Relative Nutrient Concentration Research Articles

Moringa leaf extract increases tolerance to salt stress, promotes growth, increases yield, and reduces nitrate concentration in lettuce plants

The use of large amounts of synthetic chemicals in plant cultivation harms the environment and reduces food quality. Therefore, natural alternatives should be used to protect the environment, increase food quality, and decrease food contamination. This study investigated the effect of moringa leaf extract (MLE) as a plant stimulator to enhance growth, yield, and quality of lettuce grown in a saline environment. To examine the effect of application method and extract concentration, this experiment included three levels of seed priming (0, 5 %, and 10 % MLE) and three levels of foliar spray (0, 5 %, and 10 % MLE). MLE application, either by seed priming or foliar spraying, reduced the adverse effects of salt stress and increased lettuce growth, yield, and quality. However, the combined treatment of 5 % seed soaking and 10 % foliar spray showed the best results in increasing antioxidant levels (catalase (CAT), ascorbate peroxidase (APX), and ascorbic acid), relative water content (RWC %), nutrient concentration (N, P, and K), and chlorophyll content, and maintaining membrane integrity by reducing electrolyte leakage (EL %) and sodium accumulation, leading to improved yield parameters (head diameter, head weight, and total yield), and increasing lettuce head quality by reducing nitrate concentration. The results suggest that MLE (5 % seed soaking and 10 % foliar spray) is a practical, effective, and inexpensive approach to alleviate salt stress and improve lettuce yield and quality under saline conditions. However, despite the observed positive effects, further studies are needed to understand the factors determining the response of plants to MLE application.

Trade-offs in the genetic control of functional and nutritional quality traits in UK winter wheat.

A complex network of trade-offs exists between wheat quality and nutritional traits. We investigated the correlated relationships among several milling and baking traits as well as mineral density in refined white and whole grain flour. Our aim was to determine their pleiotropic genetic control in a multi-parent population over two trial years with direct application to practical breeding. Co-location of major quantitative trait loci (QTL) and principal component based multi-trait QTL mapping increased the power to detect QTL and revealed pleiotropic effects explaining many complementary and antagonistic trait relationships. High molecular weight glutenin subunit genes explained much of the heritable variation in important dough rheology traits, although additional QTL were detected. Several QTL, including one linked to the TaGW2 gene, controlled grain size and increased flour extraction rate. The semi-dwarf Rht-D1b allele had a positive effect on Hagberg falling number, but reduced grain size, specific weight, grain protein content and flour water absorption. Mineral nutrient concentrations were lower in Rht-D1b lines for many elements, in wholemeal and white flour, but potassium concentration was higher in Rht-D1b lines. The presence of awns increased calcium content without decreasing extraction rate, despite the negative correlation between these traits. QTL were also found that affect the relative concentrations of key mineral nutrients compared to phosphorus which may help increase bioavailability without associated anti-nutritional effects of phytic acid. Taken together these results demonstrate the potential for marker-based selection to optimise trait trade-offs and enhance wheat nutritional value by considering pleiotropic genetic effects across multiple traits.

Modelling the effects of changing loads of nitrogen discharged from a sewage treatment plant on plankton dynamics in a large, urbanised bay

The input of nutrients to the coastal environment is essential to support biological productivity but an excess of nutrients can lead to eutrophication. Here we use a pelagic ecosystem model to investigate the effects of nutrient inputs from a sewage treatment plant on the plankton dynamics of Port Phillip Bay, southern Australia. The effects of a 50% increase or decrease in nitrogen concentration in the Western Treatment Plant (WTP) outfall was examined relative to the 2016–17 base case. Increasing the nitrogen concentration in the WTP discharge had only a small effect on the summer diatom bloom. This can be explained by the fact that summer diatom blooms are typically silicate rather than nitrogen limited and WTP discharges are dominated more by N than Si compared with flows from the catchment. Consequently, increasing N had a relatively greater effect on flagellates, that in turn led to an increase in abundance of zooplankton (Paracalanus) at the beginning of the spawning window for snapper, Chrysophrys auratus. Paracalanus are the preferred prey for snapper larvae and the abundance of this zooplankter can strongly influence the larval survival and recruitment of snapper. Decreasing the nitrogen load from the WTP led to a marked reduction in the planktonic production in the bay, reflecting the potential effects of factors such as drought that can lead to a reduction in nitrogen load. Overall, the effect of changing nutrient load was sensitive to differences in relative nutrient concentrations from the treatment plant versus catchment sources.

