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.     

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.     

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.     

Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Leaf age and environmental effects on gas exchange in leaves of bananas (cv. Williams) growing in a hot,arid environment

Summary

The effects of leaf segment, leaf position on the plant, leaf age and photosynthetic photon flux density (PPFD) at the leaf surface were examined on leaf gas exchange of cv. Williams banana. All measurements were made on irrigated plants at the end of the dry season (September to November) over three years in Kununurra, WA, (Lat 16×S) a hot, arid region of North Western Australia. Net photosynthesis (P_n) did not differ between the segments on the leaf except when they received different PPFD. P_n reached a maximum of 20 to 25 μmol CO₂ m^–2s^–1,9 d after the leaf had unrolled, that is when another new leaf had emerged and the measured leaf was in the second leaf position. Leaf chlorophyll concentration stabilized 7 d after unrolling but then increased slowly with time. The reduced rates of leaf gas exchange of older leaves are most likely a result of shading by younger leaves. The highest measured PPFD of 1800 (junol quanta m^–2s^–1 did not saturate P_n. Indeed, in a series of experiments, P_n measured at 1500 μmol quanta m^–2s^–1, was only 13 to 40% of the calculated maximum P_n at saturated values of PPFD, assuming P_n responds to PPFD in a hyperbolic function. In this study although P_n was lower in older leaves, the calculated internal CO₂ concentration did not increase even at high leaf temperatures and leaf-to-air vapour pressure differences. Therefore, the photochemistry of the chloroplasts did not constrain P_n. To compare gas exchange measurements among experimental treatments, care is required as leaf position and environmental effects can greatly influence results. Our data suggest that differences in P_n between treatments should take account of PPFD, especially in this environment where the maximum PPFD measured did not saturate P_n of individual leaves.     

Indicators of nitrogen status for ornamental woody plants based on optical measurements of leaf epidermal polyphenol and chlorophyll contents

Indicators of plant nitrogen (N) status adapted to woody ornamental plants are essential for the adjustment of fertilization practices in nurseries. The objective of this study was to investigate whether optical measurements of leaf epidermal polyphenol (EPhen) and chlorophyll (Chl) contents could be used as N status indicators for woody deciduous and evergreen ornamental plants. One-year-old plants of Lagerstroemia indica, Callicarpa bodinieri and Viburnum tinus were grown outdoors in containers. They received low (TN₁, 4 mg L⁻¹) or high (TN₂, 105 mg L⁻¹) levels of N during 2 months in spring and summer. TN₁ treatment limited shoot growth from 28 to 37 days after treatment initiation in Lagerstroemia and Callicarpa, respectively. Shoot growth was unaffected until day 176 in Viburnum. The mass-based leaf N content (N_M) of a sample of young expanded leaves exposed to direct sunlight was tightly correlated with shoot N content and differentiated treatments several weeks before shoot growth reduction for the three species. N_M was therefore used as an index of plant N status. EPhen and Chl contents were recorded with Dualex™ and SPAD-502 leaf-clip meters, respectively. Dualex values were strongly and negatively correlated with N_M, and differentiated the treatments early in the experiment, in all three species. SPAD values were positively correlated with N_M for Lagerstroemia and Callicarpa, but not for Viburnum, because large variations in leaf mass per area (LMA) in this species compensated for variations in leaf dry mass invested in Chl. The SPAD/Dualex ratio was used to assess changes in the proportion of leaf dry mass allocated to proteins and polyphenols in response to fertilization. It differentiated between the treatments early in the experiment and was correlated with N_M in all three species.     

The effect of water availability and quality on photosynthesis and productivity of soilless-grown cut roses

