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Phosphorus Availability (phosphorus + availability)
Selected AbstractsPhosphorus availability mediates plasticity in life-history traits and predator,prey interactions in DaphniaECOLOGY LETTERS, Issue 10 2005Punidan D. Jeyasingh Abstract We analysed growth plasticity of two Daphnia pulex clones under low-phosphorus (LP) and high phosphorus (HP) conditions, in the presence of Chaoborus kairomones to examine how food quality (P-availability) might impact life-history responses and vulnerability to predation. Overall, clone 1 grew faster, and was larger at maturity. Under HP, both clones responded to kairomones by increasing growth, age and size at maturity, and decreasing fecundity. Under LP, both clones suffered reduced growth, and fecundity. However, the magnitude of response to kairomones depended on a clone by P-availability interaction. Chaoborus presented a 1 : 1 clonal mixture under HP or LP, consumed more individuals under LP. Moreover, fewer clone 1 individuals were consumed. Studying the effects of P-availability on life histories, and predator,prey interactions may help us understand the mechanisms generating and maintaining plasticity, as well as influencing genotypic diversity and microevolutionary processes in natural populations. [source] Identification of mutants in phosphorus metabolismANNALS OF APPLIED BIOLOGY, Issue 1 2001JULIE C LLOYD Summary Phosphorus availability is often limiting for plant growth. However, little is known of the pathways and mechanisms that regulate phosphorus (P) uptake and distribution in plants. We have developed a screen based on the induction of secreted root acid phosphatase activity by low-P stress to identify mutants of Arabidopsis thaliana with defects in P metabolism. Acid phosphatase activity was detected visually in the roots of A. thaliana seedlings grown in vitro on low-P medium, using the chromogenic substrate, 5-bromo-4-chloro-3-indolyl-phosphate (BCIP). In low-P stress conditions the roots of wild-type plants stained blue, as the induced root acid phosphatase cleaved BCIP to release the coloured product. Potential mutants were identified as having white, or pale blue, roots under these conditions. Out of approximately 79 000 T-DNA mutagenised seedlings screened, two mutants with reduced acid phosphatase staining were further characterised. Both exhibited reduced growth and differences in their P contents when compared to wild-type A. thaliana. The mutant with the most severe phenotype, pho3, accumulated high levels of anthocyanins and starch in a distinctive visual pattern within the leaves. The phenotypes of these mutants are distinct from two previously identified phosphorus mutants (phol and pho2) and from an acid phosphatase deficient mutant (pupl) of A. thaliana. This suggested that the screening method was robust and might lead to the identification of further mutants with the potential for increasing our understanding of P nutrition. [source] Apparent digestibility of nutrients and energy in extruded diets from cultivars of barley and wheat selected for nutritional quality in rainbow trout Oncorhynchus mykissAQUACULTURE NUTRITION, Issue 3 2009T.G. GAYLORD Abstract A digestibility trial was conducted to elucidate potential differences in barley (Hordeum vulgare L.) lines and varieties as a first step in defining their potential for use in aquafeeds. A diverse group of six barley lines having six combinations of selected attributes, normal versus low phytic acid, normal versus waxy, and hulled versus hull-less, were chosen for evaluation along with a waxy wheat (Triticum aestivum L.) and soft white wheat. The experimental diets were manufactured by cooking extrusion and consisted of a 70% reference diet that was formulated to contain a minimal level of phosphorus and 30% test ingredient. Phosphorus availability ranged from 17 to 78% and was influenced by starch type in wheat. Apparent protein digestibility ranged from 53 to 125% and differences were observed between wheat varieties based on starch type. Apparent energy digestibility ranged from 32 to 63%, with waxy barley varieties having higher energy digestibility coefficients than normal starch varieties. Waxy starch varieties had higher starch digestibility in both barley and wheat because of the greater digestibility of amylopectin than amylose. In summary, the higher energy digestibility of waxy barley lines suggests that these varieties warrant further attention as feed ingredients for rainbow trout. [source] Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoirENVIRONMENTAL MICROBIOLOGY, Issue 9 2006Karel, imek Summary We investigated net growth rates of distinct bacterioplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus availability by analysing eight in situ manipulation experiments, conducted between 1997 and 2003, in the canyon-shaped ,ímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phosphorus limitation (range of soluble reactive phosphorus concentrations , SRP, 0.7,96 µg l,1). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate constants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betaproteobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabilities for possible life strategies of different bacterial phylogenetic lineages are discussed. [source] Ecosystem science and human,environment interactions in the Hawaiian archipelagoJOURNAL OF ECOLOGY, Issue 3 2006PETER VITOUSEK Summary 1Tansley's ecosystem concept remains a vital framework for ecological research in part because the approach facilitates interdisciplinary analyses of ecological systems. 2Features of the Hawaiian Islands , particularly the nearly orthogonal variation in many of the factors that control variation among ecosystems elsewhere , make the archipelago a useful model system for interdisciplinary research designed to understand fundamental controls on the state and dynamics of ecosystems, and their consequences for human societies. 