Maximum Water Content Research Articles

In situ studies of water relations and CO2 exchange of the tropical macrolichen, Sticta tomentosa

Diel (24‐h) time courses of CO2 exchange, water relations, and microclimate of the foliose lichen, Sticta tomentosa (Swartz) Ach., and responses to experimentally manipulated conditions were measured at a forest edge in a lower montane rainforest in Panama.Similar to earlier observations on two other rain forest lichens, daily desiccation suppressed net photosynthesis (NP) during the period when irradiation was highest. Not surprisingly, the light response curves of NP showed saturation at rather low light levels. Rehydration was associated with an initial resaturation burst of short duration, which could be demonstrated both under natural conditions and experimentally. This additional loss of CO2 seems too low to be ecologically relevant. Moreover, high thallus hydration was also detrimental to NP: at maximum water content net CO2 uptake was depressed by >50%. Although NP was well adapted to the prevailing high temperatures, the latter also stimulated dark respiration. On average, almost 60% of the diurnal carbon gain was lost during the night.In spite of these limitations, the integrated 24‐h C gain was quite high, on average 0·5% of the thallus C content. Whilst these figures were determined for horizontally exposed samples, we also assessed the role of different exposures on photosynthetic performance. Diel C gain was highest under conditions of semi‐shade (westerly exposure), which allowed long periods of activity, whilst much higher irradiance at other exposures could not be utilized for photosynthetic production: easterly exposed thalli dried out even faster than horizontally exposed samples.

Unsaturated Hydraulic Conductivity of Compacted Sand-Kaolin Mixtures

The unsaturated hydraulic conductivity of compacted sand-kaolin mixtures containing 0, 5, 10, and 30 kaolin (by dry weight) is measured for matric suctions, ψm<∼6.0 m. The measured unsaturated hydraulic conductivity (kmeasured) values are compared with predicted unsaturated hydraulic conductivity (kpredicted) values using the Brooks-Corey-Burdine and van Genuchten-Mualem relative hydraulic conductivity functions. In general, the accuracy of kpredicted decreases with an increase in kaolin content or an increase in ψm. In addition, kmeasured tends to be underpredicted for kaolin contents of 10 and 30 at relatively high suctions (1.0 m ≤ψm≤ 6.0 m) and overpredicted for kaolin contents of 0 and 5 at relatively low suctions (0.1 m ≤ψm< 1.0 m). For a given kaolin content and ψm, kpredicted based on the Brooks-Corey-Burdine function tends to be more accurate than kpredicted based on the van Genuchten-Mualem function. Finally, for 1.0 m ≤ψm≤ 6.0 m, kpredicted based on analysis using the maximum volumetric water content (θm) attained under steady-state flow conditions typically is more accurate than kpredicted based on analysis using the saturated volumetric water content, θs, where θm∼ 84–90 of θs in this study.

Thermoreversible behaviour in water of chemically crosslinked poly(2-methoxyethylacrylate-co-N,N-dimethylacrylamide)

Hydrogels of poly(N,N-dimethylacrylamide-co-2-methoxyethyl-acrylate) have been synthesized by crosslinking copolymerization, and the dimensions of swollen films at swelling equilibrium in water have been measured over a range of temperature (T). At 4°C, transparency and maximum water content are exhibited. On heating, deswelling occurs and loss of transparency develops at 35°C, opacity and deswelling being complete at 50°C. The process is reversible and the lower critical swelling temperature (T c ) is found to be 38±2°C. Although water content at any temperature increases with decreasing content of crosslinker, the latter has no discernible influence on T c . Microgels of the same copolymer have also been prepared by dispersion polymerization in 2-propanol. After dialysis in water, the diameters (D) of the microbeads in dilute aqueous suspension were measured by dynamic light scattering. D decreased from 2.3 μm at 10°C to 0.2 μm at T ≥ 50°C, and T c was located at 36 ± 2°C. Optical microscopy revealed the spherical nature and polydispersity of the beads, the dimensions of which lay in the range 7 μm > D> 0.8 μm. These copolymers were sticky in both the dry and the swollen states, which may be advantageous for coating to an inert substrate for application as a possible separation device based on thermoreversible swelling.