Low matric and to a lesser extent osmotic potential reduce significantly leaf area and rose yield. Net assimilation rate and transpiration are also negatively affected although less dramatically. Low water potential causes an increase in the water use efficiency of greenhouse roses when tested in closed, no-discharge systems. When a stable osmotic potential is maintained in open systems, using increased leaching fraction (LF), low osmotic potential results in lower water use efficiency. Osmotic potential in porous media serving for greenhouse cut-rose production is usually lower than the matric potential. However, low matric potential in porous media is usually accompanied by very low unsaturated hydraulic conductivity, causing localized zones of very low matric potential adjacent to the root–medium interface. This phenomenon, that cannot be measured using tensiometers, is the main limiting factor to water uptake by plant roots. Restricted water uptake results in low leaf water potential and cessation of leaf and shoot expansive growth.Combined effects of drought and salinity on photosynthesis have been studied for a number of agronomic crops but studies on roses have been limited. In most greenhouse crops a close relationship between total water potential in the root zone (Ψ_t^soil) and in the shoot (Ψ_t^shoot) is found and there are good indications about the plant’s ability to make osmotic adjustments in order to lower Ψ_t^shoot and prevent excessive water losses from the leaves thus maintaining the plant’s turgidity. Future studies conducted with roses can provide a better insight into the adaptive processes within the plants when exposed to salt or water stresses.     

Regulated deficit irrigation in potted Dianthus plants: Effects of severe and moderate water stress on growth and physiological responses

The purpose of this study was to analyze the physiological and morphological response of carnation plants to different levels of irrigation and to evaluate regulated deficit irrigation as a possible technique for saving water through the application of controlled drought stress. Carnations, Dianthus caryophyllus L. cultivar, were pot-grown in an unheated greenhouse and submitted to two experiments. In the first experiment, the plants were exposed to three irrigation treatments: (control); 70% of the control (moderate deficit irrigation, MDI) and 35% of the control (severe deficit irrigation, SDI). In the second experiment, the plants were submitted to a control treatment, deficit irrigation (DI, 50% of the control) and regulated deficit irrigation (RDI). After 15 weeks, MDI plants showed a slightly reduced total dry weight, plant height and leaf area, while SDI had clearly reduced all the plant size parameters. RDI plants had similar leaf area and total dry weight to the control treatment during the blooming phase. MDI did not affect the number of flowers and no great differences in the colour parameters were observed. RDI plants had higher flower dry weight, while plant quality was affected by the SDI (lower number of shoots and flowers, lower relative chlorophyll content). Leaf osmotic potential decreased with deficit irrigation, but more markedly in SDI, which induced higher values of leaf pressure. Stomatal conductance (g_s) decreased in drought conditions more than the photosynthetic rate (P_n). Osmotic adjustment of 0.3 MPa accompanied by decreases in elasticity in response to drought resulted in turgor less at lower leaf water potentials and prevented turgor loss during drought periods.     

Photosynthetic and growth responses of juvenile Chinese kale (Brassica oleracea var. alboglabra) and Caisin (Brassica rapa subsp. parachinensis) to waterlogging and water deficit

Chinese kale (Brassica oleracea var. alboglabra) and Caisin (Brassica rapa subsp. parachinensis) are leafy vegetable crops grown in south-east Asian countries where rainfall varies dramatically from excess to deficit within and between seasons. We investigated the physiological and growth responses of these plants to waterlogging and water deficit in a controlled experiment in a glasshouse. Juvenile plants were subjected to waterlogging or water deficit for 19 days in case of Chinese kale and 14 days in case of Caisin and compared with well-watered controls. Caisin tolerated waterlogging better than Chinese kale because it produced hypocotyl roots and gas spaces developed at the stem base. In Chinese kale, waterlogging reduced plant fresh weight (90%), leaf area (86%), dry weight (80%) and leaf number (38%). In contrast, waterlogging had no impact on leaf number in Caisin and reduced plant fresh and dry weights and leaf area by 60–70%. Water deficit reduced leaf area, fresh weight and dry weight of both species by more than half. Leaf number in Chinese kale was reduced by 38% but no effect occurred in Caisin. Water deficit increased the concentration of nitrogen in the leaf dry matter by more than 60% in both species and the leaf colour of water deficient plants was dark green compared with the leaf colour of well-watered plants. Soil water deficit delayed flowering of Caisin while waterlogging accelerated it. Thickening and whitening of the cuticle on the leaves of Chinese kale probably increased its ability to retain water under drought while Caisin adjusted osmotically and Chinese kale did not. Waterlogging and water deficit had strong effects on leaf gas exchange of both Brassica species. Water deficit closed the stomata in both species and this was associated with a leaf water content of 9 g g⁻¹ DW. In contrast, waterlogging reduced conductance from 1.0 to 0.1 mol H₂O m⁻² s⁻¹ in direct proportion to changes in leaf water content, which fell from 11 to 5 g g⁻¹ DW. This separation of the effects of water deficit and waterlogging on conductance was reflected in transpiration, internal CO₂ concentration and net photosynthesis. In conclusion, Chinese kale and Caisin showed rather different adaptations in response to waterlogging and water deficit. Caisin was more tolerant of waterlogging than Chinese kale and also showed evidence of tolerance of drought. There is genetic variation to waterlogging within the Brassica genus among the leafy vegetables that could be used for cultivar improvement.     

