Calcium increases sodium exclusion in olive plants

‘Picual’ olive cuttings were grown in a greenhouse under saline conditions in 2 L plastic pots containing perlite. Plants were irrigated with a nutrient solution plus 75 mM NaCl and 0, 2.5, 10 or 40 mM CaCl₂. Vegetative growth, leaf and root Na⁺ and Ca²⁺ concentrations were measured. Na⁺ toxicity symptoms were observed in plants non-treated with Ca²⁺. Shoot length was higher in Ca²⁺ treated plants, although shoot growth was reduced at 40 mM CaCl₂, probably due to the high total ion concentration reached in the external solution. Ca²⁺ supply linearly increased leaf and root Ca²⁺ concentration and decreased leaf Na⁺ concentration. However, there were no differences in root Na⁺ concentration. Results indicate Ca²⁺ may take part in the Na⁺ exclusion mechanism, mainly preventing Na⁺ transport to the shoot, that may be an important ability for survival under saline conditions.     

Plant water stress and K starvation reduce absorption of foliar applied K by olive leaves

Three-month-old mist-rooted ‘Picual’ olive cuttings were transplanted into 2-l plastics pots containing perlite as substrate and fertigated with a complete nutrient solution containing 0.05, 0.1 or 2.5 mM KCl depending on the experiment. In the first experiment, plants were sprayed with RbCl (Rb⁺ is a K⁺ analog) at a rate of 4% at 63 days after transplanting (DAT). Foliar Rb⁺ uptake through leaves increased with K⁺ concentration in the nutrient solution, indicating that foliar Rb⁺ uptake was lower when plants were K⁺ deficient than when they were adequate. On the contrary, it was observed that translocation of Rb⁺ from leaves to other organs of the plant was higher under K⁺ deficiency conditions. In the second and third experiments, when differences appeared on shoot length due to K⁺ nutritional status (0.05 or 2.5 mM KCl) at 63 DAT, a group of plants were subjected to water stress during 7 weeks. On the other hand, another group of plants (control plants) did not receive any water stress treatment during the experiments. After this period of 7 weeks, all plants were sprayed with RbCl at 4%. Leaf K⁺ concentration diminished in water-stressed plants independently of plants nutritional status. Foliar Rb⁺ uptake through leaves was restricted by water stress either in plants with low K⁺ (0.05 mM KCl) or plants with high K⁺ (2.5 mM KCl). Translocation of Rb⁺ from leaves was greater under water stress conditions in both K⁺ nutritional statuses. In conclusion, the results obtained could explain the irregular response in olive trees to foliar K⁺ sprays, particularly, when they grow in rainfed orchards.     

Yield,blossom-end rot incidence,and fruit quality in pepper plants under moderate salinity are affected by K and Ca fertilization

One of the most important factors limiting agricultural expansion and production is the restricted supply of good quality water. The present study examines the effects of K⁺ and Ca²⁺ fertilization on sweet pepper production, blossom-end rot (BER) incidence and fruit quality of pepper plants (Capsicum annuum L.) grown under moderate saline conditions. Pepper plants were grown in a controlled-environment greenhouse under hydroponic conditions with different nutrient solutions obtained by modifying the Hoagland solution. The experiment consisted on four K⁺ treatments (0.2, 2, 7 and 14 mM) +30 mM NaCl, and four Ca²⁺ treatments (0.2, 2, 4 and 8 mM) +30 mM NaCl, having in common a control without salt with 7 mM K⁺/4 mM Ca²⁺. Salinity decreased total fruit yield and marketable fruit yield by 23% and 37%, respectively. The marketable fruit yield reduction by salt treatment was mainly due to the increase in the number of fruit affected by BER. This typical physiopathy of the pepper fruits occurred between 18 and 25 days after anthesis (DAA), when the highest fruit growth rate was reached. Fruit quality parameters were also affected by salt treatment where the fruit pulp thickness and firmness were decreased, and fructose, glucose and myo-inositol fruit concentrations increased with salinity relative to fruits from control treatment. Under saline conditions an increased supply of K⁺ reduced the fruit fresh weight, the percentage of BER and the marketable yield although promoted the vegetative growth. However, increasing Ca²⁺ concentration in the nutrient solution increased the fruit production, and the marketable yield as consequence of decreasing the percentage of fruit affected with BER. Fruit quality parameters also were affected by the K⁺ and Ca²⁺ treatments.     

