Showing papers on "Phosphorus published in 1997"

Soil phosphorus: its measurement, and its uptake by plants

Abstract: Phosphorus (P) is the most important nutrient element (after nitrogen) limiting agricultural production in most regions of the world. It is extremely chemically reactive, and more than 170 phosphate minerals have been identified. In all its natural forms, including organic forms, P is very stable or insoluble, and only a very small proportion exists in the soil solution at any one time. Plant-available P may be considered in either its quantitative or intensive dimension. The quantity of available P is time-specific and crop-specific, because it is the amount of P that will come into the soil solution and be taken up by the crop during its life cycle. The intensity of available P (availability) is most easily identified with its concentration in the soil solution. The soil property controlling the relationship between the solid phase P and its concentration in solution is known as the buffering capacity. The solid phase P involved in this relationship is only a small proportion of the total P, and is known as labile P. It is usually measured by isotopic exchange, but this exchangeable P component does not include the sparingly soluble compounds that also replenish the soil solution as its concentration is depleted by plant uptake. The buffering capacity is the ability of the soil solution to resist a change in its P concentration as P is removed by plant uptake or added in fertilisers or organic materials. Buffering capacity is synonymous with sorptivity, which is a preferable term in the context of the reactivity of P fertiliser with soil. It is usually measured from an adsorption isotherm. By fitting a suitable equation, such as the Langmuir, the total sorption capacity as well as the sorption strength can be determined. Both parameters are important in understanding P availability in soils. Buffering capacity has a major effect on the uptake of labile P because it is inversely related to the ease of desorption of solid phase P and its diffusion. Available P therefore is a direct function of the quantity of labile P and an inverse function of buffering capacity. This has been demonstrated in plant uptake studies. Similarly, the most effective methods of measuring available P (soil tests) are those which remove a proportion of labile P that is inversely related to buffer capacity. Soil tests which measure the concentration of P in solution actually measure availability rather than available P, and their efficacy on a range of soils will depend on the uniformity of the soils" buffer capacities. The most effective soil test usually consists of an anionic extractant. Acidic lactate or fluoride have been found most effective in New South Wales, on a wide range of soils, except calcareous soils which neutralise the acidic component (usually hydrochloric or acetic acid) of the extractant. Sodium bicarbonate (pH 8 · 5) has been found effective on calcareous soils and is widely used throughout the world. It has proved unreliable on NSW soils, and may need more thorough evaluation on non-calcareous soils in other parts of Australia.

The Light: Nutrient Ratio in Lakes: The Balance of Energy and Materials Affects Ecosystem Structure and Process

Abstract: The amounts of solar energy and materials are two of the chief factors determining ecosystem structure and process. Here, we examine the relative balance of light and phosphorus in a set of freshwater pelagic ecosystems. We calculated a ratio of light: phosphorus by putting mixed‐layer mean light in the numerator and total P concentration in the denominator. This light: phosphorus ratio was a good predictor of the C:P ratio of particulate matter (seston), with a positive correlation demonstrated between these two ratios. We argue that the balance between light and nutrients controls “nutrient use efficiency” at the base of the food web in lakes. Thus, when light energy is high relative to nutrient availability, the base of the food web is carbon rich and phosphorus poor. In the opposite case, where light is relatively less available compared to nutrients, the base of the food web is relatively P rich. The significance of this relationship lies in the fact that the composition of sestonic material...

