Leaf Water Uptake Research Articles

Physiological Responses and Ecological Benefits of Water Uptake by Populus euphratica Leaves in Arid Areas

The absorption of atmospheric water by plants through their leaves, known as leaf water uptake, plays a crucial role in sustaining plant growth and survival in arid regions. Condensate is one of the important sources of water for plants in arid zones and plays an important role in alleviating the physiological state of plant water. In order to clarify the ecological role of the leaf absorption of condensation water, we took the dominant species of the desert Dugay forest plant, Populus euphratica, as the research object, and based on in situ leaf humidification field experiments, we comprehensively analyzed the effect of condensation water on the physiological state of P. euphratica and the ecological benefit of leaf water absorption on the arid zone by determining the parameters of the physiological indexes of the leaf, the leaf wettability, and the water-absorbing capacity of the leaf. The results showed that P. euphratica leaves have a water-absorbing ability on both sides, and under the condensation water treatment, the water potential of dawn leaves in the TR group (−1.75 ± 0.12 MPa) was significantly higher than that in the CK group (−1.41 ± 0.13 Mpa); the net photosynthetic rate of leaves in the TR group (13.08 ± 0.68 μmol·m−2·s−1) was significantly higher than that in the CK group (10.42 ± 0.57 μmol·m−2·s−1); the proline content of the TR group (22.82 ± 0.8 μg·g−1) was significantly lower than that of the CK group (68.67 ± 6.14 μg·g−1); and the leaf photosynthetic capacity, leaf osmotic adjustment, and stress tolerance affected by condensation water were significantly different (p < 0.05). A leaf’s water-absorbing ability is mainly affected by leaf wettability, the proline content, and other influencing factors. The mean FWU rate was positively correlated with the mean transpiration rate. Within the Ebinur Lake watershed, the water absorption rate of P. euphratica leaves accounts for 10.92% of the maximum transpiration rate (Tr); in 2022, the total summer leaf surface water uptake by P. euphratica was about 220.5 mol, a value that represents about 0.25% of the average annual evapotranspiration from Ebinur Lake. This study helps to improve the understanding of the impact of condensation water on the physiological ecology of the desert plant P. euphratica and provides a scientific basis for the ecological benefits of leaf water absorption in arid regions.

GROWTH, WATER RELATION, LEAF PIGMENTS AND YIELD OF SESAME AS INFLUENCED BY SIMULATED SALINE ENVIRONMENT

Salt stress is a significant environmental problem that restricts crop productivity. Despite being an important oilseed crop in Bangladesh, little is known about the phenotypic and physiological responsesof sesame (Sesamum indicum) to salinity. In order to measure the plant height,number of leaf plant-1, dry matter accumulation capability, leaf water uptake capacity, leaf chlorophyll content, and yield response six sesame genotypes viz., BD-6980, BD-7009, BD-7011,BD-6994, BD-6983, and BD-6999 were grown in pots and exposed to a 7.5 dS m-1 simulated salty environment. Thesegenotypes were chosenfor this investigation from 86 genotypes according to the relative germination percentage at 10 dS m-1 salinity. Results revealed that plant height, number of leaf plant-1, dry matter accumulation capability, leaf chlorophylls a and b content, and yield were reduced in all the genotypes, but reduction rate was lowerin genotype BD-7011.On the other hand, wateruptake capacity in sesame leaf was increment in all the genotypes under salinity but increasing rate was lower in the same genotype BD-7011. These results suggest that the sesame genotype BD-7011may be able to withstandsalt stress with little detrimental effects on the growth, physiological traits, seed yield.

Physiological mechanisms preventing plant wilting under heat stress: a case study on a wheat (Triticum durum Desf.) bound water-mutant

Wilting is the main symptom of plants suffering the dehydration stresses, but the mechanisms governing this phenomenon are yet to be completely understood. In this work, a holistic analysis of physiological traits potentially involved in leaf wilting was performed, comparing a wheat wild type (WT), Trinakria and its water-mutant (WM) with a “high affinity for bound water (BW)”. In addition to the tendency to wilt, significant differences between genotypes were observed for leaf temperature achieved under heat stress, leaf turgor loss with decreasing water potential, cuticular transpiration, and Q10 of leaf water uptake velocity. We hypothesize that mutant plants prevent the increase in leaf temperature thanks to the rapid and low energetic cost of water diffusion from the vessels to the outside, driven by the BW. Under strong thermal-induced dehydration stress, BW delays leaf wilting through its positive effects on cell wall elasticity and passive osmoregulation.

