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P Status (p + status)
Selected AbstractsGROWTH AND PHOSPHORUS UPTAKE BY THE TOXIC DINOFLAGELLATE ALEXANDRIUM CATENELLA (DINOPHYCEAE) IN RESPONSE TO PHOSPHATE LIMITATION,JOURNAL OF PHYCOLOGY, Issue 5 2010Cécile Jauzein Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO43,) concentrations in this environment over the 1970,1995 period. To determine if this dinoflagellate species has a competitive advantage in PO43, -limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO43, uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (QP and QC). Shifts in trends of QP/QC and QP per cell (QP·cell,1) along the DR gradient allowed the definition of successive P-stress thresholds for A. catenella cells. The maximal uptake rate of 33PO43, increased strongly with the decrease in DR and the decrease in QP/QC, displaying physiological acclimations to PO43, limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO43, limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO43, threshold between 0.4 and 1 ,M. As lower PO43, concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds. [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] Risk assessment methodologies for predicting phosphorus losses,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2003Oscar F. Schoumans Abstract Risk assessment parameters are needed to assess the contribution of phosphorus (P) losses from soil to surface water, and the effectiveness of nutrient and land management strategies for the reduction of P loss. These parameters need to take into account the large temporal and spatial variation in P transfer from individual fields arising from (a) changing but predictable factors such as land use, soil P status, P application rates, forms and ways of fertilization and spreading, (b) predictable but inherent factors such as soil type, soil dispersivity, slope and hydrological routing, and (c) unpredictable weather factors such as rainfall amount and intensity. In most situations, water transport is the driving force of P loss from agricultural land to surface water. Therefore, the hydrological pathways determine to a large extent the relevance of these different factors. Over the last decade several soil P tests have been proposed as a first step to link field conditions to risk of P loss. The major reason is that these soil P tests are also meaningful in discussions with farmers. Recently, more complex P loss risk parameters have been derived based on different approaches. However, the scope and purposes of these P loss risk parameters vary remarkably. Finally, there is a need to evaluate the usefulness of new P tests that can be used as an indicator of P loss risk, e.g. in relation to monitoring purposes. The implementation of the EU Water Framework Directive will increase this need. In this paper, the practicable applicability of P parameters for risk assessment is discussed in relation to purpose, scale (from field, farm to catchment), effectiveness, sensibility etc. Furthermore, a conceptual framework for P indicators is presented and evaluated, based on the outcome of the presentations and the discussions in Zurich. No translation. [source] Potential role of phosphate buffering capacity of soils in fertilizer management strategies fitted to environmental goals,JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2003Phillip Ehlert Abstract Sorption behavior and buffering of phosphorus (P) are important, both from an agricultural and an environmental point of view. The objectives of this study were to investigate: (1) the kinetics of the transfer of P from soil to soil solution and assessing P buffering capacity of soils (PBC), as a function of soil solution P; (2) the effect of PBC on soil P status fitted to environmental targets for water quality; (3) the effect of PBC on crop response. PBC was derived from the non-linear Q-I curve describing the time-dependent relationship between plant-available reserve of soil P (Q) versus soil solution P (I). The Q-I curve was determined in soil suspension using sorption and isotopic dilution methods for soil samples from French, Swedish, and Dutch field trials. Soils with low PBC values were more sensitive to the loss of P to the environment, required higher critical value in soil solution P to comply with P demand of maize, and had higher change in soil solution P per unit of P budget. In different soils, both the critical soil solution P for maize and the change in soil solution P per unit of P balance varied inversely with PBC. It is concluded that (1) PBC plays a key role in determining the agronomic and environmental threshold levels of available P content in the soils, and (2) PBC is a prerequisite for the development of more environmentally oriented fertilization recommendation systems. Potenzielle Bedeutung der Phosphat-Pufferkapazität des Bodens für umweltgerechte Düngungsstategien Bindungsverhalten und Pufferkapazität des Phosphors (P) im Boden ist wichtig, sowohl aus Sicht der Landwirtschaft als auch des Umweltschutzes. In dieser Untersuchung sollten folgende Probleme untersucht werden: (1) Kinetik des P-Transfers von der Festphase in die Bodenlösung und Abschätzung der P-Pufferkapazität (PBC) als Funktion der P-Konzentration in der Bodenlösung; (2) die Wirkung der PBC auf den Boden-P-Status im Hinblick auf Qualitätsziele für Wasser; (3) Wirkung der PBC auf die P-Aufnahme der Pflanze. Die PBC wurde abgeleitet aus der nichtlinearen Q-I-Kurve, die die zeitabhängige Beziehung zwischen dem Gehalt an pflanzenverfügbarem Boden-P (Q) und der P-Konzentration in der Bodenlösung (I) beschreibt. Die Q-I-Kurve wurde in Bodensupensionen mit Sorptions- und Isotopen-Verdünnungsmethoden an Bodenproben aus Feldversuchen in Frankreich, Schweden und den Niederlanden bestimmt. Böden mit niedriger