Relative Water Deficit Research Articles

Analysis of leaf-architecture characteristics and ecological adaptability of tree species in the upper reaches of the Chishui River

The leaf-architecture characteristics of 15 ligneous plants of the karst region of the upper reaches of the Chishui River were assessed using spatial syntax. Furthermore, the relationship between leaf-architecture characteristics, plant functional traits, and soil water-holding capacity as well as the adaptation of plant architecture to this habitat were explored. The following results were obtained: (1) The integration, connectivity, and control of primary veins are significantly better than those of secondary veins, indicating strong interveinal ranking. The integration, connectivity, and control of evergreen tree species are superior to those of deciduous tree species, suggesting a more complex spatial morphological structure of evergreen leaves. In evergreen trees, the spatial morphological structure of tree leaves is more complex than that of shrubs, while the spatial morphological structure of tree leaves of deciduous trees is simpler than that of shrubs. (2) The dry matter content of the leaves of the investigated 15 ligneous plants ranged from 10.79 to 31.83 mg·g−1. The leaf relative water deficit, maximum net photosynthetic rate, transpiration rate, and the specific leaf area content ranged from 35.15 to 66.53%, 0.4–32 μmol·m−2·s−1, 0.07–0.71 g·cm−2·h−1, and 230.15–585.39 cm2·g−1, respectively. (3) The spatial syntax index is significantly correlated with transpiration rate, leaf relative water deficit, as well as soil maximum and available water-holding capacity. (4) Based on the spatial morphological structure of leaves, four basic modes of the leaf architecture can be classified: evergreen mode with complex morphological leaf-structure, evergreen mode with lower complex morphological leaf-structure, mixed evergreen and deciduous modes with lower complex leaf-morphological structure, and deciduous mode with simple morphological leaf-structure. (5) The spatial morphological structure of leaves in karst areas effectively exposes differences of architecture among different plants. Space syntax effectively represents leaf-architecture characteristics and is important for the study of plant architecture. Understanding plant architecture characteristics and their adaptation to the environment provides a scientific basis for the selection of tree species and planting patterns in the vegetation restoration area.

More sensitive to drought of young tissues with weak water potential adjustment capacity in two desert shrubs

Water is the main limiting factor for survival and growth for desert plants, and plants can alleviate water deficits under drought by adjusting water potential (Ψ). However, the water potential adjustment capacity and water-sensitivity at the tissue level among shrub species remains unclear. The objective of this study was to evaluate water potential adjustment capacity and water-sensitivity of different tissues in Artemisia ordosica and Caragana korshinskii through calculating the water relation parameters from pressure-volume (P-V) curves. The present study found that the sensitivity coefficients, −1/β and −1/b, were gradually decreased with increasing degree of lignification in A. ordosica and C. korshinskii, suggesting that younger tissues with low lignification are more sensitive to water deficit. Additionally, the younger tissues with more negative osmotic potential at full turgor (Ψπ, sat), water potential at turgor loss point (Ψtlp), and lower the bulk modulus of elasticity (ε), the relative water deficit at turgor loss point (RWDtlp), apoplastic water fraction (AWF) and total hydraulic capacitance (Ctotal), which indicated that younger tissues have stronger turgor adjustment capacity compared to osmotic adjustment capacity and them were more easily lose water during times of decreased water potential because of higher cell wall elasticity and weaker water storage capacity. Collectively, the present study highlighted that younger tissues are more sensitive to drought due to their weaker water potential adjustment capacity and provided critical insight into water physiological mechanism or sensitivity of species to drought.

Light response process and simulation of Dendrocalamopsis oldhami in the process of gradual water loss.

