Leaf Water Parameters Research Articles

Phosphorus deficiency enhances water deficit impact on some morphological and physiological traits in four faba bean (<em>Vicia faba L.</em>) varieties

Moroccan soils, generally present low available phosphorus (P) levels which occur in almost all arid and semi-arid regions. Faba bean is one of the most significant crops in Morocco and is influenced by these constraints that affect its nutrient uptake and nitrogen fixation capacity and hence plants development. Therefore, we evaluated the response of four Vicia faba varieties - Aguadulce (Ag), Alfia (Al), Luz de Otono (LO) and Reina Mora (RM) -, grown under biological nitrogen fixation to water deficit and two phosphorus levels. The trial was conducted under greenhouse conditions and water stress was induced by keeping pots at 40% substrate field capacity (FC) versus 80% FC for the controls while phosphorus deficiency treatment consisted in the application of 25 μmol P plant−1 week−1 versus 125 μmol P plant−1 week−1 for sufficient P treatment. The results revealed a significant effect of water deficit and phosphorus deficiency either alone or combined on plants dry weights, leaf water parameters and nutrient concentrations. However sufficient phosphorus supply mitigated the adverse effects of water deficit on faba bean. We noticed significant differences between the studied varieties. Ag showed high performance concerning dry weights (1.25 g and 1.88 g plant–1 respectively for shoot and root) and high concentration of nitrogen N (4.7%) and P (0.27 mg g–1 DW) and was then qualified as the most tolerant variety to water deficit combined with P limitation. While RM was the least tolerant variety, as it showed the lowest dry weights (0.51 g and 1.4 g plant–1 respectively for shoot and root) and concentration (2.74% and 0.19 mg g–1 DW respectively for N and P). The tolerance was related to the ability to ensure efficient osmoregulation by glycine betaine accumulation, to keep leaf water balance and cell membrane stability that contribute together with adequate symbiotic nitrogen fixation to plant growth performance under combined stresses.
 Highlights - Varieties tolerant to low phosphorus and water deficiency are needed in arid and semi-arid regions with low P. - Phosphorus nutrition is advantageous for mitigating the effect of water deficit on faba bean (Vicia faba) plants and conversely, deficient P supply reduces resilience to water deficit. - The faba bean variety Aguadulce showed high tolerance to the combined effect of water deficit and phosphorus deficiency in terms of growth, leaf water potential, stomatal conductance, membrane permeability and glycine betaine accumulation. - Reina Mora was the least tolerant variety to water deficit combined with P limitation. - Combined limitation of water and phosphorus induced accumulation of glycine betaine in leaves.

Cell wall components regulate photosynthesis and leaf water relations of Vitis vinifera cv. Grenache acclimated to contrasting environmental conditions

Environmental conditions determine plants performance as they shape – among other key factors – leaf features and physiology. However, little is known regarding to the changes occurring in leaf cell wall composition during the acclimation to an environmental stress and, specially, if these changes have an impact on other leaf physiology aspects. In order to induce changes in photosynthesis, leaf water relations and cell wall main components (i.e., cellulose, hemicelluloses and pectins) and see how they co-vary, Vitis vinifera cv. Grenache was tested under four different conditions: (i) non-stress conditions (i.e., control, with high summer temperature and irradiance), (ii) growth chamber conditions, (iii) growth chamber under water stress and (iv) cold growth chamber. Plants developed in growth chambers decreased net CO2 assimilation (AN) and mesophyll conductance (gm) compared to control. Although cold did not change the bulk modulus of elasticity (ε), it decreased in growth chamber conditions and water stress. Control treatment showed the highest values for photosynthetic parameters and ε as well as for leaf structural traits such as leaf mass area (LMA) and leaf density (LD). Whereas cellulose content correlated with photosynthetic parameters, particularly AN and gm, pectins and the amount of alcohol insoluble residue (AIR) – an approximation of the isolated cell wall fraction – correlated with leaf water parameters, specifically, ε. Although preliminary, our results suggest that cell wall modifications due to environmental acclimations can play a significant role in leaf physiology by affecting distinctly photosynthesis and water relations in a manner that might depend on environmental conditions.

