Knot formation reduces water exchange by adult males of the hairworm,Paragordius varius (Nematomorpha: Gordioidea)

To examine how aggregation by hairworms may enhance survival in freshwater, we determined water balance characteristics of Paragordius varius in groups of different sizes. P. varius is hyperosmotic resulting in high body water content and functions down to one-half of water stores. Absence of a critical transition temperature implies a watertight, low-porosity cuticle. Aggregated worms lose water slowly, as a physiological consequence of reduced motor activity. The water balance strategy shifts from a reliance on high dehydration tolerance for isolated individuals, affording high water loss rates, to suppressed activation energy when aggregated, wherein blocking water gain is important when water loss is slower. Low water loss rate derives from stillness and aggregating that facilitate mating or anti-predator defense, rather than as a behavior to regulate water loss. Presence of hairworms in streams is an indicator of high-quality water that is necessary to maintain water balance.     

Survival of Helicobacter pylori in well water

The mortality of a clinical Helicobacter pylori strain was assessed by inoculating it in untreated well water, filtered well water, and autoclaved well water. Two different temperatures (5 and 25 °C) were used during the experimental period. Because Escherichia coli is commonly used as indicator of faecal pollution of water, we compared the survival of H. pylori using E. coli as indicator of its persistence. H. pylori was not culturable 48 h after inoculation, whereas the population of E. coli, monitored at the same temperature, decreased slowly, especially in filtered water. In untreated water, both H. pylori and E. coli survived less well than in filtered and autoclaved water. In general the survival of H. pylori and E. coli was better in filtered water than in autoclaved water and the ability of H. pylori to survive several days in water at 5 °C is reported, supporting the observation that H. pylori survives better at 5 °C than at higher temperature. This suggests a possible faecal–oral transmission of H. pylori in the presence of a contaminated water.     

宁夏河东沙区刺槐和丝绵木水分利用策略

刺槐和丝绵木混交林是宁夏河东沙区防护林建设的主要模式,了解刺槐和丝绵木的水分利用策略,能为区域植被恢复和防护林林分结构调整提供科学依据。以宁夏河东沙区刺槐(Robinia pseudoacacia)和丝绵木(Euonymus bungeanus)混交林为研究对象,通过监测微气象、树干液流和土壤质量含水量,结合大气降水、土壤水、植物木质部水同位素组成,采用Granier及其校正公式,运用贝叶斯混合模型(MixSIAR)和相似性比例指数(PS)研究2个树种的蒸腾耗水、水分来源和水分利用关系。结果表明：刺槐和丝绵木的蒸腾耗水量在生长季中期较高,前期和后期较小,刺槐的蒸腾耗水量是丝绵木的1.55倍;影响刺槐蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、0—40 cm土壤质量含水量和40—120 cm土壤质量含水量;影响丝绵木蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、平均气温、0—40 cm土壤质量含水量和40—120 cm土壤质量含水量;蒸腾耗水较高时,刺槐主要吸收利用中层土壤水,丝绵木主要吸收利用浅层土壤水,蒸腾耗水较低时,刺槐主要吸收利用浅层土壤水,丝绵木主要吸收利用中层土壤水;在...     

Foliar trichome- and aquaporin-aided water uptake in a drought-resistant epiphyte Tillandsia ionantha Planchon

The atmospheric epiphyte Tillandsia ionantha is capable of surviving drought stress for 6 months or more without any exogenous water supply via an as of yet to be determined mechanism. When plants were soaked in water for 3 h, leaves absorbed a remarkably large amount of water (30–40% on the basis of fresh weight), exhibiting a bimodal absorption pattern. Radiolabeled water was taken up by the leaves by capillary action of the epidermal trichomes within 1 min (phase 1) and then transported intracellularly to leaf tissues over 3 h (phase 2). The removal of epidermal trichome wings from leaves as well as rinsing leaves with water significantly lowered the extracellular accumulation of water on leaf surfaces. The intracellular transport of water was inhibited by mercuric chloride, implicating the involvement of a water channel aquaporin in second-phase water absorption. Four cDNA clones (TiPIP1a, TiPIP1b, TiPIP1c, and TiPIP2a) homologous to PIP family aquaporins were isolated from the leaves, and RT-PCR showed that soaking plants in water stimulated the expression of TiPIP2a mRNA, suggesting the reinforcement in ability to rapidly absorb a large amount of water. The expression of TiPIP2a complementary RNA in Xenopus oocytes enhanced permeability, and treatment with inhibitors suggested that the water channel activity of TiPIP2a protein was regulated by phosphorylation. Thus, the high water uptake capability of T. ionantha leaves surviving drought is attributable to a bimodal trichome- and aquaporin-aided water uptake system based on rapid physical collection of water and subsequent, sustained chemical absorption.     