Foliar Water Uptake Capacity in Six Mangrove Species

Foliar water uptake (FWU) is a mechanism that enables plants to acquire water from the atmosphere through their leaves. As mangroves live in a saline sediment water environment, the mechanism of FWU might be of vital importance to acquire freshwater and grow. The goal of this study was to assess the FWU capacity of six different mangrove species belonging to four genera using a series of submersion experiments in which the leaf mass increase was measured and expressed per unit leaf area. The foliar water uptake capacity differed between species with the highest and lowest average water uptake in Avicennia marina (Forssk.) Vierh. (1.52 ± 0.48 mg H2O cm−2) and Bruguiera gymnorhiza (L.) Lam. (0.13 ± 0.06 mg H2O cm−2), respectively. Salt-excreting species showed a higher FWU capacity than non-excreting species. Moreover, A. marina, a salt-excreting species, showed a distinct leaf anatomical trait, i.e., trichomes, which were not observed in the other species and might be involved in the water absorption process. The storage of leaves in moist Ziplock bags prior to measurement caused leaf water uptake to already occur during transport to the field station, which proportionately increased the leaf water potential (A. marina: −0.31 ± 0.13 MPa and B. gymnorhiza: −2.70 ± 0.27 MPa). This increase should be considered when performing best practice leaf water potential measurements but did not affect the quantification of FWU capacity because of the water potential gradient between a leaf and the surrounding water during submersion. Our results highlight the differences that exist in FWU capacity between species residing in the same area and growing under the same environmental conditions. This comparative study therefore enhances our understanding of mangrove species’ functioning.

Contribution of leaf water uptake to transpiration and water status in arid ecosystems

Fil: Cavallaro, Agustin. Universidad Nacional de la Patagonia San Juan Bosco. Instituto de Biociencias de la Patagonia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Centro Nacional Patagonico. Instituto de Biociencias de la Patagonia; Argentina. Universidad Nacional de la Patagonia San Juan Bosco; Argentina

Strategies of leaf water uptake based on anatomical traits.

The ability of leaves to absorb fog water can positively contribute to the water and carbon balance of plants in montane ecosystems, especially in periods of soil water deficit. However, the ecophysiological traits and mechanisms responsible for variations in the speed and total water absorption capacity of leaves are still poorly known. This study investigated leaf anatomical attributes of seven species occurring in seasonal tropical high-altitude ecosystems (rocky outcrop and forest), which could explain differences in leaf water uptake (LWU) capacities. We tested the hypothesis that different sets of anatomical leaf attributes will be more marked in plant individuals living under these contrasting environmental conditions. Anatomical variations will affect the initial rate of water absorption and the total storage capacity, resulting in different strategies for using the water supplied by fog events. Water absorption by leaves was inferred indirectly, based on leaf anatomical structure and visual observation of the main access routes (using an apoplastic marker), the diffusion of water through the cuticle, and non-glandular or glandular trichomes in all species. The results suggest that three LWU strategies coexist in the species studied. The different anatomical patterns influenced the speed and maximum LWU capacity. The three LWU strategies can provide different adaptive advantages to adjust to temporal and spatial variations of water availability in these tropical high-altitude environments.

