Water Potential

Evaluation of soybean [Glycine max (L.) Merrill] seeds vigor and its relation with field seedling emergence can provide secure indicatives of seed physiological potential. The present research studied the relationship between the electrical conductivity test and the seedling emergence of soybean in field and laboratory. The field experiment was sown in November 26th, December 3td and 10th, 2000. Laboratory tests were performed using levels of water potential in the substrate (soil) -0.03; -0.2; -0.4; and -0.6 MPa. Fourteen seed lots, seven of 'Embrapa 48' and seven of 'BRS 133' soybean cultivars were used. Laboratory tests comprised seed water content determination, before and after the accelerated aging; germination and vigor tests (accelerated aging and electrical conductivity). Germination and seedling emergence decreased as the substrate water potential was reduced, indicating a relationship among the germination, water potential and seed vigor. For the 'Embr...

Intra-specific variability can be used as
an important tool to contrast and mitigate the negative
impacts of climate change. In particular, under
Mediterranean climate conditions drought stress is
becoming a crucial issue for growers. Vine performance,
taking into account vine yield and grape composition,
is dependent on the vine capability of assimilating
CO2 and fix it into carbohydrates throughout the
growing season. Under water stress, stomatal regulation,
that allow plants to prevent excessive water loss
and t issue drying, l imi ts leaf gas exchanges.
Understanding the mechanisms regulating stomatal
closure is crucial to determine the behaviour of genotypes
under water stress. Two main mechanisms are
accredited for controlling stomatal conductance under
water stress: active mechanisms, based on the
biosynthesis of hormonal signals, mainly abscisic acid
(ABA), and passive mechanisms, mainly based on
the variation of leaf turgor pressure as the plant water
potent ial decreases dur ing water stress. New
research evidences pointed out that the capability of
genotypes to close stomata at a given stem water
potential threshold was correlated with its xylem vulnerability
to cavitation. ABA accumulation in the leaf
appears to be subsequent to stomata closure suggesting
that, in vivo, stomatal conductance mainly rely
to passive mechanism rather than to active ones.
Hydraulic properties of each genotype appear to control
their stomatal behavior under water stress consistently
with the rising opinion that intraspecific variability
of stomatal behavior cannot be discriminated into
two different categories (isohydric and anisohydric)
but should be represented as a continuum of genotypes
with different levels of anisohydry. These results
underline the need to learn more about the phenotype
of grape cultivars. Growers will be able to use such
information by planting more tolerant genotypes
depending on vineyard conditions and to use different
water potential thresholds for irrigation scheduling.

Le Liban est un pays méditerranéen avec une superficie de 10 452 km2, dont 65 % sont karstiques, il est considéré riche en eaux superficielles et souterraines, mais en dépit de cette richesse, le Liban montre une pénurie en eau à cause de la mauvaise gestion des ressources hydriques et de la variation interannuelle des pluies (6 à 7 mois de sécheresse). Cette situation hydrique nécessite le lancement des recherches ayant pour objectif la résolution du problème du manque en eau.
Ce travail a pour objective de déterminer les zones favorables à la recharge du bassin versant Abou Ali (Liban Nord) en se basant sur une approche cartographique, utilisant ainsi le système d’information géographique (SIG). La détection de ces zones potentielles de recharge de la nappe nécessite un croisement des informations spatiales relatives aux différents paramètres (lithologie, sol, densité de fracture, densité de drainage, pente et l’occupation du sol) influençant la recharge cartographiée. Une reclassification suivie d’une pondération de ces paramètres a été effectuée selon leur degré d’influence dans le processus de recharge et suivant une analyse de l’index de score cumulatif CSI. Ces paramètres analysés sont par la suite intégrés dans un SIG afin d’établir la carte des zones potentielles de recharge de la nappe souterraine. L’application du modèle de potentialité hydrique montre que 13 % de la superficie du bassin présente une potentialité hydrique très forte surtout au sud-est, 39 % montre une potentialité moyenne dans les zones ayant une lithologie marno-sableuse et calcaire-marneuses, et 20 % dénotent une potentialité faible surtout à l’ouest et au centre du bassin.

