Variation In Water Potential Research Articles

Drought response strategies of vascular epiphytes in isolated pasture trees in a Costa Rican tropical montane landscape.

Vascular epiphytes of tropical montane cloud forests are vulnerable to climate change, particularly as cloud bases elevate and reduce atmospheric inputs to the system. However, studies have generally focused on epiphytes in contiguous forests, with little research being done on epiphytes on isolated pasture trees. We investigated water relations of pasture-tree epiphytes at three sites located below and above the elevation of the average cloud base in Monteverde, Costa Rica. We measured sap velocity and four microclimate variables in both the dry and wet season of 2018. We also measured functional traits, including pressure volume (PV) curves, predawn/midday water potential, and various lab-based water relations traits. We used linear mixed models to assess the correlation between microclimate and sap velocity in both seasons and ANOVA to assess the variation in PV curve and water potential variables. The turgor loss point generally increased from the wettest to driest site. However, this trend was driven primarily by the increasing prevalence of leaf succulence at drier sites. Microclimatic variables correlated strongly with sap velocity in the wet season, but low soil moisture availability caused this correlation to break down during the dry season. Our results emphasize the vulnerability of cloud forest epiphytes to rising cloud bases. This vulnerability may be more severe in pasture trees that lack the potential buffer of surrounding forest, but additional research that directly compares the canopy microclimate conditions between forest and pasture trees is needed to confirm this possibility.

Host preference and physiological performance of the invasive hemiparasite of coastal communities <i>Cassytha filiformis</i> L. (Lauraceae)

Background: Invasive parasitic species have barely been studied despite their impact on the communities they invade. Questions: What is the host range used by the invasive parasite Cassytha filiformis in the coastal scrubland of northern Yucatan? Does C. filiformis show host preference? Does the physiological performance of C. fliformis (water deficit and chlorophyll content) vary among hosts on which it establishes and reproduces? Study species: Cassytha filiformis, an invasive hemiparasitic vine of coastal communities. Study sites and dates: Telchac, Yucatán, México. The study lasted from October 2022 to June 2023. Methods: The incidence of C. filiformis parasitism was recorded. Histological analysis confirmed parasitism, and the water potential and chlorophyll concentration of C. filiformis in its main hosts were determined. Results: C. filiformis parasitized 10 species, showing a preference for shrubs. Its main hosts were Scaevola plumieri, Phitecellobium keyense and Croton punctatus. Differences between hosts were observed in water potential variation and total chlorophyll concentration. Differences between stem types (young and mature) in chlorophyll concentration were also observed. Conclusions: C. filiformis prefers shrub species to establish. The physiological performance of C. filiformis varied depending on host identity. Differences in chlorophyll concentration between stem types of C. filiformis suggest functional physiological differences between them.

Nearly instantaneous stem diameter response to fluctuations in the atmospheric water demand.

Changes in vapour pressure deficit can lead to the depletion and replenishment of stem water pools to buffer water potential variations in the xylem. Yet, the precise velocity at which stem water pools track environmental cues remains poorly explored. Nine eucalyptus seedlings grown in a glasshouse experienced high-frequency environmental oscillations and their stem radial variations (ΔR) were monitored at a 30-s temporal resolution in upper and lower stem locations and on the bark and xylem. The stem ΔR response to vapour pressure deficit changes was nearly instantaneous (<1min), while temperature lagged behind stem ΔR. No temporal differences in the stem ΔR response were observed between locations. Punctual gravimetric measurements confirmed the synchrony between transpiration and stem ΔR dynamics. These results indicate (i) that stem-stored water can respond to the atmospheric evaporative demand much faster than commonly assumed and (ii) that the origin of the water released to the transpiration stream seems critical in determining time lags in stem water pool dynamics. Near-zero time lags may be explained by the high elasticity of eucalyptus woody tissues and the predominant water use from the xylem, circumventing the hydraulic radial barriers to water flow from/to the outer tissues.