The effects of absolute and relative nutrient concentrations (N/P) on phytoplankton in a subtropical reservoir

Abstract The elemental composition of phytoplankton is a critical factor for primary production and nutrient recycling. The increase anthropogenic nutrient input into freshwater ecosystems is affecting phytoplankton assemblage structure and its stoichiometry. Reservoirs of South China generally show low level of phosphate and it is not clear how phytoplankton can grow and occasionally bloom in such conditions. Therefore, an indoor experiment was conducted to investigate the response of natural phytoplankton communities to 25 levels of supplied nitrogen to phosphorus ratios (N/P), arising from the combination of 5 levels of N and P. Our aim was to check the effects of absolute and relative N and P on phytoplankton growth and structure. We assumed that Alkaline Phosphatase (APA) provides a way to use alternative P resource. Our hypotheses include: (1) phytoplankton stoichiometry would be in homeostasis (sensu Sterner & Elser, 2002) under different N and P treatments; (2) absolute nutrient values rather than its ratio matters for phytoplankton assemblage; and (3) phytoplankton cell size declines to lower P requirements facing P limitation. Results showed that phytoplankton in this subtropical reservoir use alternative P sources via APA to support its growth. The absolute values of N and P instead and not their ratios were important for phytoplankton. The N/P ratio cannot be a reliable indicator for nutrient limitation or phytoplankton shift. During the fast-growing phase, their elemental contents were not sensitive to supplied nutrients, and their stoichiometry was more constrained compared to that in slow-growing phase. The plasticity of cellular stoichiometry was mainly due to the variations of cellular P. Phytoplankton stoichiometry was weakly homeostatic, and this mechanism provides a strategy to keep growth relatively stable in a variable nutrient environment.

Nutritional status of ‘Hass’ and ‘Fuerte’ avocado (Persea americana Mill.) plants subjected to high soil moisture

In this study, the effect of increased soil moisture on the nutritional status of two key commercial avocado (Persea americana Μill.) cultivars, ‘Fuerte’ and ‘Hass’, was examined. The results revealed that prolonged exposure of plants to high soil water content conditions (waterlogging) reduced the total nutrient content (absolute quantity) of almost all of the nutrients in scion’s tissues (leaves and stems) of both cultivars. The decrease of nutrient content in the ‘Fuerte’ leaves was more prominent/severe compared to the ‘Hass’ leaves, which could be the outcome of the reported higher sensitivity of the cultivar to soil waterlogged conditions in previous studies. Interestingly, the inability of ‘Fuerte’ avocado plants to withstand high soil moisture conditions was not reflected in the relative concentrations of most nutrients, both in leaves and stems. Indeed, significantly higher concentrations of P, K, B, Fe, and Zn were found in the leaves of ‘Fuerte’ waterlogged plants than in well-watered ones. This fact reveals that under marginal/stressful conditions, like waterlogging, nutrient concentration in tissues does not reflect potential negative effects on total nutrient uptake of avocado plants, obviously due to concentrated nutrient phenomena primarily created by the stress-dependent growth inhibition. Therefore, total nutrient content is proposed as a more representative indicator for assessing plant response to waterlogged conditions.

Spatial distribution of nutrients and morpho-physiological indicators of salinity tolerance among five olive cultivars - The use of relative nutrient concentration as an efficient tolerance index

Olive is the most important fruit tree species grown in Mediterranean basin, where many times it grows under saline conditions, due to irrigation with low quality water. Olive response to salinity is cultivar dependent and the evaluation of native genotypes is an important tool in finding tolerant genetic material. For this reason, five Greek olive cultivars, i.e. “Koroneiki”, “Gaidourelia”, “Lefkolia Serron”, “N-K Gigas” and “Throumbolia”, were evaluated regarding their tolerance to sodium chloride salinity (0, 50, 100 and 200 mM). All cultivars exhibited a significant reduction of growth, while the most severe symptoms were found in “Gaidourelia” while “Lefkolia Serron” presented the least symptoms. The latter exhibited the lowest sodium concentration in the leaves and the highest in the roots. Both potassium to sodium and calcium to sodium ratios were high in “Gaidourelia” leaves and stems, suggesting that the use of nutrient concentration for comparison of olive tolerance among cultivars could lead to erroneous results. The best indicator proved to be the determination of nutrient relative concentration compared to corresponding cultivar’s control, as “Gaidourelia” exhibited the highest sodium relative concentration as well as the lowest nutrient ratios, revealing its inability to restrain sodium in the root level.