Pectin and cellulose cell wall composition enables different strategies to leaf water uptake in plants from tropical fog mountain

Leaf water uptake (LWU) has been observed in plants of different ecosystems and this process is distinct among different species. Four plant species from the Brazilian fog mountain fields were evaluated in order to detect if leaf water uptake capacity is related to the cell wall composition of leaf epidermis. LWU measurements and their relation to anatomical and biochemical traits were analyzed. Cell wall composition was verified through immunocytochemistry using monoclonal antibodies recognizing pectin compounds, and histochemistry with calcofluor white to track cellulose. Differences in LWU among the four species were clearly revealed. Two species presented higher maximum leaf water content and the lowest values of water absorption speed. The other two species presented opposite behavior, namely, low leaf water uptake and the highest values of water absorption speed. The anatomical traits associated with the cell wall composition corroborated the data on the different LWU strategies. The species with abundant detection of cellulose in their epidermal cell walls absorbed more water, but more slowly, while those with abundant detection of pectins absorbed water at a higher speed. These results indicate that cell wall composition regarding pectin and cellulose are significant for water uptake by the leaf epidermis. Pectin provides greater porosity and absorption speed, while cellulose provides greater hydrophilicity and greater water uptake capacity. Current data indicate that the composition of epidermal cell walls is a relevant trait for leaf water uptake.

Molecular mechanism and physiological function of trichome formation in plant

Trichome, as a protective barrier against natural hazards, plays an indispensable role in resisting ultraviolet radiation, pathogen invasion, herbivores feeding and water excessive transpiration during the process of plant growth and development. Trichomes may be unicellular or multicellular and some plants such as Arabidopsis thaliana may also have branches, according to the presence or absence of glands, it can be divided into glandular or non-glandular, the former can accumulate and secrete some alkaloids, such as nicotine and terpenoids, which have an exclusion effect on insects, while the latter can be enhanced the stress resistance during abiotic stress, such as extreme high and low temperatures, ultraviolet radiation, thereby promoting and controlling the normal growth of plants. The current study shows that the formation of trichome is co-regulation by many types and multiple genes, thus form a complex regulation network. The mechanism of the regulation and genes mining of the trichome in the dicotyledonous has made substantial progress in recent years, especially in Arabidopsis , Trichome formation in Athaliana is thought to be regulated by a competitive system, including the promotion and inhibition of the gene activities. More and more studies have shown that there are a variety of different genes can regulate the trichome formation in different plants. The genes controling trichome formation are generally a class of MYB transcription factors in Arabidopsis [31] , whereas a HD-Zip protein, Woolly (Wo) that interacts with Cyclin B2, plays an essential role for trichome formation and embryonic development in tomato. In addition, the Glabrous Rice 1(GLR1), which encodes a WUS-like homeobox gene (WOX), also regulates the formation of trichomes in rice. It was proposed that Trichome can also interact with the environment under the development process of plants, such as light refraction, light quantum radiation interception, leaf heat balance, wettability, droplet retention, water uptake and gas exchange. Leaf trichome density is variable and determined by genetic and environmental factors, climate drivers such as soil water deficit and high temperature can increase the trichome density. The studies have shown that leaf trichomes can reflect broad-spectrum electromagnetic radiation, and reducing light absorptance and modulating energy balance. Except as described above, trichome can promote gas exchange and limit pathogen growth and spread on leaves. According to the physiological characteristics of the trichome, the crop cultivation, production and utilization have important economic value and significance. In this article, We systematically reviewed and analyzed a series of related studies on the progress and physiological characteristics of genes which related to the regulation of plant trichome formation in recent years, The aim of this review was to elucidate the regulation mechanism of the trichome formation and the physiological and biochemical characteristics, so as to provide an important theoretical basis for further research on the excavation and functional characteristics of the trichome genes.

Effects of heterogeneous salinity on growth, water uptake, and tissue ion concentrations of alfalfa

Soil salinity varies greatly in the plant rhizosphere. The effect of nonuniform salinity on the growth and physiology response of alfalfa plants was determined to improve understanding of salt stress tolerance mechanisms of alfalfa. Plant growth, predawn leaf water potential, water uptake, and tissue ionic content were studied in alfalfa plants grown hydroponically for 9 days using a split-root system, with uniform salinity or horizontally nonuniform salinity treatments (0/S, 75/S, and 150/S corresponding to 0, 75, and 150 mM NaCl on the low salt side, respectively). Compared with uniform high salinity, 0/S and 75/S treatments significantly increased the alfalfa shoot dry mass and stem extension rate. Compensatory water uptake by low salt roots of 0/S and 75/S treatments was observed. However, decreased leaf Na+ concentration, increased leaf K+/Na+, and compensatory growth of roots on the low salt side were observed only following the 0/S treatment. Nonuniform salinity dose not enhance plant growth once a threshold NaCl concentration in low salinity growth medium has been reached. Compensation of water uptake from the low-salt root zone and regulation of K+/Na+ homeostasis in low salt root play more important role than regulation of leaf ions in enhancing alfalfa growth under nonuniform salinity.