PBC waren sensitiver für P-Austräge in die Umwelt, erforderten höhere Grenzkonzentrationen in der Bodenlösung zur Bedarfsdeckung bei Mais und zeigten größere Konzentrationsveränderungen in der Bodenlösung je Einheit der P-Bilanz. Die Grenzkonzentrationen in der Bodenlösung zur Bedarfsdeckung bei Mais und Konzentrationsveränderungen in der Bodenlösung je Einheit der P-Bilanz variierten in unterschiedlichen Böden invers mit Variation der PBC. Aus den Untersuchungen folgte, dass (1) die PBC ein Schlüssel-Parameter zur Bestimmung agronomischer und umweltrelevanter Grenzwerte der Gehalte an verfügbarem P im Boden ist und (2) somit eine Voraussetzung für die Entwicklung mehr umweltorientierter Systeme der Düngungsempfehlungen. [source] Phosphorus nutrition-mediated effects of arbuscular mycorrhiza on leaf morphology and carbon allocation in perennial ryegrassNEW PHYTOLOGIST, Issue 2 2005Agustín A. Grimoldi Summary ,,The aim of this work was to disentangle phosphorus status-dependent and -independent effects of arbuscular mycorrhizal fungus (AMF) on leaf morphology and carbon allocation in perennial ryegrass (Lolium perenne). ,,To this end, we assessed the P-response function of morphological components in mycorrhizal and nonmycorrhizal plants of similar size. ,,AMF (Glomus hoi) stimulated relative P-uptake rate, decreased leaf mass per area (LMA), and increased shoot mass ratio at low P supply. Lower LMA was caused by both decreased tissue density and thickness. Variation in tissue density was almost entirely caused by variations in soluble C, while that in thickness involved structural changes. ,,All effects of AMF were indistinguishable from those mediated by increases in relative P-uptake rate through higher P-supply rates. Thus the relationships between relative P-uptake rate, leaf morphology and C allocation were identical in mycorrhizal and nonmycorrhizal plants. No evidence was found for AMF effects not mediated by changes in plant P status. [source] A new dawn , the ecological genetics of mycorrhizal fungiNEW PHYTOLOGIST, Issue 2 2000D. LEE TAYLOR Many human activities, such as ore mining and smeltering, sewage sludge treatment and fossil fuel consumption, result in toxic soil concentrations of ,heavy metals' (Al, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Ti, Zn and others) (Gadd, 1993). There are also natural soils, such as serpentine, with levels of heavy metals that inhibit or preclude the growth of many plants and soil micro-organisms. However, certain plants and microorganisms do grow in these metalliferous sites. Understanding the physiology, ecology and evolution of tolerance to elevated soil metal concentrations is important in an applied setting, and is also of interest in theoretical biology. Applied importance relates to the improvement of forest health in areas subject to increasing pollution, rehabilitation of severely polluted sites by phytostabilization of metals, and metal removal using hyperaccumulating plants (Krämer, 2000; Ernst, 2000). Areas of theoretical interest include the evolution of local adaptation (Sork et al., 1993) and how it is shaped by the combined influences of natural selection, gene flow and genetic architecture, as well as metal influences on various species interactions (Pollard, 2000). A paper appears on pages 367,379 in this issue by Jan Colpaert and coworkers which adroitly combines the disparate fields of physiology, genetics and ecology to answer several outstanding questions concerning heavy metal tolerance in mycorrhizal fungi. Mycorrhizal fungi, which interact mutualistically with the majority of plant species, are well known for improving the P status of their hosts (Smith & Read, 1997). Some mycorrhizal fungi are also able to mobilize N and P from organic substrates and to provide plants with improved micronutrient and water acquisition, pathogen resistance, and a variety of other benefits (Smith & Read, 1997). One of these additional benefits is the amelioration of toxicity in metalliferous soils. [source] Interactions between the effects of atmospheric CO2 content and P nutrition on photosynthesis in white lupin (Lupinus albus L.)PLANT CELL & ENVIRONMENT, Issue 5 2006CATHERINE D. CAMPBELL ABSTRACT Phosphorus (P) is a major factor limiting the response of carbon acquisition of plants and ecosystems to increasing atmospheric CO2 content. An important consideration, however, is the effect of P deficiency at the low atmospheric CO2 content common in recent geological history, because plants adapted to these conditions may also be limited in their ability to respond to further increases in CO2 content. To ascertain the effects of low P on various components of photosynthesis, white lupin (Lupinus albus L.) was grown hydroponically at 200, 400 and 750 µmol mol,1 CO2, under sufficient and deficient P supply (250 and 0.69 µm P, respectively). Increasing growth CO2 content increased photosynthesis only under sufficient growth P. Ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) content and activation state were not reduced to the same degree as the net CO2 assimilation rate (A), and the in vivo rate of electron transport was sufficient to support photosynthesis in all cases. The rate of triose phosphate use did not appear limiting either, because all the treatments continued to respond positively to a drop in oxygen levels. We conclude that, at ambient and elevated CO2 content, photosynthesis in low-P plants appears limited by the rate of ribulose biphosphate (RuBP) regeneration, probably through inhibition of the Calvin cycle. This failure of P-deficient plants to respond to rising CO2 content above 200 µmol mol,1 indicates that P status already imposes a widespread restriction in plant responses to increases in CO2 content from the pre-industrial level to current values. [source] | ||||||||||