Effects of Ascorbic Acid and Reduced Glutathione on the Alleviation of Salinity Stress in Olive Plants

The aim of this study was to evaluate the effects of low molecular mass antioxidants and NaCl salinity on growth, ionic balance, proline, and water contents of ‘Zard’ olive trees under controlled greenhouse conditions. The experiment was carried out by spraying 2 mM of ascorbic acid (Asc) and 3 mM of reduced glutathione (GSH) on the plants that were treated with two salinity levels (0 and 100 mM NaCl) on their root medium. Plant growth parameters (leaf fresh weight, leaf dry weight, leaf number, total fresh weight, and total dry weight) were significantly improved by Asc compared with growth parameters in GSH and control plants. Higher concentrations of Na⁺ and Cl^– were observed in salt-stressed plants, while Na⁺ and Cl^– concentrations were decreased in the olive leaves that were sprayed with Asc. Salinity in the root zone caused a considerable decline in both K⁺ concentration and K/Na ratio. K⁺ concentration and K/Na ratio were significantly increased by application of Asc on plant leaves. Salinity caused an increase in electrolyte leakage (EL) compared with the control plants. Lowest EL and tissue water content (TWC) was obtained in Asc-sprayed plants, whereas TWC was increased in salt-stressed plants. Plants were subjected to salt stress and showed a higher relative water content (RWC) than the control plants. Salt stress induced proline accumulation in olive leaves. In conclusion, exogenous application of Asc is recommended to improve tolerance of olive plants under saline conditions.     

Effects of Stockosorb and Luquasorb polymers on salt and drought tolerance of Populus popularis

The effects of two types of hydrophilic polymers on drought and salt resistance of 1-year-old cuttings of Populus popularis 35–44 were investigated in this study. The polymers used in the experiments were Stockosorb 500 XL (Stockosorb) (a granular type, cross-linked poly potassium-co-(acrylic resin polymer)-co-polyacrylamide hydrogel) and Luquasorb^® product (a powder type of potassium polyacrylate), which were manufactured by Stockhausen GmbH Krefeld and BASF Corporation in Germany, respectively. Drought or salt stress significantly decreased leaf photosynthesis and transpiration, as well as plant water-consumption and dry weight. A significant reduction occurred in Drought + NaCl-stressed plants. Soils treated by 0.5% Stockosorb or Luquasorb markedly alleviated the inhibition of plant growth and leaf gas-exchange that were caused by drought and/or salt stress treatments, and the occurrence of stress-induced leaf injury was delayed for 31 and 51 days, respectively. Experimental results showed that hydrophilic polymers in root media assisted P. popularis plants to tolerate the drought and salt stresses, due to the following reasons: (1) roots took up the retained water from hydrophilic polymers when water was deficient in the soil (Stockosorb-treated plants exhibited a higher rate of water uptake); (2) under saline conditions, Stockosorb and Luquasorb held Na⁺ and Cl⁻ in the soil solution due to their high water-holding capacity, thus limiting an excessive accumulation of toxic ions in the plant organs; furthermore, the exchangeable K⁺ that contained in Stockosorb and Luquasorb resulted in an improved K⁺/Na⁺ homeostasis in salinized plants; (3) hydrophilic polymers aided the plants to tolerate an interactive impacts of drought and salt stresses, which was mainly accounted for their water- and salt-holding capacities. In comparison, the growth and survival enhancement effects of the hydrophilic polymers on Drought + NaCl-treated plants was more evident by Luquasorb application, because it supplied water to plants at a lower rate during soil drying, thus prolonging the duration of water supply and allowed roots to grow in an environment of lower salinity for a long period of salt and drought stresses.     

