Fertile organs and in situ spores of a new dipteridaceous fern Hausmannia sinensis from the Jurassic of northern China

As a representative fossil member of the dipteridaceous fern, genus Hausmannia was reported worldwide from the Mesozoic strata; however, little is known about the fertile structures, including sporangia and in situ spores, of this genus. In this study, a new species Hausmannia sinensis was identified from the Middle Jurassic of Nei Mongol (Inner Mongolia), northern China. The specimens are compressions and are well preserved with details of sporangia and in situ spores. The leaf laminae are broadly fan-shaped, with an almost entire margin. Primary and lateral veins dichotomously branch to form square or polygonal meshes. Each ultimate mesh bears one to two circular sori of 0.4 mm in diameter. Sori are exindusiate; each sorus contains three to six round to ovoid sporangia. The annulus is developed and oblique, with stomial region present in proximal position. Spores are trilete, circular to oval in shape. Both proximal and distal surfaces are covered with baculate to subverrucate sculptures. Spores range from 20 to 30 μm in diameter (average 28 μm), and are comparable to the dispersed genera Baculatisporites Thomas and Pflug and Apiculatisporis Potonié and Kremp. Hausmannia sinensis represents the first compression species of genus Hausmannia form Eurasia, which shows the combination of well-preserved sori, sporangia, annuli and in situ spore characters, and is therefore helpful for further understanding the diversity and evolution of the Dipteridaceae fern lineage through time.     

Calorimetric measurement of water transport and intracellular ice formation during freezing in cell suspensions

The current study presents a new and novel analysis of heat release signatures measured by a differential scanning calorimeter (DSC) associated with water transport (WT), intracellular ice formation (IIF) and extracellular ice formation (EIF). Correlative cryomicroscopy experiments were also performed to validate the DSC data. The DSC and cryomicroscopy experiments were performed on human dermal fibroblast cells (HDFs) at various cytocrit values (0–0.8) at various cooling rates (0.5–250 °C/min). A comparison of the cryomicroscopy experiments with the DSC analysis show reasonable agreement in the water transport (cellular dehydration) and IIF characteristics between both the techniques with the caveat that IIF measured by DSC lagged that measured by cryomicroscopy. This was ascribed to differences in the techniques (i.e. cell vs. bulk measurement) and the possibility that not all IIF is associated with visual darkening. High and low rates of 0.5 °C/min and 250 °C/min were chosen as HDFs did not exhibit significant IIF or WT at each of these extremes respectively. Analysis of post-thaw viability data suggested that 10 °C/min was the presumptive optimal cooling rate for HDFs and was independent of the cytocrit value. The ratio of measured heat values associated with IIF (q_IIF) to the total heat released from both IIF and water transport or from the total cell water content in the sample (q_CW) was also found to increase as the cooling rate was increased from 10 to 250 °C/min and was independent of the sample cytocrit value. Taken together, these observations suggest that the proposed analysis is capable of deconvolving water transport and IIF data from the measured DSC latent heat thermograms in cell suspensions during freezing.     

Plant vitrification solution 2 lowers water content and alters freezing behavior in shoot tips during cryoprotection

Plant shoot tips do not survive exposure to liquid nitrogen temperatures without cryoprotective treatments. Some cryoprotectant solutions, such as plant vitrification solution 2 (PVS2), dehydrate cells and decrease lethal ice formation, but the extent of dehydration and the effect on water freezing properties are not known. We examined the effect of a PVS2 cryoprotection protocol on the water content and phase behavior of mint and garlic shoot tips using differential scanning calorimetry. The temperature and enthalpy of water melting transitions in unprotected and recovering shoot tips were comparable to dilute aqueous solutions. Exposure to PVS2 changed the behavior of water in shoot tips: enthalpy of melting transitions decreased to about 40 J g H2O(-1) (compared to 333 J g H2O(-1) for pure H2O), amount of unfrozen water increased to approximately 0.7 g H2O g dry mass(-1) (compared to approximately 0.4 g H2Og dry mass(-1) for unprotected shoot tips), and a glass transition (T(g)) at -115 degrees C was apparent. Evaporative drying at room temperature was slower in PVS2-treated shoot tips compared to shoot tips receiving no cryoprotection treatments. We quantified the extent that ethylene glycol and dimethyl sulfoxide components permeate into shoot tips and replace some of the water. Since T(g) in PVS2-treated shoot tips occurs at -115 degrees C, mechanisms other than glass formation prevent freezing at temperatures between 0 and -115 degrees C. Protection is likely a result of controlled dehydration or altered thermal properties of intracellular water. A comparison of thermodynamic measurements for cryoprotection solutions in diverse plant systems will identify efficacy among cryopreservation protocols.     