Effects of boron excess in nutrient solution on growth, mineral nutrition, and physiological parameters of Jatropha curcas seedlings

AbstractJatropha curcas L. has recently attracted the attention of the international research community due to its potential as a biodiesel crop. In addition, its high resistance to drought and salinity is well known. Under arid and semiarid conditions, boron (B) concentrations in irrigation water can be higher than desired when water from industry, urban areas, or desalination is used. However, the growth and physiological responses of J. curcas plants to B excess in the irrigation water are unknown. Therefore, a greenhouse experiment was conducted to study the effects of B excess in the nutrient solution (0.25, 2, 4.5, and 7 mg L–1 B, applied as H3BO3) on plant growth, mineral concentration in the different plant tissues, photosynthesis, water relations, chlorophyll fluorescence, chlorophyll concentration (as SPAD values), and composition of carbohydrates. Plant growth decreased with increasing B concentration in the nutrient solution; growth reduction was higher for roots than for leaves or stems. The B concentration increased in all plant tissues, in the following order: leaf > root > stem. These data indicate that the roots of J. curcas are more sensitive to B toxicity than the leaves and that B has restricted mobility inside these plants, accumulating mainly in the basal and middle leaves via the transpiration stream. Increasing B concentration in leaves decreased the ACO2 and the stomatal conductance, but the leaf water parameters were not affected. The data for chlorophyll concentration and chlorophyll fluorescence indicated that nonstomatal factors were involved in the ACO2 decline, whereas decreases in the parameters of PSII photochemistry due to B toxicity suggest that there was structural damage in chloroplasts. There was also a general tendency for a decrease in nonstructural carbohydrates in all plant tissues, possibly due to the decline in ACO2. With excess B, the concentrations of K and Mg increased in leaves due to a decrease in the growth, while a typical antagonistic effect between B and P was evident from the P concentration decrease in leaves. In summary, J. curcas should be considered a B‐sensitive plant, as a leaf B concentration of 1.2 mg (g dw)–1 caused a growth decline of approximately 30%.

Estimation of leaf water content in cotton by means of hyperspectral indices

The knowledge of vegetation water conditions can contribute to drought assessment. Remote sensing has a proven ability to assess vegetation properties. In this study, all two-band combinations (350–2500nm) in the ratio type of vegetation index (RVI) and the normalized difference type of vegetation index (NDVI) were performed on cotton leaf raw spectral reflectance (R) and the first derivative reflectance (DR). The correlation coefficient (r) between all two-band combinations and two leaf water parameters (EWT: equivalent water thickness, and FMC: fuel moisture content) were determined, and the results of this comprehensive analysis were presented by matrix plots. Band centers (λ1 and λ2) and band widths (Δλ1 and Δλ2) that combine to form the best indices were identified for EWT and FMC through matrix plots. Then the evaluation of the predictive power of three predictors, i.e. single narrow band reflectance, the widely used published water indices and the best band combination indices, were performed. The results shown that the new indices DR1647/DR1133 and DR1653/DR1687, proposed by two-band combinations, were considered as the optimal indices for EWT and FMC estimation, respectively. The models based on these two best combination indices could explain 58% and 67% variability in EWT and FMC, respectively. Besides, bands with center wavelengths in region from 950nm to 1100nm, and 1650nm to 1750nm were represented almost all selected bands. The study should further our understanding of the relationships between leaf water content and hyperspectral reflectance.

Photosynthesis by six Portuguese maize cultivars during drought stress and recovery

Photosynthesis, chlorophyll fluorescence, and leaf water parameters were measured in six Portuguese maize (Zea mays L.) cultivars during and following a period of drought stress. The leaf relative water content (RWC) responded differently among cultivars but except for cultivar PB369, recovered close to initial values after watering was restored. Photosynthetic rate and stomatal conductance decreased with drought but more slowly in cultivars PB269 and PB260 than in cultivars AD3R, PB64, PB304 and PB369. Water use efficiency (WUE) decreased during the water stress treatment although with cultivar PB260 the decrease was marked only when the RWC fell below 40%. Recovery of WUE was seen with all cultivars except PB369. The maximum quantum efficiency of photosystem II, the photochemical quenching coefficient, the electron transport rate in PSII and the estimated functional plastoquinone pool tended to decrease with drought, while the non-photochemical quenching coefficient increased. The parameters estimated from chlorophyll fluorescence did not recover in PB369, during re-watering. The results show that PB260 and PB269 were the most tolerant and PB369 was the least tolerant cultivars to water stress. The variation found among the cultivars tested suggests the existence of valuable genetic resources for crop improvement in relation to drought tolerance.

