uptake and germination. Embryos of malting barley contributed less than 4% of total seed weight, and metabolic heat production during Phase I of germination was negligible compared to that due to hydration. Embryos accounted for 74% of seed mass for winterfat, and the majority of heat produced in Phase I was due to metabolic heat release. The total heat production rate in Phase I decreased rapidly in malting barley due to slowing of hydration reactions, but increased gradually in winterfat due to an increasing metabolic rate. The heat production rate at the end of Phase II was about twice as high in malting barley as in winterfat. This indicates a higher metabolic activity for malting barley than for winterfat seeds during germination, which may have also contributed to the rapid increase in the heat production rate of malting barley seedlings during Phase III, compared to the gradual increase in heat production rate of winterfat. The comparison between excised embryos and intact seeds indicates that the covering tissues delay radicle emergence in malting barley, but not in winterfat, due to differences in seed structure between the two species.

Our common view on water uptake by terrestrial plants is that it occurs via absorption by roots from the soil substrate. However, it has long been known that plants exhibit alternative water-absorption strategies, particularly in drought-prone environments. Examples include many tropical epiphytic orchids which use a specialized structure called velamen radicum around their aerial roots for moisture absorption directly from the air (Capesius & Barthlott 1975), specialized trichomes in bromeliads (Andrade 2003, Benzing 1990), uptake by hydathodes into leaves of species inhabiting dry desert ecosystems of Namibia (Martin & von Willert 2000) and foliar absorption by coastal California redwoods during the summer fog season (Burgess & Dawson 2004). One of the most intriguing and yet, least-studied examples of adaptations to severe water limitation is found with desiccation-tolerant plants (also called resurrection plants). During drought periods, the water content of these plants can equilibrate with the low relative humidity of the air to the point that the plants appear dead. However, when water is supplied, these plants fully rehydrate (Alpert 2000, Bewley & Krochko 1982) and become physiologically active. Desiccation-tolerant vascular plants are rare in most ecosystems but diverse in tropical inselbergs (granitic outcrops; Porembski & Barthlott 2000). Relatively little is known about inselberg species particularly from an ecophysiological perspective (see Lüttge 1997 and Klüge & Brulfert 2000 for reviews).

Uptake and loss of water by six lichen species from the Argentine Islands, Antarctic Peninsula, were studied in their natural habitat and in laboratory studies. Under field conditions, during a period of rain, uptake of moisture ranged from 15% d w h−1 for Usnea antarctica to almost 90% for Mastodia tesselata. Loss rates after the rain ceased were lower than the uptake rates and ranged from 8.5% d w.h−1 in Umbilicaria decussata to 38.8% in M. tesselata. A comparison of thalli of M. tesselata from the shoreline with thalli collected further inland showed significant differences in maximum water content and in rates of water loss and uptake between thalli from these sites, which could be ascribed to the presence of salt in the thalli of M. tesselata from the shore. Thallus samples of Usnea antarctica collected from an exposed site showed lower uptake rates and higher loss rates of water than samples collected from a more sheltered site. Under laboratory conditions the maximum moisture content ranged from 67% in Usnea antarctica to 391% in M. tesselata. Exposed to an atmosphere of c. 40% relative humidity and c. 15°C, lichen thalli lost their water during the first hour of the experiment at rates ranging from 34% of the maximum moisture content in Umbilicaria propagulifera to 70% in U. decussata. Rates of water loss diminished with time, and after 4–6 hours equilibrium was reached, with water contents of 14–16% of thallus dry weight. The microclimate is the driving force for the thallus water regime. Specific differences in rates of water loss and water uptake depend on the morphology and anatomy of the lichen thalli. The results of the laboratory experiments agree with those from the field study. However, local differences in microclimatic or other environmental factors can be responsible for significant differences in the water regime of thalli of the same species, a result which can only be obtained from field studies.

Introduction. A previous paper showed that Al in the nutrient solution affected thegrowth, biomass production and chemical composition of bananas (Musa spp.). This paper aims atproviding complementary results on the effect of Al on water and nutrient uptake by young banana plants.Materials and methods. Vitroplants of five cultivars (Grande Naine, Agbagba, Obino l'Ewaï, Igitsiriand Kayinja) were grown for 40 d in a phytotron with a temperature close to that of their cropping areas.Dilute nutrient solutions without Al and with 78.5 μM Al were supplied continuously with peristalticpumps. Measurements of daily water and nutrient uptake were carried out twice a week. Rhizosphereacidification or alcalinisation were also monitored. Results and discussion. Aluminium reduced plantwater uptake and cumulative detrimental effects were observed. After 40 d, water uptake was only 30-40% of the control. Without Al, nutrient uptake (Ca, Mg, K, P, NO3-N, NH4-N) increased with time,whereas Al inhibited the uptake of all elements, particularly Mg. As for water absorption, cumulativeeffects were observed: after 40 d, most nutrient uptake rates were reduced by more than 50% relatively tothe control. The plantain bananas, Agbagba and Obino l'Ewaï, were more resistant to Al than the others.Changes of temperature are likely to modify Al sensitivity as one cultivar, Kayinja, showed greater Alsensitivity at 28/25°C than at 24/20°C.