The Effects of Longwave Radiation in a Small Cumulus Cloud

Abstract The effects of longwave radiation in a small cumulus cloud are investigated by a combination of a three-dimensional radiative transfer model as well as a slab-symmetric cloud dynamics model. The calculations indicate that longwave radiative cooling substantially enhances the maximum cloud water content. For a run in an environment without wind shear, the maximum increase reaches 96%. The total cloud water content was also increased somewhat (maximum 20%). The effects of longwave cooling at different stages of development of the simulated cloud were further examined and analyzed. In the initial stage of the development, the augmentation of cloud water content near the cloud top and sides is traced mainly to the direct effect of longwave radiative cooling on cloud microphysics (i.e., radiative cooling reduces the local temperature and hence the saturation water vapor pressure, which leads to additional condensation). In the mature stage of the cloud, the increase of total cloud water content arises...

Water uptake and protein release characteristics of a new methacrylate-based polymer system

A novel polymer system comprising poly(ethyl methacrylate) (PEMA) powder gelled with hydroxyethylmethacrylate (HEMA), n-butylmethacrylate (nBM) monomer mixtures has been produced. The monomers were combined in different ratios to vary the relative hydrophobicity of the system. Surface and bulk properties of this copolymer system were investigated. Surfaces were relatively featureless with little variation due to composition. Contact angles ranged from 76 to 83°. Equilibrium water content of the polymers was directly related to the mole fraction of HEMA content. The uptake of water in the earlier stages was proportional to t 1 2 , consistent with a diffusion process; the slope of this plot enabled diffusion coefficients to be measured. The maximum equilibrium water content was 16%. Water uptake was reduced in phosphate-buffered saline, but addition of bovine serum albumin did not affect water uptake. Desorption was also linear on a t 1 2 plot in the early stages. There was a direct relationship between water uptake and loss. The polymer system was capable of releasing albumin; the amount of albumin released was inversely related to the HEMA content of the system. The relationship of the properties of the polymer system to biological interactions and potential applications are discussed.

High proton conductivity in barium yttrium stannate Ba 2YSnO 5.5

Ba 2YSnO 5.5 is found to crystallize in a perovskite structure with a=848 pm. The compound may be hydrated (Δ H hydr.°=−101.5 kJ mol −1, Δ S hydr.°=−92.5 J mol −1 K −1) to a high degree (maximum water content=13.5 mol%) which leads to the formation of protonic charge carriers (OH O ⋅) and the occurrence of very high proton conductivity with low activation enthalpy ( E a=0.51 eV) comparable to that of BaCeO 3 based materials which are the oxides with the highest proton conductivities reported so far. The conductivity contributions from native ions (V O ⋅⋅, h ⋅) are found to be negligible for temperatures below 600°C. In contrast to BaCeO 3 based materials Ba 2YSnO 5.5 shows good chemical durability with respect to carbonate formation. However, structural instability becomes apparent in a high grain boundary impedance, a collapse of the structure upon reduction and the macrocracking induced by lattice strain resulting from hydration.

Accurate Two-phase Oil Well Testing At High Water-oil Ratios

Abstract Industry standard well testing equipment using two-phase separation is often inadequate when used to test wells which produce at very high water-oil ratios. In the Redwater field, which currently produces at an average water:oil ratio of 115:1, two-phase tested wells have had their oil production overstated by as much as a factor of two. This paperdescribes inexpensive equipment and procedural improvements that were made to two-phase well testing systems in the Redwater field that resulted in dramatic improvements in well test accuracy. Background The Redwater oilfield was discovered in 1948 by Imperial Oil Limited. Early development was rapid and by 1952, 975 wells had been drilled on 40 acre spacing. Oil production comes from a Leduc age carbonate reef located some 945 m beneath the surface. The pool, which is supported by a strong bottom water drive, contained 1.3 billion barrels of original oil in place of which 63.5% is recoverable under primary production. Large submersible pumps were installed in' the 1970s to increase production and since the early 1980s the field has experienced a harmonic oil production decline and a continuing rise in water production. Oil production today is 1,500 m3/day compared with the peak rate of about 20,000 m3/day in the early 1970s. Water production is currently 170,000 m3/day for a field average water-oil ratio of 115: 1. The pool is not unitized but rather is competitively operated by 12 companies. The four major companies, who together own 96% of the pool, share a common gathering system and fieldgate battery where custody transfer occurs. Crude sharing is based on individual well tests conducted by each operator. The facilities installed to conduct well tests vary widely among producers. While some tests are conducted using three-phase test separators which separate oil, gas, and water into three distinct and separately metered streams, many are conducted using two-phase (liquid and gas) separators and sampling equipment. It is the two-phase facilities in particular that have proven to be inadequate in providing accurate well tests, particularly at the high water-oil ratios experienced in the Redwater field. Two-phase Well Test Equipment Two phase oil well testing equipment involves a two-phase separator which separates liquid and gaseous phases, and an automaticsampling system which is used to determine the water and oil content of the liquid flow stream. There are many (perhaps 20 or more) designs of samplers that are commonly used in well testing applications. In Redwater, these standard oil field equipment setups have proven to be inadequate for the intended application. The American Petroleum Institute (API) does not provide any recommendations on well testing or on sampling as it applies to well testing. In the API Manual of Petroleum Measurement Standards: Chapter 8-Sampling(1), there are standards for sampling of petroleum and petroleum products. However, these guidelines apply to custody transfer measurements of homogeneous pipeline products where the maximum water content is not greater than three to perhaps 5%. In well testing applications it is very typical to have to sample fluids with significantly higher water contents.