Glass-forming property of the system diethyl sulphoxide/water and its cryoprotective action on Escherichia coli survival

In this work the thermal properties of diethyl sulphoxide (Et2SO), as well as its cryoprotective ability are studied and related to other well-known cryoprotectant substances, like dimethyl sulphoxide (Me2SO). We have investigated the thermal properties of Et2SO/water systems using Differential Scanning Calorimetry at a very low heating/cooling rate (2 degrees C/min). Liquid/solid or glassy/crystalline transitions have been observed only for the solutions with content of Et2SO ranging from 5 up to 40% w/w and/or greater than 85%. In the 45-75% w/w Et2SO range we have found a noticeable glass-forming tendency and a great stability of the amorphous state to the reheating. In samples with Et2SO content ranging from 80 to 85%, we observed a great stability of the glass forming by cooling, but a lesser stability to the subsequent reheating. The glass-forming tendency of these solutions is discussed in terms of existing competitive interactions between molecules of Et2SO, on the one hand, and Et2SO and water molecules, on the other hand. The results are well explainable on the basis of the model structure of water/Et2SO solutions, deduced by Raman and infrared studies [J. Mol. Struct. 665 (2003) 285-292]. The cryoprotective ability of Et2SO on Escherichia coli survival has been also investigated, and a comparison among Et2SO and other widely used cryoprotectants, like Me2SO and glycerol has been done. Survival of E. coli, determined after freezing-thawing process, was maximal at 45% w/w Et2SO (more than 85% viability). It should be noted that at the same concentration the survival is only about 35% in the presence of Me2SO and not more than 15% in the presence of glycerol. These features are well consisted with the glass-forming properties of Et2SO.     

Components and fractions for differently bound water molecules of dipalmitoylphosphatidylcholine-water system as studied by DSC and H-NMR spectroscopy

Differently bound water molecules of dipalmitoylphosphatidylcholine (DPPC)-H₂O system were investigated with differential scanning calorimetry (DSC). According to a method previously reported by us, the ice-melting DSC curves of the DPPC-H₂O samples of varying water contents were deconvoluted into multiple components, and the ice-melting enthalpies for the individual deconvoluted components were used to estimate average molar ice-melting enthalpies for freezable interlamellar and bulk waters, respectively. With these average molar ice-melting enthalpies, the numbers of differently bound water molecules of the DPPC-H₂O system were calculated at varying water contents and were used to construct a water distribution diagram of this system. Furthermore, to evaluate the reliability of the present DSC deconvolution method, ²H-NMR T₁ measurements of DPPC-²H₂O system were carried out at 5 °C of the gel phase temperature, and components and fractions for differently bound water (²H₂O) molecules were estimated from the analysis of nonexponential magnetization recovery curves.     

Detection and persistence of fecal Bacteroidales as water quality indicators in unchlorinated drinking water

The results of this study support the use of fecal Bacteroidales qPCR as a rapid method to complement traditional, culture-dependent, water quality indicators in systems where drinking water is supplied without chlorination or other forms of disinfection. A SYBR-green based, quantitative PCR assay was developed to determine the concentration of fecal Bacteroidales 16S rRNA gene copies. The persistence of a Bacteroides vulgatus pure culture and fecal Bacteroidales from a wastewater inoculum was determined in unchlorinated drinking water at 10 °C. B. vulgatus 16S rRNA gene copies persisted throughout the experimental period (200 days) in sterile drinking water but decayed faster in natural drinking water, indicating that the natural microbiota accelerated decay. In a simulated fecal contamination of unchlorinated drinking water, the decay of fecal Bacteroidales 16S rRNA gene copies was considerably faster than the pure culture but similar to that of Escherichia coli from the same wastewater inoculum.     