Foliar water uptake in the needles of Pinus torreyana

The natural habitat of Pinus torreyana, the Torrey pine, is restricted to two locales in coastal Southern California that experience substantial fog and low clouds during the dry months of a Mediterranean climate. In similar semi-arid climate systems that encounter fog or low clouds, many plants can capture atmospheric moisture and are capable of direct foliar water uptake to reduce water stress. In this study, we investigated if the needles of P. torreyana are also capable of direct water uptake. In addition to water immersion, we measured the surface properties along a needle using microdroplets. The droplet contact angle is a measure of surface wettability, and the droplet absorption is a measure of localized foliar water uptake. The results showed that the entire length of the P. torreyana needle, including under the base sheath, is hydrophilic and capable of direct water uptake. The spatial gradients of the wettability and the water uptake along the needle are relatively small. Moreover, the wettability and water uptake increase from young shoots to one-year and two-year old needles. Our results also showed that the decrease in water uptake at higher contact angles can be described by a linear regression. Compared with the leaves of four shrubs in the same habitat, Heteromeles arbutifolia, Malosma laurina, Rhus integrifolia, and Eriodictyon crassifolium, the P. torreyana needles have lower contact angles and higher water uptake rates.

     

Assessing the true status of the fish species Labeo cylindricus (Peters 1868) (Teleostei: Cyprinidae) in Lake Baringo,Kenya

Eutrophication contributes to the proliferation of alien invasive weed species such as water hyacinth Eichhornia crassipes. Although the South American moth Niphograpta albiguttalis was released in South Africa in 1990 as a biological control agent against water hyacinth, no post-release evaluations have yet been conducted here. The impact of N. albiguttalis on water hyacinth growth was quantified under low-, medium- and high-nutrient concentrations in a greenhouse experiment. Niphograpta albiguttalis was damaging to water hyacinth in all three nutrient treatments, but significant damage in most plant parameters was found only under high-nutrient treatments. However, E. crassipes plants grown in high-nutrient water were healthier, and presumably had higher fitness, than plants not exposed to herbivory at lower-nutrient levels. Niphograpta albiguttalis is likely to be most damaging to water hyacinth in eutrophic water systems, but the damage will not result in acceptable levels of control because of the plant's high productivity under these conditions. Niphograpta albiguttalis is a suitable agent for controlling water hyacinth infestations in eutrophic water systems, but should be used in combination with other biological control agents and included in an integrated management plan also involving herbicidal control and water quality management.     

Effect of hydration upon the thermal stability of tropocollagen and its dependence on the presence of neutral salts

The endotherm enthalpy changes ΔH_D and temperatures T_D of thermal denaturation of tropocollagen fibers were measured by DSC calorimetry as functions of water content. The denaturation temperatures decrease with increasing water content. The enthalpy change values increase sharply in the range 0–28% of water content, where a maximum of 14.3 cal g^?1 is reached. The effect of water uptake on the enthalpy term is explained by water bridge formation within the collagen triple helix. Evidence is given for the existence of approximately three intercatenary water bridges per triplet at the enthalpy maximum, their H-bond energy amounting to approximately 4000 kcal/mol of protein. In the 30–60% range of water content, ΔH_D decreases by 2 cal^?1 probably due to interactions between secondary water structures and the stabilizing intrahelical water bonds. The influence of two neutral potassium salts, with a structure-stabilizing and a structure-breaking anion (F^? and I^?), on the hydration dependence of ΔH_D and T_D was also studied. It was shown that the primary hydration is not influenced by these ions, but that T_D and ΔH_D are altered in an ion specific way in the presence of interface and bulk water. Hydrophobic interactions do not explain the experimental results. A reaction mechanism of the effects of ions upon the structural stability of collagen is proposed and discussed in terms of interactions of the medium water molecules with the intrahelical water bonds, and in terms of proton-donor/proton-acceptor equilibria between peptide groups, hydrated ions, and intrahelical water molecules.     