In vitro and in vivo degradation of films of chitin and its deacetylated derivatives

Chitin was deacetylated to various extents with NaOH to obtain partially and thoroughly deacetylated chitins. The specimens used in this study were deacetylated by 0 (chitin), 68.8, 73.3, 84.0, 90.1 and 100 mol% (chitosan). Films with a thickness of 150 μm were prepared from these specimens by the solution casting method. The equilibrated water contents of the films were 52.4 (chitin), 73.8 (68.8 mol%), 64.2 (73.3 mol%), 61.8 (84.0 mol%), 57.8 (90.1 mol%) and 49.7 wt% (chitosan), while the tensile strengths of the water-swollen films were 244 (chitin), 197 (68.8 mol%), 232 (73.3 mol%), 320 (84.0 mol%), 293 (90.1 mol%) and 433 g mm −2 (chitosan). The maximum water content and the minimum tensile strength observed for a specimen deacetylated between 0 and 68.8 mol% may be ascribed to the lowered crystallinity by deacetylation of chitin, since both chitin and chitosan are crystalline polymers. Unlike their physical properties, in vitro and in vivo degradations of these films occurred less rapidly without passing a maximum or minimum, as their degree of deacetylation became higher. The in vitro degradation was carried out by immersing the films in buffered aqueous solution of pH 7 containing lysozyme at 37 °C, while the in vivo degradation was studied by subcutaneously implanting the films in the back of rats. It was found that the rate of in vivo biodegradation was very high for chitin and 68.8 mol% deacetylated chitin, compared with that for the 73.3 mol% deacetylated chitin. The films which were more than 73.3 mol% deacetylated showed slower biodegradation. Interestingly, the tissue reaction towards highly deacetylated derivatives including chitosan was very mild, although they had cationic primary amines in the molecule.

Morphological effects on the water balance of Antarctic foliose and fruticose lichens

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.

Effect of changes in water content on photosynthesis, transpiration and discrimination against 13CO2 and C18O16O in Pleurozium and Sphagnum.

Photosynthetic gas exchange characteristics of two common boreal forest mosses, Sphagnum (section acutifolia) and Pleurozium schreberi, were measured continuously during the time required for the moss to dry out from full hydration. Similar patterns of change in CO2 assimilation with variation in water content occurred for both species. The maximum rates of CO2 assimilation for Sphagnum (approx. 7 μmol m-2 s-1) occurred at a water content of approximately 7 (fresh weight/dry weight) while for Pleurozium the maximum rate (approx. 2 μmol m-2 s-1) occurred at a water content of approximately 6 (fresh weight/dry weight). Above and below these water contents CO2 assimilation declined. In both species total conductance to water vapour (expressed as a percentage of the maximum rates) remained nearly constant at a water content above 9 (fresh weight/dry weight), but below this level declined in a strong linear manner. Short-term, "on-line" 13CO2 and C18O16O discrimination varied substantially with changes in moss water content and associated changes in the ratio of chloroplast CO2 to ambient CO2 partial pressure. At full hydration (maximum water content) both Sphagnum and Pleurozium had similar values of 13CO2 discrimination (approx. 15). Discrimination against 13CO2 increased continuously with reductions in water content to a maximum of 27 in Sphagnum and 22 in Pleurozium. In a similar manner C18C16O discrimination increased from approximately 30 at full hydration in both species to a maximum of 150 in Sphagnum and 90 in Pleurozium, at low water content. The observed changes in C18O16O were strongly correlated to predictions of a mechanistic model of discrimination processes. Field measurements of moss water content suggested that photosynthetic gas exchange by moss in the understory of a black spruce forest was regularly limited by low water content.