Biomass allocation, relative competitive ability and water use efficiency of two dominant species in semiarid Loess Plateau under water stress

A better understanding of the growth and interspecific competition of native dominant species under water stress should aid in prediction of succession in plant communities. In addition, such research would guide the selection of appropriate conservation and agricultural utilization of plants in semiarid environments that have not been very well characterized. Biomass production and allocation, relative competitive ability and water use efficiency of one C₄ herbaceous grass (Bothriochloa ischaemum) and one C₃ leguminous subshrub (Lespedeza davurica), both important species from the semiarid Loess Plateau of China, were investigated in a pot-cultivation experiment. The experiment was conducted using a replacement series design in which B. ischaemum and L. davurica were grown with twelve plants per pot, in seven combinations of the two species (12:0, 10:2, 8:4, 6:6, 4:8, 2:10, and 0:12). Three levels of water treatments included sufficient water supply (HW), moderate water stress (MW) and severe water stress (LW). These treatments were applied after seedling establishment and remained until the end of the experiment. Biomass production and its partitioning, and transpiration water use efficiency (TWUE) were determined at the end of the experiment. Interspecific competitive indices (competitive ratio (CR), aggressiveness (A) and relative yield total (RYT)) were calculated from the dry weight for shoots, roots and total biomass. Water stress decreased biomass production of both species in monoculture and mixture. The growth of L. davurica was restrained in their mixtures for each water treatment. L. davurica had significantly (P < 0.05) greater root:shoot allocation than B. ischaemum for each water treatment and proportion within the replacement series. Aggressiveness (A) values for B. ischaemum with respect to L. davurica were negative only at the proportions of B. ischaemum to L. davurica being 8:4 and 10:2 in LW treatment. B. ischaemum had a significantly (P < 0.05) higher CR value under each water treatment, and water stress considerably reduced its relative CR while increased that of L. davurica. RYT values of the two species indicated some degree of resource complimentarity under both water sufficient and deficit conditions. The results suggest that it is advantageous for growing the two species together to maximize biomass production, and the suggested ratio was 10:2 of B. ischaemum to L. davurica because of significantly higher (P < 0.05) RYT and TWUE under low water availability condition.     

Thermal stability and redox properties of M. tuberculosis CuSOD

The superoxide dismutase from Mycobacterium tuberculosis is the only Cu-containing superoxide dismutase that lacks zinc in the active site. To explore the structural properties of this unusual enzyme, we have investigated its stability by differential scanning calorimetry. We have found that the holo-enzyme is significantly more stable than the apo-protein or the partially metallated enzyme, but that its melting temperature is markedly lower than that of all the other characterized eukaryotic and prokaryotic Cu,Zn superoxide dismutases. We have also observed that, unlike the zinc-free eukaryotic or bacterial enzymes, the active site copper of the mycobacterial enzyme is not reduced by ascorbate, confirming that its redox properties are comparable to those typical of the enzymes containing zinc in the active site. Our findings highlight the role of zinc in conferring stability to Cu,Zn superoxide dismutases and indicate that the structural rearrangements observed in M. tuberculosis Cu,SOD compensate for the absence of zinc in achieving a fully active enzyme.     

Germination responses to temperature and water potential in Jatropha curcas seeds: a hydrotime model explains the difference between dormancy expression and dormancy induction at different incubation temperatures

Background and Aims

Jatropha curcas is a drought-resistant tree whose seeds are a good source of oil that can be used for producing biodiesel. A successful crop establishment depends on a rapid and uniform germination of the seed. In this work we aimed to characterize the responses of J. curcas seeds to temperature and water availability, using thermal time and hydrotime analysis,

Methods

Thermal and hydrotime analysis was performed on germination data obtained from the incubation of seeds at different temperatures and at different water potentials.

