Review of salinity effects on abundance,growth, and survival of nearshore life stages of pink shrimp (Farfantepenaeus duorarum)

The pink shrimp (Farfantepenaeus duorarum) has been selected as an ecological indicator to assess ecological effects on estuaries of implementation of the Comprehensive Everglades Restoration Plan that seeks to restore historical freshwater flows and nearshore salinity regimes in southern Florida. Concern over altered freshwater delivery impacts on pink shrimp productivity was expressed as early as the 1960s. The present review assessed pink shrimp scientific literature of the past 75+ years (>500 publications) to glean information relevant to understanding potential influence of freshwater management on pink shrimp productivity. The review was organized around “Essential Fish Habitat” metrics concerning abundance, growth, survival, distribution, productivity, and behavior. It summarizes previous pink shrimp field, laboratory, and modeling studies. Where possible, statistical analyses and meta-analyses of previously published data were performed to investigate consistency among independent findings. Pink shrimp occur in a wide range of salinities (0.5–67 ppt). A majority of studies (53.3%) reported maximal abundance between ∼20 to 35 ppt salinities. One laboratory study reported maximal growth at 30 ppt. Meta-analysis of reported growth rates did not yield results due to non-convergence of regression models. Reported survival was maximal at ∼30 ppt and remained high (>80% survival) across salinities of ∼15 to 40 ppt. A regression model that combined survival data across studies confirmed a previously reported parabolic relationship between salinity and survival; in this regression, 35 ppt maximized survival. Productivity, conditional upon survival and growth, was maximized at polyhaline (18–30 ppt) conditions. Inshore hypersalinity (>40 ppt) may elicit young pink shrimp behavioral cues counterproductive to settlement in nearshore areas. Virtually no information exists regarding postlarval pink shrimp movement or preference relative to salinity gradients. Realization and preservation of nearshore polyhaline conditions and elimination of hypersalinity should maximize growth, survival, and density, thus improving pink shrimp productivity. New and updated statistical models predicting pink shrimp distribution, abundance, growth, survival, and productivity relative to salinity conditions are needed to better guide freshwater management decisions.     

Interactive effects of salinity and water depth on the growth of Melaleuca ericifolia Sm. (Swamp paperbark) seedlings

Melaleuca ericifolia Sm. (Swamp paperbark) is a common tree species in freshwater and brackish wetlands in southern and eastern Australia. The survival of this species in many wetlands is now threatened by increased salinity and inappropriate water regimes. We examined the response of 5-month-old M. ericifolia seedlings to three water depths (exposed, waterlogged and submerged) at three salinities (2, 49 and 60 dS m⁻¹). Increasing water depth at the lowest salinity did not affect survival, but strongly inhibited seedling growth. Total biomass, leaf area and maximum root length were highest in exposed plants, intermediate in waterlogged plants and lowest in submerged plants. Although completely submerged plants survived for 10 weeks at the lowest salinity, they demonstrated negative growth rates and were unable to extend their shoots above the water surface. At the higher salinities, M. ericifolia seedlings were intolerant of waterlogging and submergence: all plants died after 9 weeks at 60 dS m⁻¹. Soil salinities increased over time, and by Week 10, exceeded external water column salinities in both the exposed and waterlogged treatments. In exposed sediment, ∼90% of plants survived for 10 weeks at 60 dS m⁻¹ even though soil salinities reached ∼76 dS m⁻¹. No mortality occurred in the exposed plants at 49 dS m⁻¹, and small but positive relative growth rates were recorded at Week 10. We conclude that at low salinities M. ericifolia seedlings are highly tolerant of sediment waterlogging, but are unlikely to tolerate prolonged submergence. However, at the higher salinities, M. ericifolia seedlings are intolerant of waterlogging and submergence and died rapidly after 5 weeks exposure to this combination of environmental stressors. This research demonstrates that salinity may restrict the range of water regimes tolerated by aquatic plants.     

