Water relations of three cowpea cultivars (Vigna unguiculata,L.)

The effects of soil water stress imposed at different growth stages of three cowpea varieties, namely, Adzuki (an erect type), Ife Brown (semi erect) and New Era (a spreading type) on growth, floral abscission and yield were investigated in the greenhouse. Stomatal density, aperture and behaviour as influenced by soil water potential was also evaluated. Root system development, grain yield, soil water content and potentials were determined in a field experiment. Soil moisture stress significantly reduced the growth and yield (34–46%) of the three cowpea cultivars. Although grain yield reduction was highest (36.8%) when stress was imposed at flowering/podding stage for Ife Brown, the variety New Era showed no reduction in yield. Floral abortion which increased with a decrease in matric potential may also be linked with imperfect aeration conditions. The choice of these cultivars for intercropping purposes should take cognisance of depth of rooting, lateral root spread, and root density, which affect water extraction at different soil depths, leaf area index, stomatal density, aperture and behaviour to decreased soil water potential all of which differed widely amongst the cultivars.     

海洋深层矿物水可有效促进人体脱水后再水合

为了探讨摄入海洋性矿物质水对脱水后再水合作用的影响,本研究招募18名年轻男性为受试者,采双盲交叉实验设计,将所有受试者平均分成安慰剂组与海洋性矿物质组,于高温环境进行单次中强度运动至脱水体重的3%,摄入脱水量1.5倍的水份,在脱水后4 h内测量尿液量,并在脱水后24 h和48 h测量体重、尿液颜色、血红细胞与血比容。研究表明:摄入水份后24 h体重已经恢复至脱水前,但是两组无显著差异;摄入海洋性矿物质在4 h内所产生的尿液量高于安慰剂组;血红细胞数目与血比容于补水后24 h与48 h低于脱水前,但是两组无显著差异;尿液颜色在补水后24～48 h高于脱水前,但是摄入海洋性矿物质在24 h的尿液颜色低于安慰剂组。本研究初步认为,摄入海洋性矿物质可以加速身体恢复的程度,建议摄入海洋性矿物质来促进身体的再水合作用。     

Varietal influence of intercropped cowpea on the growth,yield and water relations of maize

The effects of three cowpea varieties namely, NewEra (a spreading type), Adzuki (an erect type) and Ife Brown (semi-erect) intercropped with maize on growth, yield and water relations of maize were investigated in the greenhouse and in the field. Cowpea varietal effects were significant on soil water extraction but insignificant on the performance of maize.     

Water relations of the tomato during fruit growth

Fruit and stem water potentials of tomato plants were measured continuously for several days using automated psychrometers. A linear voltage displacement transducer was used to simultaneously measure diameter changes on an adjacent fruit. A strong correlation was observed between the water potential gradient of the fruit and stem, and changes in fruit diameter. Fruit diameter increased when the apoplasmic water potential gradient favoured solution flow into the fruit and fruit shrinkage occurred only when the water potential gradient was inverted. Based on our data and other published data (Ehret & Ho 1986; Lee 1989a) on phloem transport in tomato, we have concluded that low stem water potentials have an immediate and direct effect on phloem turgor; reducing the driving force for sap flow into the fruit. Since fruit water potential remained relatively constant, the diurnal variation in stem water potential was sufficient to account for the correlation with changes in fruit diameter. There are consequences with respect to predicting the accumulation of dry matter in tomato fruit.     

Some physiological comparisons between the resurrection grass, Eragrostis nindensis, and the related desiccation-sensitive species, E. curvula

Both the poikilochlorophyllous resurrection grass, Eragrostisnindensis, and the desiccation sensitive species, E.curvula, dehydrate to a relative water content (RWC) of less than5% in two weeks. On rewatering, most E. nindensisleaves (except the older, outer ones) rehydrate and resume normal metabolicactivity within a few days, whereas E. curvula does notrecover. There is a controlled loss of photosynthetic pigments, paralleled witha gradual shutdown in gas exchange during dehydration of E.nindensis. On rehydration respiration resumes almost immediately butphotosynthesis only restarts at 70% RWC by which time chlorophyll hasbeen resynthesised and anthocyanin content reduced. In contrast, photosyntheticactivity in E. curvula is maintained down to 40%RWC, after which further drying results in a sudden breakdown of thephotosynthetic system and its pigments. At this point, electrolyte leakage andincreases F_V/F_M decreases such that belowca. 40% RWC, metabolism is irreparably damaged.Interestingly, the older outer leaf in most tillers of E.nindensis does not rehydrate. These leaves show signs of membranedamage and curl in an irregular manner similar to those of E.curvula during dehydration.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydration effects on thermoregulation and performance in the heat