Retain or repel? Droplet volume does matter when measuring leaf wetness traits.

Leaf wetness is an important characteristic linked to a plant's strategies for water acquisition, use and redistribution. A trade-off between leaf water retention (LWR) and hydrophobicity (LWH) may be expected, since a higher LWH/lower LWR may enhance photosynthesis, while the opposite combination may increase the leaf water uptake (LWU). However, the validation of the ecological meaning of both traits and the influence of droplet volume when measuring them have been largely neglected. To address these questions, LWR and LWH of 14 species were measured using droplets of between 5 and 50 μL. Furthermore, the ability of those species to perform LWU was evaluated through leaf submergence in water. The droplet-volume effect on absolute values and on species ranking for LWR and LWH was tested, as well as the influence of water droplet volume on the relationship between leaf wetness traits and LWU. Variations in droplet volume significantly affected the absolute values and the species ranking for both LWR and LWH. The expected negative correlation between leaf wetness traits was not observed, and they were not validated as a proxy for LWU. The water droplet volume does matter when measuring leaf wetness traits. Therefore, it is necessary to standardize the methodological approach used to measure them. The use of a standard 5 μL droplet for LWH and a 50 μL droplet for LWR is proposed. It is cautioned that the validation of both traits is also needed before using them as proxies to describe responses and effects in functional approaches.

Ecophysiology of leaf trichomes.

This review examines how leaf trichomes influence leaf physiological responses to abiotic environmental drivers. Leaf trichomes are known to modulate leaf traits, particularly radiation absorptance, but studies in recent decades have demonstrated that trichomes have a more expansive role in the plant-environment interaction. Although best known as light reflectors, dense trichome canopies modulate leaf heat balance and photon interception, and consequently affect gas exchange traits. Analysis of published studies shows that dense pubescence generally increases reflectance of visible light and near-infrared and infrared radiation. Reflective trichomes are also protective, reducing photoinhibition and UV-B related damage to leaf photochemistry. Little support exists for a strong trichome effect on leaf boundary layer resistance and transpiration, but recent studies indicate they may play a substantive role in leaf water relations affecting leaf wettability, droplet retention and leaf water uptake. Different lines of evidence indicate that adaxial and abaxial trichomes may function quite differently, even within the same leaf. Overall, this review synthesises and re-examines the diverse array of relevant studies from the past 40 years, illustrating our current understanding of how trichomes influence the energy, carbon and water balance of plants, and highlighting promising areas for future research.

The significance of leaf water repellency in ecohydrological research: a review

ABSTRACTNumerous studies in materials science and chemistry have expanded our understanding of the repellency of water droplets from surfaces. Much of the inspiration for the development of synthetic water‐repellent materials came from the examination of water‐repellent properties of animals and plants in the natural environment. The hydrological significance of water repellency in the natural environment remains an underexplored research topic. Although the hydrological significance of soil water repellency has become well established in the ecohydrology and water resources literature, fewer studies have examined the significance of leaf water repellency. This review examines the properties of leaf water repellency, the methodologies used to calculate leaf water repellency, the leaf surface properties that promote leaf water repellency, and the significance of leaf water repellency in ecohydrological research. The repellency of a water droplet by a leaf surface is functionally important among plant species and may reflect selective strategies that either favour leaf water uptake in drought‐prone environments or promote higher photosynthetic efficiency during prolonged periods of precipitation through higher repellency. Information on the functional significance of leaf water repellency in hydrologic models could enhance our understanding of the delivery of water resources to municipal reservoirs and fill in a missing gap in our understanding of leaf water repellency as a process that influences discharge, and by extension, water resources. Copyright © 2012 John Wiley & Sons, Ltd.