Effects of water and salt stresses on growth,water relations and gas exchange in Rosmarinus officinalis

Summary

Plants of Rosmarinus officinalis were submitted to water and salt stress, independently. The effects of water or salt stress on growth, water relations and gas exchange were investigated in order to understand the tolerance and adaptative mechanisms of R. officinalis to these types of stress. Under both stress conditions, plants developed avoidance mechanisms to minimise water loss based on morphological and physiological changes (e.g., reduction of plant biomass and leaf area, stomatal closure). Only under salt stress conditions were treated plants able to maintain turgor via osmotic adjustment, which was achieved by the uptake of Na⁺ and Cl^– ions. Osmotic adjustment was not observed in R. officinalis plants submitted to water stress. The results indicate that high accumulation of Na⁺ and Cl^– ions was responsible for the growth reduction observed in salinised plants. However, the growth reduction observed in water-stressed plants was caused by a dehydration process.     

Effect of NaCl on growth,ion composition and ascorbic acid concentrations of capsicum fruit

Potted plants of Capsicum annuum, cultivar ‘Long Sweet Yellow’, were restricted to two fruits each and supplied with 0, 10, 25 and 50 mM NaCl. Chloride concentrations exceeded sodium concentrations in ripe fruit from all salt-treatments. The difference was 2.5-fold in ripe fruit from plants treated with 50 mM NaCl. Fruits from the 50 mM treatment were markedly lower in fresh weight and were of a more intense colour than control fruit. Fruit ripening was accelerated by all salt-treatments, but the fresh weight to dry weight ratio of ripe fruit was reduced; the reduction was in proportion to the stress applied.A significant correlation was found between fruit ascorbic acid and Ca^{2 +} concentrations. Fruit Ca^{2 +} was reduced by salinity, but the reduction was not in proportion to sodium chloride concentration. Additional calcium nitrate in the nutrient solution increased the Ca^{2 +} content and ascorbic acid concentration in fruit on control plants but not in fruit from plants treated with 50 mM NaCl. Instead, these fruit showed a marked increase in Na⁺.     

Moderating water stress in tomato (Lycopersicon esculentum Mill.) plants by application of specific nitrogen doses

Summary

The effect of different doses of nitrogen on water stress in tomato (Lycopersicon esculentum Mill. ‘Royesta’) plants grown in a sandy soil and exposed, or not, to long-term water stress was studied. Nitrogen dose treatments consisted of Hoagland’s solution (N1 treatment), Hoagland’s solution + 40 mM NO₃^– (N2 treatment), or Hoagland’s solution + 80 mM NO₃^– (N3 treatment) applied every 3 d, for a total of seven applications following plant establishment. Subsequently, daily application of 80% (stressed) or 100% (unstressed) of the water evapotranspired by control plants the previous day was combined, factorially, with the three nitrogen treatments, for a period of 2 weeks. The leaf fresh weight (FW) at full turgor:leaf dry weight (DW) ratio was high in plants under the N1 and N3 stress treatments, with no significant difference between them soon after the start and at the end of the water stress treatment. However, the N2 treatment produced a significant increase in the ratio in well-watered plants, but not in water-stressed plants at the end of the stress period. The surface area per leaf was greater in stressed than in control plants, except for N2. Leaf water potential was greatly reduced in stressed N2 and N3 plants, but was unaltered in their well-watered counterparts. The significant increases in relative water content at the turgor loss point (around 3%) and in cell membrane rigidity (an increase of more than 125% in the bulk modulus of elasticity) clearly indicate an osmotic adjustment in stressed N2 plants, confirming that this N dose moderated the effects of the water stress imposed on N2 plants.     