High thallus water content severely limits photosynthetic carbon gain of central European epilithic lichens under natural conditions.

Experiments under controlled conditions have shown that net photosynthesis (NP) of many lichens is depressed when their thalli are highly hydrated. In this study we characterise the light and water content (WC) dependency of CO2 exchange for selected epilithic lichens in the laboratory and match this against samples monitored in their natural habitat by a novel, fully automatic cuvette. Laboratory measurements showed that, at a photosynthetic photon flux density (PPFD) of 1500 μmol m-2 s-1, NP of the epilithic foliose lichen Xanthoria calcicola was reduced by about 85% (compared to NP at optimal water content) when the thallus was suprasaturated (maximal hydration was defined as WC after spraying, submerging and subsequent removal of adhering water droplets by shaking). Only after loss of about 80% of its maximal WC were the highest rates of NP possible. This depression was still substantial at 50 μmol m-2 s-1 PPFD. Responses were similar for the crustose epilithic species Lecanora muralis. CO2 exchange of both lichens was monitored under natural conditions by means of the cuvette built into a man-made wall-a common habitat of the species-in the Botanical Garden, Würzburg. For both species, rates of NP were low during and after heavy rain even if incident PPFD and temperature were favourable. This situation occurred frequently and could last through all daylight hours, resulting in a negative carbon balance when nocturnal rates of respiration were high. Often, after rainfall, there was a brief, high peak of NP when optimal WC was transiently attained before metabolic activity finally ceased through desiccation. Other periods with profitable rates of NP occurred after moderate moistening of the lichens by dew, fog or light rain. The lichens were found to perform identically in the field and laboratory. When the two data sets were compared it was clear that the full range of WC produced in the laboratory also occurred in nature and that the productivity of the epilithic lichens was regularly and severely limited by high WC. It is concluded that blockage of diffusive pathways for CO2 in the thallus through high water contents is an important ecological factor for productivity of these central European epilithic lichens.

Measurements of transpiration from savannah shrubs using sap flow gauges

Sap flow gauges were used to measure transpiration from the shrub component of a 7-year-old agricultural fallow in Niger, West Africa. The aim of the study was to provide the data necessary to develop and validate multi-source models of evaporation from semi-arid land surfaces by measuring transpiration from a single component of the vegetation. The vegetation at the study site was a type of savannah, consisting of scattered shrubs, with an understorey of annual grasses and herbs. Sap flow measurements were restricted to Guiera senegalensis J.F. Gmel., the dominant shrub species. Sap flows were measured throughout the wet season of 1990 (June–September), using sap flow gauges operating on a constant power heat balance principle. Sap flow rates measured in individual stems were strongly related to leaf area and net radiation. Strong positive correlations were observed between the hourly mean flow rates measured in different stems. Daily transpiration, T, averaged across a 0.25 ha sample plot was compared with daily total evaporation (measured by eddy correlation), E. T was calculated by scaling up from sap flow measurements in a sample of stems to the whole plot by using the frequency distribution of stem diameter in the plot, and assuming that sap flow in each stem was proportional to its basal cross-sectional area. E varied from about 2 mm day −1 at the start of the wet season to 4–6 mm day −1 during August and September, when maximum leaf area and soil profile water content were observed. E, a measure of evaporation from all plant and soil sources, always exceeded T. At the end of two dry periods in June and July, when soil evaporation and transpiration from the herb understorey probably totalled about 0.5 mm day −1, E was only 0.7–0.9 mm day −1 greater than T, suggesting that the scaling procedure adopted gave reasonable estimates of bush transpiration. Over the whole wet season, transpiration from G. senegalensis accounted for 35% of the total wet season rainfall of 454 mm.

A comparison of total precipitation values estimated from measurements and a 1D cloud model

Abstract. The purpose of this study is to establish a relation between observed total precipitation values and estimations from a one-dimensional diagnostic cloud model. Total precipitation values estimated from maximum liquid water content, maximum vertical velocity, cloud top height, and temperature excess are also used to provide an equation for the total precipitation prediction. Data for this study were collected in Istanbul during the autumns of 1987 and 1988. The statistical models are developed with multiple regression technique and then comparatively verified with independent data for 1990. The multiple regression coefficients are in the range of 75% to 80% in the statistical models. Results of the test showed that total precipitation values estimated from the above techniques are in good agreement, with correlation coefficient between 40% and 46% based on test data for 1990.