The Relative Concentrations of Nutrients and Toxins Dictate Feeding by a Vertebrate Browser, the Greater Glider Petauroides volans.

Although ecologists believe that vertebrate herbivores must select a diet that allows them to meet their nutritional requirements, while avoiding intoxication by plant secondary metabolites, this is remarkably difficult to show. A long series of field and laboratory experiments means that we have a good understanding of the factors that affect feeding by leaf-eating marsupials. This knowledge and the natural intraspecific variation in Eucalyptus chemistry allowed us to test the hypothesis that the feeding decisions of greater gliders (Petauroides volans) depend on the concentrations of available nitrogen (incorporating total nitrogen, dry matter digestibility and tannins) and of formylated phloroglucinol compounds (FPCs), potent antifeedants unique to Eucalyptus. We offered captive greater gliders foliage from two species of Eucalyptus, E. viminalis and E. melliodora, which vary naturally in their concentrations of available nitrogen and FPCs. We then measured the amount of foliage eaten by each glider and compared this with our laboratory analyses of foliar total nitrogen, available nitrogen and FPCs for each tree offered. The concentration of FPCs was the main factor that determined how much gliders ate of E. viminalis and E. melliodora, but in gliders fed E. viminalis the concentration of available nitrogen was also a significant influence. In other words, greater gliders ate E. viminalis leaves with a particular combination of FPCs and available nitrogen that maximised the nutritional gain but minimised their ingestion of toxins. In contrast, the concentration of total nitrogen was not correlated with feeding. This study is among the first to empirically show that browsing herbivores select a diet that balances the potential gain (available nutrients) and the potential costs (plant secondary chemicals) of eating leaves. The major implication of the study is that it is essential to identify the limiting nutrients and relevant toxins in a system in order to understand feeding behaviour.

Production of domoic acid by laboratory culture of the red alga Chondria armata

To clarify the production mechanisms and biologic functions of domoic acid (DA) by the red alga Chondria armata, we established a laboratory culture of C. armata. The alga grew better in modified PES medium (mPES) without trace metals or manganese than in unmodified mPES (seawater + nitrate, phosphate, iron, trace metals, vitamins, and 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid), suggesting that C. armata is especially hypersensitive to the toxicity of excessive manganese. C. armata cultured in N·P·Fe medium (seawater + nitrate, phosphate, and iron) grew best (mean growth rate 828.4%) at a relative nutrient concentration of 50%. Liquid chromatography-mass spectrometry analysis of the algal extracts revealed that the DA content of the cultured explants (2273–3308 ppm) was 4–5 fold higher than that of wild specimens. The extract of pooled explants (60 g) was purified by activated charcoal treatment and several types of column chromatography to afford ca. 10 mg DA. The 1H-nuclear magnetic resonance spectrum of the preparation was indistinguishable from the previously reported spectrum of DA, indicating that C. armata itself has an ability to produce DA.

Cylindrospermopsis raciborskii dominates under very low and high nitrogen-to-phosphorus ratios