Irrigation of Myrtus communis plants with reclaimed water: morphological and physiological responses to different levels of salinity

Summary

The influence of irrigation with different sources of reclaimed water on physiological and morphological changes in Myrtus communis plants was investigated to evaluate their adaptability to such conditions. M. communis plants, growing in a growth chamber, were subjected to four irrigation treatments over 4 months (120 d): a control [tap water (0.8 dS m^–1), leaching 10% (v/v) of the applied water] and three reclaimed water irrigation treatments, namely 1.5 dS m^–1 leaching 25% (v/v) of the applied water (RW1), 4.0 dS m^–1 leaching 40% (v/v) of the applied water (RW2), and 8.0 dS m^–1 leaching 55% (v/v) of the applied water (RW3). After treatment, all plants were irrigated with tap water, as for the control plants, for a further 2 months (60 d). At the end of the first period (4 months), none of the myrtle plants showed any adverse change in biomass and the average total dry weight (DW) increased by 53% in treatment RW2. However, at the end of the treatment and recovery period (180 d), accumulations of Cl^– ions, and especially Na⁺ ions, negatively affected the growth of all RW3 plants. Plants irrigated with all three reclaimed water samples had increased difficulty in taking-up water from the substrate (i.e., they had lower leaf water potential and relative water content values). RW2 plants showed a better response in their gas exchange parameters. The use of reclaimed water decreased leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios, but no chlorosis or necrosis were observed. The three reclaimed water samples had different effects on the myrtle plants depending on the specific chemical properties of the water. Leaching was found to be important to minimise the negative effects of salinity in the irrigation water.     

硝酸钙处理对菊花扦插生根及抗氧化酶活性的影响

以切花菊品种‘万盛’为材料,研究了不同浓度Ca(NO₃)₂处理对菊花扦插生根及其过程中插穗叶片超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）活性以及膜质过氧化产物丙二醛（MDA）含量的影响。结果表明,60 mg·L^-1 Ca²⁺处理的生根数最多,而且插穗鲜样质量和干样质量也比对照明显增加,而80 mg·L^-1Ca²⁺处理的生根数、插穗鲜样质量和干样质量以及生根率比对照减少。60 mg·L^-1 Ca²⁺处理的SOD、POD、CAT和APX活性与其它处理相比显著增加,MDA含量明显减少。以上结果表明,在菊花扦插过程中,采用适当浓度的Ca2+处理可以提高插穗叶片SOD、POD、CAT和APX等保护酶的活性和降低MDA含量,从而促进菊花扦插生根,并提高扦插苗品质。     

Morpho-Physiological Responses of Grape Rootstock ‘Dogridge’ to Arbuscular Mycorrhizal Fungi Inoculation Under Salinity Stress

Effects of arbuscular mycorrhizal fungi (AMF) alone or in combination with bacterial consortium (AMF+BC) inoculation prior to induced salinity (NaCl @ 150 or 250 mM) were studied on root growth; plant biomass; leaf area; Na⁺ and K⁺ contents; leaf water potential (Ψ_w); osmotic potential (Ψ_π); photosynthesis rate (P_n); and contents of chlorophyll, phytohormones, and polyamines in the grape rootstock ‘Dogridge’, popular among Indian vine growers. AMF inoculation in the NaCl untreated rootstocks plants increased root growth, root and shoot biomass, and leaf area and improved leaf Ψ_w, Ψ_π, P_n, and chlorophyll content, and also countered the stress-induced decline in the NaCl treated plants. The abscisic acid (ABA), cytokinins, and polyamine-spermidine and spermine contents in the leaves of NaCl untreated or treated were significantly increased by the AMF inoculation. Among the treatments, AMF with BC was relatively more effective than AMF alone with respect to changes in above morpho-physiological characters. The results depicted that AMF (AMF alone or AMF+BC) inoculation significantly improved salinity tolerance of grape rootstock and tolerance is induced by improvements in plant water balance, K⁺:Na⁺ ratio, and P_n, besides distinct accumulations in ABA and polyamines-spermine and spermidine. The above findings have potential in suggesting the AMF usefulness in improving the efficacy of ‘Dogridge’ rootstock in grape cultivation under salt affected soils.     