Moving lamps increase leaf photosynthetic capacity but not the growth of potted gerbera

To investigate the responses of leaf photosynthesis and plant growth to a moving lighting system, potted gerberas (Gerbera jamesonii H. Bolus ex J.D. Hook “Festival”) were grown under supplemental lighting in a greenhouse with either a stationary or a moving lighting system positioned above the benches. The stationary system consisted of a fixed high pressure sodium (HPS) lighting system, while the moving lighting system consisted of a moving HPS fixture attached to a cable system to move the light fixture back and forth over the crop. In both cases, the supplemental lighting was applied from 6:00 to 24:00 h with the same supplemental daily light integral (4.9 mol m⁻² day⁻¹). Moving lamps significantly increased leaf photosynthetic capacity as represented by light saturated net CO₂ exchange rate (NCER) (A_sat), light- and CO₂-saturated rate of NCER (A_max), maximum rate of Rubisco carboxylation (V_cmax), maximum rate of electron transport (J_max) and rate of triose phosphate utilization. However, in situ leaf NCER and stomatal conductance, leaf chlorophyll content index, leaf area, leaf thickness, fresh weight of plants were significantly lower under moving lighting than under stationary lighting. It is suggested that the reduced growth of plants under moving lighting might be due to (1) the overall lower light use efficiency of leaves under moving lighting than those under stationary lighting; (2) the slower response time of the photosynthetic system compared to the rate of change in light intensity under moving lighting.     

Responses of eggplant to drought. I. Plant water balance

Eggplant (Solanum melongena L.) is known to have a higher resistance to drought than have other vegetables. Studies were made to see whether this property can be explained by its physiological responses. Water was withheld from plants and measurements were made of sap osmotic potential (ψ_os), leaf pressure potential (ψ_p), stomatal diffusive resistance to water vapour (r_s), relative water content of leaf (RWC), whole plant transpiration, leaf water potential (ψ_leaf), and soil water potential (ψ_soil). The first 4 parameters varied linearly with ψ_leaf and transpiration varied exponentially. There was a parabolic relation between ψ_leaf and ψ_soil. The severely stressed plants were rewatered and underwent the same measurements 1 day later (“recovery treatment”). Compared with some other vegetables reported in the literature, ψ_p and RWC remained higher in droughted eggplant. This species has also a better stomatal control on transpiration. There was an after-effect of drought on the stomates. In recovery treatment, ψ_p values exceeded those of the control. This may have functional significance in resumption of growth after stress is alleviated.     

Plant growth regulators and flowering of Brunonia and Calandrinia sp.

Brunonia australis R. Br (Goodeniaceae) and Calandrinia (Portulacaceae), native to Australia, are potential new flowering potted plants. This research investigated the role of daylength and growth regulators, Gibberellic acid (GA₃) and paclobutrazol (Pac), to control vegetative growth, peduncle elongation and flowering of Brunonia and Calandrinia. Plants were grown under long days (16 h), short days (11 h) and 8 weeks under short day then transferred to long day (SDLDs). Plants in each daylength were treated with GA₃, Pac, and GA₃+ Pac. GA₃ was applied as 10 μL drop of 500 mg L⁻¹ concentration to the newest mature leaf. A single application of Pac was applied as a soil drench at 0.25 mg a.i. dose per plant. Both Brunonia and Calandrinia flowered earlier in long days but still flowered in short days, so both can be classified as facultative LD plants. Brunonia under SDLDs were more vigorous and attractive than plants under LDs while still being more compact than plants under SDs. In Brunonia, GA₃ promoted earlier flowering and increased the number of inflorescences under SDs. Pac at 0.25 mg a.i. per plant applied alone or in combination with GA₃ had extended flower development in Brunonia, and resulted in a reduced number of inflorescences per plant compared to the control plants. Vegetative growth of Calandrinia was similar under LDs, SDs and SDLDs, whereas GA₃ application increased plant size. Pac-treated Calandrinia looked compact and attractive, and Pac application did not affect time to flower and flower number.     