AFLP markers in the detection of Scirpus × mariqueter (CYPERACEAE) hybrid in China

Scirpus × mariqueter Tang & F.T. Wang (CYPERACEAE) is a pioneer plant of the tidal zone of estuaries of East Asia. Amplified fragment length polymorphisms (AFLP) were used to infer the relationship between S. × mariqueter and its putative progenitors, Scirpus planiculmis F. Schmidt and Scirpus triqueter L. The genetic distance between S. × mariqueter and S. triqueter was much higher than that between S. × mariqueter and S. planiculmis, and samples of S. × mariqueter and those of S. planiculmis did not form a monophyletic group, while the S. triqueter group formed a distinct monophyletic group. However, we also detected an apparent clustering of individuals of S. × mariqueter and S. planiculmis separately. Our results disprove the hybrid origin of S. × mariqueter and rather suggest that it is more closely related to S. planiculmis.     

Growth of eight Gambierdiscus (Dinophyceae) species: Effects of temperature,salinity and irradiance

Little is known about how the growth of individual Gambierdiscus species responds to environmental factors. This study examined the effects of temperature (15–34 °C), salinity (15–41) and irradiance (2–664 μmol photons m⁻² s⁻¹) on growth of Gambierdiscus: G. australes, G. belizeanus, G. caribaeus, G. carolinianus, G. carpenteri, G. pacificus and G. ruetzleri and one putative new species, Gambierdiscus ribotype 2. Depending on species, temperatures where maximum growth occurred varied between 26.5 and 31.1 °C. The upper and lower thermal limits for all species were between 31–34 °C and 15–21 °C, respectively. The shapes of the temperature vs. growth curves indicated that even small differences of 1–2 °C notably affected growth potentials. Salinities where maximum growth occurred varied between 24.7 and 35, while the lowest salinities supporting growth ranged from <14 to 20.9. These data indicated that Gambierdiscus species are more tolerant of lower salinities than is generally appreciated. Growth of all species began to decline markedly as salinities exceed 35.1–39.4. The highest salinity tested in this study (41), however, was lethal to only one species, Gambierdiscus ribotype 2. The combined salinity data indicated that differences in salinity regimes may affect relative species abundances and distributions, particularly when salinities are <20 and >35. All eight Gambierdiscus species were adapted to relatively low light conditions, exhibiting growth maxima at 50–230 μmol photons m⁻² s⁻¹ and requiring only 6–17 μmol photons m⁻² s⁻¹ to maintain growth. These low light requirements indicate that Gambierdiscus growth can occur up to 150 m depth in tropical waters, with optimal light regimes often extending to 75 m. The combined temperature, salinity and light requirements of Gambierdiscus can be used to define latitudinal ranges and species-specific habitats, as well as to inform predictive models.     

Comparison of salinity tolerance of three Atriplex spp. in well-watered and drying soils

Members of the Chenopodiaceae are well adapted to both salt and drought stress and can serve as model species to understand the mechanisms of tolerance in plants. We grew Atriplex hortensis (ATHO), A. canescens (ATCA), and A. lentiformis (ATLE) along a NaCL salinity gradient under non-water-limited conditions and in drying soils in greenhouse experiments. The species differed in photosynthetic carbon fixation pathway, capacity for sodium uptake, and habitat preferences. Under non-water-limited conditions, ATLE (C4) maintained high growth rates up to 30 g L⁻¹ NaCl. ATHO (C3) had lower growth than ATLE at high salinities, while ATCA (C4) grew more slowly than either ATLE or ATHO and showed no net growth above 20 g L⁻¹ NaCl. ATHO and ATLE accumulated twice as much sodium in their shoots as ATCA, but all three species had increasing sodium levels at higher salinities. Potassium, magnesium and calcium levels were relatively constant over the salinity gradient. All three species showed marked accumulation of chloride across the salinity gradient, whereas nitrate, phosphorous and sulfate decreased with salinity. The effect of drought was simulated by growing plants in sealed pots with an initial charge of water plus NaCl, and allowing them to grow to the end point at which they no longer were able to extract water from the soil solution. Drought and salinity were not additive stress factors for Atriplex spp. in this experiment. NaCl increased their ability to extract water from the soil solution compared to fresh water controls. ATLE showed increased shoot dry matter production and increased water use efficiency (WUE) as initial salinity levels increased from 0 to 30 g L⁻¹ NaCl, whereas dry matter production and WUE peaked at 5 g L⁻¹ for ATHO and ATCA. Final soil moisture salinities tolerated by species were 85 g L⁻¹, 55 g L⁻¹ and 160 g L⁻¹ NaCl for ATHO, ATCA and ATLE, respectively. C4 photosynthesis and sodium accumulation in shoots were associated with high drought and salt tolerance.     