Exogenous CaCl2 reduces salt stress in sour jujube by reducing Na+ and increasing K+, Ca2+, and Mg2+ in different plant organs

In this study, we investigated the effects of 10 mM CaCl₂ on membrane permeability, malondialdehyde (MDA), reactive oxygen species (ROS), and Na⁺, K⁺, Ca²⁺, and Mg²⁺ concentrations in different organs of sour jujube grown under 150 mM NaCl stress. Our results showed 73% leaf wilting in the Na treatment. The Na treatment significantly increased leaf superoxide (O₂^.?) production rates, hydrogen peroxide (H₂O₂) concentrations, cell membrane permeability, MDA concentrations, and Na⁺ concentrations in roots, stems, and leaves. The Na treatment significantly reduced K⁺, Ca²⁺,and Mg²⁺ concentrations in roots, but increased K⁺ concentrations in stems. Compared with the Na treatment, 39% of the leaves showed wilting symptoms in the Na+Ca treatment. The Na+Ca treatment significantly decreased leaf O₂^.? production rates, H₂O₂ concentrations, cell membrane permeability, and MDA concentrations. Moreover, the Na+Ca treatment (1) significantly reduced Na⁺ concentrations in roots, stems, and leaves; (2) significantly increased root K⁺ concentrations; (3) significantly increased K⁺/Na⁺ ratios in roots; (4) significantly increased Ca²⁺ concentrations in stems and leaves, and Mg²⁺ concentrations in roots. In conclusion, exogenous CaCl₂ reduces NaCl stress in sour jujube by reducing Na+ concentrations and increasing K⁺, Ca²⁺, and Mg²⁺ concentrations in various plant organs.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.     

Cloning of Ceylon olive (Elaeocarpus serratus L.) using conventional methods

Ceylon olive (Elaeocarpus serratus L.; family Elaeocarpaceae) is an under-utilised edible fruit tree that is sparsely distributed in the southern peninsula of the Indian sub-continent. Fresh and ripened fruit are edible and are used to prepare value-added products such as squash, jams and pickles. Methods to produce clonal E. serratus plants using softwood cuttings, air-layers, and grafts were investigated. Softwood cuttings were collected during the wet summer season (June–August) and showed 96.7% rooting success following 2.5 mM indole-3-butyric acid (IBA) treatment for 3 h. Hardwood cuttings collected during the wet summer season and subjected to IBA treatment failed to root. The duration of the auxin treatment significantly influenced the rooting percentage of softwood cuttings. Seasonal variations in the rooting response of softwood cuttings was also noted. The wet summer (June–August) was the best season for rooting softwood cuttings. Air-layers of hardwood branches, prepared during the wet summer season by pre-treating with 7.5 mM IBA resulted in 87.1% rooting. The spliced grafting technique could be applied also to elite Ceylon olive clones, with 70% and 50% survival rates of softwood and hardwood grafts, respectively. Ceylon olive could therefore be cloned by adopting these methods. Propagation based on softwood cuttings would facilitate moderate-scale cloning of this valuable, elite germplasm.     

Pre-conditioning ornamental plants to drought by means of saline water irrigation as related to salinity tolerance

This study examines the feasibility of using saline irrigation water for commercial pot cultivation of three ornamentals: Calceolaria hybrida, Calendula officinalis and Petunia hybrida. Two saline treatments were assayed: irrigation with low saline tap water (electrical conductivity = 1.16 dS m⁻¹), and irrigation with a high saline solution of NaCl 100 mM + CaSO₄ 10 mM + MgSO₄ 2.5 mM (electrical conductivity = 12.5 dS m⁻¹). When the control plants reached marketable size the watering was stopped and the plant response to drought was studied. Petunia and Calceolaria were tolerant to salinity. Petunia saline-treated plants reduced their growth slightly and increased N and chlorophyll contents in the leaves. Calceolaria experienced a strong reduction in growth and a delay in flowering but no toxicity symptoms or mortality was recorded. These species were moderate NaCl accumulators. Calendula was sensitive to salinity: 16% of the plants died and the surviving ones experienced a heavy reduction of growth, a decrease in chlorophyll and a large accumulation of NaCl in the leaves. Saline pre-conditioned plants of Calceolaria and Petunia were tolerant to drought. In these plants, leaf water content and, specifically, leaf relative water content were sustained longer than in non-pre-conditioned plants throughout the drought period. In Calendula, leaf relative water content decreased at the same rate in pre-conditioned and non-pre-conditioned plants. Consequently, salinization did not confer drought resistance upon this species. Possible factors determining the tolerance to drought in saline pre-conditioned plants are discussed.     