Phosphorus-limited bacterioplankton growth in the Sargasso Sea

Abstract: Oceanic central gyres cover large areas of the earth and contribute significantly to global productivity. Oceanic phytoplankton production is believed to be Limited by nitrogen (N) in central gyres and iron (Fe) in high-nutrient low-chlorophyll regions. Bacterioplankton have been less studied but are believed to be limited by organic carbon. We report here that bacterioplankton in the Sargasso Sea were phosphorus (P) limited on cruises in 1992 and 1993. This assertion is supported by measurements of high dissolved and particulate N:P and C:P ratios, high alkaline phosphatase activity and phosphate uptake rates, and bacterioplankton growth rate responses In bioassays where inorganic P was added. Particulate C:P ratios were always higher than the Redfield ratio (106:l) and occasionally greater than 400:l. N:P ratios were 75:l and 46:l on 2 cruises and tlme-series data indicated that ratios were always greater than 24:l over nearly a 2 yr span. Phosphate concentrations were extremely low in the euphotic zone (< 10 nM) and biomass-normalized alkaline phosphatase activities indicated moderate to severe P limitation, with most severe lunitation occurring in the spring. Bioassays indicated that heterotrophic bacteria may be P limited in the northwestern Sargasso Sea, especially in the spring. Limitation by P and not dissolved organic carbon may explain why dissolved organic carbon accumulates in the water column at that time.

Phosphorus and bacterial growth in drinking water.

Abstract: The availability of organic carbon is considered the key factor to regulate microbial regrowth in drinking water network. However, boreal regions (northern Europe, Russia, and North America) contain a large amount of organic carbon in forests and peatlands. Therefore, natural waters (lakes, rivers, and groundwater) in the northern hemisphere generally have a high content of organic carbon. We found that microbial growth in drinking water in Finland is highly regulated not only by organic carbon but also by the availability of phosphorus. Microbial growth increased up to a phosphate concentration of 10 micrograms of PO4-P liter-1. Inorganic elements other than phosphorus did not affect microbial growth in drinking water. This observation offers novel possibilities to restrict microbial growth in water distribution systems by developing technologies to remove phosphorus efficiently from drinking water.

Accumulation and Storage of Phosphate and Minerals

Abstract: Developing seeds store reserve levels of phosphorus and minerals, mobilization of which during germination provides the mineral nutrition essential for optimal early seedling growth. This process also functions as a component of the inorganic P and mineral homeostasis mechanisms necessary for nominal cellular function. The storage and resup-ply of phosphorus centers around the synthesis and breakdown of phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate). Phytic acid is often deposited as a mixed, ‘phytin’ salt, primarily of potassium and magnesium. Thus phytin deposition and re-mobilization also represents an important component of mineral cation storage. Exceptions to this may include iron and calcium storage and homeostasis, for which non-phytin mechanisms may play major roles. There has been recent progress in the molecular biology of several components of phosphorus and mineral storage pathways. These include studies of myo-inositol synthesis, some aspects of myo-inositol phosphate metabolism, protein body transport functions, and calcium and iron storage proteins. Recent genetic studies bring into question the paradigm that phytic acid synthesis is essential to phosphorus storage or inorganic P homeostasis. Much additional progress is required, particularly concerning the synthetic pathway to phytic acid, before a thorough or truly detailed understanding of the molecular biology of P and mineral storage processes is obtained.

Influence of catchment topography on water chemistry in southeastern Québec Shield lakes

Abstract: For 30 Canadian Shield lakes of southeastern Quebec, catchment slope and lake morphometry account for 50-70% of the variability of chlorophyll a (Chl a), dissolved organic carbon (DOC), total phosp...

Phosphate exchange across the sediment-water interface when shifting from anoxic to oxic conditions : an experimental comparison of freshwater and brackish-marine systems

Abstract: Comparative, experimental studies on sediment cores from freshwater andbrackish-marine conditions reveal major differences in the benthic exchangeof phosphate across the sediment-water interface when shifting from anoxicto oxic conditions The flux of phosphate to the sediment during this shiftwas found to be mediated mainly by scavenging from newly formed colloidalferric oxohydroxide The capacity of the iron-rich particles to scavengephosphorus depended on the stoichiometric ratio between dissolved iron andphosphorus built up in the supernatant water during reducing conditions Thefreshwater system was characterized by high iron to phosphorus ratios in thedissolved phase and thus most of the phosphate was incorporated into thecolloidal iron oxohydroxide during the oxygenation In contrast, the marinesystems reached lower iron to phosphorus ratios during the anoxic period whichresulted in less efficient phosphate scavenging Consequently, significantamounts of phosphate remained dissolved in the marine systems after the changeto oxic conditions, possibly increasing the proportion of phosphate recycledto the euphotic zone Manganese showed a consistent redox-dependent behaviourin all the investigated systems, but interacted neither with phosphate norwith iron