Key Results

Base and optimum temperatures were 14·4 and 30 °C, respectively. Approximately 20 % of the seed population displayed absolute dormancy and part of it displayed relative dormancy which was progressively expressed in further fractions when incubation temperatures departed from 25 °C. The thermal time model, but not the hydrotime model, failed to describe adequately final germination percentages at temperatures other than 25 °C. The hydrotime constant, θ_H, was reduced when the incubation temperature was increased up to 30 °C, the base water potential for 50 % germination,Ψ_b(50), was less negative at 20 and 30 °C than at 25 °C, indicating either expression or induction of dormancy. At 20 °C this less negative Ψ_b(50) explained satisfactorily the germination curves obtained at all water potentials, while at 30 °C it had to be corrected towards even less negative values to match observed curves at water potentials below 0. Hence, Ψ_b(50) appeared to have been further displaced to less negative values as exposure to 30 °C was prolonged by osmoticum. These results suggest expression of dormancy at 20 °C and induction of secondary dormancy above 25 °C. This was confirmed by an experiment showing that inhibition of germination imposed by temperatures higher than 30 °C, but not that imposed at 20 °C, is a permanent effect.

Conclusions

This study revealed (a) the extremely narrow thermal range within which dormancy problems (either through expression or induction of dormancy) may not be encountered; and (b) the high sensitivity displayed by these seeds to water shortage. In addition, this work is the first one in which temperature effects on dormancy expression could be discriminated from those on dormancy induction using a hydrotime analysis.     

The distribution of tree and grass roots in savannas in relation to soil nitrogen and water

Here we describe the fine root distribution of trees and grasses relative to soil nitrogen and water profiles. The primary objective is to improve our understanding of edaphic processes influencing the relative abundance of trees and grasses in savanna systems. We do this at both a mesic (737 mm MAP) site on sandy-loam soils and at an arid (547 mm MAP) site on clay rich soils in the Kruger National Park in South Africa. The proportion of tree and grass fine roots at each soil depth were estimated using the δ¹³C values of fine roots and the δ¹³C end members of the fine roots of the dominant trees and grasses at our study sites. Changes in soil nitrogen concentrations with depth were indexed using total soil nitrogen concentrations and soil δ¹⁵N values. Soil water content was measured at different depths using capacitance probes. We show that most tree and grass roots are located in the upper layers of the soil and that both tree and grass roots are present at the bottom of the profile. We demonstrate that root density is positively related to the distribution of soil nitrogen and negatively related to soil moisture. We attribute the negative correlation with soil moisture to evaporation from the soil surface and uptake by roots. Our data is a snapshot of a dynamic process, here the picture it provides is potentially misleading. To understand whether roots in this system are primarily foraging for water or for nitrogen future studies need to include a dynamic component.     

The effect of drought on photosynthesis in two epiphytic and two terrestrial tropical fern species

Water-withholding for 5 to 7 weeks and subsequent re-watering were made on potted plants of two epiphytic (E) and two terrestrial (T) fern species, which were collected from a seasonal tropical rainforest and had been grown in a screenhouse with 5 % irradiance for 4 months. During the water stress, the two E species completely closed stomata when frond relative water content (RWC) reached about 70 % with fairly constant maximum photochemistry efficiency (F_v/F_m), while the two T species kept partial stomata opening until RWC reached 45 % and reduction in F_v/F_m at the late stage. Also, chlorophyll content as indicated by a spectral reflectance index was gradually reduced in three species. Physiological recovery was completed after 3-d re-watering for the E species, which was more rapid than for the T species. The gas exchange measurements and regression analyses indicated higher photosynthetic water use efficiency in the E species than in the T species.     