Contrasting responses facing peak drought in seedlings of two co-occurring oak species

Summary To evaluate leaf physiological mechanisms involved in plant tolerance to water deficit between sites of varying overstorey density, we investigated leaf water relations of two broadleaved oaks (Quercus petraea (Matt.) Liebl. and Quercus pyrenaica Willd.) planted within a dense Scots pine stand, in a thinned adjacent area and in a nearby gap at a Mediterranean, mid-mountain field site. Leaf water parameters were estimated in established seedlings at the end of June and August over two consecutive years by measuring pressure–volume relationships with the pressure chamber technique. Plant water status was always similar in both species, and it was lower in August than June due to lower soil moisture at the end of summer. Higher light and diurnal water deficits in the gap were associated to more negative osmotic potentials. Impacts of overstorey density on some leaf water parameters depended on the species. While Q. pyrenaica showed active osmotic adjustment across sites, seedlings of Q. petraea were unable to cope with increased water deficit by osmotic adjustment in the unthinned dense area. While Q. pyrenaica showed consistent increases in the maximum bulk modulus of elasticity (emax) from June to August across sites, emax decreased in the unthinned dense area for seedlings of Q. petraea. These results could reflect distinct species strategies to cope with water deficit under the low-light conditions created by a dense overstorey. Higher leaf osmotic adjustment and bulk modulus of elasticity in Q. pyrenaica seedlings at peak summer drought might confer on them a competitive advantage during establishment in dry sub-Mediterranean understories. Opening of moderate canopy gaps in dense Scots pine stands improves some leaf mechanisms involved in drought tolerance in oak seedlings.

Elevated atmospheric CO2 does not modify osmotic adjustment to light and drought in the Mediterranean oak Quercus suber L.

The current ongoing increase in the atmospheric CO2 concentration is an unquestionable fact. Thus, plants are bound to live in a more enriched CO2 world in a not far-off future. In this new framework, regeneration of forest tree species may be modified as a consequence of the change in the current patterns of seedling response to other environmental resources, such as water or light. We studied the impact of an elevated CO2 concentration on the interaction of drought and light upon the water relations of cork oak (Quercus suber L.) seedlings. In a complete factorial design of contrasting light (HL vs LL), water (WW vs S) and CO2 levels (800 ppm vs 370 ppm), we analysed the influence of each factor and its interaction in the modification of different leaf water parameters in potted seedlings after a 6 months experimental period. These parameters were derived from the construction, with leaf materials, of the P-V curves: osmotic potential at full turgor (Ψπ100), osmotic potential at zero turgor (Ψπ0), modulus of elasticity at full turgor (εmax), and the ratio dry/turgor weight (DW/TW). Doubling of the CO2 levels over the current concentration (380 ppm) did not change any of the studied leaf water parameters, while light and water availabilities had a significant influence. This result does not exclude changes in other basic physiological parameters that could modify the pattern of cork oak regeneration responding to a CO2 enriched atmosphere in the future, and under climatic conditions different to the current ones.

Transient increase of de novo amino acid synthesis and its physiological significance in water-stressed white clover.

In white clover (Trifolium repens L. cv. Regal) the kinetics of de novo synthesis of amino acid and protein were compared by tracing 15N under well-watered (control) or water-deficit conditions. The physiological relationship between ammonia concentration, in response to the change in leaf water parameters, and de novo synthesis of amino acid and protein was also assessed. Leaf and root dry mass were not significantly affected for the first 3 d, whereas metabolic parameters such as total N and ammonia were significantly affected within the first day of water-deficit treatment. Inhibitory effect of water deficit on N acquisition from the soil was significant throughout the experimental period. Water deficit induced a significant increase in ammonia concentration in leaves during the first 3 d, and in roots for only the first day. In both leaves and roots, an increase in de novo amino acid synthesis, which peaked in leaves within the first 3 d of water-deficit treatment (Ψw ≥ -1.18 MPa), was observed. The rate of decrease in de novo protein synthesis gradually accelerated as the duration of the water-deficit treatment increased. There was a significant positive relationship between ammonia production and the increase in de novo amino acid synthesis during the first 3-d period, but not during the later period (day 3-day 7). This experiment clearly indicates that the increase in de novo amino acid synthesis caused by water deficit is a transient adaptive response occurring during the first few days and that it is associated with the increased ammonia concentrations, which in turn arise in response to a decrease in de novo protein synthesis.