Caulerpa taxifolia responses to hyposalinity stress

An investigation into salinity responses of Caulerpa taxifolia was undertaken in a series of laboratory trials to evaluate the use of hyposalinity stress as an eradication strategy. The effect of instantaneous (or shock) exposure to reduced salinity (10 ppt) on the effective quantum yield (EQY) of C. taxifolia for different incubation periods (15, 30, 45, 60, 90, 180, 360, 720 and 1440 min) indicated that 180 min or more at this salinity was required to kill the alga. Average EQY declined by 88.2 ± 4.6% (mean ± S.E.) of the pre-treatment level for the 180 min treatment but were as much as 96.6 ± 2.5% lower than pre-treatment EQY for the 1440 min exposure. Exposure for 90 min or less resulted in an intermediate response, whereas lesser exposures (60, 30 and 15 min) had no lasting effect on C. taxifolia health. The effect of gradual changes in salinity, as might be anticipated in an eradication scenario, on EQY of C. taxifolia was investigated through the dilution of seawater (35 ppt) over different time scales (5 h, 2, 4, 7 and 27 days). In all trials >5 h, the response to hyposalinity was the same regardless of the rate of change in salinity with all treatments resulting in a marked loss in EQY below ∼15 ppt. Declines in the average ratio of EQY after to EQY before for 4, 7 and 27 days treatments (85.2 ± 8.2%, 78.8 ± 9.05% and 77.3 ± 18.2% of pre-treatment levels, respectively), were significantly larger than the 5 h treatment (2.6 ± 4.4% of pre-treatment levels). The 2 days salinity reduction (48.5 ± 17.1%) resulted in an intermediate response. In the 5 h treatment, the exposure to salinities below 15 ppt was less than 3 h, which given the result of the preceding trial explains the lack of substantial EQY response as the minimum exposure period required to kill the alga at 10 ppt is ≥180 min. There is thus no evidence that C. taxifolia is capable of acclimation to gradual reductions in salinity. Consequently, hyposalinity is an effective means of killing the algae and may prove highly effective for populations in relatively small, contained water bodies.     

The impact of arbuscular mycorrhizal fungi in mitigating salt-induced adverse effects in sweet basil (Ocimum basilicum L.)

Salinity is one of the serious abiotic stresses adversely affecting the majority of arable lands worldwide, limiting the crop productivity of most of the economically important crops. Sweet basil (Osmium basilicum) plants were grown in a non-saline soil (EC = 0.64 dS m⁻¹), in low saline soil (EC = 5 dS m⁻¹), and in a high saline soil (EC = 10 dS m⁻¹). There were differences between arbuscular mycorrhizal (Glomus deserticola) colonized plants (+AMF) and non-colonized plants (−AMF). Mycorrhiza mitigated the reduction of K, P and Ca uptake due to salinity. The balance between K/Na and between Ca/Na was improved in +AMF plants. Growth enhancement by mycorrhiza was independent from plant phosphorus content under high salinity levels. Different growth parameters, salt stress tolerance and accumulation of proline content were investigated, these results showed that the use of mycorrhizal inoculum (AMF) was able to enhance the productivity of sweet basil plants under salinity conditions. Mycorrhizal inoculation significantly increased chlorophyll content and water use efficiency under salinity stress. The sweet basil plants appeared to have high dependency on AMF which improved plant growth, photosynthetic efficiency, gas exchange and water use efficiency under salinity stress. In this study, there was evidence that colonization with AMF can alleviate the detrimental salinity stress influence on the growth and productivity of sweet basil plants.     

