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Nutrient Conditions (nutrient + condition)
Kinds of Nutrient Conditions Selected AbstractsWeedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant-dominated shallow lakesFRESHWATER BIOLOGY, Issue 3 2010ANGELA L. BERESFORD Summary 1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within-lake experimental manipulation and (ii) comparative, among-lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within-lake scale, and were associated with increased periphyton at the among-lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within-lake scale. However, at the among-lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among-lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest. [source] Calcium balance in Daphnia grown on diets differing in food quantity, phosphorus and calciumFRESHWATER BIOLOGY, Issue 11 2009XUE-JIA HE Summary 1.,The influences of dietary phosphorus (P) and food concentration on the calcium (Ca) balance in Daphnia magna were examined in this study at two different ambient Ca concentrations (0.5 and 10 mg Ca L,1). Daphnia were grown by feeding the young adults differentially under contrasting dietary P conditions [molar C : P ratio = c. 900 and c. 90 as low P (LP) and high P (HP), respectively], ambient Ca concentrations [0.5 mg and 10 mg Ca L,1 as low Ca (LCa) or high Ca (HCa), respectively] and food levels [0.15 or 1.5 mg C L,1 as low food (LF) or high food (HF), respectively] for 5 days. 2.,The specific Ca contents of daphniids (1.9,6.5% of dry weight,1) increased with increasing Ca concentration, food level and dietary P content, although the food level did not affect the Ca content in the HPHCa treatment. A radioactive tracer method showed that the food level did not affect the influx of Ca from the water under LP conditions, but the Ca influx under HP conditions doubled with a HF level. A LP condition also led to a decrease in Ca influx with a HF level. 3.,During the 3 days of efflux, generally only a small proportion of Ca (2.6,3.3%) was retained by the daphniids, but this retention increased (14,23%) under low ambient Ca concentrations and under P-limitation. Excretion was the most important pathway for Ca loss (accounting for 50,60% of body Ca), followed by moulting (20,47%), but the relative contribution of these two pathways (excretion and moulting) did not vary among all the different treatments. The absolute loss of Ca through excretion and moulting, on the contrary, differed with different ambient Ca concentrations and dietary P conditions. A HF level led to an increase in the loss rates in most cases. 4.,Our study strongly suggested that there is an interaction between an essential metal (Ca) and macronutrients (C and P) in freshwater crustaceans with HCa and P contents. The results imply that variation in environmental nutrient conditions may change the Ca budget in crustaceans and may affect the dynamics of Ca in the epilimnion of freshwaters. [source] Do phytoplankton communities correctly track trophic changes?FRESHWATER BIOLOGY, Issue 10 2005An assessment using directly measured, palaeolimnological data Summary 1. Measurements of total phosphorus (TP) concentrations since 1975 and a 50-year time series of phytoplankton biovolume and species composition from Lake Mondsee (Austria) were combined with palaeolimnological information on diatom composition and reconstructed TP-levels to describe the response of phytoplankton communities to changing nutrient conditions. 2. Four phases were identified in the long-term record. Phase I was the pre-eutrophication period characterised by TP-levels of about 6 ,g L,1 and diatom dominance. Phase II began in 1966 with an increase in TP concentration followed by the invasion of Planktothrix rubescens in 1968, characterising mesotrophic conditions. Phase III, from 1976 to 1979, had the highest annual mean TP concentrations (up to 36 ,g L,1) and phytoplankton biovolumes (3.57 mm3 L,1), although reductions in external nutrient loading started in 1974. Phases II and III saw an expansion of species characteristic of higher nutrient levels as reflected in the diatom stratigraphy. Oligotrophication (phase IV) began in 1980 when annual average TP concentration, Secchi depth and algal biovolume began to decline, accompanied by increasing concentrations of soluble reactive silica. 3. The period from 1981 to 1986 was characterised by asynchronous trends. Annual mean and maximum total phytoplankton biovolume initially continued to increase after TP concentration began to decline. Reductions in phytoplankton biovolume were delayed by about 5 years. Several phytoplankton species differed in the timing of their responses to changing nutrient conditions. For example, while P. rubescens declined concomitantly with the decline in TP concentration, other species indicative of higher phosphorus concentrations, such as Tabellaria flocculosa var. asterionelloides, tended to increase further. 