Trace Element Composition of Fertilizers and Soil Amendments

Abstract: The use of fertilizers and soil amendments has raised concern regarding the toxic accumulation of their trace components in the environment. The objective of this research was to evaluate the trace element and heavy metal composition of a wide variety of fertilizers and soil amendments. Thirty-five elements, including priority pollutants, were determined in 24 materials. A microwave HNO 3 -HF-H 2 O 2 -H 3 BO 3 digestion procedure was used to dissolve the samples. Selected solid samples were directly analyzed by neutron activation analysis, while atomic absorption and inductively-coupled plasma atomic emission spectrometric determinations were carried out on the digests. The trace element and heavy metal concentrations generally decreased in the following sample order: rock phosphate > sewage sludge > phosphorus fertilizer > organic amendments and liming materials > K fertilizers > N fertilizers. Relatively high concentrations of toxic elements in the sewage sludge, rock phosphate, and phosphorus fertilizer samples suggest that these materials should be the primary target materials for environmental evaluations.

Marine nitrogen: Phosphorus stoichiometry and the global N:P cycle

Abstract: Nitrogen supply is often assumed to limit marine primary production A global analysis of total nitrogen (N) to phosphorus (P) molar ratios shows that total N:P is low (<16:1) in some estuarine and coastal ecosystems, but up to 100:1 in open oceans This implies that elements other than N may limit marine production, except in human impacted, estuarine or coastal ecosystems This pattern may reconcile conflicting enrichment studies, because N addition frequently increases phytoplankton growth where total N:P is expected to be low, but P, Fe, or Si augment phytoplankton growth in waters where total N:P is high Comparison of total N:P stoichiometry between marine and freshwaters yields a model of the form of the aquatic N:P cycle

Effects of soil phosphorus availability, temperature and moisture on soil respiration in Eucalyptus pauciflora forest

Abstract: Rates of soil respiration (CO2 efflux) were measured for a year in a mature Eucalyptus pauciflora forest in unfertilized and phosphorus-fertilized plots. Soil CO2 efflux showed a distinct seasonal trend, and average daily rates ranged from 124 to 574 mg CO2 m−2 hr−1. Temperature and moisture are the main variables that cause variation in soil CO2 efflux; hence their effects were investigated over a year so as to then differentiate the treatment effect of phosphorus (P) nutrition.

Methods of preparation of C-substituted phosphorus ylides and their application in organic synthesis

Abstract: Methods of preparation of phosphorus ylides substituted at the carbon atom of the P=C group with atoms of various elements and their application in organic synthesis are systematised and generalised The bibliography includes 508 references

Cost-Effective Nutrient Reductions to the Baltic Sea

Abstract: Due to eutrophication caused by heavy loads of nitrogen and phosphorus, the biological conditions of the Baltic Sea have been disturbed: large sea bottom areas without any biological life, low stocks of cods, and toxic blue green algaes. It is recognized that the nitrogen and phosphorus loads to the Baltic Sea must be reduced by 50% in order to restore the sea. The main purpose of this paper is to calculate cost effective nitrogen and phosphorus reductions to the Baltic Sea from the nine countries surrounding the Baltic Sea. The results show a significant difference in minimum costs of decreasing nitrogen and phosphorus loads to the Sea: approximately 12 000 millions of SEK per year and 3 000 millions of SEK respectively for reductions by 50%. It is also shown that a change from a policy of cost-effective nutrient reductions to a policy where each country reduces the nutrient loads by 50% increase total costs for both nitrogen and phosphorus reductions by about 300%. The results are, however, sensitive to several of the underlying assumptions and should therefore be interpreted with much caution.

RenaGel, a novel calcium- and aluminium-free phosphate binder, inhibits phosphate absorption in normal volunteers.