The photosynthesis response of the leaves of 2-year-old potted Dendrocalamopsis oldhami seedlings under continuous and multistage soil moisture was measured and analyzed by using a porta-ble photosynthetic system (Li-6400) during the natural water consumption process from artificial watering to saturated soil water. The results showed that there was less obvious photoinhibition in leaves of D. oldhami grown in the region where the relative soil water content (SRWC) was from 53.5% to 95.6%. There was a higher net photosynthetic rate in relative water deficit environment with the relative soil water content from 53.5% to 69.6%. When SRWC was below 33.6%, there was a significant photoinhibition. When the relative soil water changed, the Pn max value simulated by rectangular hyperbola model was much higher than measured value. The simulated light saturation point (LSP) value fitted by the rectangular hyperbola model, the non-rectangular hyperbola model and the exponential model was much lower than the measured value, and the simulation of the light-response curve under extreme water shortage conditions had larger differences between the fitted values and the observed data. Both the stomatal limitation value (Ls) and water use efficiency (WUEinst) showed a similar response process as the relative soil water decreased. Both of them increased first and then decreased, with the maximum value appeared in the range of 53.5%≤SRWC≤69.6%. Such a result showed a similarity and representative with the Pn max of photosynthesis light-response processes under changing soil moisture. The optimal humidity management range of SRWC for normal photosynthesis in leaves of D. oldhami was from 53.5% to 69.6%. In addition, it had good adaptability to higher soil water content (69.6%≤SRWC≤95.6%). Rectangular hyperbola modified model could well simulate the light-response of photosynthesis under different soil water conditions (23.1%≤SRWC≤95.6%), while the other three models had their own limitations.

<b>Calibration and testing of an agrometeorological model for the estimation of soybean yields in different Brazilian regions

This study was designed to calibrate and test an agrometeorological model over 18 growing seasons in three soybean production areas in Brazil: Passo Fundo (Rio Grande do Sul State), Londrina (Parana State), and Dourados (Mato Grosso do Sul State). The soybean potential yield (Yp) was determined by two methods: estimated using the FAO Agroecological Zone Model or based on the maximum yield published by the Brazilian Institute of Geography and Statistics (IBGE), increased by 10, 20 and 30%. The estimate of actual yield (Ya) was calculated by correcting Yp for the relative water deficit at different growth stages. The results showed that the best performance was obtained when the Yp was represented by the maximum yield increased by a certain percentage. The model showed satisfactory Ya estimates for the three locations, generating R 2 values of 0.64, 0.46 and 0.70, with mean absolute errors (MAE) of 303, 289 and 259 kg ha -1 for Passo Fundo, Londrina and Dourados, respectively. In a global analysis, the performance of the model was satisfactory, with an R 2 , agreement modified index (d 1 ), confidence index (C) and MAE of 0.64, 0.52, 0.71 and 300 kg ha -1 , respectively.

Quantifying Medicago sativa Yield under Deficit Irrigation Technique in Sandy Soil

Deficit irrigation technique was introduced to find the best means to conserve irrigation water in arid lands. The most common model describing deficit irrigation is water yield response model. The main advantage of such model is that it can predict relative yield drop, which arises from relative water deficit, in order to maximize the economic return. The disadvantage of the model is that it uses evapotranspiration (ET), estimated by using meteorological data, which affects the applicability of the model when there is no weather station near the field. Furthermore, the sudden changes of weather parameters and the differences of the areas covered with green plant at different growth stages might also, affect the model applicability. Therefore, the research objectives were suggesting a modified version of FAO model, using soil moisture data instead of meteorological data to provide greater accuracy and applicability and validating the proposed model. Pot experiment was conducted to achieve these objectives. Four levels of soil available water were chosen to irrigate five cultivars of Medicago sativa (as one of the most important grazing crops) cultivated in two different soils (un-reclaimed). The results showed positive linear correlation between available soil water and crop yield at all the experimental treatments. Regression equations were developed to predict crop yield resulting from water deficit. The study indicated that the maximum yield is not necessarily the optimal one to maximize the profit in arid lands. The study recommended the modified model to predict yield drop and water saving and also, presented guidelines for water management of other similar plants grown in arid lands. Research Article

A Clinical Approach to the Treatment of Chronic Hypernatremia

Hypernatremia is a commonly encountered electrolyte disorder occurring in both the inpatient and outpatient settings. Community-acquired hypernatremia typically occurs at the extremes of age, whereas hospital-acquired hypernatremia affects patients of all age groups. Serum sodium concentration is linked to water homeostasis, which is dependent on the thirst mechanism, arginine vasopressin, and kidney function. Because both hypernatremia and the rate of correction of hypernatremia are associated with significant morbidity and mortality, prompt effective treatment is crucial. Chronic hypernatremia can be classified into 3 broad categories, hypovolemic, euvolemic, and hypervolemic forms, with each form having unique treatment considerations. In this teaching case, we provide a clinically based quantitative approach to the treatment of both hypervolemic and hypovolemic hypernatremia, which occurred in the same patient during the course of a prolonged illness.