Leaf water uptake strategy of desert plants in the Junggar Basin, China

Aims Our objective is to understand leaf water uptake strategy of desert plants and the relationship between leaf water uptake capability and plant ecological functional types in the southeastern Junggar Basin, China. Methods We collected or classified (by the inverse of the normal cumulative distribution function) information from 51 species from five plant communities: growth form, life form, leaf texture trait, leaf surface trait, leaf wa- ter uptake content, percentage increase in leaf water content, leaf water deficit, specific leaf area and leaf dry mat- ter content. The correlation coefficient and degree of association were calculated between each pair of traits based on information theory. One-way analysis of variance and Fisher's multiple comparison, if applicable, were carried out on means of different soft ecological functional types at the community scale, for comparing leaf water uptake content and the percentage increase in leaf water content. Important findings Leaf water uptake content is more appropriate than percentage increase in leaf water for assessing plant leaf water uptake capability. Plant life form is the most rational soft trait to replace hard plant eco- logical functional ones in studying plant leaf water uptake strategy. There are tradeoffs between aboveground and belowground water uptake strategies and between leaf water consumption and uptake in the desert ecosystem.

Simulation of crop water and mineral relations in greenhouse soilless culture

A composite model was developed for water and mineral relations of greenhouse tomato ( Solanum lycopersicum L.) cultivated in semi-closed or open soilless (rockwool) culture. The model simulated on a daily basis: (i) the evolution of crop leaf area index and water uptake using empirical equations; and (ii) the variations of ion concentrations and electrical conductivity (EC) in the recirculating or drainage nutrient solution using a mass balance equation based on the concept of ion uptake concentration. The model was calibrated using measured data collected in previous works and validated in two independent experiments carried out in 2005 and 2007. In these experiments, different fertigation strategies were tested using nutrient solutions prepared with saline (9.5 mol m −3 NaCl) water. In semi-closed systems, the recirculating nutrient solution was discharged whenever EC exceeded a pre-defined threshold (4.5, 6.5 or 7.5 dS m −1, depending on the experiment) and/or nitrate (NO 3 −) concentration was lower than 1.0 mol m −3. This value was selected because 20 mg L −1 (1.43 mol m −3) is the limit imposed to NO 3 − concentration of wastewater discharged into surface water by the current Italian legislation. In open system, the crop was irrigated with full-strength nutrient solution without recirculation of drainage water. In both years, fertigation strategy did not affect significantly crop growth, fruit yield and water uptake. In most cases, simulations of seasonal crop water uptake were within the confidence interval of the measurements with a maximum deviation of −6%. The model predicted acceptably the time course of EC and ion concentration in recirculating (semi-closed systems) or drainage (open system) nutrient solution. A moderate discrepancy between observations and simulations was found for NO 3 − concentration, especially during the first weeks after planting. In general, there was a good agreement between simulated and measured values of total water and nitrogen (N) use. In 2005, simulated values of N uptake in semi-closed systems were −11% to +5% of measured values. Prediction of N uptake was less accurate in 2007, when simulated values were +17% of measured values. In open system, the model underestimated N uptake (−17%) mainly due to overestimation of N leaching (+6%). Applications of the composite model for operative management of soilless culture and for scenario analysis are discussed.

Kinetic analyses of plant water relocation using deuterium as tracer – reduced water flux of Arabidopsis pip2 aquaporin knockout mutants

Due to reduced evaporation and diffusion of water molecules containing heavier isotopes, leaf water possesses an elevated (18)O or (2)H steady-state content. This enrichment has been exploited in plant physiology and ecology to assess transpiration and leaf water relations. In contrast to these studies, in this work the (2)H content of the medium of hydroponically grown Arabidopsis thaliana was artificially raised, and the kinetics of (2)H increase in the aerial parts recorded during a short phase of 6-8 h, until a new equilibrium at a higher level was reached. A basic version of the enrichment models was modified to establish an equation that could be fitted to measured leaf (2)H content during uptake kinetics. The fitting parameters allowed estimation of the relative water flux q(leaf) into the Arabidopsis rosette. This approach is quasi-non-invasive, since plants are not manipulated during the uptake process, and therefore, offers a new tool for integrated analysis of plant water relations. The deuterium tracer method was employed to assess water relocation in Arabidopsis pip2;1 and pip2;2 aquaporin knockout plants. In both cases, q(leaf) was significantly reduced by about 20%. The organ and cellular expression patterns of both genes imply that changes in root hydraulic conductivity, as previously demonstrated for pip2;2 mutants, and leaf water uptake and distribution contributed in an integrated fashion to this reduced flux in intact plants.