Calcium starvation increases salt susceptibility in olive plants but has no effect on susceptibility to water stress

Summary

The responses of leaf water status, growth, and ion concentrations to water or to saline stresses were compared in olive cuttings of different Ca²⁺ status. Mist-rooted ‘Picual’ olive cuttings were grown in a greenhouse in 2 l plastic pots containing perlite. A nutrient solution with or without 2.5 mM CaCl₂ was initially used to irrigate the plants. When the Ca²⁺-starved plants differed in height from the Ca²⁺-treated plants, water or saline stress (i.e., no irrigation or 75 mM NaCl, respectively) were applied. The results indicated that Ca²⁺ increased growth in saline-treated plants, but not in water-stressed plants. After 98 d growth, the stresses were relieved and the plants were irrigated again with or without Ca²⁺. Growth increased and leaf water status was increased during this recovery period, but no direct effects of Ca²⁺ were observed in the response of plants to stress-relief. We suggest that the beneficial effect of Ca²⁺ on tolerance to salt stress in olive plants was related to protection against Na⁺ toxicity, because there was no response of water-stressed plants to the supply of Ca²⁺.     

Induction of drought tolerance by paclobutrazol and irrigation deficit in Phillyrea angustifolia during the nursery period

Phillyrea angustifolia is a native Mediterranean species, which has recently been considered suitable for landscaping purposes. We hypothesize that hardening plants in the nursery could increase their tolerance of drought after transplanting. The effects of paclobutrazol (PBZ) and different irrigation regimes applied to seedlings planted in 4.5-L plastic pots were investigated. PBZ was applied as a substrate drench at 0 mL L⁻¹ (untreated control), 30 mL L⁻¹ and 40 mL L⁻¹ per plant and three drip irrigation treatments were used: I100, plants watered at water-holding capacity, I60, plants watered to 60% of I100, and I40, plants watered to 40% of I100. Plants were pot-grown in an unheated greenhouse near the Mediterranean coast of SE Spain. A reduction in plant height and stem diameter was observed one month after being drenched by PBZ. The irrigation regime significantly affected plant height after three months of cultivation and did not affect stem diameter during the nursery period. Significant interaction between the irrigation regime and PBZ dose was evident for plant height during the nursery period. I100 and untreated PBZ plants had the lowest stomata density. PBZ doses significantly reduced canopy weight and leaf area compared with the control. I60 plants showed the greatest leaf area and canopy dry weight, and the highest root length, dry weight, volume and number of forks. Both I60 and I40 treatments showed an equally high water use efficiency (WUE) (calculated as the total plant dry matter divided by the total amount of water supplied by the irrigation treatments). In general, PBZ induced a suite of morphological adaptations (increased root-to-shoot ratio and stomata density, decreased leaf area reduction, fine roots, etc.) that might allow the plants to tolerate drought after transplanting.     

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.     

Particulate matter pollution capture by leaves of seventeen living wall species with special reference to rail-traffic at a metropolitan station

Atmospheric Particulate Matter (PM) constitutes a considerable fraction of urban air pollution, and urban greening is a potential method of mitigating this pollution. The value of living wall systems has received scant attention in this respect. This study examined the inter-species variation of particulate capture by leaves of seventeen plant species present in a living wall at New Street railway station, Birmingham, UK. The densities of different size fractions of particulate pollutants (PM₁, PM_2.5 and PM₁₀) on 20 leaves per species were quantified using an Environmental Scanning Electron Microscope (ESEM) and ImageJ image-analysis software. The overall ability of plant leaves to remove PM from air was quantified using PM density and LAI (Leaf Area Index); any inter-species variations were identified using one-way Anova followed by Tukey’s pairwise comparison. This study demonstrates a considerable potential for living wall plants to remove particulate pollutants from the atmosphere. PM capture levels on leaves of different plant species were significantly different for all particle size fractions (P < 0.001). Smaller-leaved Buxus sempervirens L., Hebe albicans Cockayne, Thymus vulgaris L. and Hebe x youngii Metcalf showed significantly higher capture levels for all PM size fractions. PM densities on adaxial surfaces of the leaves were significantly higher compared to abaxial surfaces in the majority of the species studied (t-test, P < 0.05). According to EDX (Energy Dispersive X-ray) analysis, a wide spectrum of elements were captured by the leaves of the living wall plants, which were mainly typical railway exhaust particles and soil dust. Smaller leaves, and hairy and waxy leaf surfaces, appear to be leaf traits facilitating removal of PM from the air, and hence a collection of species which share these characters would probably optimize the benefit of living wall systems as atmospheric PM filters.     