Effects of water restriction on nitrogen metabolism and urea recycling in the macropodid marsupialsMacropus eugenii (tammar wallaby) andThylogale thetis (red-necked pademelon)

Summary The effects of water restriction on nitrogen metabolism were compared in the semi-arid adapted tammar wallaby (Macropus eugenii) and a wallaby from a moist forest environment, the red-necked pademelon (Thylogale thetis).On a medium (9 to 13%) protein diet water restriction depressed dry matter and nitrogen intakes in both species. Nitrogen balance remained positive, but fell further in the pademelons. Urea excretion decreased in the tammars, but increased in the pademelons. Urea recycling as a proportion of urea entry rate tended to increase in the tammars but not in the pademelons. These findings suggest thatT. thetis is not as well adapted asM. eugenii to coping with water shortages.In a second experiment water restriction depressed nitrogen balance in tammars on both high (15%) and low (5%) protein diets, but only on the latter diet did nitrogen balance become negative. Urea recycling was greater on the low than on the high protein diet, but was unaffected by water restriction. Although better able to withstand water stress,M. eugenii was unable to cope with both water stress and a low protein diet together. The reported ability ofM. eugenii to maintain water intake by drinking sea water during the dry season when fresh water is unavailable and vegetation is of low protein content is thus of great ecological significance.     

白刺沙堆退化与土壤水分的关系

近几十年来,我国西北干旱区白刺沙堆退化严重,导致固定沙丘活化,流沙掩埋绿洲,造成了严重危害。如何尽可能长期保持白刺沙堆的稳定、防止白刺沙堆活化成为绿洲保护和沙漠化防治急需解决的问题。在多年野外观察的基础上,提出了"土壤水分收支不平衡所导致的土壤水分减少是白刺沙堆退化的主要原因"的研究假设。但是,由于缺少长期的野外观测试验,这个假设一直未被很好地证明。为了证明这个假设,在甘肃民勤的绿洲外围选择了雏形、发育、稳定和死亡四个退化阶段的白刺沙堆,于2008年1月至2012年6月利用中子水分仪和土壤烘干称重法对土壤水分进行了长期观测。结果表明:各样地的土壤含水量均呈现出2008年最大,2009年和2011年次之,2010年最小的趋势。年内变化是春季土壤含水量最低,夏季逐渐增加,随后逐渐减小。在不同发育阶段,雏形阶段的土壤含水量最大,且降水容易下渗。稳定和死亡阶段的白刺沙堆土壤含水量很低,降水难以下渗,只有大的降水事件发生时,水分才可以下渗。因此,稳定和死亡阶段白刺沙堆的土壤水分经常在植物的凋萎点之下,是造成白刺沙堆退化重要原因。证明了"土壤水分减少是白刺沙堆退化的原因"的研究假设。研究结果对今后的植物固沙实践活动会有积极的参考意义。     

Response of the invader Cortaderia selloana and two coexisting natives to competition and water stress

Alien species’ resistance and adjustment to water stress and plant competition might largely determine the success of invasions in Mediterranean ecosystems because water availability is often limiting biomass production. Two outdoor pot experiments were conducted to test the hypotheses that at the recruitment stage the invader perennial tussock grass Cortaderia selloana is a superior competitor, and that it is more resistant to water stress than the two coexisting native species of the same functional group, Festuca arundinacea and Brachypodium phoenicoides. C. selloana reduced aboveground biomass of target native species, but not more than target native species on each other. Moreover, C. selloana did not resist interspecific competition more than target native species. Under control conditions, C. selloana did not have larger specific leaf area (SLA) and root–shoot ratio (R/S) ratio than target native species, contradicting the general statement that these traits are associated to invasiveness. F. arundinacea was the species which performed best but also the one most affected by water stress. Both C. selloana and B. phoenicoides performed in a similar way under water stress conditions. However, the alien species’ capacity to adjust to water stress, indicated by the increase in the root–shoot ratio under moderate and severe water stress, was slightly better than that of B. phoenicoides. Overall, at early recruitment stages, C. selloana is not a better competitor than the coexisting native species. However, it seems to be more resistant to water stress because as water becomes scarce C. selloana maximizes water uptake and minimizes water losses more than the native species.     

Coexistence of Juncus articulatus L. and Glyceria australis C. E. Hubb. in a temporary shallow wetland in Australia.

Juncus articulatus, a species introduced to Australia, is codominant over large areas of Mother of Ducks Lagoon but is rare in other lagoons. It occurs widely within the lagoon but is concentrated in lower, wetter areas that are more disturbed by birds and cattle. This suggests that J. articulatus may be separated over elevation (and therefore water regime) and disturbance gradients from the native grass Glyceria australis, the dominant species in the lagoon. This paper compares the growth and interaction of G. australis and J. articulatus under different water regimes. The species responded differently to water regime both in monoculture and in mixture. Above ground production of J. articulatus was greatest under fluctuating water levels, least under a damp water regime and intermediate under flooded conditions. G. australis production was greatest under the damp, least under the flooded and intermediate under the fluctuating water regime. The outcome of interaction is dependent on water regime and time. After one year J. articulatus was the superior competitor under all water regimes. At the end of two years J. articulatus was still the superior competitor under fluctuating and flooded water regimes but not under the damp regime. The change in outcome after two years was due to the competitive superiority of G. australis during the second year under all water regimes. The relative importance and the management implications for the invasive potential of J. articulatus are assessed in shallow Australian wetlands with fluctuating water regimes.     