Root allocation and water uptake patterns in riparian tree saplings: Responses to irrigation and defoliation

The genus Populus relies on shallow groundwater for successful recruitment and is often the focus of riparian restoration efforts. Under some circumstances mature trees take up a substantial proportion of their water from unsaturated soil water derived from growing season rainfall, but it is unknown how Populus saplings may alter root allocation patterns and water use in response to water availability and carbon limitations. Although it has been inferred that root allocation differs with changes in water uptake patterns as determined with stable isotope studies, this notion has rarely been tested. We conducted a glasshouse experiment with Populus fremontii (Frémont cottonwood) saplings to determine how allocation to fine and coarse roots, leaf gas exchange, root respiration and water uptake from hydrologically isolated upper and lower soil compartments would be altered by above- and belowground resource limitations. Aboveground carbon limitations were imposed with defoliation. Belowground resource limitations were imposed by maintaining high or low soil water availability in lower soil compartment. Isotopically labeled water was supplied in pulses to upper soil compartments to determine the proportion of transpiration water derived from each compartment. Above- and belowground resource limitations differentially altered use of surface water pulses and affected patterns of fine root allocation. Proportional use of water sources was plastic and changed in response to water availability and defoliation. Changes in fine root biomass allocation were associated with changes in water-source use for water-stressed plants. Defoliated plants in both watering treatments used proportionally less of the surface pulse than undefoliated plants. In contrast, plants that were water limited, but not carbon limited had a higher ratio of shallow fine roots to deep fine roots and took up proportionally more water from the surface pulse. These data suggest that carbon limited saplings take up less water with shallow roots. Thus, P. fremontii exhibited belowground allocation tradeoffs in response to spatial heterogeneity of soil water and carbon limitations. Furthermore, our data suggest that successful recruitment events may be influenced by the occurrence of summer rainfall, and by factors affecting canopy carbon gain.

Fractionation change of hydrogen isotopes in trees due to atmospheric pollutants

Atmospheric pollution effects on hydrogen fractionation in trees are demonstrated for the first time in this study. The δ 2H ring-cellulose series obtained for black spruce trees at a site near a SO 2-emitting smelter display short-term fluctuations superimposed on a first order −11‰ shift coincident with the onset of smelter operations. The isotopic depletion in trees exposed to various levels of SO 2 diminish with increasing distance relative to the location of the smelter, and it is not detected at the most distant selected stand, 116 km downwind from the point source. Both the spatial and temporal isotopic trends likely result from the combined effects of leaf transpiration, biochemical processes and water uptake by the root system. The spatial and temporal trends of δ 2H values are the reverse of the δ 13C trends previously obtained for the same tree ring series. These coupled isotopic fractionations underline an important response of trees to pollution stresses likely generated by ambient atmospheric SO 2 concentrations. The degradation of global air quality during the last 150 yr likely generated large scale modifications in the way terrestrial vegetation grows. In this respect, hydrogen dendrogeochemistry combined with other tracers such as C isotope ratios constitutes a new tool to evaluate the past behavior of forest ecosystems in terms of C uptake and acclimation to various types of atmospheric pollution.

Response of sunflower ( Helianthus annuus L.) to sowing date and plant density under Mediterranean conditions