The effect of short-term flooding on the sap flow, gas exchange and hydraulic conductivity of young apricot trees

The effect of short-term flooding was examined in 2-year-old apricot trees (Prunus armeniaca cv. Bulida). Six apricot trees of similar appearance were submitted to two treatments: three were irrigated daily, while the others were flooded for a period of 50 h by submerging the pots in plastic water tanks. The trees were removed from the water, drained and then placed in the same conditions as the control plants. A decrease in transpiration in the flooded trees with respect to the control plants was evident. The daily pattern of soil O2 concentration and plant hydraulic resistance followed a similar trend during the flooding. However, this relationship was not maintained throughout the experiment, since the O2 values increased rapidly when the waterlogging ceased, while plant hydraulic resistance only recovered at the end of the experiment when the original root system, damaged by flooded conditions, was replaced with new roots. In flooded trees, the midday leaf water potential decreased progressively from the beginning of flooding, but gradually recovered when the waterlogging ceased. Leaf conductance values of treated plants were slow to recover, reaching values of the control plants 8 days after the leaf water potential had recovered. The close relationship observed during most of the experiment between the leaf water parameters, leaf conductance and plant hydraulic conductance indicate that hydraulic messages are likely to play a dominant role in co-ordinating the observed responses of the shoot.

De novo protein synthesis in relation to ammonia and proline accumulation in water stressed white clover.

The kinetics of protein incorporation from newly-absorbed nitrogen (N, de novo protein synthesis) was estimated by 15N tracing in 18-week-old white clover plants (Trifolium repens L. cv. Regal) during 7 d of water-deficit treatment. The physiological relationship between kinetics and accumulation of proline and ammonia in response to the change in leaf-water parameters was also assessed. All leaf-water parameters measured decreased gradually under water deficit. Leaf and root dry mass was not significantly affected during the first 3 d when decreases in leaf-water parameters were substantial. However, metabolic parameters such as total N, proline and ammonia were significantly affected within 1 d of commencement of water-deficit treatment. Water-deficit treatment significantly increased the proline and NH3-NH4+ concentrations in both leaves and roots. There was a marked reduction in the amount of N incorporated into the protein fraction from the newly absorbed N (NANP) in water-deficit stressed plants, particularly in leaf tissue. This reduction in NANP was strongly associated with an increased concentration of NH3-NH4+ in roots (P≤0.05) and proline (P≤0.01) in leaves and roots. These results suggest that proline accumulation may be a sensitive biochemical indicator of plant water status and of the dynamics of de novo protein synthesis in response to stress severity.

Water deficit effects on osmotic adjustment and solute accumulation in leaves of annual clovers

Annual clovers are very popular forage crops in the Mediterranean areas. However, their herbage and seed yields are often reduced by high temperatures and water stress occurring during spring and summer. Field experiments using the four most widely grown forage legumes, berseem ( Trifolium alexandrinum L.), crimson clover ( T. incarnatum L.), Persian clover ( T. resupinatum L.) and squarrosum clover ( T. squarrosum L.), were conducted in 1992 and 1993 at Foggia (Italy) to evaluate the osmotic adjustment capability and the relevant contribution of inorganic and organic solutes in response to water deficits. Soil water depletion reduced leaf water potential ( Ψ w) and leaf osmotic potential at full turgor ( Ψ π 100) in both years. In particular, berseem and squarrosum clovers showed lower values (−1.46 and −1.51 MPa on average, for Ψ w and Ψ π 100, respectively). Furthermore, water-stressed plants showed an increase in potassium, reducing sugars and proline concentrations and a decrease in non-reducing sugar contents. Generally, about 80% of the measured cellular osmotic potential was attributable to assayed osmotically active solutes; the inorganic ions represented the major contributors (about 59%). However, only proline levels appeared to change clearly in terms of relative contribution to Ψ π 100, showing an increase of about 2.2%, under water-stressed conditions. Statistically significant differences ( P≤0.05) in the osmotic adjustment trait were not found for either species or year. Because clover species showed the same value for solute accumulation capability (0.34 MPa), degree of tolerance to dehydration and turgor maintenance but differed in leaf water parameters, other physiological and/or morphological traits will have to be investigated to better explain the performance of each species under water-stress conditions. However, the tendency of crimson and Persian clovers to maintain high leaf water potentials could be an example of a stress-avoidance mechanism.