Alleviation of salt-induced adverse effects in eggplant (Solanum melongena L.) by glycinebetaine and sugarbeet extracts

Two eggplant cultivars, Dilnasheen and Bemisal, were selected to assess whether pure GB and sugarbeet extract could effectively ameliorate the harmful effects of salt stress on eggplant (Solanum melongena L.), under saline conditions. Salt stress markedly suppressed the growth, yield, photosynthetic capacity, internal CO₂ level, transpiration, and stomatal conductance in both cultivars. Potassium (K⁺) and Ca²⁺ contents and K⁺/Na⁺ ratios of both root and leaf were also reduced, while GB and proline in leaves, and Na⁺ and Cl⁻ contents in roots and leaves were significantly enhanced. Exogenously applied glycinebetaine and sugarbeet extracts significantly counteracted the salt-induced adverse effects on growth, yield, various gas exchange characteristics, GB and leaf K⁺, Ca⁺, Cl⁻ and Na⁺. However, GB and sugarbeet extract showed differential effects on photosynthetic rate, stomatal conductance and transpiration, internal CO₂ level, C_i/C_a ratio, leaf K⁺, Ca²⁺, and Cl⁻ contents, and K⁺/Na⁺ ratio. Sugarbeet extract proved better than the GB in improving growth, photosynthetic rate, transpiration, stomatal conductance, yield and GB accumulation. Since, sugarbeet extract contains a substantial amount of GB along with a variety of other important nutrients so it was found as effective as pure GB in improving growth and some key physiological processes in eggplant under salt stress. Thus, it can be used as an alternative cheaper source of GB for its use as an ameliorative agent for protecting plants against the hazardous effects of salt stress.     

Salicylic acid or heat acclimation pre-treatment enhances the plasma membrane-associated ATPase activities in young grape plants under heat shock

Proton pumps play an important role in the physiological activities of plants. Changes in membrane-associated H⁺- and Ca²⁺-ATPase activities in heat-shocked plants after heat acclimation (HA) or salicylic acid (SA) pre-treatment in annual young grape plants (Vitis vinifera L. cv. Jingxiu) were investigated. ATPase activity was assayed through biochemical analysis in which two-phase partitioning was used to purify plasma membranes and cerium trichloride was precipitated with an electromicroscopic cytochemical method. The plasmalemma H⁺- and Ca²⁺-ATPase activities were higher in HA- or SA-pre-treated plants than in controls. The stability of H⁺- and Ca²⁺-ATPase activities in pre-treated plants always remained at higher levels during subsequent heat shock treatment, which was consistent with the observations made using an electromicroscope. A number of cerium phosphate grains representing enzyme activity in HA- or SA-pre-treated plants were observed 6 h following heat shock, whereas no grains were found in control plants under the same conditions. These results suggest that the changes in the activities of plasma membrane H⁺- and Ca²⁺-ATPase contributed to the thermotolerance induced by either HA or SA pre-treatment in young grape plants and the two pre-treatments may have had the some same regulatory mechanism.     

Mineral nutrient requirements and effects of CO2 enrichment on Gerbera microcuttings

Summary

The effects of CO2 concentration (350 and 1200 μmol mol^-1), growing media (peat + perlite, 3:1, peat + coco dust, 1:1; and coco dust alone), and concentration of nutrient solution (EC 2.1 and 2.8 mS cm^-1) on growth of gerbera microcuttings, leaf nutrient content, and the chemical properties of the growing media were investigated. Plants grown in peat + coco dust had the highest dry weights of leaves and roots. There were no significant differences in the fresh and dry weights of leaves and roots due to concentration of nutrient solution. CO₂ enrichment increased all growth variables, except leaf number. Leaf nutrient content of gerbera cuttings and chemical properties of growing media after eight weeks of growth, with reference to all treatments, are discussed and presented as tables.     