The productivity of rainfed sunflower under Mediterranean conditions depends strongly on the water availability and the efficiency of its utilisation by the crop. Amongst other factors, sowing date and plant density may interact decisively with water supply. Two field trials were conducted in the South of Portugal on a Vertisol to evaluate the effect of these two factors on the productivity of several sunflower cultivars with different growth cycle. The study of the effect of the sowing date was carried out over 4 years and comprised four cultivars and four sowing dates with the last one corresponding to the traditional sowing date. The second trial included 3 sowing densities (2.5, 5.0 and 7.5 seeds m −2) and three cultivars, and was performed over 2 years. An early sowing date led to a simultaneous increase of leaf area duration (LAD) and water uptake during the critical period between flower bud appearance and flowering. The earlier sowing dates also increased the number of seeds per area without decreasing its weight, resulting in higher crop yields. Although significant, the difference in crop yields between densities was low in absolute terms. Crop yield was highest with the medium plant density ( P 2: 3.5 plants m −2). Whereas LAD between flower bud appearance to flowering and flowering to maturity increased from the lowest ( P 1: 1.7 plants m −2) to the highest density ( P 3: 4.6 plants m −2), the water uptake did not vary significantly between densities during these two periods and decreased even slightly for the highest plant density. The lowest plant density increased significantly the mean seed weight in relationship to the other two plant densities, but that was not enough to compensate the significant decrease in seeds m −2. The higher mean seed weight of P 2 was sufficient to compensate the slightly lower number of seeds m −2 in relation to P 3.

Salinity effects on the leaf water relations components and ion accumulation patterns in Avicennia germinans (L.) L. seedlings.

Physiological traits involved in leaf water relations were evaluated in Avicennia germinans (L.) L. seedlings growing at different salinities in the field. Analysis of pressure-volume (P-V) curves and sap osmometry were combined to evaluate osmotic adjustment and cell elasticity, and the contribution of accumulated inorganic ions to osmotic potential was estimated. Seedlings growing in soils with interstitial water salinity above that of normal sea water showed a modification of the relationship between water potential and relative water content. Thus, their leaf osmotic potential at maximum turgor (Ψπ(max)) and at zero turgor (Ψπ(0)) was 1.41 and 1.82 MPa lower respectively, than that of the seedlings from the low salinity site. Volumetric moduli of elasticity () were between 17 and 23 MPa. Thus, ɛ was about 6 MPa lower in high-salinity plants indicating that their cells were slightly more elastic. Ionic concentration analysis showed that Σ [anions] and Σ [cations] were higher in the high-salinity site (22-35%) while the water content per unit dry mass was only 12-17% lower. Reduction in water content was insufficient to explain the increase in ion concentration. Ion concentration explained 73 and 66% of the osmotic potential estimated by P-V curves for leaves from low- and high-salinity sites, respectively. In conclusion, this study provided evidence that leaves of A. germinans seedlings adapt to hypersaline soils by increasing solute concentration by 52% and cell elasticity by 26%. Both processes allow leaf water uptake and turgor maintenance over a large range of soil water potential.

Quantification of Growth Drought Tolerance and Avoidance of Blue Grama Seedlings1

AbstractPlanting failures with blue grama [Bouteloua gracilis (HBK.) Lag.] prompted the investigation of relationships between physiological and morphological traits and seedling drought resistance. The objectives of this study were to quantify the tolerance and avoidance components of growth drought resistance, determine the conditions under which measurements should be made, and assess the variability among seedlings in characteristics that contribute to drought resistance. Blue grama seedlings were restricted to the seminal primary root, irrigated to maintain favorable soil moisture conditions, and retained in plant growth chambers at either a low or a high relative humidity. When leaf area had increased to the maximum that could be supported by water from the root, tiller water potential was determined for a quantification of growth drought tolerance; and total leaf diffusion resistance, water uptake, and green leaf‐blade area were determined for a quantification of growth drought avoidance. Growth drought tolerance, defined as the plant drought that is just sufficient to halt the increase of seedling leaf area, varied among seedlings from about −20 to −40 bars. Growth drought avoidance, defined as the difference between plant drought and the drought of the shoot environment, is related to total leaf diffusion resistance, maximum capacity for water uptake, and seedling leaf area. Estimates of total leaf diffusion resistance varied among seedlings from 6 to 23 sec cm−1 and maximum rates of water uptake varied from 1 to 8 g day−1. Differences among accessions in capacity for water uptake suggest that improvements might be made in a plant breeding program. Additional work is needed to determine whether drought tolerance and total leaf diffusion resistance are heritable traits. The concept of growth drought resistance is particularly useful because it can be quantified for individual seedlings.