Effect of high salinity on Atriplex portulacoides: Growth,leaf water relations and solute accumulation in relation with osmotic adjustment

Atriplex (Halimione) portulacoides is a halophyte with potential interest for saline soil reclamation and phytoremediation. Here, we assess the impact of salinity reaching up to two-fold seawater concentration (0–1000 mM NaCl) on the plant growth, leaf water status and ion uptake and we evaluate the contribution of inorganic and organic solutes to the osmotic adjustment process. A. portulacoides growth was optimal at 200 mM NaCl but higher salinities (especially 800 and 1000 mM NaCl) significantly reduced plant growth. Na⁺ and Cl⁻ contents increased upon salt exposure especially in the leaves compared to the roots. Interestingly, no salt-induced toxicity symptoms were observed and leaf water content was maintained even at the highest salinity level. Furthermore, leaf succulence and high instantaneous water use efficiency (WUE_i) under high salinity significantly contributed to maintain leaf water status of this species. Leaf pressure–volume curves showed that salt-challenged plants adjusted osmotically by lowering osmotic potential at full turgor (Ψ_π¹⁰⁰) along with a decrease in leaf cell elasticity (values of volumetric modulus elasticity (ε) increased). As a whole, our findings indicate that A. portulacoides is characterized by a high plasticity in terms of salt-response. Preserving leaf hydration and efficiently using Na⁺ for the osmotic adjustment especially at high salinities (800–1000 mM NaCl), likely through its compartmentalization in leaf vacuoles, are key determinants of such a performance. The selective absorption of K⁺ over Na⁺ in concomitance with an increase in the K⁺ use efficiency also accounted for the overall plant salt tolerance.     

Tropical seagrass species tolerance to hypersalinity stress

The long-term sustainability of seagrasses in the subtropics and tropics depends on their ability to adapt to shifts in salinity regimes, particularly in light of present increases in coastal freshwater extractions and future climate change scenarios. Although there are major concerns world-wide on increased salinity in coastal estuaries, there is little quantitative information on the specific upper salinity tolerance of tropical and subtropical seagrass species. We examined seagrass hypersalinity tolerance under two scenarios: (1) when salinity is raised rapidly simulating a pulsed event, such as exposure to brine effluent, and (2) when salinity is raised slowly, characteristic of field conditions in shallow evaporative basins; the first in hydroponics (Experiments I and II) and the second in large mesocosms using intact sediment cores from the field (Experiment III). The three tropical seagrass species investigated in this study were highly tolerant of hypersaline conditions with a slow rate of salinity increase (1 psu d⁻¹). None of the three species elicited total shoot mortality across the range of salinities examined (35–70 psu over 30 days exposures); representing in situ exposure ranges in Florida Bay, a shallow semi-enclosed subtropical lagoon with restricted circulation. Based on stress indicators, shoot decline, growth rates, and PAM florescence, all three species were able to tolerate salinities up to 55 psu, with Thalassia testudinum (60 psu) and Halodule wrightii (65 psu) eliciting a slightly higher salinity threshold than Ruppia maritima (55 psu). However, when salinity was pulsed, without a slow osmotic adjustment period, threshold levels dropped 20 psu to approximately 45 psu for T. testudinum. While we found these three seagrass species to be highly tolerant of high salinity, and conclude that hypersalinity probably does not solely cause seagrass dieoff events in Florida Bay, high salinity can modify carbon and O₂ balance in the plant, potentially affecting the long-term health of the seagrass community.     

Changes of lipid content and fatty acid composition of Schizochytrium limacinum in response to different temperatures and salinities

The growth, lipid content and fatty acid composition of Schizochytrium limacinum OUC88 at different temperatures (16, 23, 30 and 37 °C) and salinities (0, 0.9, 1.8, 2.7 and 3.6%, w/v) were analyzed. The strain grew better and lipid contents were higher at 16–30 °C and salinity at 0.9–3.6% (w/v). The adaptive responses of this microbe to temperature and salinity were mainly to regulate the degree of fatty acid unstauration to maintain the normal membrane lipid physical state. However, at 37 °C and 0 salinity, the growth of the strain was inhibited obviously and the lipid content reduced significantly and, some important changes occurred in fatty acid composition, especially the odd-numbered fatty acids 15:0 and 17:0 which amounts increased greatly. In addition, the ratio of DHA to DPA changed at different temperatures and salinities.     