During exercise, sweat output often exceeds water intake, producing a water deficit or hypohydration. The water deficit lowers both intracellular and extracellular fluid volumes, and causes a hypotonic-hypovolemia of the blood. Aerobic exercise tasks are likely to be adversely effected by hypohydration (even in the absence of heat strain), with the potential affect being greater in hot environments. Hypohydration increases heat storage by reducing sweating rate and skin blood flow responses for a given core temperature. Hypertonicity and hypovolemia both contribute to reduced heat loss and increased heat storage. In addition, hypovolemia and the displacement of blood to the skin make it difficult to maintain central venous pressure and thus cardiac output to simultaneously support metabolism and thermoregulation. Hyperhydration provides no advantages over euhydration regarding thermoregulation and exercise performance in the heat.     

Sexual dimorphism in the tusked frog, Adelotus brevis (Anura:Myobatrachidae): the roles of natural and sexual selection

At least two adaptive processes can lead to the evolution of sexual dimorphism: sexual selection (e.g. male-male combat) or natural selection (e.g. dietary divergence). We investigated the adaptive significance of a distinctive pattern of sexual dimorphism in a south-eastern Australian frog, Adelotus brevis. Male Adelotus grow larger than female conspecifics, have larger heads relative to body size, and have large paired projections (‘tusks’) in the lower jaw. All of these traits are rare among anurans. We quantified the degree of dimorphism in Adelotus, and gathered data on diets and mating systems of this species to evaluate the possible roles of sexual selection and dietary divergence in favoring die evolution of these sexually dimorphic traits. Analysis of prey items in alimentary tracts revealed significant sex differences in prey types. For example, females ate proportionally more arthropods and fewer molluscs than did males. However, this difference is likely to be a secondary consequence of habitat differences between the sexes (due in turn to their different reproductive roles) rather than a selective force for the evolution of sexual dimorphism. Calling males spend their time in moist habitats where pondsnails are abundant, whereas females are more often encountered in the drier arthropod-rich woodlands. A three-year behavioural ecology study on a field population revealed that reproductive males engage in agonistic interactions, with the sexually dimorphic tusks used to attack rivals. Larger body size contributed to male reproductive success. Small males were excluded from calling sites and, among the calling males, larger animals had higher reproductive success (numbers of matings) than did smaller individuals. Hence, the atypical pattern of sexual dimorphism in Adelotus brevis seems to have resulted from sexual selection for larger body size and tusk size in males, in the context of male-male agonistic behaviour, rather than natural selection for ecological divergence between the sexes.     

Feed intake, forestomach fluid volume, dilution rate and mean retention of fluid in the forestomach during water deprivation and rehydration in camels (Camelus sp.)

Camels were deprived of water for 11 days. Before and during water deprivation and during rehydration changes in body weight, feed and water intake were measured. Using the liquid marker Cr-EDTA forestomach fluid volume, mean fluid retention and fluid dilution in the forestomach were estimated. At the eleventh day of water deprivation hay intake had decreased to only 9.6% of controls, dilution rates had decreased to 31%, mean retention time of fluid in the forestomach had increased to 189%. At the end of dehydration flow of saliva of 2 l/h mainly contributed to the still rather high dilution rates. Thereby buffering capacity and flow of fluid into the forestomach for microbial digestion as well as the outflow from the forestomach were maintained. At the beginning of rehydration camels drank 97 l within a few minutes, and animals thereby replaced all the water lost. Following this first huge water intake water is rapidly absorbed from the forestomach, and forestomach volume decreased again to dehydration values. At the third day of rehydration control values were reached again. Although feed intake decreased dramatically during water deprivation, functions of the forestomach can be maintained sufficiently mainly due to saliva inflow. This explains the mostly rapid recovery of camels when water is available again.     