In freshwater ecosystems, a variety of factors mediate phytoplankton community structure, including herbivore community structure, light availability, temperature, mixing, and absolute and relative nutrient concentrations (total nitrogen (TN), total phosphorus (TP)). Ecological stoichiometry examines how the nutrient content of organisms and their environment may mediate population-, community-, and ecosystem-level processes. The manipulation of N:P ratios is a widely regarded tool for managing phytoplankton species composition given that nitrogen-fixing cyanobacteria should dominate algal communities under relatively low N:P (<64:1, by atoms) given their ability to convert dissolved dinitrogen gas into organic nitrogen. However, due to the physiological expense of nitrogen fixation, diazotrophs should be outcompeted by non-nitrogen fixing phytoplankton under higher N:P when other environmental factors are similar. We tested this hypothesis in a field experiment using 2500-L limnocorrals installed in a eutrophic lake (ambient N:P ∼40:1 (by atoms); TN ∼1360 μgL−1; TP ∼75 μgL−1). At the start of the experiment, we randomly assigned limnocorrals among the ambient (40:1) and low (7:1) or high (122:1) N:P treatments (n = 4 replicates/treatment), which were established by adding P or N at the start of the experiment, respectively. The phytoplankton community in the enclosures at the start of the experiment was diverse (i.e., 18 phytoplankton genera) and dominated by chlorophytes (including Coelastrum and Scenedesmus (30% and 13% of total biomass, respectively)) and cyanobacteria (including Anabaena and Cylindrospermopsis (23% and 17% of total biomass, respectively)). In contrast to predictions based on ecological stoichiometry, the phytoplankton community in all N:P treatments increased in abundance and was almost entirely composed of the nitrogen-fixing cyanobacterium, Cylindrospermopsis raciborskii, by the conclusion of the study. Moreover, concentrations of the cyanobacterial neurotoxin, saxitoxin, were enhanced under the two highest N:P conditions. The ability of C. raciborskii to dominate phytoplankton communities under such extreme N:P shows that short-term management of nutrient stoichiometry through fertilization is not likely to be effective for controlling blooms of this noxious cyanobacterium and may help to explain the rapid expansion of this invasive species to temperate latitudes.

Influences on the formation and evolution of Physarum polycephalum inspired emergent transport networks

The single-celled organism Physarum polycephalum efficiently constructs and minimises dynamical nutrient transport networks resembling proximity graphs in the Toussaint hierarchy. We present a particle model which collectively approximates the behaviour of Physarum. We demonstrate spontaneous transport network formation and complex network evolution using the model and show that the model collectively exhibits quasi-physical emergent properties, allowing it to be considered as a virtual computing material. This material is used as an unconventional method to approximate spatially represented geometry problems by representing network nodes as nutrient sources. We demonstrate three different methods for the construction, evolution and minimisation of Physarum-like transport networks which approximate Steiner trees, relative neighbourhood graphs, convex hulls and concave hulls. We extend the model to adapt population size in response to nutrient availability and show how network evolution is dependent on relative node position (specifically inter-node angle), sensor scaling and nutrient concentration. We track network evolution using a real-time method to record transport network topology in response to global differences in nutrient concentration. We show how Steiner nodes are utilised at low nutrient concentrations whereas direct connections to nutrients are favoured when nutrient concentration is high. The results suggest that the foraging and minimising behaviour of Physarum-like transport networks reflect complex interplay between nutrient concentration, nutrient location, maximising foraging area coverage and minimising transport distance. The properties and behaviour of the synthetic virtual plasmodium may be useful in future physical instances of distributed unconventional computing devices, and may also provide clues to the generation of emergent computation behaviour by Physarum.

POTASSIUM SULFATE IMPROVES WATER DEFICIT TOLERANCE IN MELON PLANTS GROWN UNDER GLASSHOUSE CONDITIONS

Interactive effects of water stress and potassium (K) on some physiological attributes and nutritional status of melon (Cucumis melo L. cv. ‘Tempo F1’) plants were assessed in a pot experiment. Treatments used were: (1) control or well-watered (WW) + K1, (2) WW + K2, (3) WW + K3, (4) water stress (WS) + K1, (5) WS + K2, and (6) WS + K3. Water stress (WS) was imposed by maintaining the moisture level equivalent to 50% pot capacity, whereas well-watered (WW) pots (control) were maintained at full pot capacity (100% PC). Hoagland's nutrient solution was modified to supply K as potassium sulfate (K2SO4) at 6, 9, and 12 mM for K1, K2, and K3 treatments, respectively. Water stress reduced fruit yield, total dry matter, chlorophyll content and relative water content (RWC), but increased proline accumulation in the melon plants. However, additional supply of K as 3 or 6 mM significantly enhanced all the earlier mentioned physiological parameters, but the values were still not the same as the levels of the control treatment. Water stress also reduced leaf calcium (Ca) and K of the melon plants, but additional supply of K to the root zone increased the levels of both nutrients much higher than those at the control (C) treatment. Our study revealed that additional supply of K improved water stress tolerance in melon plants by enhancing chlorophyll, relative water content and concentrations of some essential nutrients in leaves.