Study on Spatiotemporal Transport Characteristics of Soil Moisture in Layered Heterogeneous Vadose Zone Based on HYDRAS-3D

The heterogeneity of layered soils affects the transport processes of water in the vadose zone. However, the mechanism of soil moisture transport in the vadose zone under heterogeneous media conditions, especially the three-dimensional transport mechanism, is a frontier problem to be studied. In order to reveal the law of soil water transport in the vadose zone under heterogeneous media, this paper constructs a three-dimensional model of water transport using HYDRAS-3D (V 2.x) software through in situ tests of water transport in 3 × 3 × 4 m sample and verifies and analyzes the model. The vertical distribution and variability of soil water content and the temporal and spatial rules of soil water transversal transport at the soil–layer interface were analyzed. The results indicate that after adjusting the parameters in the HYDRAS-3D model using measured values, the simulation results are reasonable, and the model has high reliability. To represent the water content variability characteristics of the test tube profile, water movement in the vadose zone was classified as follows: (I) steady period (April–September, less affected by rainfall), (II) slow change period (January–March), and (III) rainfall rapid change period (June, when the impact of rainfall on the test cylinder was greater). The two largest values of the soil water potential variation gradient, 19.9 and 17.8 cm/d, were observed in the silty clay layer of the test cylinder, and the influence of evaporation and infiltration in the silty clay layer was most notable at the interface. The lateral transport of soil water at the interface was influenced to a certain degree by the layered heterogeneity, wherein the fine sand layer exhibited the most pronounced impact. This was followed by silt and silty clay layers, with the silt layer showing the lowest degree of influence. The research results can provide scientific reference for the rational planning of water resources in the Yinchuan Plain.

Sap flow and transpiration of young Brazilian mahogany plants submitted to soil water potential variation

Brazilian mahogany (Swietenia macrophylla King) is a forest species of economic and environmental interest due to its wood’s great finish and its use in recovering and recomposing ecosystems. However, clarification on how this species uses water resources is still necessary. This study proposes to evaluate sap flow and transpiration behavior in young Brazilian mahogany plants under variable conditions of soil water potential. We conducted the study in a protected environment and cultivated the plants in weighing lysimeters wherein the soil underwent potential variations between -10 kPa and -35 kPa during periods of water restriction, rehydration, and full irrigation. To quantify water use in the mahogany plants, we measured sap flow through heat pulses, transpiration through the weighing lysimeters, and evapotranspiration by weather variables. Sap flow and transpiration are affected negatively by soil water potential variation. The leaves lost water to the atmosphere under water deficit conditions, even with the absence of upward sap flow. Sap flow was restored four days after irrigation had resumed.

Variation in the water use and gas exchange of two Brazilian tropical dry forest phytophysiognomies in response to successional stage

Water availability is the main limiting factor to plants growth in tropical dry forests, influencing vegetation ecophysiological responses throughout ecological succession. In this study, we analyzed the water potential and gas exchange in two phytophysiognomies of a Brazilian tropical dry forest, along a chronosequence and in moments of low and high VPD. We selected an area of Crystalline Caatinga (CC) and Arboreal Caatinga (AC), and in both sites delimited three plots at different successional stages (initial, intermediate, and late). At each collection site within areas at each successional stage, we sampled the four most abundant species. For CC plants, water potential and gas exchange were similar at all successional stages, regarding VPD, and higher than in AC site. Trees growing in the AC site showed more plastic responses than those in the CC area, mainly in gas exchange, whereas CC plants (mainly herbs) showed a higher variation in water potential. We established that this differential response occurred due to the structure of the plant community and soil water availability. Trees’ leaf traits tend to present long-term responses, and we observed that vegetation in the AC site showed most markedly differences among successional stages than plants in CC site.

Salinity effects on water potential and the normalized difference vegetation index in four species of a saline semi-arid ecosystem.