3Analyses of rain forest sites arrayed on a substrate age gradient from c. 300 years to over 4 million years across the Hawaiian archipelago demonstrate that the sources of calcium and other essential cations shift from > 80% rock-derived in young sites to > 80% derived from marine aerosol on substrates older than 100 000 years. Rock-derived phosphorus is retained longer within ecosystems, but eventually long-distance transport of continental dust from Asia becomes the most important source of phosphorus. 4A biogeochemical feedback from low nutrient availability to efficient resource use by trees to slow decomposition and nutrient regeneration accentuates the geochemically driven pattern of low phosphorus availability and phosphorus limitation to net primary productivity in the oldest site. 5Variations in ecosystem biogeochemistry across the archipelago shaped the development and sustainability of Polynesian agricultural systems in the millennium between their discovery of Hawai'i and contact by Europeans. Irrigated pondfields were largely confined to stream valleys on the older islands, while rain-fed dryland systems occupied a narrow zone of fertile, well-watered soils on the younger islands. 6The ecosystem approach often represents the most appropriate level of organization for analyses of human influences on ecological systems; it can play a central role in the design and analysis of alternative agricultural, industrial and residential systems that could reduce the human footprint on the Earth. [source] Can phosphorus limitation contribute to the maintenance of sex?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2009A test of a key assumption Abstract Why sex is so common remains unclear; what is certain is that the predominance of sex despite its profound costs means that it must confer major advantages. Here, we use elemental and nucleic acid assays to evaluate a key element of a novel, integrative hypothesis considering whether sex might be favoured because of differences in body composition between sexuals and asexuals. We found that asexual Potamopyrgus antipodarum, a New Zealand snail, have markedly higher bodily phosphorus and nucleic acid content per unit mass than sexual counterparts. These differences coincide with and are almost certainly linked to the higher ploidy of the asexuals. Our results are the first documented body composition differences between sexual and asexual organisms, and the first detected phenotypic difference between sexual and asexual P. antipodarum, an important natural model system for the study of the maintenance of sex. These findings also verify a central component of our hypothesis that competition between diploid sexuals and polyploid asexuals could be influenced by phosphorus availability. [source] MACROALGAL TISSUE NUTRIENTS AS INDICATORS OF NITROGEN AND PHOSPHORUS STATUS IN THE FLORIDA KEYSJOURNAL OF PHYCOLOGY, Issue 2000Hanisak M. D. This study used the tremendous biochemical and ecological diversity of macroalgae to assess nitrogen and phosphorus availability at a broad, ecosystem-level scale in the Florida Keys and nearby waters. Spatial variation in tissue nutrients (carbon, C; nitrogen, N; phosphorus, P) of dominant macroalgae were assessed, both as ratios and absolute values, along 12 inshore-offshore transects in the Florida Keys and at 10 stations in nearby Florida Bay. The resulting detailed analysis demonstrated spatial and temporal patterns in macroalgal tissue nutrients. The transect data revealed no universal inshore-offshore patterns in tissue nutrients and no obvious "hotspots" of nutrient enrichment. Similarly, when data were compared among segments, there was no universal geographical pattern in tissue nutrients for all species. The most striking result was that the N and P status of macroalgae in Florida Bay was significantly different than other locations. Macroalgae collected from Florida Bay generally had higher N and lower P levels than algae collected elsewhere. The most common inshore-offshore pattern was higher %N and lower %P availability inshore; however, limited inshore-offshore differences in N:P ratio suggests that both nutrients were generally readily available in proportional amounts required by the various species. Most species in this study had higher %N, and to a lesser extent, higher %P and %C in March than in July. Based on the published literature on other species of macroalgae, it appears that N and P are generally available in sufficient quantities that most macroalgal growth is not limited by either nutrient. [source] Nutrient requirements of ephemeral plant species from wet, mesotrophic soilsJOURNAL OF VEGETATION SCIENCE, Issue 3 2001Emiel; Brouwer van der Meijden (1996) Abstract. Nanocyperion plant communities occur on wet, more or less nutrient-poor and sparsely vegetated soils in temperate climates and are characterized by tiny, very shortlived plant species. Most of these have become locally extinct. It is generally assumed that drainage and eutrophication were the most important reasons for this decrease. However, chemical analysis of soil pore water from plots on growth sites of these ephemerals showed that phosphorus availability was relatively high. In a greenhouse experiment, the growth of ephemeral species was strongly limited by the amount of available phosphorus, whereas there was little or no limitation to the growth of other plant species from this habitat. At low phosphorus concentrations, the ephemeral species reached their reproductive phase within the same period, but showed a strong reduction in the amount of flowers that were produced. We concluded that ephemeral species in particular require