空气湿度与土壤水分胁迫对紫花苜蓿叶表皮蜡质特性的影响

选用2个抗旱性不同的紫花苜蓿品种,敖汉(强抗旱)和三得利(弱抗旱),设置空气湿度(45%-55%和75%-85%)和土壤水分胁迫(75%和35%田间持水量)处理,分析紫花苜蓿叶表皮蜡质含量、组分及晶体结构、气体交换参数、水势及脯氨酸含量的变化规律。结果表明,单独土壤水分胁迫时,紫花苜蓿叶表皮蜡质晶体结构及蜡质总量无显著变化;敖汉蜡质组分中烷类、酯类含量增加,醇类含量下降;三得利醇类含量下降,烷类、酯类含量变化不显著。低空气湿度胁迫时,两品种蜡质总量无显著变化,烷类和酯类含量显著增加,醇类含量显著下降,叶表皮片状蜡质晶体结构熔融呈弥漫性,扩大了对叶表面积的覆盖,其蒸腾速率显著低于正常湿度。复合胁迫处理时,叶表皮片状蜡质晶体结构继续呈弥漫性,烷类、酯类、未知蜡质组分含量均高于单独胁迫处理,醇类含量最低,而蜡质总量除三得利显著高于对照外,其余均无显著差异。紫花苜蓿叶表皮蜡质各组分含量(除醇类)及蜡质总量与光合速率呈显著负相关,与蒸腾速率无显著相关关系。蜡质总量与叶水势呈显著正相关。总体上,敖汉蜡质总量显著高于三得利,蜡质组分中烷类物质的增加有助于提高植株的抗旱性。在复合胁迫下,强抗旱品种主要通过气孔因素控制水分散失,而弱抗旱品种通过气孔和非气孔因素共同控制植物水分散失。     

Analysis of biochemical variations and microRNA expression in wild (Ipomoea campanulata) and cultivated (Jacquemontia pentantha) species exposed to in vivo water stress

The current study analyses few important biochemical parameters and microRNA expression in two closely related species (wild but tolerant Ipomoea campanulata L. and cultivated but sensitive Jacquemontia pentantha Jacq.G.Don) exposed to water deficit conditions naturally occurring in the field. Under soil water deficit, both the species showed reduction in their leaf area and SLA as compared to well-watered condition. A greater decrease in chlorophyll was noticed in J. pentantha (~50 %) as compared to I. campanulata (20 %) under stress. By contrast, anthocyanin and MDA accumulation was greater in J. pentantha as compared to I. campanulata. Multiple isoforms of superoxide dismutases (SODs) with differing activities were observed under stress in these two plant species. CuZnSOD isoforms showed comparatively higher induction (~10–40 %) in I. campanulata than J. pentantha. MicroRNAs, miR398, miR319, miR395 miR172, and miR408 showed opposing expression under water deficit in these two plant species. Expression of miR156, miR168, miR171, miR172, miR393, miR319, miR396, miR397 and miR408 from either I. campanulata or J. pentantha or both demonstrated opposite pattern of expression to that of drought stressed Arabidopsis. The better tolerance of the wild species (I. campanulata) to water deficit could be attributed to lesser variations in chlorophyll and anthocyanin levels; and relatively higher levels of SODs than J. pentantha. miRNA expression was different in I. campanulata than J. pentantha.     

Increased rate of drying reduces metabolic inequity and critical water content in radicles of Cicer arietinum L.

Orthodox seed serves as easily accessible model to study desiccation-sensitivity in plant tissues because once they undergo germination, they become sensitive to desiccation imposed injuries. In the proposed study, effects of rate of drying on the viability, electrolyte leakage, superoxide accumulation, lipid-protein oxidation and antioxidant enzymes were explored in excised radicles of Cicer arietinum L. under dehydration and wet storage. For both the drying conditions, desiccation could be explained by exponential and inverse functions. Under rapid drying tissue viability as scored by germination efficiency and tetrazolium staining remained 100 % all through the analysis (24 h) but declined remarkably after 0.30 g g⁻¹ fresh mass water content (4 days) under slow drying. Moreover, precipitous fall in tissue viability was observed after 2 weeks of wet storage. Rapid drying was also accompanied with limited amounts of electrolyte leakage, superoxide radical, malondialdehyde and protein hydroperoxide, together with enhanced level of protein. Additionally, activities of both superoxide dismutase and ascorbate peroxidase were increased in rapidly dried radicles, but guaiacol peroxidase was declined. In contrary, above referred biomarkers were observed to perform either inversely or poorly during slow drying and wet storage suggesting that above documented alterations might be the resultant of ageing and not desiccation. Gathered data demonstrated that increased drying lowers the critical water content for tissue survival and also reduces the risk of damage resulting from aqueous-based deleterious reactions. Additionally, it also showed that growing radicles are a popular model to explore desiccation-sensitivity in plant tissues and/or seeds.     