This study was carried out during January 2020–December 2020 in a semi-desert ecosystem in southern Sonora, Mexico, to determine the annual and daily variations in water potential and the normalized difference vegetation index (NDVI) of Bursera fagaroides Engl., Monogr. Phan., Parkinsonia aculeata L., Sp. Pl.; Prosopis laevigata (Humb. & Bonpl. ex Willd.), and Atriplex canescens (Pursh) Nutt. Soil electrical conductivity, cation content, and physical characteristics were determined at two depths, and water potential (ψ) was measured in roots, stems, and leaves. The daily leaf ψ was measured every 15 days each month to determine the duration of stress (hours) and the stress intensity (SI). The electrical conductivity determinations classified the soil in the experimental area as strongly saline. A significant difference was noted in electrical conductivity between soil depths. The four studied species showed significant gradients of ψ in their organs. In this soil, all four species remained in a stressed condition for approximately 11 h per day. The mean SI was 27%, and B. fagaroides Engl., Monogr. Phan. showed the lowest value. The four species showed increased NDVI values during the rainy months, with P. laevigata (Humb. & Bonpl. ex Willd.) and Parkinsonia aculeata L., Sp. Pl. showing the highest values. The capacity for ψ decrease under saline conditions identified A. canescens (Pursh) Nutt., B. fagaroides Engl., Monogr. Phan. and P. aculeata L., Sp. Pl. as practical and feasible alternatives for establishment in saline soils in southern Sonora for purposes of soil recovery and reforestation.

Stomatal regulation and water potential variation in European beech: challenging the iso/anisohydry concept.

The iso/anisohydric continuum has been used to classify tree species' drought response strategies. The range over which stomata are regulating leaf water potential (ψl) before turgor loss occurs can be described with metrics such as the dependence of ψl on soil water potential (ψsoil) and the size of 'hydroscape area' (HA), but corresponding field data from adult trees are scarce. We examined the stomatal conductance (gs)-ψl relationship in its temporal (diurnal vs seasonal and interannual) and spatial (within-crown vs between-site) variation in European beech, using extensive ψl and gs measurements in the canopy of four beech stands across a precipitation gradient, and complemented the data set by published ψl and gs measurements in further Central European beech stands (including the extreme 2018 drought) in order to cover the full water potential operation space of the species. Both metrics characterize beech as a strictly anisohydric species with δψl/δψsoil>>1 and HA=4MPa2. However, stomates close sensitively in response to increasing vapor pressure deficit, disproving the widely assumed dependence of large ψl variation on looser stomatal control. Characterizing the water status regulation mechanisms of trees requires separating diurnal from day-to-day variation in ψl and gs. The large diurnal and seasonal ψl variation in beech leaves is partly caused by a low leaf tissue elasticity, suggesting that a whole-plant perspective with consideration of osmotic and elastic tissue properties and stem and root hydraulics is needed for fully understanding ψl regulation and the drought tolerance strategy of trees.

Drought responses and phenotypic plasticity of Maprounea guianensis populations in humid and dry tropical forests

Abstract The wide distribution of Maprounea guianensis populations in contrasting environments (dry and humid forests) in the Chapada Diamantina, northeastern Brazil, can indicate the phenotypic plasticity of this species in relation to seasonal rainfall, drought regimes, and soil characteristics at different sites. Functional traits were measured in five individuals in each vegetation types. Water potential, succulence, thickness and density leaf, were evaluated during the dry and rainy periods; wood density and the saturated water content of the wood were evaluated in rainy period. Rainfall was monitored monthly for two years. The functional traits and the phenotypic plasticity indices (PPI) were submitted to analysis of variance. Our results demonstrated seasonal and spatial variations in plant functional traits. We found a low capacity for storing water in leaves and woody tissues, associated with soil properties and the seasonal rainfall/drought regimes, conditioning water potential variations that were greatest during the rainy season. Local environmental parameters influenced variations in the functional traits of M. guianensis populations, reflecting phenotypic plasticity. We highlight the connections between drought regimes and plant responses, demonstrating the importance of functional traits associated with water availability (especially water potential). Our study evidences the factors associated with the wide distribution of M. guianensis.

Comparing water potential variables under different water stress levels: a case study on Carménère grapevines

Comparing water potential variables under different water stress levels: a case study on Carménère grapevines

No local adaptation in leaf or stem xylem vulnerability to embolism, but consistent vulnerability segmentation in a North American oak.