a minimum amount of phosphorus for reproduction. Other species on nutrient-poor, wet soils have a longer life span and can postpone flowering in nutrient-poor soils. In contrast to other short-lived plant species from the same habitat, the growth of ephemeral species was barely stimulated by enhanced nitrogen availability. Apparently, the ephemerals are adapted to low nitrogen concentrations. The occurrence on nitrogen-poor and relatively phosphorus-rich soils suggests that this community may be very sensitive to nitrogen deposition. Reduced phosphorus availability below the minimum requirements of ephemerals, for example after acidification or the exclusion of human activities, has possibly contributed to the decrease of ephemeral plant species. [source] Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petuniaPLANT CELL & ENVIRONMENT, Issue 12 2008HYE-JI KIM ABSTRACT The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive ,Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in ,Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception , not production , regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than ,Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus. [source] Sources and bioavailability of phosphorus fractions in freshwaters: a British perspectiveBIOLOGICAL REVIEWS, Issue 1 2001C. S. REYNOLDS ABSTRACT This paper seeks a perspective on the forms of phosphorus which promote aquatic eutrophication, with the particular quest of establishing their sources. A short background traces the development of understanding of nutrient enrichment and the suppositions about the relative contributions of agriculture, sewage and detergent residues. Most aquatic systems, and their primary producers, are naturally deficient in biologically-available phosphorus. Aquatic plants have evolved very efficient phosphorus uptake mechanisms. The biomass responses to an increase in the supply of phosphorus are stoichiometrically predictable. The most bioavailable forms of phosphorus are in solution, as orthophosphate ions, or are readily soluble or elutable from loose combinations. Ready bioavailability coincides well with what is measurable as molybdate-reactive (MRP) or soluble-reactive phosphorus (SRP). Most other forms, including phosphates of the alkaline earth metals, aluminium and iron are scarcely available at all. Orthophosphate ions sorbed to metal oxides and hydroxides are normally not biologically available either, except through weak dissociation (,desorption'). The production of alkaline phosphatase provides organisms with an additional mechanism for accelerating the sequestration of phosphate from organic compounds. Bioavailable phosphate is liberated when redox- or alkali-sensitive metal hydroxides dissolve but these processes are minor contributors to the biological responses to nutrient enrichment. Most of the familiar eutrophication is attributable to the widespread application of secondary sewage treatment methods to the wastes emanating from a burgeoning and increasingly urbanised human population. The use of polyphosphate-based detergents, now in decline, has contributed to the problem. In aquatic systems, the additional phosphorus raises the biological supportive capacity, sometimes to the capacity of the next limiting factor (carbon, light, hydraulic retention or of another nutrient). At high orthophosphate loadings, the straight stoichiometric yield relationship between biomass yield and phosphorus availability is lost. Movements of phosphorus and its recycling within aquatic systems do not prevent the slow gravitation of phosphorus to the bottom substrata. The phosphorus retentivity of sediments depends upon their chemical composition. While oxide-hydroxide binding capacity in the surface sediments persists, they act as a sink for phosphorus and a control on further cycling. Iron-rich and clay-rich sediments perform best in these conditions; calcareous sediments least so. Eutrophication may lead to the exhaustion of sediment P-binding capacity. Non-sorbed phosphate is readily recyclable if primary producers have access to it. Recycling is most rapid in shallow waters (where sediment disturbance, by flow, by wind action and through bioturbation, is frequent) and least in deep ventilated sediments. The contributions of phosphorus from catchments are assessed. The slow rate of weathering of (mostly apatitic) minerals, the role of chemical binding in soils and the incorporation and retentivity by forested terrestrial ecosystems each contribute to the minimisation of phosphorus leakage to drainage waters. Palaeolimnological and experimental evidence confirms that clearance of land and ploughing its surface weakens the phosphorus retentivity of catchments. The phosphorus transferred from arable land to drainage remains dominated by sorbed fractions which are scarcely bioavailable. Some forms of intensive market gardening or concentrated stock rearing may mobilise phosphates to drainage but it is deduced that drainage from agricultural land is not commonly a major source of readily bioavailable phosphorus in water. Careful budgeting of the phosphates in run-off from over-fertilised soils may nevertheless show that a proportionately small loss of bioavailable phosphorus can still be highly significant in promoting aquatic plant production. The bioavailable-phosphorus (BAP) load achieving the OECD threshold of lake eutrophy (35 mg P m,3) is calculated to be equivalent to a terrestrial loss rate of approximately 17.5 kg BAP km,2 year,1), or only 1,2% of a typical fertiliser application. The output is shown to be comparable with the P yield from secondary treatment of the sewage produced by a resident population of 30,44 persons km,2. With tertiary treatment, the equivalence is with approximately 200 persons km,2. [source] | |||||||||||||