Long-term water balances in La Violada Irrigation District (Spain): II. Analysis of irrigation performance

Abstract The analysis of long-term irrigation performance series is a valuable tool to improve irrigation management and efficiency. This work focuses in the assessment of irrigation performance indices along years 1995–2008, and the cause–effect relationships with irrigation modernization works taking place in the 4000 ha surface-irrigated La Violada Irrigation District (VID). Irrigation management was poor, as shown by the low mean seasonal irrigation consumptive use coefficient (ICUC = 51%) and the high relative water deficit (RWD = 20%) and drainage fraction (DRF = 54%). April had the poorest irrigation performance because corn (with low water demand in this month) was irrigated to promote its emergence, whereas winter grains (with high water demands in this month) were not fully irrigated in water-scarce years. Corn, highly sensitive to water stress, was the crop with best irrigation performance because it was preferentially irrigated to minimize yield losses. The construction of a new elevated canal that decreased seepage and drainage fractions, the entrance in operation of six internal reservoirs that would increase irrigation scheduling flexibility, and the on-going transformation from surface to sprinkler irrigation systems are critical changes in VID that should lead to improved ICUC, lower RWD and lower DRF. The implications of these modernization works on the conservation of water quantity and quality within and outside VID is further discussed.

What is the proximate cause for size-dependent ecophysiological differences in vascular epiphytes?

Size-related variation in physiological parameters as diverse as photosynthetic capacity, abscisic acid relationships or the relative water deficit at stomatal closure have been reported for a large number of vascular epiphytes, but the proximate mechanism behind these observations has not been identified. We test four possible reasons for size-related changes in photosynthetic capacity, leaf-N content and specific leaf area: (i) plant size itself, (ii) plant age or developmental stage, (iii) previous nutrition, or (iv) previous water regime. A suite of study species and approaches were used: a 'natural experiment' with the orchid Polystachya foliosa; an experimental field study with another orchid, Dimerandra emarginata; and a study under controlled conditions with the tank bromeliad, Vriesea sanguinolenta. Neither size, age nor differences in water supply caused differences in leaf N and photosynthetic capacity, while low supply of nutrients yielded, and high supply with nutrients completely removed, size-related trends. The observed size-related trends are thus a consequence of in situ differences in nutrient acquisition. Arguably, the improved nutrient status of larger plants under natural conditions results from larger tanks, holding moisture for increasingly longer intervals, which allows longer periods of decomposition of detritus and of nutrient uptake.

Antitranspirant functions of stem periderms and their influence on corticular photosynthesis under drought stress

Transpiration and photosynthesis of current-year stems and adult leaves of different deciduous tree species were investigated to estimate their probable influence on carbon balance. Peridermal transpiration of young stems was found to be rather small as compared to the transpiration of leaves (stem/leaf like 1/5–1/20). A characteristic that was mainly attributable to the lower peridermal conductance to water and CO2, which made up only 8–28% of stomatal conductance. Water vapour conductance was significantly lower in stems, but also non-responsive to PAR, which led to a comparatively higher water use efficiency (WUE, ratio assimilation/transpiration). Thus, although corticular photosynthesis reached only 11–37% of leaf photosynthesis, it may be a means of improving the carbon balance of stems under limited water availability. The influence of drought stress on primary photosynthetic reactions was also studied. Under simulated drought conditions the drying time needed to provoke a 50% reduction (t 50) in dark- and light-adapted PSII efficiency (Fv/Fm, ΔF/Fm′) was up to ten times higher in stems than in leaves. Nevertheless, up to a relative water deficit (RWD) of around 40–50% dark-adapted PSII efficiency of leaves and stems was rather insensitive to dehydration, showing that the efficiency of open PS II reaction centres is not impaired. Thus, it may be concluded that in stems as well as in leaves the primary site of drought damage is at the level of dark enzyme reactions and not within PSII. However, enduring severe drought caused photoinhibitory damage to the photosynthetic apparatus of leaves and stems; thereby RWD50 values (= RWD needed to provoke a 50% reduction in Fv/Fm ad ΔF/Fm′) were comparably lower in stems as compared to leaves, indicating a possibly higher drought sensitivity of the cortex chlorenchyma.