Vulnerability to embolism varies between con-generic species distributed along aridity gradients, yet little is known about intraspecific variation and its drivers. Even less is known about intraspecific variation in tissues other than stems, despite results suggesting that roots, stems and leaves can differ in vulnerability. We hypothesized that intraspecific variation in vulnerability in leaves and stems is adaptive and driven by aridity. We quantified leaf and stem vulnerability of Quercus douglasii using the optical technique. To assess contributions of genetic variation and phenotypic plasticity to within-species variation, we quantified the vulnerability of individuals growing in a common garden, but originating from populations along an aridity gradient, as well as individuals from the same wild populations. Intraspecific variation in water potential at which 50% of total embolism in a tissue is observed (P50 ) was explained mostly by differences between individuals (&gt;66% of total variance) and tissues (16%). There was little between-population variation in leaf/stem P50 in the garden, which was not related to site of origin aridity. Unexpectedly, we observed a positive relationship between wild individual stem P50 and aridity. Although there is no local adaptation and only minor phenotypic plasticity in leaf/stem vulnerability in Q.douglasii, high levels of potentially heritable variation within populations or strong environmental selection could contribute to adaptive responses under future climate change.

Below-ground hydraulic constraints during drought-induced decline in Scots pine

Below-crown hydraulic resistance, a proxy for below-ground hydraulic resistance, increased during drought in Scots pine, but larger increases were not associated to drought-induced defoliation. Accounting for variable below-ground hydraulic conductance in response to drought may be needed for accurate predictions of forest water fluxes and drought responses in xeric forests. Hydraulic deterioration is an important trigger of drought-induced tree mortality. However, the role of below-ground hydraulic constraints remains largely unknown. We investigated the association between drought-induced defoliation and seasonal dynamics of below-crown hydraulic resistance (a proxy for below-ground hydraulic resistance), associated to variations in water supply and demand in a field population of Scots pine (Pinus sylvestris L.) Below-crown hydraulic resistance (rbc) of defoliated and non-defoliated pines was obtained from the relationship between maximum leaf-specific sap flow rates and maximum stem pressure difference estimated from xylem radius variations. The percent contribution of rbc to whole-tree hydraulic resistance (%rbc) was calculated by comparing stem water potential variations with the water potential difference between the leaves and the soil. rbc and %rbc increased with drought in both defoliated and non-defoliated pines. However, non-defoliated trees showed larger increases in rbc between spring and summer. The difference between defoliation classes is unexplained by differences in root embolism, and it is possibly related to seasonal changes in other properties of the roots and the soil-root interface. Our results highlight the importance of increasing below-ground hydraulic constraints during summer drought but do not clearly link drought-induced defoliation with severe below-ground hydraulic impairment in Scots pine.

Seasonal Variation of Some Bioactive Compounds and Physiological Characteristics in Peony (Paeonia lactifl ora Pall.)

We determined the phenolic and total flavonoid contents and some physiological characteristics (water potential, chlorophyll fluorescence, chlorophyll index) of Paeonia lactiflora Pall., growing in the Botanical Garden, Mongolian Academy of Sciences. Cultivated plants were harvested at the beginning of vegetation (May), flowering (June), seed formation (July), seed dispersal (August) and end of vegetation season (September). Phenolic content in leaf and stem was increased during the vegetation period and the highest level was reached during the seed formation stage, and it decreased at the end of the vegetation stage. On the contrary, the total flavonoid content in leaf and stem is decreased linearly as the development stages advanced and the highest level was observed at the flowering stage. Variations of water potential, chlorophyll fluorescence and chlorophyll index of cultivated P. lactiflora, increase at the beginning of vegetation and flowering stages, and decrease from seed formation stage to end of the vegetation stage.