Ornamental characters,ion accumulation and water status in Arbutus unedo seedlings irrigated with saline water and subsequent relief and transplanting

Arbutus unedo seedlings were grown in a greenhouse and submitted to three irrigation treatments (salinity period) using solutions with an EC of 0.85 dS m^?1 (control treatment), 5.45 dS m^?1 (S1) and 9.45 dS m^?1 (S2). After 16 weeks, growth and ornamental characters, leaf water potentials, gas exchange and ion concentrations were determined. After the salinity period, plants were exposed to a relief period for 1 month, whereby half of the plants were transplanted to field conditions and the other half into 24 cm diameter plastic pots. Salinity induced a significant decrease in shoot biomass and leaf area but root/shoot ratio was increased. Plant height was significantly inhibited by salinity. The ornamental characters were affected in the treated plants, with symptoms of salt injury, such as burning of leaf margin. Leaf water potentials decreased with increasing salinity, more significantly at predawn than at midday. The relationship between net photosynthesis (P_n) and leaf conductance (g_l) was linear for all treatments and the same values of P_n are associated with lower values of g_l for the saline treatments than for control treatment. The concentration of Cl^? in leaves increased with increasing salinity and was higher than the corresponding concentration of Na⁺. Na⁺ and Cl^? contents were higher in the leaves than in the roots in both saline treatments. The K⁺ and Ca²⁺ levels were lower in the treated plants than in control plants and applied salinity reduced the K⁺/Na⁺ ratio in leaves, stems and roots, the decrease being much greater for leaves than for roots. The Ca²⁺/Na⁺ ratio fell with salinity in all parts of the plants. At the end of the relief period leaf water potentials were recovered mainly in field conditions. S2 treatment showed lower values of P_n and g_l than control and S1 treatments in pot conditions and in field conditions S1 showed the lowest values for P_n and g_l.     

Soil salinity and drought alter wood density and vulnerability to xylem cavitation of baldcypress (Taxodium distichum (L.) Rich.) seedlings

We investigated the role of hydraulic conductivity, wood density, and xylem cavitation in the response of baldcypress (Taxodium distichum) seedlings to increased soil salinity and drought. One-year-old, greenhouse-grown seedlings were irrigated daily with a 100 mM (≈6‰) salt solution or once per week with fresh water (drought). Controls were irrigated daily with fresh water. Gas exchange rates of stressed plants were reduced by approximately 50% (salt) and 70% (drought), resulting in a 50–60% reduction in diameter growth for both treatments. Stem-specific hydraulic conductivity (K_{S native}) of stressed plants was 33% (salt) and 66% (drought) lower than controls and we observed a strong positive correlation between K_{S native} and gas exchange. In addition, we found a strong relationship between CO₂ assimilation rate (A) and the soil-to-leaf hydraulic conductance (k_L). The relationship was identical for all treatments, suggesting that our moderate salt stress (as well as drought) did not affect the photosynthetic biochemistry of leaves, but rather reduced A via stomatal closure. Lower K_{S native} of stressed plants was associated with increased wood density and greater resistance to xylem cavitation. Xylem pressures causing 50% loss of hydraulic conductivity (P₅₀) were ?2.88 ± 0.07 MPa (drought), ?2.50 ± 0.08 MPa (salt) and ?2.01 ± 0.04 MPa (controls). P₅₀s were strongly correlated with wood density (r = ?0.71, P < 0.01) and K_{S native} (r = 0.74, P < 0.01). These findings support the hypothesis that there is a significant trade-off between a plant's cavitation resistance and its hydraulic efficiency. The results of the present study indicate that stressed plants partitioned their biomass in a way that strengthened their xylem and reduced vulnerability to xylem cavitation. Hence, these seedlings could be better suited to be planted in environments with elevated soil salinity. For most parameters (especially P₅₀), drought had an even more pronounced effect than salinity. This is important as nurseries could produce “stress-acclimated” seedlings simply by reducing irrigation amounts and would not have to contaminate the soils in their nursery beds with salt applications.     