白刺沙包浅层土壤水分动态及其对不同降雨量的响应

以乌兰布和沙漠典型白刺沙包为研究对象,使用EC-5土壤水分传感器对其浅层(0—50 cm)土壤水分进行长期连续监测,分析了白刺沙包不同深度土层对不同降雨量的响应及整个生长季的土壤水分动态特征。结果表明:降雨是乌兰布和沙漠白刺沙包土壤水分的最重要补给源,降雨量大小是影响浅层土壤水分补给深度的决定因素。小于10 mm的降雨完全被表层(0—10 cm)土壤吸收,无法补给10 cm以下土壤水分;10—20 mm的降雨对土壤水分的补给深度达到20 cm;20—30 mm的降雨对土壤水分的补给深度达到40 cm,大于30 mm的降雨补给深度可达到50 cm,甚至更深土层。在研究区降雨量以小于20 mm降雨为主的情况下,20 cm以下土层土壤水分逐步恶化,久之将有利于浅根系草本植物的生长,不利于白刺的生长繁殖。因此,这种降雨格局将对浅层土壤水分及植被演替产生重要影响。     

Identification and characterization of the water gap in physically dormant seeds of Geraniaceae, with special reference to Geranium carolinianum

Background and Aims

Physical dormancy in seeds of species of Geraniaceae is caused by a water-impermeable palisade layer in the outer integument of the seed coat and a closed chalaza. The chalazal cleft has been reported to be the water gap (i.e. location of initial water entry) in innately permeable seeds of Geraniaceae. The primary aim of this study was to re-evaluate the location of the water gap and to characterize its morphology and anatomy in physically dormant seeds of Geraniaceae, with particular reference to G. carolinianum.

Methods

Length, width, mass, anatomy and germination of two seed types (light brown and dark brown) of G. carolinianum were compared. Location, anatomy and morphology of the water gap were characterized using free-hand and microtome tissue sectioning, light microscopy, scanning electron microscopy, dye tracking, blocking and seed-burial experiments.

Key Results

Treatment with dry heat caused a colour change in the palisade cells adjacent to the micropyle. When placed in water, the ‘hinged valve’ (blister) erupted at the site of the colour change, exposing the water gap. The morphology and anatomy in the water-gap region differs from those of the rest of the seed coat. The morphology of the seed coat of the water-gap region is similar in G. carolinianum, G. columbinum, G. molle and G. pusillum and differs from that of the closely related species Erodium cicutarium.

Conclusions

Dislodgment of swollen ‘hinged valve’ palisade cells adjacent to the micropyle caused the water gap to open in physically dormant seeds of G. carolinianum, and it was clear that initial water uptake takes place through this gap and not via the chalazal opening as previously reported. This water gap (‘hinged valve gap’) differs from water gaps previously described for other families in morphology, anatomy and location in the seed coat.     

Biomass partitioning and water content relationships at the branch and whole-plant levels and as a function of plant size in Elaeagnus mollis populations in Shanxi, North China

Understanding of the biomass (dry weight) allocation and water relations in populations will provide useful information on the growth patterns and resource-allocation dynamics. By destructive sampling, foliage, branch and root biomass were measured in the endangered shrub Elaeagnus mollis populations growing in Shanxi province, North China. Biomass partitioning and water content relationships were compared at the branch and whole-plant levels, and as a function of basal diameter (plant size). The biomass was mainly distributed in the bigger branches at the branch level, and in the branch wood at the whole-plant level, and branch biomass (but not foliage or root biomass) increases significantly with increasing basal diameter. As a result, branch wood became the major biomass pool, even though considerable biomass was also allocated to the roots. However, the relative water content decreased from the periphery of the crown to the interior of the shrub at the branch level, and from the aboveground to the belowground at the whole-plant level though no significant variation among foliage, branches, and roots. Yet it increased significantly for the whole-plant with increasing basal diameter. The ratio of belowground to aboveground biomass was smaller than 1.0, even as a function of basal diameter. These growth responses indicated a strong adaptation to the shrub’s growing conditions. Biomass was primarily allocated above the ground and the aboveground components grew faster than the belowground one.     