Comparison of growth,leaf water relations and gas exchange of Cistus albidus and C. monspeliensis plants irrigated with water of different NaCl salinity levels

Four-month-old potted Cistus albidus and Cistus monspeliensis plants growing in a greenhouse were submitted to saline stress from 9 August to 2 December, using irrigation water containing 0, 70, and 140 mM NaCl. C. monspeliensis plants are more tolerant to saline irrigation water than C. albidus plants, mainly due to their capacity to resist stress with a lower plant biomass and canopy area; furthermore, they showed no leaf necrosis symptoms. Under saline stress conditions the main growth limiting factor in both species was photosynthesis. Both Cistus species responded to saline stress by developing avoidance and tolerance mechanisms. The avoidance mechanisms took place at a morphological and physiological level. Morphologically, the reduction in the canopy area can be considered a mechanisms for regulating water loss via transpiration. Treated C. monspeliensis plants showed a greater capacity to absorb water and were able to conserve it more efficiently than C. albidus plants. Tolerance mechanisms included Na⁺ and Cl⁻ inclusion and osmotic adjustment. However, the reaction of each species to osmotic adjustment was different, because in C. monspeliensis plants the osmotic adjustment was unable to prevent a decrease in leaf turgor. The curvilinear relationship between P_n and g_l observed in C. monspeliensis plants indicated stomatal limitation of photosynthesis below a leaf conductance of about 160 mmol m⁻² s⁻¹. In C. albidus plants, a linear relationship between photosynthesis and leaf conductance rather a curvilinear model was significant, indicating limitation of the photosynthetic capacity.     

Measurement system of whole-canopy carbon dioxide exchange rates in grafted cucumber transplants in which scions were exposed to different water regimes using a semi-open multi-chamber

A continuous CO₂ measurement system was developed to monitor the CO₂ exchange rate of the whole canopy of grafted transplants using semi-open multiple chambers. Air heating or cooling and humidification inside a healing box were under control, if needed. To test the system, the gas exchange rate of the cucumber (Cucumis sativus L.) transplants grafted onto pumpkin (Cucurbita maxima cv. ‘New-Shintozwa’) was analysed. During the healing and acclimatisation of the grafted cucumber plants, the air temperature in the box remained constant at night but ranged above 1 °C of a set value under high humidity in daytime. The relative humidity was kept within the set point during the daytime, and it nearly reached 100% at night when not controlled. The cucumber seedlings were exposed to different water stresses before grafting, and the water potentials of each treatment were −0.579 (non-stressed), −0.814 (mildly water-stressed), and −0.870 MPa (strongly water-stressed) on grafting. At the water-stressed scions, leaf expansion was inhibited by 30.9–53.3% compared with the non-stressed scions. Therefore, the gas exchange rates of the strongly water-stressed scions based on the leaf area were decreased to 72.7% compared with the non-stressed scions. After grafting, the apparent photosynthesis of the transplants of all treatments was negative, with higher respiration in the strongly water-stressed scions during the initial period of healing. However, they turned to positive values and exceeded those of the non-stressed scions from three days after grafting. This result provides critical information that the water column is physiologically connected between the stock and scion within two days after grafting. As a result of water stress, the leaf area and dry weight of the transplants in the strongly water-stressed scions were inhibited by 67.5% and 83% compared with the non-stressed scions at the end of acclimatisation. In contrast, the relative growth rate and graft-take of the strongly water-stressed transplants were slightly increased, which suggests that the water stress prior to grafting alleviated the water demand of the scion. This system may provide useful information for diagnosis at the early stage by monitoring the whole canopy's photosynthesis over a long term.