Salt uptake and shoot water relations in mangroves

The effects of salinity on water relations and ion concentrations were investigated in seedlings of the mangroves Avicennia alba, Bruguiera gymnorrhiza, Heritiera littoralis and Xylocarpus granatum grown at salinities of 0, 10, 20, 30, 40 and 60‰. All four species survived and grew at salinities ranging from 0 to 40‰, but none survived at a salinity of 60‰. The concentration of sodium and chloride in the xylem sap increased with increasing salinity in both A. alba and B. gymnorrhiza. Sodium and chloride concentrations in the xylem sap of A. alba grown at 40‰ salinity both reached 114 mol m⁻³, about 15% of the external concentration around the roots. The xylem sap of B. gymnorrhiza grown at 40‰ salinity, by contrast, contained only 7.0 mol m⁻³ sodium and 4.1 mol m⁻³ chloride, about 1% of their concentrations in the external solution around the roots. The results indicated that B. gymnorrhiza, which does not have salt-secreting glands, was more effective at excluding salt than A. alba, which has salt-secreting glands.Analysis of pressure–volume curves showed that the bulk modulus of elasticity increased with increasing salinity. This was accompanied by a decrease in shoot water potential, mainly associated with a reduction in shoot osmotic potentials with increasing salinity. The decrease in osmotic potential was attributed to increasing solute concentrations, particularly sodium and chloride, in the leaves of all species except H. littoralis, which had little sodium and chloride in the leaves.     

Photosynthetic and physiological responses of Kandelia candel L. Druce seedlings to duration of tidal immersion in artificial seawater

The present study demonstrates the influence of the duration of periodical waterlogging with artificial seawater on the photosynthetic and physiological responses of Kandelia candel L. Druce seedlings, the pre-dominant species of subtropical mangroves in China. Artificial tidal fluctuations applied here closely mimicked the twice daily tidal inundation which mangroves experience in the field. All the seedlings were immersed in artificial seawater during 70-day cultivation. Similar trends with increasing duration of immersion occurred in photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO₂ concentration, where significant decreases occurred only in long time treatments of 10 or 12 h. Water used efficiency and chlorophyll contents showed lower in medium periods and higher in long periods of immersion. This indicates that the increase in pigment contents of leaves was ineffective in promoting P_n under long time immersion. Light saturation points under short time waterlogging (0–4 h) occurred at light intensities of 800–1000 μmol/m²/s, and at around 400 μmol/m²/s in long time treatments (8–12 h). Long periods of tidal immersion therefore significantly inhibited photosynthesis of mature leaves. Alcohol dehydrogenase and oxidase activity in roots both increased under longer immersion periods, suggesting that roots are sensitive to anaerobiosis under long term waterlogging. The activities of peroxidase and superoxide dismutase in mature leaves increased in 8 h and 10 h treatments, respectively. The content of malondialdehyde in mature leaves increased under long time treatments. Abscisic acid accumulation in mature leaves also had a sharp increase from 8 h to 12 h inundation. Even though the anti-oxidative enzymes were induced by waterlogging, this was not sufficient to protect the seedlings from senescence. The results suggested that K. candel seedlings completely tolerated tidal immersion by seawater up to about 8 h in each cycle, which matches the natural distribution of K. candel in inter-tidal zones of China.     