Some mycorrhizal plants exhibit greater resistance than nonmycorrhizal plants to aluminium toxicity. This has not yet been shown for banana despite its importance as a cash and food crop in tropical regions, although bananas are sensitive to aluminium stress. We studied the effects of the arbuscular mycorrhizal fungus Glomus intraradices in alleviating aluminium toxicity in the banana cultivar Grande Naine grown in a continuous-nutrient-flow cultivation system using dilute solution. The micropropagated plants, some of which were inoculated with arbuscular mycorrhizal fungus, were grown for 40 d in pots filled with sand, and continuously irrigated with a nutrient solution containing up to 180 μM of aluminium. Water and nutrient uptake were measured once a week for 24 h, and root arbuscular mycorrhizal fungal colonization, biomass production, and mineral content of roots and shoots were measured at harvest. The root arbuscular mycorrhizal fungal colonization was large, and not significantly influenced by aluminium treatment. The effects of aluminium on both mycorrhizal and nonmycorrhizal plants were: decrease in biomass production, water and nutrient uptake, and magnesium content of roots and shoots; greater aluminium content in roots than in shoots; and increase in potassium and phosphorus content, particularly in roots. A significant positive effect of arbuscular mycorrhizal fungi on plant growth was observed with aluminium treatment, and was most pronounced at the highest concentration. The benefits, compared with nonmycorrhizal plants, included: increase in shoot dry weight, uptake of water and of most nutrients, and in calcium, magnesium and phosphorus content, particularly in roots; decrease in aluminium content in root and shoot; and delay in the appearance of aluminium-induced leaf symptoms. These results indicate that arbuscular mycorrhizal fungi could be effective in alleviating aluminium toxicity to banana plants.

Developmental changes in the root apex and accompanying changes in lateral root growth and root hydraulic conductivity were examined for Opuntia ficus-indica (L.) Miller during rapid drying, as occurs for roots near the soil surface, and more gradual drying, as occurs in deeper soil layers. During 7 d of rapid drying (in containers with a 3-cm depth of vermiculite), the rate of root growth decreased sharply and most root apices died; such a determinate pattern of root growth was not due to meristem exhaustion but rather to meristem mortality after 3 d of drying. The length of the meristem, the duration of the cell division cycle, and the length of the elongation zone were unchanged during rapid drying. During 14 d of gradual drying (in containers with a 6-cm depth of vermiculite), root mortality was relatively low; the length of the elongation zone decreased by 70%, the number of meristematic cells decreased 30%, and the duration of the cell cycle increased by 36%. Root hydraulic conductivity (LP) decreased to one half during both drying treatments; LP was restored by 2 d of rewetting owing to the emergence of lateral roots following rapid drying and to renewed apical elongation following gradual drying. Thus, in response to drought, the apical meristems of roots of O. ficus-indica near the surface die, whereas deeper in the substrate cell division and elongation in root apices continue. Water uptake in response to rainfall in the field can be enhanced by lateral root proliferation near the soil surface and additionally by resumption of apical growth for deeper roots.

The objective of this study was to determine if infection by arbuscular mycorrhizal fungi alters water uptake by roots under well watered to severely droughted conditions. Safflower and wheat plants were grown with and without the mycorrhizal fungi, Glomus etunicatum or G. intraradices in nutrient-amended soil under environmentally controlled conditions to yield mycorrhizal and non-mycorrhizal plants with similar leaf areas, root length densities, d. wt, and adequate tissue phosphorus and nitrogen. Specific water uptake rates (cm3 of water cm−1 root length d−1) were estimated non-destructively at various depths in the soil from changes in the soil water content measured using a gamma attenuation method. When soil water was severely depleted, changes in soil water potentials were also measured with soil psychrometers. Roots from both plant species extracted water at the fastest rate from the upper soil layers when the soil water content was high, and later, extracted water primarily from deeper depths as water in the upper soil layers was depleted. Mycorrhizal infection did not affect the rates at which roots extracted water from soil whether soil moisture conditions were at their wettest condition, at container capacity, or at the driest extreme when soil water potentials ranged from −1·5 to −2·0 MPa and the plants were completely wilted. Plant water relations were also largely unaffected by infection. Mycorrhizal infection did not alter the ability of plants to extract water from soil even during extreme drought.