4. These data therefore do not support the hypotheses that a reduction in TP concentration is accompanied by (i) an immediate decline in total phytoplankton biovolume and (ii) persistence of the species composition characterising the phytoplankton community before nutrient reduction. [source] Fungal endophytes reduce regrowth and affect competitiveness of meadow fescue in early succession of pasturesGRASS & FORAGE SCIENCE, Issue 3 2010S. Saari Abstract Systemic- and seed-transmitted fungal endophytes are suggested to enhance competitive dominance of agronomic grasses by increasing plant growth and defence against herbivores. We studied whether Neotyphodium uncinatum endophyte infection frequencies of meadow fescue (Schedonorus pratensis) and botanical composition of pastures are affected by 4, 5, 7 and 21 years of grazing by dairy cattle. We then examined with one greenhouse and two field experiments, whether endophyte infection and clipping affect regrowth of young or mature plants relative to nutrient availability in soil. The frequencies of infected plants and the number of plant species were less in grazed parts of the pastures. Endophytes significantly reduced relative regrowth and dry biomass of regrowth of the grass irrespective of nutrient levels in a 1-year-old field (on an average 18% in 2 months) and under high nutrient conditions in the greenhouse experiment (on an average 3% in 3 months) respectively. However, effects of endophytes were not detected in 5-year-old fields and under low nutrient conditions in the greenhouse. In contrast to past studies, our results demonstrate that grazing may negatively affect endophyte,grass symbiosis and number of plant species of successional pastures, and suggest that the effects of endophytes may be linked to the ontogeny of the host. [source] Herbivore and neighbour effects on tundra plants depend on species identity, nutrient availability and local environmental conditionsJOURNAL OF ECOLOGY, Issue 1 2008Anu Eskelinen Summary 1I performed a factorial transplant experiment to test the roles of plant,plant interactions, herbivory by mammal grazers and resource availability for plant performance in two contrasting habitat types in a mountain tundra environment. 2Three perennial dicot herbs, Solidago virgaurea, Erigeron uniflorus and Saussurea alpina, were used as target plants to study the effects of neighbour removal and grazer exclusion, and nutrient enrichment and liming on plant growth, survival and reproductive success. These treatments were replicated in two contrasting habitat types, infertile acidic and fertile non-acidic tundra heaths. 3The effects of plant,plant interactions on Saussurea varied from facilitation in infertile acidic habitats to competition in fertile non-acidic habitats and in nutrient-enriched conditions, while the overall performance of Saussurea was strongly negatively influenced by the presence of grazers, the effects being greater when plants were fertilized and in fertile non-acidic heaths. Erigeron performed better under nutrient-enriched conditions than in unfertilized plots, when neighbours had been removed. Solidago was negatively affected by grazing and this impact was greater in nutrient-enriched plots and in non-acidic heaths than in acidic heaths and for unfertilized controls. There were no interactions between neighbour removal and herbivory in any of the three species, indicating that these processes operated independently. 4Grazer-preferred tall plants are strongly limited by consumption by mammal herbivores in nutrient-enriched conditions and in inherently fertile habitats. By contrast, arctic,alpine specialists and species of low stature experience increased competition with neighbouring vegetation in fertile habitats and in enriched nutrient conditions. 5Synthesis. Overall, the results suggest that the strength and directions of plant,plant and plant,herbivore interactions depend on plant species identity and are modified by soil edaphic factors to govern vegetation processes in tundra plant communities. These findings have important implications for understanding the forces structuring vegetation in barren tundra ecosystems under a changing environment. [source] Differential selection of growth rate-related traits in wild barley, Hordeum spontaneum, in contrasting greenhouse nutrient environmentsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004K. J. F. Verhoeven Abstract Across-species comparisons show that inherent variation in relative growth rate (RGR) and its underlying traits are correlated with habitat productivity. In this study, we test the hypothesis that growth rate-related traits confer differential selective effects in contrasting nutrient environments. We specifically test whether high RGR is targeted by selection in nutrient-rich environments whereas low values of traits that underlie RGR [specific leaf area (SLA), leaf mass fraction and leaf area ratio (LAR)] confer a direct fitness advantage in nutrient-poor environments, resulting in selection of low RGR as a correlated response. We measured RGR, its underlying component traits, and estimated fitness in a range of wild barley (Hordeum spontaneum) accessions grown under high and low nutrient conditions. Selection on component traits differed between the two environments, while total selection of RGR was not significant. Using multiple regression and path analysis to estimate direct fitness effects, a selective advantage of high LAR and SLA was demonstrated only under