Stomatal sensitivities to changes in leaf water potential, air humidity, CO2 concentration and light intensity, and the effect of abscisic acid on the sensitivities in six temperate deciduous tree species

To characterise the stomata of six temperate deciduous tree species, sets of stomatal sensitivities to all the most important environmental factors were measured. To compare the importance of abscisic acid (ABA) in the different stomatal responses, the effect of exogenous ABA on all the stomatal sensitivities was determined.Almost all the stomatal sensitivities: the sensitivity to a decrease in leaf water potential, air humidity, CO₂ concentration ([CO₂]) and light intensity, and to an increase in [CO₂] and light intensity were the highest in the slow-growing species, and the lowest in the fast-growing species. Drought increased the sensitivity to the environmental changes that induce a decrease in the stomatal conductance, and decreased the sensitivity to the changes that induce an increase in this conductance. The sensitivities of the slow-growers were most strongly affected by drought and ABA. Therefore the success of the slow-growers in their ecological niches can be based on the highly sensitive and strictly regulated responses of their stomata. The fast-growers had the highest sensitivity to an increase in leaf water potential and this sensitivity was sharply reduced by drought and ABA. Thus, the dominance of the trees in riparian areas can be based on the ability of their stomata to quickly reach high conductance in well-watered conditions and to efficiently decrease this rate during drought.Stomatal sensitivities to the hydraulic environmental factors (water potentials in plant and air) had higher values in well-watered trees and a more pronounced response to drought than the sensitivities to the photosynthetic environmental factors ([CO₂] and light intensity). Thus, the hydraulic factors most likely prevail over the photosynthetic factors in determining stomatal conductance in these species.In response to exogenous ABA, the rates of stomatal closure, following a decrease in air humidity and light intensity, and an increase in [CO₂], were accelerated. Stomatal opening following an increase in air humidity and light intensity and a decrease in [CO₂] was replaced by slow closing. The rate of stomatal opening following an increase in leaf water potential was reduced. As the sensitivities to changes in light were modified less by the ABA than the other stomatal sensitivities, the prediction of stomatal responses on the basis of the sensitivity to light alone should be excluded in stomatal models.     

Properties of pullulan-based blend films as affected by alginate content and relative humidity

Pullulan-sodium alginate blend films were prepared and characterized as a function of water activity (a_w). At low a_w, the incorporation of alginate into pullulan film increased the tensile strength and elastic modulus, but decreased the elongation at break of the composite films; the opposite trends were observed at elevated a_w. Above 0.43 a_w, water exerted a typical plasticization effect upon the biopolymer blends. As a_w increased from 0.23 to 0.43, an anti-plasticization effect was observed as tensile strength and elastic modulus increased. The glass transition temperature of all samples decreased substantially as aw increased from 0.23 to 0.84 due to the plasticization effect of water. Within this a_w range, one transition temperature was observed for all film specimens. The stretching vibration band of O-H was investigated using attenuated total reflection Fourier transform infrared spectroscopy to identify the various species of water interacting with the polysaccharide films.     

Modelling reveals endogenous osmotic adaptation of storage tissue water potential as an important driver determining different stem diameter variation patterns in the mangrove species Avicennia marina and Rhizophora stylosa

Background

Stem diameter variations are mainly determined by the radial water transport between xylem and storage tissues. This radial transport results from the water potential difference between these tissues, which is influenced by both hydraulic and carbon related processes. Measurements have shown that when subjected to the same environmental conditions, the co-occurring mangrove species Avicennia marina and Rhizophora stylosa unexpectedly show a totally different pattern in daily stem diameter variation.

Methods

Using in situ measurements of stem diameter variation, stem water potential and sap flow, a mechanistic flow and storage model based on the cohesion–tension theory was applied to assess the differences in osmotic storage water potential between Avicennia marina and Rhizophora stylosa.

Key results

Both species, subjected to the same environmental conditions, showed a resembling daily pattern in simulated osmotic storage water potential. However, the osmotic storage water potential of R. stylosa started to decrease slightly after that of A. marina in the morning and increased again slightly later in the evening. This small shift in osmotic storage water potential likely underlaid the marked differences in daily stem diameter variation pattern between the two species.

Conclusions

The results show that in addition to environmental dynamics, endogenous changes in the osmotic storage water potential must be taken into account in order to accurately predict stem diameter variations, and hence growth.