Quantifying the effects of nitrogen on fruit growth and yield of cucumber crop in greenhouses

Nitrogen supply can improve crop growth and yield. An over-use of nitrogen fertilizer in greenhouse crop productions, however, causes many environmental problems. The aim of this study was to quantify the effects of nitrogen on fruit growth and yield so as to facilitate the optimization of nitrogen management for cucumber (Cucumis sativus) crop in greenhouses. Four experiments with different levels of nitrogen treatments, substrates and planting dates on cucumber (cv. Deltastar) were conducted in greenhouses located at Shanghai during 2005 and 2007. Using data of one experiment, seasonal time courses of leaf nitrogen content (N_L), leaf area per plant (LA), and the number of fruits growing per plant (n_FG), as well as time course of the length of individual fruit growing on the plant (L_F(i)) under different levels of nitrogen supply conditions were, respectively, determined as functions of a photo-thermal index (PTI). The impact of N_L on LA was determined by curve fitting to the experimental data. The source/sink ratio (LA/n_FG), an indicative of the source size per fruit, was then derived from the seasonal time courses of LA and n_FG. The impact of N_L on L_F(i) was indirectly quantified by the relationship between source/sink ratio (LA/n_FG) and the elongation rate of individual fruit (R_FL(i)). Both the harvest date and fresh weight (W_F(i)) of individual fruit growing at different node, and number of harvested fruits (n_FH) were then calculated as functions of the fruit length. These quantitative relationships were assembled to form a model for predicting the effects of nitrogen on fruit growth and yield (fruit fresh weight per plant). Independent data from other experiments were used to validate the model. Our model gives satisfactory predictions of cucumber fruit growth and yield under different levels of nitrogen supply and growing season conditions. The coefficient of determination (r²) and the relative root mean squared error (rRMSE) between the predicted and measured values are, respectively, 0.92 and 0.22 (r², rRMSE) for leaf area per plant, 0.90 and 0.24 for the number of fruits growing on the plant, 0.91 and 0.22, 0.90 and 0.23, and 0.92 and 0.21, respectively, for the length, harvest date and fresh weight of individual fruit growing on the plant, 0.94 and 0.20 for yield. The model may be used for the optimization of nitrogen management for cucumber production in greenhouses. Further model calibration and test would be needed when applying this model to a wider range of conditions.     

Comparison of three pea cultivars (Pisum sativum) regarding their responses to direct and bicarbonate-induced iron deficiency

The aim of this work was to explore leaf characteristics underlining the difference in the sensitivity of pea cultivars (cv. Kelvedon, Douce and Lincoln) to Fe deficiency. Plants were grown in a greenhouse under controlled conditions in continuously aerated solution. Three treatments were used: 30 μM Fe (+Fe), 0 μM Fe (−Fe); direct deficiency and 30 μM Fe + 10 mM NaHCO₃ (+Fe+Bic); indirect deficiency for 12 days. Growth parameters, iron status, potassium content, chlorophyll fluorescence and photosynthetic capacity were studied. Our results showed that Fe deficiency led to a significant decrease of chlorophyll index (SPAD readings) and bivalent iron content in all Pisum sativum cultivars. The lower reduction was observed in Fe-deficient plants of Kelvedon and Douce. In addition, shoot length and whole plant dry weight were not affected by Fe deficiency in the latter cultivars. Both tolerant cultivars showed higher accumulation of potassium content in their leaves compared with the sensitive one. Moreover, both chlorophyll fluorescence ratios (F_v/F_m and F_v/F₀) were significantly decreased in all cultivars under both Fe deficiency treatments. The photosynthetic electron transport activity was reduced in the sensitive cultivar, especially in the absence of iron. The adverse effect of bicarbonate-induced Fe deficiency on the above mentioned parameters were more pronounced than that of the direct one. The capacity of both tolerant cultivars to preserve adequate chlorophyll synthesis, photosynthetic capacity and plant growth under iron-limiting conditions is related to the suitable nutrition of their leaves in ferrous iron, due to (at least partially) their higher potassium content.     