Water relations and leaf gas exchange properties in some elite canola (Brassica napus) lines under salt stress

In order to examine whether growth of eight genetically diverse canola (Brassica napus) lines under salt stress is positively associated with their rate of photosynthesis and other gas exchange related attributes, 20‐day old plants of all eight lines were subjected to salinised soil containing 2.4 dS m^?1 NaCl (control), 4 dS m^?1 NaCl, 8 dS m^?1 NaCl or 12 dS m‐¹ NaCl. The lines DGL (non canola) and Dunkeld were found to be salt tolerant and Rainbow and Cyclon salt sensitive with regard to shoot dry matter production and seed yield under saline conditions. In most of the lines there was a negative relationship between growth and net CO₂ assimilation rate. For example, the salt sensitive line Cyclon was the lowest and Con‐III the highest, and the salt tolerant line Dunkeld intermediate in net CO₂ assimilation rate under salt stress. Stomatal conductance was found to be lower in the salt sensitive line Cyclon, followed by the salt tolerant line Dunkeld along with Oscar. Water use efficiency estimated as Pn/E was moderate in the salt sensitive line Cyclon and the salt tolerant line Dunkeld. In conclusion, high salt tolerance of Dunkeld and DGL (non‐canola) was not positively associated with net CO₂ assimilation rate or Pn/E.     

Effect of rootstock on apple (Malus domestica) tree water relations

The effects of rootstock on mid-season water relations, under orchard conditions of non-limiting soil moisture, were determined for bearing 'Empire' apple trees ( Malus domestica Borkh.) on the clonal rootstocks M9, M26, M7, MM106, and MM104 (most to least dwarfing) in their sixth and seventh growing seasons. Stem water potentials (ψ^stem) of trees on M9 and M26 were more negative at midday, under warm, sunny conditions, than were the trees on the other three rootstocks. However, change in ψ^stem per change in stem distance through the canopy (water potential gradient) did not vary among rootstocks at midday. There was no rootstock effect on diurnal variation in transpiration or stomatal conductance. Differences in water storage capacitance, relative to tree size, were determined in a separate study but did not account for the differences observed in ψ^stem. Calculated hydraulic conductivities of xylem water transport suggest that rootstocks differ in their ability to conduct water to the scion, but hydraulic conductivity of the scion was not affected by rootstock. Root-stock differences in hydraulic conductivity were not accounted for by differences in tree size.     

Molecular phylogeny of the Australian frog genera Crinia, Geocrinia, and allied taxa (Anura: Myobatrachidae).

We present a mitochondrial gene tree for representative species of all the genera in the subfamily Myobatrachinae, with special emphasis on Crinia and Geocrinia. This group has been the subject of a number of long-standing taxonomic and phylogenetic debates. Our phylogeny is based on data from approximately 780 bp of 12S rRNA and 676 bp of ND2, and resolves a number of these problems. We confirm that the morphologically highly derived monotypic genera Metacrinia, Myobatrachus, and Arenophryne are closely related, and that Pseudophryne forms the sister group to these genera. Uperoleia and the recently described genus Spicospina are also part of this clade. Our data show that Assa and Geocrinia are reciprocally monophyletic and together they form a well-supported clade. Geocrinia is monophyletic and the phylogenetic relationships with the genus are fully resolved with two major species groups identified: G. leai, G. victoriana, and G. laevis; and G. rosea, G. alba, and G. vitellina (we were unable to sample G. lutea). We confirm that Taudactylus forms the sister group to the other myobatrachine genera, but our data are equivocal on the phylogenetic position of Paracrinia. The phylogenetic relationships among Crinia species are well resolved with strong support for a number of distinct monophyletic clades, but more data are required to resolve relationships among these major Crinia clades. Crinia tasmaniensis and Bryobatrachus nimbus form the sister clade to the rest of Crinia. Due to the lack of generic level synapomorphies for a Bryobatrachus that includes C. tasmaniensis, we synonymize Bryobatrachus with Crinia. Crinia georgiana does not form a clade distinct from other Crinia species and so our data do not support recognition of the genus Ranidella for other Crinia species. Crinia subinsignifera, C. pseudinsignifera, and C. insignifera are extremely closely related despite differences in male advertisement call. A preliminary investigation of phylogeographic substructure within C. signifera revealed significant divergence between samples from across the range of this species.     