Carbon and nitrogen enhancement in Cambisols and Vertisols by Acacia spp. in eastern Burkina Faso: Relation to soil respiration and microbial biomass

The current study tested the contribution of native Acacia species of the Sudano-Sahelian zone to improving organic carbon and nitrogen level in Cambisols and Vertisols with specific focus on variation in microbial biomass ( C mic), soil basal respiration ( C resp) and metabolic quotient ( qCO 2). The results show enrichment in total organic carbon ( C total), in total nitrogen ( N total) and higher clay content under Acacia canopies as compared to adjacent open grasslands. The relative nutrient concentration in Acacia cover showed an increase in C mic ranging from 203 to 572 μg g −1 whereas in adjacent open grassland it varied from 100 to 254 CO 2–C μg g −1. As a function of C mic ( r = 0.60), C total ( r = 0.70) and N total ( r = 0.70), C resp was higher under Acacia canopies than open grassland and this difference was more pronounced when measured over lengthier incubation periods (10–21 days). A lower qCO 2 under Acacia cover (except for one site) demonstrated a change in microorganisms communities structure and higher substrate use efficiency as compared to open grassland. The results also show that soil texture, as well as vegetation cover, influenced microbial processes. The negative correlation between clay content and carbon mineralization ( C resp/ C total, qCO 2), and positive linear relation between clay and C mic supported the hypothesis that finer soil texture protects soil microbial biomass against degradation and limits organic matter mineralization. The specific effects of soil typology and vegetation cover on C mic and qCO 2 variability were significant, but the greater effects were attributed to vegetation cover.

Nutrient and light availability to white spruce seedlings in partial and clearcut harvested aspen stands

White spruce is a commercially important tree species in Canada’s boreal forest, and studies are underway to determine the best conditions for planting nursery grown seedlings in the field. Here, we studied effects of low thinning (1/3 harvested), shelterwood (2/3 harvested), and clear-cut harvesting on soil chemical properties, on the growth and nutrition of white spruce seedlings, and on diffuse non-intercepted (DIFN) light levels at 75 cm above the soil surface. The study was conducted on a nutrient-rich clayey soil in the Abitibi region of Québec. DIFN light was lowest in non-harvested control plots and increased curvilinearly with basal area removal. Thus, DIFN light in clear-cut plots was more than twice the amount in shelterwood plots. At three years post-planting, significant linear relationships were found between DIFN light and seedling growth parameters, which were significantly higher in clear-cut than in other treatment plots. Harvesting treatments had no significant effects on soil chemical properties or on four indices of mineral N availability. Needle mass increased with harvesting intensity. Mg and K concentrations in current-year needles were lower in clear-cut than in other treatment plots. In previous-year needles, Ca concentration was higher and Mg concentrations lower in clear-cut plots, whereas as K concentration was higher in non-harvested control plots. Nutrient concentrations were nearly all sufficient in all harvesting treatments according to diagnostic norms established for white spruce. Relative nutrient content (mg nutrient needle–1) of current-year late-summer needles increased, whereas relative nutrient concentration (mg nutrient mg–1 needle) varied slightly, with increasing harvesting intensity, indicating that all nutrients were sufficient in all treatments. There were significant linear relationships between seedling growth and needle Ca, Mg and K concentrations. We conclude that light availability, rather than nutrient limitations, is the main determinant of white spruce seedling growth on these fertile soils.

Diagnosing phosphorus status of natural grassland in the presence of white clover

The phosphorus nutrition index (PNI) method proved to be suitable for diagnosing P nutrition level over a wide range of grass swards. It is based on relative nutrient concentrations and relies on a critical curve for optimum P concentration which is a function of sward N concentration. The objectives of this paper were to verify to what extent this method was valid for P nutrition diagnosis when white clover was present in the sward in view of the fact that white clover N concentration is frequently reported to be much higher than that of grass and to remain constant whatever the amount of biomass produced. For this purpose we analysed the effect of N addition on N and P concentrations in white clover and rye grass grown in pure stands with unlimited P supply in a garden collection and compared it with clover behaviour in a field experiment on a natural grassland with a similar P status. Clover displayed a different affinity for P according to whether it grew in a pure or mixed sward. In a pure stand, we observed a very significant effect of N on N and P concentrations measured in individual organs and whole plants; the highest N concentrations were measured in clover. This species behaved differently from ryegrass: for a given level of N supply, plant N concentration decreased when petioles were added to the laminae samples, while P concentrations remained constant; for rye grass both N and P concentrations decreased when sheaths were added to laminae. Clover in mixed swards had a lower P nutritional status than when grown in a pure stand, due to its lower capacity to compete with grasses for light capture and P acquisition. Analysis of data from the literature demonstrated that differences in response between clover and grass were more pronounced under limited P supply, when clover displayed a lower ability than grasses to adjust P concentration to that of N due to its lower capacity to adapt to low P availability. As a consequence it became even less competitive. We concluded that there are limitations to the use of nutrient diagnosis systems based on relative concentrations when the herbage contains a large proportion of white clover and proposed that only the non-clover fraction should be used for diagnosis to avoid excessive P application when PNIs are used for fertiliser recommendations.