Behaviour in suckling mink kits under farm conditions: effects of accessibility of drinking water

Mortality in mink kits held under conventional farm conditions is believed to be related to dehydration and at least partially to thereby associated competitive aggression. In this study we demonstrated that licking saliva from the commissure of the dam's lips might serve to complement the kits’ fluid supply in a period of relative water deficit and that increasing drinking activity is correlated with reduced aggression. Moreover, we found that easier accessibility of drinking water under farm conditions decreases saliva licking. We suggest that measuring enhanced saliva licking may be used as a possible parameter to detect the risk for dehydration in an early stage. Herewith possible competitive aggressive interactions between the kits for water can be reduced.

Effect of water shortage on six potato genotypes in the highlands of Bolivia (II): water relations, physiological parameters

Six potato genotypes were grown in containers in the highlands of Bolivia under three water regimes: R0 (well-irrigated controls); R1 (progressive drought after tuberisation and recovery period), and R2 (no recovery). Soil water content (theta(w)), leaf relative water deficit (RWD), leaf water potential (psi(w)), stomatal resistance (r(s)) and chlorophyll fluorescence were evaluated. The objective of this research was to characterise the drought adaptation of the potato genotypes studied, and to identify physiological indicators of drought tolerance. Under drought conditions, cultivar Alpha maintained the highest theta(w) and the lowest RWD. Cultivar Luky exhibited a high r(s) and cultivar Alpha showed the lowest r(s), especially at the end of the R2 treatment. The relations RWD-psi(w), theta(w)-RWD and theta(m)-psi(w) were not affected by genotype or treatment. Chlorophyll fluorescence measurements revealed, in all genotypes, a very high drought resistance of the photosynthetic apparatus, which was not affected in a RWD range of 0-50%. No significant correlation was found between tuber yield and the measured physiological parameters.

Geographical variation in water relations, hydraulic architecture and terpene composition of Aleppo pine seedlings from Italian provinces.

Ecotypic variations in leaf conductance, soil-to-leaf hydraulic conductance, components of tissue water potential, hydraulic architecture parameters and xylem embolism were examined in greenhouse-grown two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings from six origins representing the geographic range of the species in Italy. Cortical resin composition of the seedlings was also determined. Measurements were made on well-watered seedlings and on seedlings subjected to recurring severe drought. Drought-stressed seedlings had lower mean leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than well-watered seedlings. They also exhibited more negative osmotic potentials, higher relative water deficit at incipient plasmolysis, but a similar maximum modulus of elasticity. Drought-stressed seedlings showed a higher degree of xylem embolism, a lower Huber value, lower leaf specific conductivity and lower specific conductivity than well-watered seedlings. Drought-stressed seedlings of provenances from more xeric habitats (Tremiti, Porto Pino and Mottola) had greater leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than drought-stressed seedlings of provenances from more mesic habitats (Imperia, Otricoli and Vico del Gargano). They also showed higher osmotic adjustment and a lower degree of xylem embolism. Among provenances, there were no significant differences in hydraulic architecture parameters in response to the drought treatment; however, Tremiti and Porto Pino seedlings displayed smaller drought-induced reductions in specific conductivity and leaf specific conductivity, respectively, than seedlings from other provenances. These differences suggest that seedlings from xeric provenances, especially Tremiti, have greater resistance to desiccation than seedlings from mesic provenances. No clear association was found between terpene variability and the other traits investigated, although terpene composition was related to the geographical distribution of the provenances. We conclude that the drought-tolerance responses of Tremiti make it a more suitable provenance than the others for establishment on sites prone to severe soil water deficits.

Effect of water deficit on photosynthetic oxygen exchange measured using 18O2 and mass spectrometry in Solanum tuberosum L. leaf discs

The effect of leaf dehydration on photosynthetic O2 exchange of potato (Solanum tuberosum L., cv. Haig) leaf discs was examined using 18O2 as a tracer and mass spectrometry. In normal air (350 μl·l−1CO2) and under an irradiance of 390 μmol photons·m−2·s1, a relative water deficit (RWD) of about 30% severely decreased net O2 evolution and increased O2 uptake by about 50%, thus indicating an enhancement of photorespiration. Increasing CO2 concentrations diminished O2 uptake and stimulated net O2 evolution both in well-hydrated and in dehydrated (RWD of about 30%) leaves. Much higher CO2 concentrations (up to 4%) were required to observe a complete effect of CO2 in dehydrated leaves. The chloroplastic CO2 concentration at the ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) level (Cc) was calculated from O2-exchange data in both well-hydrated and dehydrated leaves, assuming that the specificity factor of Rubisco was unaffected by desiccation. When plotting net O2 photosynthesis as a function of Cc, a similar relationship was obtained for well-hydrated and waterstressed leaf discs, thus showing that the main effect of water deficit is a decrease of the chloroplastic CO2 concentration. At saturating CO2 levels, the non-cyclic electron-transport rate, measured either as gross O2 photosynthesis or as the chlorophyll fluorescence ratio (Fm -Fs)/Fm, was insensitive to water deficit, provided RWD was below 40%. In this range of RWD, the decrease in gross O2 photosynthesis observed in normal air was attributed to the inability of oxidative processes to sustain the maximal electron-flow rate at low chloroplastic CO2 concentration. The maximal efficiency of photosystem II, estimated as the chlorophyll fluorescence ratio (Fm -F0)/Fm measured in dark-adapted leaves, was not affected by water deficits up to 60%.