A multilevel trait-based approach to the ecological performance of Microcystis aeruginosa complex from headwaters to the ocean

The Microcystis aeruginosa complex (MAC) clusters cosmopolitan and conspicuous harmful bloom-forming cyanobacteria able to produce cyanotoxins. It is hypothesized that low temperatures and brackish salinities are the main barriers to MAC proliferation. Here, patterns at multiple levels of organization irrespective of taxonomic identity (i.e. a trait-based approach) were analyzed. MAC responses from the intracellular (e.g. respiratory activity) to the ecosystem level (e.g. blooms) were evaluated in wide environmental gradients. Experimental results on buoyancy and respiratory activity in response to increased salinity (0–35) and a literature review of maximum growth rates under different temperatures and salinities were combined with field sampling from headwaters (800 km upstream) to the marine end of the Rio de la Plata estuary (Uruguay-South America). Salinity and temperature were the major variables affecting MAC responses. Experimentally, freshwater MAC cells remained active for 24 h in brackish waters (salinity = 15) while colonies increased their flotation velocity. At the population level, maximum growth rate decreased with salinity and presented a unimodal exponential response with temperature, showing an optimum at 27.5 °C and a rapid decrease thereafter. At the community and ecosystem levels, MAC occurred from fresh to marine waters (salinity 30) with a sustained relative increase of large mucilaginous colonies biovolume with respect to individual cells. Similarly, total biomass and, specific and morphological richness decreased with salinity while blooms were only detected in freshwater both at high (33 °C) and low (11 °C) temperatures. In brackish waters, large mucilaginous colonies presented advantages under osmotic restrictive conditions. These traits values have also been associated with higher toxicity potential. This suggest salinity or low temperatures would not represent effective barriers for the survival and transport of potentially toxic MAC under likely near future scenarios of increasing human impacts (i.e. eutrophication, dam construction and climate change).     

Responses of grafted tomato (Solanum lycopersiocon L.) to abiotic stresses in Saudi Arabia

Quantity and quality of irrigation water are considered the most imperative limiting factors for plant production in arid environment. Adoptions of strategies can minimize crop water consumption while nonexistent yield reduction is considered challenge for scholars especially in arid environment. Grafting is regarded as a promising tool to avoid or reduce yield loss caused by abiotic stresses. Tomato (Solanum lycopersium Mill.), commercial cultivar Faridah was grafted on Unifort rootstock and grown under regulated deficit irrigation (RDI) (100%, 80% and 60% ETc), using two types of irrigation water, fresh (EC = 0.86 dS/m) and brackish (EC = 3.52 dS/m). The effects of grafting and RDI on water use efficiency, vegetative growth, yield, fruit quality were investigated. Plant vegetative growth was reduced under water and salinity stresses. Grafting the plant significantly improves the vegetative growth under both conditions. The results showed that crop yield, Ca⁺² and K⁺ were considerably increased in grafted tomato compared to non-grafted plants under water and salinity stresses. Grafted tomato plants accumulated less Na⁺ and Cl⁻, especially under high levels of salinity compared to non-grafted plants. Grafting tomato plants showed a slight decrease on the fruit quality traits such as vitamin C, titratable acidity (TA) and total soluble solids (TSS). This study confirmed that grafted tomato plants can mitigate undesirable impact of salt stress on growth and fruit quality.     

Effect of environmental and nutritional factors on growth and azaspiracid production of the dinoflagellate Azadinium spinosum

Azadinium spinosum, a small dinoflagellate isolated from the North Sea, is a producer of azaspiracids (AZAs), a group of biotoxins associated with human illness following ingestion of contaminated shellfish. Using batch and continuous cultures of A. spinosum, the present study investigated the effects of different environmental and nutritional factors (salinity, temperature, photon flux density, aeration, culture media, nitrogen sources, phosphate source, and N/P ratios) on growth, maximum cell concentration, and AZA cell quota.Azadinium spinosum grew in a wide range of conditions; from 10 ̊C to 26 ̊C and salinities from 30 to 40, under irradiances ranging from 50 μmol m⁻² s⁻¹ to 250 μmol m⁻² s⁻¹, with or without aeration. Growth and maximum cell concentration were highest at a salinity of 35, at temperatures between 18 ̊C and 22 ̊C, and with aeration. Concerning AZA cell quota, the most significant effect was observed at low temperature; the AZA cell quota was more than 20 times higher at 10 ̊C (220 fg cell⁻¹) than at temperatures between 18 ̊C and 26 ̊C. A. spinosum grew on all media tested with only slight differences in growth rate and AZA cell quota. In continuous culture, lowering the concentration of nutrients (0.5 strength of a modified K-medium) in the inflow improved AZA cell quota whereas higher concentration (doubling the normal strength of K-medium) improved maximal cell concentration. A. spinosum grew on different sources of nitrogen tested (nitrate, urea, ammonium) with almost no effect on toxin cell quota and growth, except that adding ammonium caused a decrease in growth.These first experiments on Azadinium spinosum increased our knowledge on factors affecting its growth and toxin production; furthermore, these results allowed and improved particularly A. spinosum production in pilot scale photobioreactors for AZA isolation.     