Concentration of pig slurry by evaporation: anaerobic digestion as the key process

Nutrient redistribution between areas with a structural pig slurry surplus and those with a shortage, is limited by the high cost of transportation and spreading, due to the high water content in slurry (more than 90%) and its relative low nutrient concentration. Water can be removed from slurry by evaporation, through the application of waste heat from a power plant or from other processes. Apart from obtaining a concentrate with an obviously higher nutrient concentration than the original slurry, another objective is to obtain clean water as condensate. The objective of this work was to study the batch vacuum evaporation of pig slurry liquid fraction, to evaluate the economic feasibility and to evaluate condensate quality as a function of both pH (4, 5 and 6) and pig slurry type (fresh slurry and anaerobically digested slurry). Results showed that condensate characteristics (ammonia nitrogen, VFA, COD) were strongly dependent on these variables. Previous anaerobic digestion presented clear advantages: it provided a fraction of the required energy and it removed organic matter, preventing its volatilisation in the evaporation process and providing higher quality condensates. These advantages make the combined treatment strategy economically more feasible than the evaporation process alone.

Mineral deficiencies in seedlings of two Mediterranean hardwood species

Mineral deficiencies are common during the seedling growth in forestry nurseries, as well as during the initial establishment of the plantations. The aim of this work was to study the effects of nitrogen, phosphorus, potassium and iron deficiencies in two Mediterranean hardwood species: Quercus suber L. and Ceratonia siliqua L. The test was made in hydroponic liquid culture, using solutions lacking N, P, K or Fe and a control solution. The test lasted 139 days for Quercus suber and 190 days for Ceratonia siliqua, and was developed with 50% of shade. During this period, morphological attributes (height, dry weight of aerial part and root) and physiological attributes (relative chlorophyll content and nutrient concentration in leaves) were determined, as well as the visible symptoms caused by the respective nutrient deficiencies. Nutrient deficiencies affected morphological and physiological attributes, and in some cases visual symptoms appeared. In addition, other determinations like relative chlorophyll content (SPAD) and nutrient foliar concentration are suggested to assure a correct diagnosis.

Effects of deficit irrigation on growth, yield and fruit quality of eggplant under semi-arid conditions

Eggplant (Solanum melongena L.) cv. Pala was grown in the field from March to August 2001 in order to investigate the effects of deficit irrigation on fruit yield and quality (i.e. soluble dry matter, fruit size), leaf relative water content, leaf area index (LAI), leaf chlorophyll concentration, electrolyte leakage, and leaf nutrient composition (N, P, K) in eggplant. Treatments were: (1) well-watered treatment receiving 100% replenishment of A pan evaporation on a daily basis (C); (2) water-stressed treatment receiving 90% replenishment of A pan evaporation at 4-day intervals (WS1); (3) water-stressed treatment receiving 80% replenishment of A pan evaporation at 8-day intervals (WS2); and (4) water-stressed treatment receiving 70% replenishment of A pan evaporation at 12-day intervals (WS3). A total of 1276 mm of water was applied to C treatment, and the seasonal water use of eggplant ranged from 905 to 1373 mm. The C treatment had the highest yield as well as the largest and the heaviest fruit. WS1 did not significantly affect fruit yield or fruit size but fruits were slightly lighter; plant height, stem diameter, and shoot and root dry weights, LAI, leaf relative water content, nutrient concentrations, and chlorophyll concentrations in leaves were the same as in C; SDM was higher than C. The WS2 and WS3 treatments caused reductions in most parameters, except water-soluble dry matter (SDM) concentrations in fruits, compared with the unstressed (C) treatment. WS2 and WS3 treatments enhanced fruit quality (in terms of SDM) and increased electrolyte leakage compared with C. WS2 and WS3 reduced marketable yield by 12% and 28.6%, respectively, compared with C. The highest total water use efficiency and irrigation water use efficiency were in WS2, resulting in a 20.4% water saving compared with C. The results revealed that the optimal irrigation strategy for eggplant could depend on balancing the situational requirements in terms of irrigation water, yields, and fruit size and quality.