Abstract: Background Available phosphate binders contain aluminium or calcium which can be associated with undesirable effects. RenaGel, cross-linked poly (allylamine hydrochloride), is a non-absorbed phosphate-binding polymer, free of calcium and aluminium. We conducted this study to examine the safety and phosphate binding efficacy of RenaGel in volunteers. Methods During 18 days (days 0-17) at the clinical study unit, 24 subjects consumed a phosphate-controlled diet designed to provide 37.5 mmol (1200 mg) elemental phosphorus per day. From the morning of day 5 to the morning of day 9, urine and faeces were collected. Average baseline urine and faecal phosphorus contents were determined. On days 9-16, the subjects received either RenaGel 1 g, 2.5 g, or 5 g or placebo three times per day immediately prior to the meals. From the morning of day 13 to the morning of day 17, urine and faeces were again collected and phosphorus contents on treatment were determined. Results RenaGel inhibited dietary phosphate absorption as measured by a decline in average daily urinary phosphorus excretion and an increase in average daily fecal phosphorus excretion. Average urine phosphorus contents on treatment were 27.2 mmol (870 mg) per day in the placebo group vs 23.8 mmol (762 mg), 19.5 mmol (625 mg), and 16.6 mmol (530 mg) per day in the RenaGel 1-g, 2.5-g, and 5-g groups. Average daily faecal phosphorus content on treatment was markedly higher in the RenaGel 5-g group, 19.1 mmol (611 mg) per day vs 10.7 mmol (342 mg) per day for the placebo group. RenaGel also decreased total serum cholesterol by 0.71 mmol/L (27.5 mg/dl), 0.55 mmol/l (21.3 mg/dl), and 1.08 mmol/l (41.8 mg/dl) for the RenaGel 1-g, 2.5-g, and 5-g groups. RenaGel was well tolerated with adverse events similar to placebo. Conclusions RenaGel is a safe, effective, and well tolerated phosphate binder in normal volunteers. The degree of phosphate binding consistent with its potential use as a phosphate binder in renal failure patients.

The responses of wild‐type and ABA mutant Arabidopsis thaliana plants to phosphorus starvation

Abstract: The growth patterns of plants subjected to phosphorus starvation resemble those caused by treatment with ABA, suggesting that ABA could mediate the response of the plant to phosphorus starvation. We examined the role of ABA in phosphorus stress by comparing growth and biochemical responses of Arabidopsis thaliana ABA mutants aba-1 and abi2-1 to those of wild-type plants. We first characterized acid phosphatase production of wild-type Arabidopsis in response to phosphorus starvation. We found that several acid phosphatase isozymes are present in roots and shoots, but only a subset of these isozymes are induced by phosphorus stress, and they are induced in both organs. Production of acid phosphatase in response to phosphorus stress was not affected by the aba-1 or abi2-1 mutations. Low phosphorus also resulted in decreased growth of both wild-type and ABA mutant plants, and the root-to-shoot ratio was increased in both wild type and mutants. Anthocyanins accumulated in response to phosphorus stress in both wild-type and mutant plants, but the increase was reduced in the aba-1 mutant. Thus, two different ABA mutants responded normally in most respects to phosphorus stress. Our data do not support a major role for ABA in coordinating the phosphorus-stress response.

Sequential extractions and 31P-NMR spectroscopy of phosphorus forms in animal manures, whole soils and particle-size separates from a densely populated livestock area in northwest Germany

Abstract: The solubility and forms of phosphorus (P) were investigated in manures from chicken and pigs, eight whole soil samples and clay-, silt-, and sand-size separates from an arable and a grassland soil. Total P (Pt) in liquid pig manure (16.2 g kg–1) and dry chicken manure (26.2 g kg–1) was distributed between residual P (39–41% Pt), H2SO4–P (17–27% Pt), labile resin- and NaHCO3–P (24–39% Pt), and NaOH-P (3–10% Pt). Most soils had larger proportions of NaOH-P and residual P, indicating reactions of manure-derived P compounds with pedogenic oxides and humic substances. Clay-size separates had the highest P-concentrations in all fractions and were particularly enriched in exchangeable and labile P forms. Solution 31P-nuclear magnetic resonance (NMR) spectra of 0.5 M NaOH extracts from manures and some soil samples showed greater signal intensities for orthophosphate and monoester P than 0.1 M NaOH extracts. This can be explained by alkaline hydrolysis phosphate diesters at higher NaOH concentrations and/or by preferential extraction of diesters at lower concentrations. The 31P-NMR spectra showed differences between the two manures and confirmed that increasing proportions of ester-P can be expected if they are spread to soils. The NaOH extracts of soil samples were characterized by large proportions of orthophosphate-P (mean 77% of assigned P compounds), which seemed to be slightly enriched in clay fractions whereas the extracts from silt contained more ester-P. Sequential extractions and 31P-NMR spectroscopy both showed that these excessively manured soils are likely to lose large amounts of P.