Effects of thinning in a Pinus sylvestris L. stand on foliar water relations of Fagus sylvatica L. seedlings planted within the pinewood

Planting of beech in old Scots pine plantations could facilitate the extension of adjoining small natural populations of beech in the centre of the Iberian Peninsula. To be successful the survival and growth of seedlings after outplanting must be compatible with microclimatic conditions within thinned pine woods. The present paper deals with water relations in beech seedlings following the variation of available radiation and water as a result of thinning. The seedlings were established under an old Scots pine plantation. After pine felling, four situations were generated in terms of radiation. Hemispherical photographs were taken, and global relative irradiance was calculated for every treatment. During two growing seasons predawn water potential (Ψpd) was measured and leaf water parameters were derived from P–V curves. The Ψpd diminished through the season in all four situations, and the highest values were found when pine density was lowest. Osmotic potential at turgor lost (Ψπo) was higher in early summer. A negative relationship was found between osmotic potential at full turgor (Ψπ full) and symplast solute content on a dry weight basis (Ns). Under the lowest irradiance (unthinned pine trees), Ψπ full and Ψπ o were the highest and the bulk modulus of elasticity (emax) the lowest; emax decreased in response to the lowest Ψpd measured at the end of summer 1998. It was followed by a reduction in the symplastic relative water content and Ns, irrespective of the irradiance. Osmotic adjustment, as a drought tolerance mechanism, was limited under shade conditions (unthinned pine trees), restricting the acclimation of beech seedlings to drought. Therefore, the presence of overstory, necessary for a successful implantation, should not be extended for too many years because of the risk of negative effects on growth and survival, particularly after frequent dry summers.

Leaf water characteristics and drought acclimation in sunflower genotypes.

The responses of leaf water parameters to drought were examined using three sunflower (Helianthus annuus L.) genotypes. Osmotic potential at full water saturation (π100), apoplastic water fraction (AWF) and bulk elastic modulus (BEM) were determined by pressure-volume curve analysis on well watered or on water-stressed plants (−1.0 MPa Ψ1 < −1.5 MPa) previously drought-pretreated or not. The drought-pretreated plants were subjected to a 7-day drought period (predawn leaf water potential reached −0.9 MPa) followed by 8 days of rewatering. In well watered plants, all genotypes in response to drought acclimation displayed a significantly decreased π100 associated with a decrease in the leaf water potential at the turgor-loss point (decrease in Ψtlp was between 0.15 and 0.21 MPa, depending on the genotype). In two genotypes, drought acclimation affected the partitioning of water between the apoplastic and symplastic fractions without any effect on the total amount of water in the leaves. As a third genotype displayed no modification of AWF and BEM after drought acclimation, the decreased π100 was only due to the net accumulation of solutes and was consistent with the adjustment of the photochemical efficiency observed previously in this genotype in response to drought acclimation. In water-stressed plants, the osmotic adjustment (OA) can increase further beyond that observed in response to the drought pretreatment. However, the maintenance of photosynthetic rate and stomatal conductance at low leaf water potentials not only depends on the extent of osmotic adjustment, but also on the interaction between OA and AWF or BEM. Adaptative responses of leaf water parameters to drought are thus quite contrasted in sunflower genotypes.

Tree rooting patterns and soil water relations of healthy and damaged stands of mature oak (Quercus robur L. and Quercus petraea (Matt.) Liebl.)