Koeleria macrantha: performance and distribution in relation to soil and plant calcium and magnesium.

• The reported sensitivity of Koeleria macrantha (Poaceae) to soil magnesium, resulting in its absence from South Wales dolomitic limestone, was examined here in relation to varying ionic Ca to Mg ratios, and by cultivation in different limestone soils. • In a growth cabinet experiment, shoot and root Ca and Mg concentration and dry weight yield were determined for five edaphically varied populations of K. macrantha grown from tillers, over a range of Ca:Mg concentrations. The influence of relative concentrations of other nutrients was also investigated. In addition, K. macrantha plants were cultivated on Carboniferous, Magnesian and dolomitic limestone soils. • Total plant Ca: Mg ranged from 0.3 to >20 mille-equivalents. Optimal substrate ratios (from 25:1 to 0.1:1), and response to different concentrations of nutrients varied between the populations. Cultivation on dolomitic limestone soil produced the highest yields. • The adverse effect on yields of all populations with low substrate Ca: Mg was much lower than predicted. Results suggest K. macrantha has a higher substrate Mg tolerance than other members of the Poaceae: its reported absence from the South Wales dolomitic limestone is unlikely to be due to soil magnesium sensitivity.

Long‐term phytoplankton‐nutrient interactions in a shallow coastal sea: Algalcommunity structure, nutrient budgets, and denitrification potential

In the eutrophic Marsdiep, the westernmost tidal inlet of the Wadden Sea, phytoplankton biomass, and production almost doubled at the end of the 1970s and remained high ever since. Principal component analysis of 21‐yr (1974–1994) high‐resolution time series of the 32 most numerous marine algal species revealed that the phytoplankton community changed drastically both between 1976 and 1978 and again between 1987 and 1988, and that it was relatively stable in‐between (1974–1976, 1978–1987) and thereafter (1988–1994). These major changes in phytoplankton biomass and species composition coincided with changes in absolute and relative (TN:TP) nutrient concentrations. During the summer of 1977, the Marsdiep shifted from a rich, but phosphorus‐controlled system to an even more eutrophic but nitrogen‐controlled environment. The system reshifted towards P‐control between 1987 and 1988. The coincidence of the shifts in relative nutrient concentrations and phytoplankton species composition implies a strong causal relationship between TN:TP ratios and phytoplankton community structure. Among diatoms, the observed increase in phytoplankton biomass under eutrophic N‐controlled conditions was particularly due to an increase of the abundance of larger algae. Our results indicate that the N budget of the area is correlated with the community structure, suggesting enhanced loss of nitrogen to the sediment through increased deposition of larger algal cells.

An Epizootic of Vibriosis in Ecuadorian Pond‐Reared Penaeus vannamei Boone (Crustacea: Decapoda)

AbstractA massive ephtic of vibriosis, named “sindroma gaviota” (or sea gull syndrome = SGS) by local shrimp fanners, began in November 1989 and continued through May 1990 in nursery and grow‐out ponds in a number of shrimp farms located in the Gulf of Guaynquil near Cunyaquil, Ecuador. The level of cumulative mortalities ranged from slight in some ponds to more than 90% in others. Examination of affected shrimp, Penaeus vannamei Boone, led to the isolation of several closely related Vibrio species. The predominant species were identified as Vibrio parahaemolyticus, V. vulnificus, and V. alginolyticus using the API‐NFT system. Several of the strains exhibited a transient luminescence and some were positive for urease, an unusual trait for these species. Comparisons of the antimicrobial sensitivity patterns between farm and hatchery isolates from 1989–1990 and hatchery isolates from 1987–1989 indicate that the 1989–1990 pond isolates were not of hatchery origin. The epizootic coincided with the second year of a severe drought in Ecuador. Thus, the discharge of fresh water by the Guayas River was reduced and salinities and relative nutrient concentrations were elevated in the Gulf of Guaynquil. These environmental conditions were ideal for the increased growth of the causative vibrios in the estuarine waters and are believed to be factors that contributed to the 1989–1990 SGS epizootic.