Susceptibility to postharvest peel pitting in Citrus fruits as related to albedo thickness, water loss and phospholipase activity

To study the influence of albedo thickness and phospholipase activity on the incidence of postharvest peel pitting (PP) in citrus fruit the tangor Ortanique, mandarin, with a thin albedo and tolerant to peel pitting were compared to that of the sensitive Navelate Navel orange with a thick albedo. Fruit from both cultivars was subjected to identical postharvest practices consisting of washing and/or waxing on a commercial packline and thereafter the fruit was stored for 3 weeks at 30% or 90% relative humidity (RH). For comparison, other fruit lots were washed manually and stored as above. Periodically, water loss, water, osmotic and turgor potentials were monitored and peel pitting incidence was evaluated. For both cultivars fruit weight loss was higher in packline than in manually processed, however, only ‘Navelate Navel’ orange fruit developed peel pitting with higher incidence in the packline treatments compared with manually processed fruit. In addition, wax coating exacerbated this effect leading to higher pitting of ‘Navelate Navel’ orange. Accordingly, water potential variations were more pronounced in wax coated fruit from ‘Navelate Navel’ orange as compared to ‘Ortanique’ mandarin. Furthermore, Phospholipase D and A2 (PLD and PLA2) activities were higher in the peel from the pitting susceptible cultivar, suggesting their activation by sharper changes in peel water potential. Collectively, results suggest that water movement through cell layers in a thick albedo is related to postharvest peel pitting and support the notion that inability to properly adjust water status in peel tissue after prolonged water stress results in cell collapse and tissue damage. Moreover, enhanced phospholipase activity appears to be also a response of peel tissues to conditions causing peel pitting.

Herb Hydraulics: Inter- and Intraspecific Variation in Three Ranunculus Species.

The requirements of the water transport system of small herbaceous species differ considerably from those of woody species. Despite their ecological importance for many biomes, knowledge regarding herb hydraulics remains very limited. We compared key hydraulic features (vulnerability to drought-induced hydraulic decline, pressure-volume relations, onset of cellular damage, in situ variation of water potential, and stomatal conductance) of three Ranunculus species differing in their soil humidity preferences and ecological amplitude. All species were very vulnerable to water stress (50% reduction in whole-leaf hydraulic conductance [kleaf] at -0.2 to -0.8 MPa). In species with narrow ecological amplitude, the drought-exposed Ranunculus bulbosus was less vulnerable to desiccation (analyzed via loss of kleaf and turgor loss point) than the humid-habitat Ranunculus lanuginosus Accordingly, water stress-exposed plants from the broad-amplitude Ranunculus acris revealed tendencies toward lower vulnerability to water stress (e.g. osmotic potential at full turgor, cell damage, and stomatal closure) than conspecific plants from the humid site. We show that small herbs can adjust to their habitat conditions on interspecific and intraspecific levels in various hydraulic parameters. The coordination of hydraulic thresholds (50% and 88% loss of kleaf, turgor loss point, and minimum in situ water potential) enabled the study species to avoid hydraulic failure and damage to living cells. Reversible recovery of hydraulic conductance, desiccation-tolerant seeds, or rhizomes may allow them to prioritize toward a more efficient but vulnerable water transport system while avoiding the severe effects that water stress poses on woody species.