Application of the Entropy-Enthalpy Relationship in Water Transport through Plant Roots

Water transport through plant roots is determined by a single layer of cells, so that water passes through a plasmamembrane-cytoplasm-plasmamembrane system. The water transport shows an exponential relationship with temperature in two phases with an abrupt transition. The Arrhenius activation parameters log A and E are calculated for the two phases of water transport below and above the transition temperature. Between log A and E two linear and parallel relationships are observed, one for each phase of water transport. The difference of log A between these two relationships is a measure for a change in entropy in cell water structure at the transition temperature. The change in entropy was small (13.4 J · mol^?1· K^?1) in comparison to the difference in activation energy E for water transport above and below the transition temperature. The role of the plasmamembrane and cytoplasm in determining the cell water structure is discussed.     

Water balance of over-wintering beetles in relation to strategies for cold tolerance

The vapour pressure of the haemolymph of a supercooled insect is higher than the vapour pressure of the haemolymph of a frozen insect at the same temperature. The aim of the study was to see whether this may affect the water loss of freeze-avoiding and freezetolerant, over-wintering beetles. The rates of water loss were determined on freeze-tolerant Pytho depressus larvae and Upis ceramboides adults. Within each species one group was kept supercooled whereas another group was frozen. All groups were incubated at-5°C. Both species displayed significantly lower rates of water loss when they were frozen than when they were supercooled. Values of respiratory rate and water loss of freeze-avoiding and freeze-tolerant species were compared to corresponding values of desert beetles. The results indicate that the freeze-avoiding species have lower rates of cuticular water loss than freeze-tolerant species. This indicates that the freeze-avoiding species have developed more efficient water-saving mechanisms than freeze-tolerant species. The reason for this may be that the haemolymph in frozen animals will be in vapour pressure equlibrium with the ice in the hibernaculum and thus there is no danger of desiccation during winter. The supercooled insects will have a vapour pressure of the haemolymph that is higher than the vapour pressure of water in the surrounding air and will thus lose water.Abbreviations BW body weight - BW_i initial body weight - BW_t body weight at time t - P vapour pressure difference between the water in the haemolymph and the water in the air - DWL_t dry weight loss at time t - M _w rate of metabolic water production - MF_w mol fraction of water, in the haemolymph - MO₂ rate of oxygen consumption - Osm osmolality of the haemolymph - P _a vapour pressure of water in the air - P _h vapour pressure of water in the haemolymph - P _w vapour pressure of pure water - Q a constant (2,02 1 oxygen per g fat metabolized) relating oxygen consumption to dry weight loss when fat is metabolized - R a constant (1,89 1 oxygen per g water produced) relating metabolic water production to oxygen consumption when fat is metabolized - R _dwl rate of dry weight loss - RH relative humidity of the air - RWC_i initial relative water content measured by weighing - RWC_t relative water content at time t - STP standard temperature and pressure     

Aquaporin water channel in the salivary glands of the Formosan subterranean termite Coptotermes formosanus is predominant in workers and absent in soldiers

Termite society is unique because the worker caste fetches and carries free water, utilizing it as a solvent for nest construction and gallery building and to maintain wetness for their nestmates. Such water management in a social organization relies largely upon the function of the workers in the colony, as well as on the individuals controlling the location and movement of water inside their bodies. The movement of water via aquaporins (AQPs; water channels) into and out of cells is a key feature of the numerous physiological functions related to whole‐insect water balance. In the present study, the homologue of the water‐specific Drosophila AQP [Drosophila integral protein (DRIP)] is characterized in workers of the Formosan subterranean termite Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), a highly active wood decomposer. Immunoblot analysis of DRIP‐type AQP using an antibody from the silkworm Bombyx mori reveals that the Coptotermes DRIP (formerly cloned as ‘CfAQP1’) with a molecular mass of approximately 25.7 kDa is expressed predominantly in the salivary (labial) gland of the workers. The Coptotermes DRIP is present at the basal plasma membrane of the parietal cells, as demonstrated by immunocytochemistry. By contrast, there is no DRIP detected within the salivary glands of soldier termites, and neither caste expresses DRIP in their labial gland reservoir (water sac), a tissue that is suggested to have a function as a water sink. The AQP present in the salivary glands is of physiological importance with respect to salivation, aiding in the secretion of cellulolytic enzymes for wood ingestion by the workers of the subterranean termite.     