nutrient-rich conditions. While supporting the view that observed associations between habitat richness and some RGR-component traits reflect adaptation to differing nutrient regimes, our data suggest that direct selection targets component traits rather than RGR itself. [source] OPTIMAL CONDITIONS FOR THE GROWTH AND POLYSACCHARIDE PRODUCTION BY HYPSIZIGUS MARMOREUS IN SUBMERGED CULTUREJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 4 2009PING WANG ABSTRACTS In submerged cultivation, many nutrient variables and environmental conditions have great influence on the growth and polysaccharide production by Hypsizigus marmoreus. Plackett,Burman design was used to determine the important nutrient factors. A central composite experimental design and surface response methodology were employed to optimize the factor levels. Prediction models for dry cell weight (DCW), polysaccharide outside cells (EPS) and polysaccharide inside cells (IPS) under important nutrient conditions were developed by multiple regression analysis and verified. By solving the equations, the optimal nutrient conditions for highest EPS production (9.62 g/L) were obtained at 6.77 g cornstarch/L, 36.57 g glucose/L, 3.5 g MgSO4/L and 6.14 g bean cake powder/L, under which DCW and IPS were 16.2 g/L and 1.46 g/L, close to the highest value under their corresponding optimal conditions. Optimal environmental conditions were obtained at 10% inoculation dose, 45 mL medium in a 250 mL flask, pH 6.5, 25C and 200 rpm according to the results of single-factor experiment design. PRACTICAL APPLICATIONS Hypsizigus marmoreus polysaccharides have many functional properties, including antitumor, antifungal and antiproliferative activities, and free-radical scavenging. Liquid cultivation could produce a higher yield of polysaccharides and more flexible sequential processing methods of H. marmoreus, compared with traditional solid-state cultivation. However, the cell growth and production of polysaccharides would be influenced by many factors, including nutrient conditions and environmental conditions in the liquid cultivation of H. marmoreus. Keeping the conditions at optimal levels can maximize the yield of polysaccharides. The study not only found out the optimal nutrient conditions and environmental conditions for highest cell growth and yield of polysaccharides, but also developed prediction models for these parameters with important nutrient variables. Yield of polysaccharide inside of cells was also studied as well as polysaccharides outside of cells and cell growth. The results provide essential information for production of H. marmoreus polysaccharides by liquid culture. [source] Top-down and bottom-up control in an eelgrass,epiphyte systemOIKOS, Issue 5 2008Sybill Jaschinski Nutrient supply and the presence of grazers can control primary producers in aquatic ecosystems, but the relative importance of bottom-up and top-down effects remains inconclusive. We conducted a mesocosm experiment and a field study to investigate the independent and interactive effects of nutrient enrichment and grazing on primary producers in an eelgrass bed Zostera marina. Nutrient treatments consisted of ambient or enriched (2× and 4× ambient) concentrations of inorganic nitrogen and phosphate. Grazer treatments consisted of presence or absence of field densities of the common isopod Idotea baltica. We found strong and interacting effects of nutrients and grazing on epiphytes. Epiphyte biomass and productivity were enhanced by nutrient enrichment and decreased in the presence of grazers. The absolute amount of epiphyte biomass consumed by grazers increased under high nutrient supply, and thus, nutrient effects were stronger in the absence of grazing. The effects of grazers and fertilisation on epiphyte composition were antagonistic: chain-forming diatoms and filamentous algae profited from nutrient enrichment, but their proportions were reduced by grazing. Eelgrass growth was positively affected by grazing and by nutrient enrichment at moderate nutrient concentrations. High nutrient supply reduced eelgrass productivity compared to moderate nutrient conditions. The monthly measured field data showed a nitrogen limitation for epiphytes and eelgrass in summer, which may explain the positive effect of nutrient enrichment on both primary producers. Generally, the field data suggested the possibility of seasonally varying importance of bottom-up and top-down control on primary producers in this eelgrass system. [source] Interspecific and intraspecific interactions between salt marsh plants: integrating the effects of environmental factors and density on plant performanceOIKOS, Issue 2 2002Jonathan M. Huckle There has been much debate about the role of plant interactions in the structure and function of vegetation communities. Here the results of a pot experiment with controlled environments are described where three environmental variables (nutrients, sediment type and waterlogging) were manipulated factorially to identify their effects on the growth and intensity of interactions occurring between Spartina anglica and Puccinellia maritima. The two species were grown in split-plot planting treatments, representing intraspecific and interspecific