At three sites in northwestern Germany, which represent the centres of the present oak damage, root distribution and biomass beneath healthy and damaged trees of mature pedunculate oak (Quercus robur L.; Neuenburg site) and sessile oak (Q. petraea [Matt.] Liebl.; Lappwald and Sprakensehl sites) were investigated, and soil texture, bulk density, duration of waterlogging periods and the water available in the mineral soil were determined. For Neuenburg and Sprakensehl, the available soil water was related to leaf water parameters determined in a separate investigation. At the clayey and hydromorphic sites of Neuenburg and Lappwald, the measurements were performed in each one healthy and one damaged part of the site, which differed in the number of oaks with crown damage. In the damaged stand of Neuenburg, the clay content of the subsoil was higher than in the healthy stand, and the soil water availability was reduced especially in dry periods. Compared to healthy oaks of the healthy stand, the density of finest plus fine roots as well as the biomasses of finest roots were lower beneath damaged oaks of the damaged stand. With decreasing relative available soil water (actually available water in relation to water available at the saturation state), the relative leaf water content decreased in damaged, but not in healthy oaks. At Lappwald, similar differences in soil water availability between the healthy and the damaged stand were found, but had no effect on the distribution or biomass of the roots. At the sandy site (Sprakensehl), the available soil water decreased drastically during a dry period, and predawn leaf water potentials of both healthy and damaged oaks declined with decreasing relative available soil water. However, the damaged oaks were not inferior to the healthy ones with respect to root density and biomass. It is concluded that, in the damaged stand of Neuenburg, the high clay content of the subsoil, which results in prolonged periods of waterlogging, in sharp changes from waterlogging to drought and decreased water availability in dry periods, is the reason for the reduced biomass and density of roots of the pedunculate oak. Thus, in northwestern Germany, unfavourable soil water relations are considered as a factor contributing to crown damage of pedunculate oak at hydromorphic sites, but not to damage of sessile oak.

Effects of salinity on growth, shoot water relations and root hydraulic conductivity in tomato plants

Growth, shoot water relations and root hydraulic conductivity were studied in tomato plants (Lycopersicon esculentum cv. INCA9) subjected to different salt concentrations in the root medium. Two experiments were carried out at Instituto Nacional de Ciencias Agrícolas (INCA), Cuba, during May and June 1995. In the first experiment, plants were grown for 13 days in a nutrient solution with 0 or 100 mM NaCl. In the second experiment, the hydraulic conductivity was measured on roots submerged in nine different concentrations of NaCl up to 200 mM. The effect of temperature treatments between 0 and 50 °C on root hydraulic conductivity was also examined. Shoot growth, leaf water potential, leaf stomatal conductance, leaf relative water content and root hydraulic conductivity values decreased more rapidly in the treated plants than in control plants. A strong correlation was found between the root hydraulic conductivity and leaf water parameters, indicating that water flow through the roots was the main factor controlling shoot water relations.

Effect of defoliation on the photosynthetic parameters and yield components under flooded and drought conditions in rice varieties.

Defoliation treatment (clipping half of every leaf blade) was applied to rice varieties under drought and flooded conditions to determine its effect on the photosynthetic parameters, water balance, yield components and drought response of the plants. In the first experiment, photosynthetic and related leaf water parameters were measured in three upland varieties, (Moroberekan, IAC 1246 and Sensho), two lowland varieties (Bosque and IR 8) and one dwarf mutant variety (Daikoku 1). Under flooded condition, the defoliation treatment increased the photosynthetic and transpiration rates with a concomitant increase of the leaf water content and leaf diffusive conductance. The effect particularly pronounced in the tall upland varieties. When the water supply was restricted, the defoliation retarded the loss of soil moisture and accordingly the varieties maintained a high photosynthetic rate for a longer period. However, when the soil moisture tension reached a value of 40 cbar, the photosynthetic rate and leaf diffusive conductance became similar in magnitude in both the defoliated and nondefoliated plants. The decrease of photosynthetic rate by water shortag'e was the smallest in the dwarf mutant and the largest in the lowland varieties. In the second experiment, the effect of defoliation on yield components was examined in the early upland varieties (Sensho and Rikuto Norin 24), one early lowland variety (Bosque) and one dwarf mutant variety (Daikoku 1). Under flooded condition, the defoliation treatment decreased the yield components except for the tiller number of the tall varieties, resulting in a decrease of grain weight per plant in every variety. However, under drought condition, defoliation alleviated the decrease of several yield components, resulting in a lower decrease of grain weight per plant except for the dwarf mutant. It was concluded that defoliation was effective in preventing drought damage in tall varieties with large leaves. It was postulated that the lowest decrease of the photosynthetic rate under drought condition in the dwarf mutant was associated with the presence of short and thicker leaves, and that such a short-leaved plant was able to avoid drought damage.