Primi Processi di Germinazione in Pinus Pinea L. var. Fragilis Du Hamel

Abstract

Early stages of germination in PINUS PINEA L. var. FRAGILIS Du Hamel. — The main stages of the hydration process preceeding germination and accompaning root elongation have been observed in Pinus pinea L. seeds, by means of vital colours (Congo red, neutral red, acid fuchsine).

The results are as follows:

a) water penetrates easily through the outer shell of the seed reaching its deepest layer which is less permeable to water. Two or three days were required in our experience for water could overcome this barrier.

b) The inner shell (known as « soft shell ») is almost water-proof and seems to draw water towards the micropilar pole of the seed, so that the first region of the seed which sucks up water is the micropile.

c) Through the micropile water enters the seed and imbibes the column, the pericolumn and the endosperm cells.

The endosperm swells with water until the seed shell blows up, because of the inside pressure. At this time water freely penetrates the seed everywhere.

In natural conditions we may infer that the first tissues which take contact with the soil water are the column and pericolumn. As a certain amount of time is required for penetration of water as far as the column (two or three days in experience conditions) germination starts only after a given amount of water is available in the soil for a certain period of time.

When seed hydration is performed the embryo root starts elongating and gets out of the seed.

The behaviour of the column, the pericolumn and the root cap during the early stages of germination are dexcribed.     

Influence of root density on the critical soil water potential

Estimation of root water uptake in crops is important for making many other agricultural predictions. This estimation often involves two assumptions: (1) that a critical soil water potential exists which is constant for a given combination of soil and crop and which does not depend on root length density, and (2) that the local root water uptake at given soil water potential is proportional to root length density. Recent results of both mathematical modeling and computer tomography show that these assumptions may not be valid when the soil water potential is averaged over a volume of soil containing roots. We tested these assumptions for plants with distinctly different root systems. Root water uptake rates and the critical soil water potential values were determined in several adjacent soil layers for horse bean (Vicia faba) and oat (Avena sativa) grown in lysimeters, and for field-grown cotton (Gossypium L.), maize (Zea mays) and alfalfa (Medicago sativa L.) crops. Root water uptake was calculated from the water balance of each layer in lysimeters. Water uptake rate was proportional to root length density at high soil water potentials, for both horse bean and oat plants, but root water uptake did not depend on root density for horse bean at potentials lower than −25 kPa. We observed a linear dependency of a critical soil water potential on the logarithm of root length density for all plants studied. Soil texture modified the critical water potential values, but not the linearity of the relationship. B E Clothier Section editor     

水体溶氧影响陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)对完全水淹的耐受力

溶氧是水环境中一个重要的环境因子,为了探讨水中的溶氧含量水平是否会对陆生植物的耐淹能力造成影响,研究了陆生植物喜旱莲子草(Alternanthera philoxeroides)和牛鞭草(Hemarthria altissima)在遭受不同溶氧含量水体完全淹没后的生长表现、存活情况和非结构碳水化合物的变化。实验结果表明:(1)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的存活。受高溶氧水体完全水淹的喜旱莲子草和牛鞭草主茎的完好程度和存活叶的数量均显著高于遭受低溶氧水体完全水淹的喜旱莲子草和牛鞭草,喜旱莲子草和牛鞭草在高溶氧水体完全水淹后的生物量比低溶氧水体完全水淹后要高;(2)水体中的溶氧含量显著影响了处于完全水淹环境中的喜旱莲子草和牛鞭草的生长,受高溶氧水体完全水淹的喜旱莲子草主茎伸长生长和不定根生长显著强于受低溶氧水体完全水淹的喜旱莲子草,在不定根的生长上牛鞭草也具有同样的表现。(3)高溶氧水环境有利于减小被完全淹没的喜旱莲子草和牛鞭草的碳水化合物消耗,两种植物在受高溶氧完全水淹后体内具有的非结构性碳水化合物含量均比受低溶氧完全水淹后高。(4)喜旱莲子草比牛鞭草能更好地耐受完全水淹,当处于低溶氧完全水淹时表现得更为明显,本研究表明入侵物种喜旱莲子草比本地物种牛鞭草具有更强的环境适应能力和水淹耐受能力。