Nutrient Behaviour During Post-flood Recovery of the Richmond River Estuary, Northern NSW, Australia

Abstract: Dissolved and particulate inorganic and organic forms of phosphorus and nitrogen, suspended sediments, dissolved silica and physico-chemical parameters were examined in the Richmond River Estuary following a small flood event. Under flood conditions, nutrient concentrations were elevated, estuarine processes were bypassed and freshwater, sediments and nutrients were discharged directly onto the continental shelf. The Estuary recovered by way of a salt wedge penetrating landward along the channel bottom, and progressed from a small highly stratified, through a moderately stratified, to a large vertically homogeneous system. Flushing times were the dominant control on the degree to which nutrients were internally processed, with most of the river-supplied nutrients transformed under normal conditions due to very long flushing times. Dissolved inorganic phosphorus is apparently removed at low salinities by adsorption to iron and aluminium colloidal oxyhydroxides which aggregate and undergo sedimentation. At higher salinities, dissolved inorganic phosphorus is apparently desorbed due to a sharp rise in pH. Dissolved nitrate and silica were probably depleted by phytoplankton, and some nitrate may also have been removed through denitrification. As the riverine supply of nutrients is potentially nitrogen limited (i.e. low dissolved inorganic nitrogen: dissolved inorganic phosphorus), primary production for much of the year appears to be supported by the benthic flux of ammonium produced by the mineralization of particulate organic nitrogen deposited during the recovery stage. When this benthic supply of ammonium is exhausted, riverine nitrate becomes an important source of nitrogen. There also appears to be continuous wind-driven resuspension and deposition of bottom materials under the shallow well-mixed conditions that prevail during normal conditions. A three-stage (flood, recovery, normal) conceptual model is presented, which may be more applicable to highly variable Australian estuaries than the typical North American and West European estuarine models found in the literature.

Soil-derived phosphorus in surface runoff from grazed grassland

Abstract: Seven 1 ha grazed lysimeter plots, managed as intensive grassland for the last 12 years, were monitored for total phosphorus (TP) and molybdate reactive phosphorus (MRP) in surface runoff plus interflow to 30 cm depth, for up to ten events during 1994. The mean MRP and TP concentrations determined were 40 and 122 μg 1−1, respectively, but the data were heavily skewed by low frequency high intensity events. Thus concentrations of MRP and TP of over 1200 and 1700 μg 1−1 respectively were determined in extreme events, causing a TP export of up to 18 g ha−1 per h and, during one event of 30 h duration, over 0.5 kg TP ha−1 was estimated to have been removed, representing a significant proportion of the triple super phosphate fertiliser added 6 days earlier. One storm was monitored at 3 h intervals and the patterns for TP concentration and TP load were closely related to discharge. MRP concentration did not follow the hydrographic pattern. Excluding the low frequency high intensity events, an empirical model TP (μg 1−1) = 58 + [42 × discharge] (1 s−1) was postulated, which although significant (P = 0.0053), only accounted for 14% of the relationship. It was thus concluded that understanding of release mechanisms in the majority of high frequency, low intensity events is inadequate. Conversely, during one period of high phosphorus (P) export, the mechanisms responsible were suggested to be a combination of the presence of cattle (excretal returns and poaching), timing of inorganic P fertiliser additions, and intensity of rainfall. Grassland soils are a significant source of diffuse P inputs to surface and estuarine waters and may cause eutrophication.