Nitrogen and irradiance levels affecting net photosynthesis and growth of young coffee plants (Coffea arabica L.)

Summary

Shoot growth attributes, leaf anatomical changes and net photosynthetic rates were determined in young coffee plants fertilized at high and low levels and subjected to shade or full sunlight. High nitrogen supply increased plant height irrespective of the light level imposed during growth, and promoted a larger leaf area in plants of the shade treatment. Specific leaf weight was 15% higher in plants grown in full sunlight than in shaded plants, at both nitrogen levels. The number of leaves developed on the orthotropic stem increased significantly under full irradiance and high nitrogen availability. Leaves were 11% thicker ih unshaded plants than in shaded ones, because of the increased size of the palisade and spongy parenchyma tissues. More thylakoids per granum and more grana per chloroplast were observed in shade-grown plants, mainly in those given high nitrogen treatment. Total nitrogen content expressed on a leaf-area basis was higher in sun plants supplemented with nitrogen, whereas chlorophyll a and b and protochlorophyll contents increased in shade-grown plants. Net photosynthetic rate in high nitrogen plants reached 7.19 µmol CO₂ m^?2 s^?1 in the full irradiance treatment, and 5.46 µmol CO₂ m^?2 s^?1 in shaded plants. Maximum net photosynthetic rates in the low nitrogen plants were 5.28 and 4.90 µmol CO₂ m^?2 s^?1 in sun and shade plants, respectively. Increased photosynthetic light saturation was observed in high irradiance plants (628 µmol m^?2 s^?1) relative to shade plants (359 µmol m^?2 s^?1) in the high nitrogen treatment. The same pattern was observed in low nitrogen plants. The apparent quantum yield of shade acclimated plants was 14% higher than in those grown in full sunlight. Our results indicate that coffee may be classified as a facultative shade species, exhibiting features of sun adapted plants coupled with shade acclimation attributes, this fairly high adaptive capacity to shade:sun transition being strongly influenced by the level of nitrogen nutrition given to the plants.     

Salinity stress in tomatoes can be alleviated by grafting and potassium depending on the rootstock and K-concentration employed

Plant production under salinity requires increased capacity for K⁺ homeostasis. For this purpose, supplementary K₂SO₄ in the nutrient solution and grafting on a tolerant rootstock were employed in two experiments to test whether grafting, potassium and their interactions can alleviate salinity stress in tomato (Solanum lycopersicum L.). In Exp-ion, plants were cultivated for 122 days to compare different ionic compositions: EC 9 dS m⁻¹ in EC_all (by macro-nutrients) and in EC_NaCl (by 64.2 mM NaCl), EC 12 dS m⁻¹ in EC_K (EC_NaCl + 25.8 mM K⁺). Exp-K⁺ was established to compare K⁺ concentrations of 6, 16 and 36 mM at 150 mM NaCl. In both Experiments, ‘ZS-5’, selected as a salt sensitive cultivar, was either self-grafted or grafted onto the cultivar ‘Edkawi’, reported as salt tolerant. Yield and growth, minerals, gas exchange, soluble sugars, and proline were analyzed. Different ionic treatments affected almost all characteristics considered while differences between rootstocks were rarely observed. No pronounced differences were found in shoot growth, yield and gas exchange between EC_all and EC_NaCl. EC_K did not show any salinity alleviative effects but inhibited even growth compared with the other treatments. In Exp-K⁺, 16 mM K⁺ increased plant growth, leaf soluble sugars and proline concentrations. 36 mM K⁺ did not further reduce upper leaf Na⁺ although leaf K⁺ concentration increased significantly. The results indicated that the response of tomato plant to NaCl stress was principally attributed to the osmotic component in Exp-ion, excessive K⁺ showed no mitigating effect on fruit yield and shoot growth. However, 16 mM K⁺ in the root environment enhanced the salt adaptive capacity of plants stressed at 150 mM NaCl. The use of the tolerant rootstock resulted in no ameliorative effects, owing to its susceptibility to blossom-end rot, failure in enhancing photosynthesis, and ineffectiveness of restraining the long-distance transport of Na⁺.