Fraser fir ( Abies fraseri (Pursh) Poir.) is an endemic tree species found only in refugial mountain-top forests in the southern Appalachian Mountains, USA. Very few studies have investigated the ecophysiology of this species in its natural environment. We measured and compared photosynthetic gas exchange and water relations of understory germinant seedlings (<3 cm height), older seedlings (>3 years old and ~0.15–1 m tall), and saplings (>10 years old and ~1–2 m tall) on a leaf-level basis. No significant differences in gas exchange were found among the age classes, although midday xylem water potentials were significantly different among the age classes. Differences in maximum photosynthesis (Amax) were <13%, ranging between 2.4 and 2.7 μmol·m–2·s–1 (P = 0.26). Maximum leaf conductances (gmax) were between 0.16 and 0.18 mol·m–2·s–1, varying less than 13% (P = 0.15). Midday xylem water potentials were similar between SE and SA (–1.2 to –1.4 MPa), but GS values were signi...

In the granite-gneiss basement of the Zou basin, drinking water access
is mainly provided by fracture aquifers. In order to facilitate the borehole
drilling, this study, on one hand, established the fracture map and on the other hand evaluated the groundwater potential in this part of Benin. First, Sobel directional filters are used to extract a representation of the fracture network. From these data, three majority directions are identified: N180-N30, N90-N110 and N60-N70. Other minority groups, in particular, N130-N140, also affect these crystalline and crystallophyllian formations. The fracture lengths are concentrated in a range of 1 to 2 km (65 %) and the extreme values lower than 1 km and greater than 2 km are respectively 12.7 % and 22 %. This set of direction reveals an average fracture density of 2.4 km.km-2 with areas such as the South of Iroukou having low values (0.8 ± 0.9 km.km-2) and high values in Dassa (5.2 ± 0.9 km.km-2). These results are useful for drilling because more than 60% of boreholes located within 200 m of an identified fracture is positive. In addition, other maps such as alteration thickness, lithology, drainage, rainfall, and slope are confronted with fracture density using multi-criteria decision analysis. Based on the contribution of each map to groundwater availability, the weights are 0.158, 0.074, 0.126, 0.302, 0.065 and 0.275, respectively. It turns out after spatial analysis that the basin is characterized by a very low (9.2 %) to low (18 %) potential towards Djidja, Gangan and Glazoué, moderate (24.7 %) in the Zoudji and Yagbo and good (27.5 %) to very good (20.6 %) around Savalou. The water potential of these blocks of aquifers can change significantly even at the local scale. Despite the constraints, these resources are essential to achieving the Sustainable Development Goal 6 in the basin, of course after a thorough study of the aquifers in order to guarantee drinking water supply of the populations and the durability of the boreholes.

SUMMARY Acacia karroo is a leguminous tree listed in most of the Algerian territory. It is a salt-tolerant species and a multipurpose tree in agroforestry. However, the defence mechanisms underlying salt tolerance of this species are still unknown. In this study, the effects of salt stress on various morpho-physiological and biochemical traits of A. karroo were investigated. Three-months-old plants were submitted to increasing salt concentrations (0, 200, 400 and 600 mM NaCl), for a period of 21 days. Stem length was not significantly affected by salinity. Increasing salinity reduced the length of root. Number of leaves was maintained constant at 200 and 400 mM NaCl but was reduced slightly at 600 mM NaCl. Also, an increase in crown diameter by 30% under mild and high salt stress was observed. Furthermore, salt tolerance index was not affected at all salinity levels. The leaf mass area was not affected by saline conditions. Salt treatments did not produce a notable change in the relative water content of leaves, indicating a relatively high resistance as well to dehydration, which will certainly contribute to some degree of salt tolerance in A. karroo. Relative water loss from excised leaves was significantly higher at 200 mM and similar at high concentration of NaCl as compared to control. The result of variance analysis for the major effect of salinity showed that salt stress significantly decreased the content of photosynthetic pigment in leaves at higher concentrations of NaCl. However, at 200 mM of NaCl, an enhancement of chlorophyll b, total chlorophylls and carotenoids content was observed. At the same level, chlorophyll a presented a constant content compared with control. In conclusion, although plants suffered from salt stress, as shown by the degradation of photosynthetic, they continued their vegetative growth and maintained their internal water potential under salinity conditions. Therefore, A. karroo is a potential halophytic species to be cultivated in saline lands and make it favourable for agroforestry practices.

The level of precipitation in the coastal towns & islands of the Hormozgan province is very low, but the relative humidity so high that wets the soil at below dew point temperatures and could therefore be utilized for relieving the water shortage, to some extents by employing water harvesting systems from fog & air moisture. The inhabitants of Qeshm Island have made efforts from the ancient times to collect air moisture along rainwater gathering. The reminders of these efforts are 366 small wells drilled in stone, which are now a tourist attraction. This method is also applied today in a less elaborate manner. This research has been carried out to study the feasibility of water harvesting from fog and air moisture in the coastal towns and islands of the Hormozgan province of Iran on the northern shores of the Persian Gulf. To examine the potential water in the atmosphere, the data from Bandar Abbass synoptic station with a statistical period of 1961-2005 was reviewed and the humidit...