Water Losses in the Patagonian Steppe: A Modelling Approach

In this paper we sought to answer questions related to the long—term soil water dynamics of the Patagonian steppe: What are the magnitude and seasonal dynamics of transpiration, evaporation, and deep percolation? How do these fluxes respond to fluctuations in annual precipitation? What is the pattern of soil water availability? We developed a soil water model for the steppe with a daily time step. The model gives weekly cumulative values of transpiration, evaporation, and drainage, maximum and minimum water content for the different soil layers in each week, and the weekly frequency of days with soil water potential higher than — 1 MPa for each layer. The model was tested against three sets of experimental data. Simulated data of total water losses were significantly correlated with observed data, and the slope did not differ significantly from 1 nor the y—intercept from O. On a long term basis, evaporation accounted for 56% of total water loss, transpiration 34%, and deep percolation the remaining 10%. Transpiration and evaporation had asynchronic dynamics. Evaporation was high during the coldest and wettest months of the year (mainly winter months). Transpiration, on the contrary, reached maximum values when energy and water availability were simultaneously high in late spring—early summer. Drainage took place during the coldest months, when most of precipitation occurred, and the soil remained near field capacity. Both evaporation and transpiration had a positive response to an increase in precipitation. However, the proportion of total water loss following these pathways decreased with increasing precipitation. Drainage had a positive exponential relationship with winter precipitation. Probabilities of soil water potential higher than – 1 MPa in the upper soil layer were very low during most of the warm season (P&lt;0.15). At the beginning of the growing season the wettest layer was located at an intermediate depth (10—20 and 20—40 cm), and moved downward so at the end, only deep roots had high soil water availability.

Preparation and characterization of poly(ε-caprolactone) polymer blends for the delivery of proteins

A series of ternary blend matrices, based on high- and low-molecular-weight poly(ε-caprolactone) (PCL) and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer (Synperonic L61), has been developed for the delivery of proteins. The inclusion of Synperonic L61 served to enhance the water content of the matrix available for protein diffusion. Blends comprising high-molecular-weight PCL (PCL H) and Synperonic L61 alone were found by scanning electron microscopy to be incompatible over a wide composition range. The addition of a low-molecular-weight PCL (PCL L) enhanced compatibility of the polymeric components. Analysis of the dynamic mechanical and thermal properties of these blends showed a significant shift in the glass transition temperature of the material (−38 to −55 °C), as the weight fraction of Synperonic L61 increased to 30 wt%, indicative of limited miscibility of the components in the non-crystalline phase. All ternary blended matrices showed a higher degree of hydration relative to homogeneous PCL H. The maximum water content could be modified by adjusting the weight fraction of Synperonic L61 in the blend. The rate of release of a model protein, bovine serum albumin (BSA), from matrices containing Synperonic L61 was considerably higher than that from PCL H and PCL H/PCL H alone. Analysis of the release mechanisms of BSA from these matrices suggested that, whilst diffusion was the predominant mode of protein transport, the elution of Synperonic L61 from blended matrices during the dissolution caused a notable deviation from Fickian control.

Parameterization of Bulk Condensation in Numerical Cloud Models

The accuracy of the moist saturation adjustment scheme has been evaluated using a three-dimensional explicit microphysical cloud model. It was found that the error in saturation adjustment depends strongly on the CCN concentration in the ambient atmosphere. The scheme provides rather accurate results in the case where a sufficiently large number of CCN (on the order of several hundred per cubic centimeter) is available. However, under conditions typical of marine stratocumulus cloud layers with low CCN concentration, the error in the amounts of condensed water vapor and released latent heat may be as large as 40%–50%. A revision of the saturation adjustment scheme is devised that employs the CCN concentration, dynamical supersaturation, and cloud water content as additional variables in the calculation of the condensation rate. The revised condensation model reduced the error in maximum updraft and cloud water content in the climatically significant case of marine stratocumulus cloud layers by an order of magnitude.