addition series experiments, to determine individual and interactive effects of environmental factors and plant interactions on plant biomass. Above-ground growth of both species involved interactions between the environmental and planting treatments, while below-ground, environmental factors affected the biomass irrespective of planting treatments. It was suggested that this difference in growth response is evidence that in our experiment plant interactions between the two species occur primarily at the above-ground level. The intensity of plant interactions varied in a number of ways. First, interactions between Spartina and Puccinellia were distinctly asymmetrical, Puccinellia exerting a competitive effect on Spartina, with no reciprocal effect, and with a facilitative effect of Spartina on Puccinellia in low nutrient conditions. Second, the interactions varied in intensity in different environmental conditions. Interspecific competitive effects of Puccinellia on Spartina were more intense in conditions favourable to growth of Puccinellia and reduced or non-existent in environments with more abiotic stress. Third, intraspecific competition was found to be less intense for both species than interspecific interactions. Finally, the intensity of plant interactions involving both species was more intense above ground than below ground, with a disproportionate reduction in the intensity of interspecific competition below relative to above ground in treatments with less productive sediments and greater immersion. This is interpreted as reflecting a potential mechanism by which Spartina may be able to evade competitive neighbours. [source] Leaf senescence is delayed in maize expressing the Agrobacterium IPT gene under the control of a novel maize senescence-enhanced promoterPLANT BIOTECHNOLOGY JOURNAL, Issue 2 2004Paul R. H. Robson Summary We have genetically modified maize plants to delay leaf senescence. A senescence-enhanced promoter from maize (PSEE1) was used to drive expression of the Agrobacterium cytokinin biosynthesis gene IPT in senescing leaf tissue. Three maize lines expressing IPT from PSEE1, Sg1, Sg2 and Sg3, were analysed in detail, representing mild, intermediate and extreme expression, respectively, of the delayed-senescence phenotype. Backcross populations segregating for the presence or absence of the PSEE1XbaIPTNOS transgene also simultaneously segregated for the senescence phenotype. At the time of ear leaf emergence, individuals of lines Sg1 and Sg2 segregating for the presence of the transgene carried about three fewer senescing leaves than control (transgene-minus) segregants, and IPT transcript levels were higher in leaves at incipient senescence than in young leaves. Leaves of transgenic Sg3 plants were significantly greener than controls and progressed directly from fully green to bleached and dead without an intervening yellowing phase. IPT transcript abundance in this line was not related to the initiation of senescence. Extended greenness was accompanied by a delay in the loss of photosynthetic capacity with leaf age. The delayed-senescence trait was associated with relatively minor changes in morphology and development. The phenotype was particularly emphasized in plants grown in low soil nitrogen. The reduced ability of the extreme transgenic line Sg3 to recycle internal nitrogen from senescing lower leaves accounted for significant chlorosis in emerging younger leaves when plants were grown in low nutrient conditions. This study demonstrates that the agronomically important delayed-senescence (,stay-green') trait can be engineered into a monocot crop, and is the first example outside Arabidopsis of senescence modification using a homologous senescence-enhanced promoter. [source] Estuarine Restoration of Submersed Aquatic Vegetation: The Nursery Bed EffectRESTORATION ECOLOGY, Issue 4 2010Angela Hengst The historic decline of submersed aquatic vegetation (SAV) in mesohaline regions of Chesapeake Bay, United States involved a diversity of plant species. The recent modest recovery is mostly, however, associated with a single, prolific but ephemeral species, Ruppia maritima. Two previously abundant and more stable species, Potamogeton perfoliatus and Stuckenia pectinata, have shown virtually no evidence of recovery. Based on previous studies that demonstrated the ability of R. maritima stands to enhance water clarity and nutrient conditions for SAV growth, we hypothesized that these beds would serve as effective "nursery" areas to incite transplant success for other SAV. We conducted experiments in a two-phase study at small and large spatial scales designed to explore this "nursery effect" as a restoration approach to increase plant species diversity. The first phase was conducted at small spatial scales to test effects of patch density by planting P. perfoliatus and S. pectinata into bare, sparse, and densely vegetated areas within three similar R. maritima beds in a tributary of Chesapeake Bay. Mean seasonal percent survivorship and shoot density were significantly higher in bare patches compared to vegetated patches. In the second phase of the study, P. perfoliatus was transplanted into separate R. maritima beds of different densities to