平潭岛典型海岸草丛沙堆植物群落水势日变化特征及其影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 平潭岛典型海岸草丛沙堆植物群落水势日变化特征及其影响因素 DOI: 10.5846/stxb201411172277 作者: 作者单位: 中山大学地理科学与规划学院,中山大学地理科学与规划学院,中山大学地理科学与规划学院,中山大学地理科学与规划学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(41101011,41371030);中央高校基本科研业务费专项资金(121gpy15) Diurnal variations of water potential and its influencing factors in typical plant communities on coppice dunes of pingtan island Author: Affiliation: School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University,School of Geography and Planning,Sun Yat-Sen University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:水势是反映植物受到环境胁迫的重要指标之一,可用来确定其受胁迫的程度和适应能力大小。以福建省平潭岛海岸典型沙生植物老鼠艻(Spinifex littoreus)形成的草丛沙堆为研究对象,选取晴朗无云的天气,采用PSYPRO水势测量系统对其植物叶、茎水势及其所形成的沙堆土壤水势进行测定,同时采用HUMIPORT10手持式温湿度计对当日的气象要素进行同步观测。结果表明:(1)老鼠艻的叶水势呈现出与早晚高午间低相反的反梯度现象,叶、茎水势的日变化均表现为"M"型变化趋势,除18:00后,其它时间均表现为叶片水势下降、茎干水势上升,并且发现叶、茎水势的变化趋势存在位相后移现象;(2)老鼠艻的叶、茎水势在10:00时差异达到最大的0.65MPa,且茎水势高于叶水势,在14:00左右,植物茎水势出现低于叶水势的反常现象,在18:00时叶、茎水势趋于相同;(3)除表层30cm外,其它层土壤水势日变化特征总体表现为从早晨开始下降,14:00达到最低,但总体变化不明显;(4)随着深度增加,草丛沙堆土壤水势呈现为依次增加的趋势,但80cm以下土壤水势变化不显著(P > 0.1);(5)叶水势与大气水势具有较好的相关性,且变化显著(P < 0.1),与茎水势及浅层土壤水势有一定相关性,但变化不显著(P > 0.1),与50cm以下土壤水势均无相关性。 Abstract:Water potential is one of the most important factors that reflect environmental stress on plants, and can be used to identify the level of stress a plant experiences and its adaptation ability. This study focused on the coppice dunes formed by the psammophyte Spinifex littoreus on Pingtan Island, Fujian province. The PSYPRO Water Potential System was used to determine the water potential of the leaves, stems, and soil, and a HUMIPORT10 hand-held hygrometer was used to simultaneously measure the meteorological variables on cloudless, sunny days. Spinifex littoreus showed an opposite pattern of leaf water potential, which is in contrast to the normal phenomenon of increased leaf water potential in the morning and evening compared to that at midday. The diurnal variations of leaf and stem water potential all demonstrated an 'M’ curve pattern, indicating a decrease of leaf water potential and increase of stem water potential in daytime, until 18:00. Furthermore, we found that the changes of leaf water potential occurred later than those of stem water potential. The biggest discrepancy between stem and leaf water potential, reaching 0.65MPa, appeared at 10:00, when stem water potential was higher than leaf water potential. At about 14:00, an abnormal phenomenon appeared, in which leaf water potential was higher than stem water potential, but at about 18:00, leaf and stem water potential tended to be the same. With the exception of soil water potential at 30cm, the diurnal variation of soil water potential showed a decrease starting in the morning, which reached the minimum at 14:00; however, this tendency was not statistically significant(P > 0.1). With increasing depth, the soil water potential showed a tendency to increase, but this trend disappeared below a depth of 80cm. Strong correlations and significant changes (P < 0.1) in water potential were observed between the atmosphere water potential and leaf. Leaf, stem, and 30-cm-deep soil water potential showed some correlations, but the variations were not statistically significant (P > 0.1). Leaf water potential was not correlated with the water potential of soil at other depths. 参考文献 相似文献 引证文献

Limitations and usefulness of maximum daily shrinkage (MDS) and trunk growth rate (TGR) indicators in the irrigation scheduling of table olive trees

Maximum daily trunk shrinkage (MDS) is the most popular indicator derived from trunk diameter fluctuations in most fruit trees and has been reported to be one of the earliest signs in the detection of water stress. However, in some species such as olive trees (Olea europaea L.), MDS does not usually change in water stress conditions and trunk growth rate (TGR) has been suggested as better indicator. Most of this lack of sensitivity to drought conditions has been related to the relationship between the MDS and the water potential. This curvilinear relationship produces an uncertain zone were great variations of water potential do not imply any changes of MDS. The MDS signal, the ratio between measured MDS and estimated MDS with full irrigation, has been thought to be a better indicator than MDS, as it reduces the effect of the environment.. On the other hand, though literature results suggest an effect of environment in TGR values, there are not clear relationship between this indicator and meteorological data. The aims of this work are, on one hand, to study the improvements of the baseline approach in the MDS signal and, on the other, study the influence of several meteorological variables in TGR. Three years’ data from an irrigation experiment were used in to carry out the MDS analysis and six years’ data for full irrigated trees during pit hardening period were used for TGR study. The comparison between MDS vs. water potential and MDS signal vs. water potential presented a great scattering in both relationships. Values of MDS signal between 1.1 and 1.4 were always identified with moderate water stress conditions (−1.4 to −2MPa of water potential). However, since this MDS signal values are around the maximum in the curvilineal relationship with water potential, greater values of MDS signal (in the range of 1.1–1.4) were not necessary lower values of water potential. In addition, during low fruit load seasons MDS signal was not an accurate indicator. On the other hand, absolute values of several climatological measurements were not significantly related with TGR. Only daily increments explain part of the variations of TGR in full irrigated trees. In all the data analysed, the daily increment of average vapour pressure deficit was the best indicator related with TGR. The increase of this indicator decreased TGR values. In addition, the agreement between this indicator and TGR was affected for fruit load. Great yield seasons decrease the influence of VPD increment in TGR.