Drought tolerance, growth partitioning and vigor in eucalypt seedlings and rooted cuttings.

To clarify the physiological basis of productivity differences among rooted cuttings and seedlings of eucalypt species, relationships between morphology and water relations were examined in 4-month-old seedlings of Eucalyptus grandis W. Hill ex Maiden, E. urophylla S.T. Blake and E. cloeziana F. Muell. and in 4-month-old rooted cuttings of three E. grandis cultivars. Four-month-old seedlings had greater dry weights, lower leaf area/root dry weight (LA/RDW) ratios and lower shoot/root dry weight (S/R) ratios than 4-month-old rooted cuttings. For all cultivars of E. grandis, tall rooted cuttings, as defined by height at age 4 weeks, had greater dry weights by age 4 months and lower LA/RDW and S/R ratios than short rooted cuttings. There were differences in height growth, dry matter productivity and relative shoot and root development among cuttings of different E. grandis cultivars, but these differences were not as great as the differences between short and tall grades of the same cultivar and between seedlings and cuttings. Consistent with the differences in LA/RDW and S/R ratios, seedlings had higher daytime water potentials (Psi(x)) than cuttings, and tall cuttings had higher daytime values of Psi(x) than short cuttings. Differences in Psi(x) were also related to stomatal conductance (g(wv)), which was up to 300% greater in short cuttings than in tall cuttings. Among seedlings, those of E. cloeziana, which had the smallest dry weight at age 4 months, had the highest g(wv), whereas those of E. grandis, which had the greatest dry weight at age 4 months, had the lowest g(wv). Unlike seedlings and the tall cuttings, short cuttings lost turgor when subjected to drought. The differences observed in susceptibility to water stress may account in part for the associated differences in dry matter production. Xylem pressure potential and relative water deficit at zero turgor did not differ significantly among the types of plants studied, which suggests that differences in growth rates were not the result of differences in dehydration tolerance.

Soil and cotton responses to tillage and ameliorant treatments in a brown clay soil. 1. Soil responses and water use

Furrow-irrigated cotton was grown for two seasons on a previously uncultivated dense clay soil to which the following treatments had been applied :--normal ploughing (18 cm), precision ripping (30 cm), deep ploughing (40 cm), deep ripping (60 cm), and deep ploughing and deep ripping combined, with and without applications of gypsum at 10 tons an acre or organic matter at 2 1/2 tons an acre. The deep tillage significantly increased the porosity of the subsoil, but this extra porosity had largely been lost by the end of the second season. Neither the gypsum nor the organic matter addition had a significant effect upon its rate of decline. Despite the effect on porosity the deep tillages had only small and mostly non-significant effects upon water increment at irrigation. The gypsum treatment, but not the organic matter, increased water entry to the subsoil at irrigation, and this W-as apparently a result of improved hydraulic conductivity and aggregate stability, particularly in the surface layers. Considerable leaching of chloride occurred from the 30-60 cm subsoil zone in both gypsum treated and deep-tilled plots, but not in organic matter plots, and an accumulation of chloride occurred in the 0-10 cm layer (the hill) in gypsum treated plots. The increased water intake to the subsoil resulting from gypsum treatment was matched by increased water use in the following period, and hence a reduction in relative water deficit of Leaves during the peak period of water demand. Neither the organic matter nor the deep tillages had appreciable influence on water uptake. Water use during periods of peak demand was about 6 mm a day for gypsum treated plots, and this was probably lower than mould have been obtained with water freely available at all times. On the other treatments it can he inferred that water use was even further reduced by lack of available water.