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash (Cucurbita pepo L. cv. ‘Rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m^?1, 0.8 mM NaCl) and a high salinity level (6.2 dS m^?1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the inclusion of 1 mM of Si in the salinized nutrient solution mitigated the salinity-associated suppression of both growth and yield. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO₂ concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew (Podosphaera xanthii) infection in the leaves at both salinity levels. These results indicate that the supply of at least 1 mM of Si via the nutrient solution is capable of enhancing both tolerance to salinity and resistance to powdery mildew in soilless cultivations of zucchini squash.     

Kinetics of cellulose hydrolysis by halostable cellulase from a marine Aspergillus niger at different salinities

Kinetics of cellulose hydrolysis with halostable cellulase from a marine Aspergillus niger was analyzed at different salinities. Cellulase activity in 8% NaCl solution was 1.43 folds higher than that in NaCl free solution. Half saturation constant, K_m (15.6260 g/L) and the rate constant of deactivation, K_de (0.3369 g/L h) in 8% NaCl solution was lower than that (18.6364 g/L), 0.3754 (g/L h) in NaCl free solution. The maximum initial hydrolysis velocity, V_max (25.5295 g/L h), in 8% NaCl solution was higher than that in NaCl free solution (25.0153 g/L h). High salinity increased affinity to the cellulase to the substrate and thermostability. Halostable cellulase from a marine Aspergillus niger was valuable for cellulose hydrolysis under high salinity conditions.     

Influence of inoculation with plant growth promoting rhizobacteria (PGPR) on tomato plant growth and nematode reproduction under greenhouse conditions

Numerous species of soil bacteria which flourish in the rhizosphere of plants or around plant tissues stimulate plant growth and reduce nematode population by antagonistic behavior. These bacteria are collectively known as PGPR (plant growth promoting rhizobacteria). The effects of six isolates of PGPR Pseudomonas putida, Pseudomonas fluorescens, Serratia marcescens, Bacillus amyloliquefaciens, Bacillus subtilis and Bacillus cereus, were studied on tomato plant growth and root knot nematode reproduction after 45 days from nematode infection. The highest number of shoot dry weight/g (43.00 g) was detected in the plant treated with S. marcescens; then P. putida (34.33 g), B. amyloliquefaciens (31.66 g), P. fluorescens (30.0 g), B. subtilis (29.0 g), B. cereus (27.0 g) and nematode alone (untreated) 20 g/plant. While the highest number of plant height was observed when plant was treated with S. marcescens, P. fluorescens, P. putida, B. amyloliquefaciens and P. putida 52.66, 50.66, 48 and 48 cm respectively. No significant differences were seen between previous treatments but only had significant differences compared with untreated plant. The highest number of fruit/plant was observed when plants were treated with S. marcescens (10.66), then B. amyloliquefaciens (8.66), P. putida (8), P. fluorescens (8) and B. cereus (7.66). No significant differences between the last 4 treatments, but all had significant differences compared with untreated plants. The highest weight of plant yield (g) was observed with S. marcescens (319.6 g/plant) and the lowest weight of plant yield was observed in plants treated with nematode alone (untreated). On the other hand, the lowest numbers of J₂/10 g of soil (78), galls/root, (24.33) galls/root, egg masses/root (12.66) and egg/egg masses were observed in the plants treated with S. marcescens.