test the effect of bed scale plant density on P. perfoliatus survival and growth. Transplant success of P. perfoliatus was positively correlated with the density of R. maritima among all sites. [source] Environmental changes in man-made coastal dune pools since 1850 as indicated by sedimentary and epiphytic diatom assemblages (Belgium)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2003Luc Denys Abstract 1.Diatom assemblages of man-made coastal dune wetlands between Blankenberge and Heist (Belgium), dating from 1852 to 1929 and sampled from herbarium specimens of macrophytes, were compared with more recent samples collected in the remaining calcareous dune marshes and pools in this area. 2.Overall, nutrient conditions inferred from the reference assemblages were fairly eutrophic for phosphorus. Only a minority of the historical assemblages pointed to presumably nitrogen-limited conditions. 3.Significant alterations in general assemblage composition were observed, including a marked decline of epiphytic species, and a decrease in the compositional variation in sediment diatom assemblages. These changes can be attributed mainly to an increased availability of nutrients and degradable organic matter since the mid 1970s. No changes in the salinity range seem to have occurred, suggesting fairly stable hydrological conditions. 4.Possible causes for eutrophication include increased atmospheric deposition of nutrients, but also more site-related phenomena such as guanotrophication, angling and, perhaps, effects of nature management on soil,nutrient cycling. Their relative importance needs to be established and further monitoring is necessary. 5.Measures are required to reduce nutrient levels of both permanently and periodically inundated sites and to promote small-scale habitat differentiation. Due to physical constraints, the latter will be possible only by mimicking the processes that act upon more natural dune systems in management practice. Copyright © 2003 John Wiley & Sons, Ltd. [source] Identification of gene disruptions for increased poly-3-hydroxybutyrate accumulation in Synechocystis PCC 6803BIOTECHNOLOGY PROGRESS, Issue 5 2009Keith E. J. Tyo Abstract Inverse metabolic engineering (IME) is a combinatorial approach for identifying genotypes associated with a particular phenotype of interest. In this study, gene disruptions that increase the biosynthesis of poly-3-hydroxybutyrate (PHB) in the photosynthetic bacterium Synechocystis PCC6803 were identified. A Synechocystis mutant library was constructed by homologous recombination between the Synechocystis genome and a mutagenized genomic plasmid library generated through transposon insertion. Using a fluorescence-activated cell sorting-based high throughput screen, high PHB accumulating mutants from the library grown in different nutrient conditions were isolated and characterized. While several mutants isolated from the screen had increased PHB accumulation, transposon insertions in only two ORFs could be linked to increased PHB production. Disruptions of sll0461, coding for gamma-glutamyl phosphate reductase (proA), and sll0565, a hypothetical protein, resulted in increased accumulation in standard growth media and acetate supplemented media. These genetic perturbations have increased PHB accumulation in Synechocystis and serve as markers for engineering increased polymer production in higher photosynthetic organisms. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] PRODUCTION OF PARALYTIC SHELLFISH TOXINS BY APHANIZOMENON SP.JOURNAL OF PHYCOLOGY, Issue 4 2002LMECYA 31 (CYANOBACTERIA) We examined intracellular and extracellular paralytic shellfish toxins (PST) in a strain of Aphanizomenon sp. (LMECYA31) isolated from a Portuguese freshwater reservoir throughout the growth cycle and under different conditions affected by temperature and nitrate and phosphate availability. PST concentrations and compositions were greatly influenced by cell density, growth stage, and temperature and nutrients conditions. On a per-cell basis results showed (1) the enhancement of PST cell quota after the end of exponential growth phase in nutrient replete batch cultures, (2) the absence of a PST increment at late growth stages under phosphate limitation, (3) a rise in PST maximum cell quota under nitrate depletion, and (4) the enhancement of toxin production at higher temperatures. The relative proportion of the four toxins detected, neoSTX, dcSTX, STX and GTX5, also changed within and between culture settings. While growing under phosphate rich media cells produced mainly GTX5 and neoSTX, whereas under phosphate limitation the proportion of STX and dcSTX increased substantially with culture age. Large amounts of extracellular toxins were found in the culture medium, increasing during culture time. Extracellular toxin composition in each culture was fairly constant and always similar to the intracellular composition found at late stages of growth. This further supported other research that indicates that PSTs are released to the water through cell lysis, and a significant concentration of PST may be expected to remain in the water upon the collapse of a toxic bloom or after cells removal by water treatment. [source] | ||||||||||