The effect of various abiotic stresses on germination rate, growth and soluble sugar content in Sorghum bicolor (L.) Moench cv. CSH 6 seed embryos and endosperm during early germination was investigated. Under stress conditions germination, water potential and ...

This paper examines the elimination of all agricultural policy distortions in all trading countries and agricultural production decisions in the United States, as well as subsequent environmental quality in the presence and absence of nondegradation environmental standards. The results suggest that trade liberalization has the potential to increase domestic production and boost agricultural returns by as much as 8.5 percent. Consumer surplus would likely fall, and the discharge of nutrients, sediment, and pesticides would likely increase. However, environmental policies can limit these adverse environmental impacts and mute the potential decrease in consumer surplus, while leaving increased returns to agricultural production.

The cuticle of apple basically consists of a cutin and wax layer in parallel each with different diffusion properties. Diffusion coefficients were determined for the apple cultivars 'Jonagold','Jonagored'and 'Elstar'to accurately describe moisture transport through the ...

Due to the rapid expansion of irrigated agriculture, effi cient use of the limited water resources in arid and semi-arid regions is becoming more and more vital. However, water salinity is a major problem due to its negative infl uence on the yields of many crops. It reduces citrus trees' growth and causes physiological disorders. Primarily salt-stress lowers net CO2 assimilation, stomatal conductance, and water potential of citrus tree leaves, in addition to accumulation of excessive concentration of Chloride or Sodium in leaves. A great deal of research indicates that citrus have the genetic potential to be salt-sensitive; however inheritance studies in citrus are scarce. In this paper the adverse of effects of salinity on physiological aspects of citrus are reviewed. The review summarizes the prevailing state of knowledge about the responses and tolerance of citrus trees to salinity.

Soil-atmosphere interaction has implications in different scientific research contexts and is increasingly investigated through field measurements. This paper reports a detailed description of interaction between shallow soil and atmosphere at two test sites in Oltrepò Pavese area (Northern Italy). The two test sites are in the same climatic area but are characterised by different geological features. In fact, the first objective is to compare the behaviour of two different soils, namely a clayey-sandy silt (CL) and a silty clay (CH), under similar meteorological events. Soil-atmosphere interaction is studied on the basis of long-term (about 87 and 42 months for the two test sites, respectively) monitoring data of both volumetric water content and soil water potential, recorded at different depths along two vertical soil profiles in the first two metres from ground level. Field measurements, together with meteorological data such as precipitation and air temperature, allow for clear...

In 2004 the UNHCR commissioned the use of remote sensing to map the potential of buried water reservoirs in the massive Ouaddai region in eastern Chad. The UN needed to discover renewable water sources urgently and efficiently, as the challenge of providing water to Sudanese refugees and their local host communities was overwhelming. Using a proprietary process called WATEX, French exploration firm RTF analyzed a variety of remotely sensed data to identify areas suitable for refugee camps along the Chadian border near Darfur. Early results are impressive – after drilling test wells at Wadi Dalal, one of RTF’s recommended sites, the UNHCR established a major camp in early 2005, announcing that the camp has enough water to support up to 30,000 refugees. This paper provides an overview of the data and methods employed in eastern Chad. It also provides a promising example of how geospatial technologies can support humanitarian operations in arid and semi-arid regions.

The cuticle of apple basically consists of a cutin and wax layer in parallel each with different diffusion properties. Diffusion coefficients were determined for the apple cultivars 'Jonagold','Jonagored'and 'Elstar'to accurately describe moisture transport through the ...

Two models for predicting the hydration status of lichens were developed as a first step towards a mechanistic lichen productivity model. A biophysical model included the water potential of the air, derived from measurements of air temperature, relative humidity and species-specific rate constants for desiccation and rehydration. A reduced physical model, included only environmental parameters, assuming instantaneous equilibration between the lichen and the air. These models were developed using field and laboratory data for three green algal lichens: the foliose epiphytic Platismatia glauca (L.) W. Culb., the fruticose epiphytic Alectoria sarmentosa (Ach.) Ach. and the fruticose, terricolous and mat-forming Cladina rangiferina (L.) Weber ex Wigg. The models were compared and validated for the same three species using data from a habitat with a different microclimate. Both models predicted the length and timing of lichen hydration periods, with those for A. sarmentosa and P. glauca ...