Bioavailability of the Nano-Unit 14C-Agrochemicals Under Various Water Potential.

The study was conducted to investigate the effects of water potential on bioavailability of the nano-unit 14C-cafenstrole, 14C-pretilachlor, 14C-benfuresate, 14C-simetryn and 14C-oxyfluorfen applied with or without dimepiperate or daimuron under various water potential conditions. The highest bioavailable concentration in soil solution (BCSS) was found at 60% soil moisture, while the lowest occurred at 50% soil moisture for soil-applied alone or in combination. All water potential conditions differed significantly from each other with variations in total bioavailable amount in soil solution (TBSS) when either dimepiperate or daimuron were added to the soil, and changes were directly proportional to variations in water potential. Across all treatments, TBSS at 80% soil moisture was three to four times greater than that at 50% soil moisture when applied alone or in combination with dimepiperate or daimuron. Cafenstrole and simetryn had distribution coefficient (Kd) values <64 ml g-1 and a TBSS ranging from 10 to 44 ng g-1 soil, regardless of water potential conditions applied alone or in combination. Pretilachlor and benfuresate had Kd values <15 ml g-1 and a TBSS range of 38 to 255 ng g-1 soil when applied with or without dimepiperate or daimuron.

Variación familial en plántulas de Pinus leiophylla Schiede ex Schltdl. &amp; Cham. en respuesta a la sequía: potencial hídrico y osmótico

La variación de plántulas de cuatro familias de Pinus leiophylla de diferentes procedencias se evaluó en respuesta a la sequía, considerando las variables potencial hídrico (Ψa), potencial osmótico (Ψ0), componentes y asignación de biomasa. Las familias de P. leiophylla se localizan en un huerto semillero del Colegio de Postgraduados en el Estado de México. El estudio se hizo con el fin de identificar los genotipos resistentes al estrés hídrico. Después de 26 días sin riego, 50 % de las plántulas presentaron decaimiento permanente del ápice del tallo, con Ψa = -3.35 MPa y Ψ0 = -3.23 MPa, lo que representó disminución de 596 y 112 %, respectivamente, por efecto de la sequía. La acumulación de biomasa también fue afectada significativamente (P = 0.05) en las familias evaluadas, a excepción de la procedente de San Rafael. En promedio, la biomasa de la raíz de las plántulas en sequía fue 38 % menor que las plántulas sin sequía. Las familias de P. leiophylla provenientes de San Juan Tetla y de Santa María Atepetzingo (ambas del estado de Puebla) presentaron mejor respuesta al estrés impuesto, mientras que la familia de Tlalmanalco (Estado de México) fue la más afectada.

Experimental analysis of the water retention behaviour of shales

Shales are among the most commonly considered geomaterials in current energy-related geomechanical investigations, as they are involved in engineering applications such as the extraction of natural gas, CO2 sequestration and nuclear waste storage. A deep understanding of their behaviour with regard to variations in the degree of saturation is of significance for such applications. With the aim to establish a sound protocol for shale retention behaviour analysis, this paper presents an experimental methodology that takes into account the specificities of shales such as small pore size dimensions and the large variations in water potential to be applied to induce significant changes in the degree of saturation. The technique involves the direct control of the shale water content and the subsequent measurement of the suction at equilibrium by a psychrometer. A fluid displacement technique with a non-polar liquid is also used to assess the volume changes of the shale and to compute the degree of saturation. Selected test results are presented for various shale samples that have been cored at different depths. The results indicate that important features of the retention behaviour of geomaterials are fundamental aspects to be considered when analysing the retention behaviour of shales, such as the existence of main wetting and drying paths, the hysteresis domain, and the dependency of the air entry value on the void ratio.