Maximum and minimum water contents of granitic melts: implications for chemical and physical properties of ascending magmas

New results obtained by the investigation of liquidus and solidus phase relations in the system Qz-Ab-Or and by the determination of H 2O solubility in haplogranitic melts are used to discuss the evolution of granitic (quartzo-feldspathic) magmas during their ascent in the crust. Particular attention is given to the role of H 2O and its effect on physical properties of ascending magmas. The evolution of melt fraction, H 2O content of the melt and viscosity of melt and magma during ascent are discussed for several examples (adiabatic ascent, ascent with cooling, ascent with crystal fractionation). It is shown that decompression melting processes may be very important (significant increase of the melt proportion), especially at low pressure, in magmas ascending along adiabats or with slow cooling rates. The comparison of the discussed examples shows that melts formed at low T are significantly less viscous than at high T. Although the degree of melting may remain very low in the case of dehydration melting at low temperature, the low viscosity of the generated melts may enhance the extraction of these melts from the source area to produce leucogranites.

In-situ fluorescence imaging of sol-gel thin film deposition

Pyranine was used as a fluorescence probe to monitor the chemical evolution in-situ during thin film deposition by the dip coating process. The sensitivity of the pyranine luminescence to protonation/deprotonation effects was used to quantify changes in the water/alcohol ratio in real time within the depositing film as the substrate was withdrawn from the coating reservoir. The spatially resolved spectral results clearly showed that preferential evaporation of alcohol occurred with increasing distance from the reservoir and that the maximum water content reached rather high values near the drying line. Correlation of the luminescence results with the interference pattern of the drawn films allows the solvent composition in the film to be mapped as a function of film thickness. These experiments demonstrate for the first time that luminescent organic molecules may be applied to the processing science of sol-gel thin film deposition.

Water Status and Development of the Maize Endosperm and Embryo during Drought

Drought during rain filling decreases final kernel mass in maize (Zea mays L.). Lack of assimilates or an unfavorable water status within the embryo or endosperm could limit kernel development. To test these possibilities, remobilization of reduced C and N as well as kernel and embryo water status were measured in plants exposed to a water deficit during rain fill. Irrigation was withheld from field‐grown plants after final kernel number was established. This treatment resulted in a soil moisture deficit of 224 mm and decreased endosperm and embryo mass by 16%, compared with controls. The water deficit shortened the effective filling period, but did not alter the rate of dry matter accumulation in either the endosperm or embryo. Carbohydrate reserves in leaf and stalk tissues as well as N stored in the leaves were remobilized to support kernel growth. However, grain filling ceased before these reserves were depleted completely. Grain filling continued in both well.watered and water‐deficient plants until the moisture content of the endosperm and embryo decreased to 280 and 430 g kg−1 fresh wt., respectively. Water‐deficient plants reached these values 10 d earlier because water loss from the endosperm began sooner after anthesis and maximum water content of the embryo was lower, compared with the controls. Kernel and embryo osmotic potentials (ψs) decreased rapidly late in grain filling and were − 2.2.to − 2.6 MPa when growth ceased. The results indicate that kernel water status is affected directly by drought and may be an important determinant of kernel development. They suggest that a water deficit after anthesis shortens the duration of grain filling by causing premature desiccation of the endosperm and by limiting embryo volume.

Regreening of Desiccated Leaves of the Poikilochlorophyllous Xerophyta scabrida upon Rehydration

The poikilochlorophyllous and desiccation tolerance nature of the leaves of the monocotyledonous Xerophyta scabrida and the physiological recovery of the air-dried leaves upon rehydration after a long-term desiccation is described in this paper. Water uptake through the leaf surface upon rehydration was found to be of prime importance for recovery. Field observations in the natural habitat showed that at the onset of the rainy season water uptake through the leaf surface preceded the development of new adventitious roots. In dry leaves carotenoids were found as the only photosynthetic pigments. Upon rehydration de novo chlorophyll and carotenoid synthesis began just before the leaves reached their maximum water content and specific leaf area. The accumulation of chlorophylls and carotenoids was found to rise very fast and maximum content was reached about 72 hours after rehydration. The values of the chlorophyll fluorescence ratio, F690/F735, and of the fluorescence intensities at 690 nm and at 730 nm (both at maximum Fm and steady-state fluorescence Fs) continuously decreased from the begin of regreening until reaching maximum chlorophyll content after 3 days. The fluorescence ratio F690/F735 proved to be a very suitable non-destructive diagnostic method to monitor the chlorophyll content during regreening of the poikilochlorophyllous leaves of X. scabrida upon rehydration.