Water uptake by barley roots as affected by the osmotic and matric potential in the rhizosphere

Summary The water uptake rates of roots in saline soils are depressed by the simultaneously decreasing matric and osmotic water potentials in the soil surrounding the roots (rhizospheric soil). Unfortunately there are no reliable tools available for direct measurements of the effect of decreasing water potentials in the rhizospheric soil on the uptake rate of soil water by roots. This paper presents some results of a vegetation technique for studying the effect of different combinations of osmotic and matric water potentials in the rhizospheric soil on the water uptake rates of barley roots. Water uptake rates were reduced to a greater extent by decreasing soil matric water potentials than by decreasing soil osmotic water potentials. According to the results of this experiment, there was no relationship between the total soil water potential of a sandy soil and the water uptake rates when the roots were exposed to different combinations of and .     

Relationship between soil-stored seed banks and degradation in eastern Nama Karoo rangelands (South Africa)

Landscape, local scale and seasonal composition of soil-stored seed banks of a southern African semi-arid rangeland (Nama Karoo) were investigated through assessment of seed germinated from field-collected soil. Variables included percentage above-ground canopy cover, numbers of seeds germinated, and selected physical and chemical soil characteristics. Organic matter content of soil sampled from under plant canopies (closed-canopy) is significantly higher than that of inter-canopy samples (open-canopy). Significantly more seeds germinated from closed-canopy soil samples are compared with those from open-canopy microsites. It is argued that reduction in rangeland canopy cover due to overgrazing (and resultant erosion through wind and water movement) leads to reduced seed retention by the leaf litter layer and thus by the soil. This degraded resource appears to have gradually lost an inherent buffer capacity, undermining attempts at ecological restoration and necessitating concerted and directed efforts to restore these fragile systems.     

Water relations, gas exchange characteristics, and the level of some metabolites in two cultivars of spring wheat under different N regimes

Twenty eight-day old plants of two spring wheat cultivars differing in salinity tolerance were subjected to varying levels of nitrogen (56, 112, and 224 mg N·kg⁻¹ soil) for 42 days. Both cultivars performed differently under varying soil N levels in terms of growth, and grain yield and yield components. Nitrogen levels, 112 and 224 mg·kg⁻¹ soil, caused maximal growth in Sarsabz and Barani-83, respectively. Cv Sarsabz maintained higher leaf water and turgor potentials, but lower leaf osmotic potential than those of Barani-83 at all external N regimes. Sarsabz had higher Chl a, Chl b and carotenoids contents in leaves than those in Barani-83 at 56 and 112 mg N·kg⁻¹ soil. Sarsabz had higher contents of leaf soluble proteins, soluble sugars, and free amino acids than those in Barani-83 at all external N levels. In Barani-83 net CO₂ assimilation rate remained almost unchanged, whereas in Sarsabz it decreased consistently with increase in external N level. The better growth performance of Sarsabaz as compared to Barani-83 under varying soil N levels except 224 mg N·kg⁻¹ soil was associated with maintenance of high leaf turgor potential but not with net CO₂ assimilation rate.     

Substrate relations of the African wood‐burrowing mayfly Povilla adusta Navás (Ephemeroptera,Polymitarcyidae)

Colonization of an artificial substrate (polyurethane foam) by nymphs of the wood‐burrowing mayfly Povilla adusta was studied in a natural West‐African lake (Opi Lake). Nymphs readily colonized the substrate in densities up to 11,000 m^‐2 (early instars) and at depths ≤ 1.5 m. Blocks with rough surfaces and those in close proximity to oviposition sites near‐shore, had larger densities of nymphs than did those with smooth surfaces or those placed off‐shore. The upper surfaces of submerged blocks had smaller numbers of larger nymphs than did lower surfaces. Differences in the abundance of periphyton on the various surfaces may account for some of these patterns. The generation time of P. adusta is estimated to be three months in Opi Lake.     

Water relations of compound leaves and phyllodes in Acacia koa var. latifolia

Abstract Moisture release characteristics and field measurements of physiological parameters (conductance and water potential) and environmental parameters (ambient temperature, water vapour saturation deficit and photosynthetic photon flux density) were measured for phyllodes and compound leaves of Acacia koa over a 2 month period at Hawaii Volcanoes National Park, Hawaii, to determine what differences in water relations might occur between leaf types. The phyllodes were found to contain more water at full turgor, use less water in turgor control and have stomatal conductances more closely associated with bulk leaf water status and environmental variables. These results suggest that the phyllodes are more drought adapted, whereas the compound leaves probably promote more rapid early growth during periods of high moisture availability.