Showing papers on "Phosphorus published in 2001"

Arsenic in groundwater: Testing pollution mechanisms for sedimentary aquifers in Bangladesh

Abstract: In the deltaic plain of the Ganges-Meghna-Brahmaputra Rivers, arsenic concentrations in groundwater commonly exceed regulatory limits (.50 m gL 21 ) because FeOOH is microbially reduced and releases its sorbed load of arsenic to groundwater. Neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution. The most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat. Concentrations of ammonium up to 23 mg L 21 come from microbial fermentation of buried peat and organic waste in latrines. Concentrations of phosphorus of up to 5 mg L 21 come from the release of sorbed phosphorus when FeOOH is reductively dissolved and from degradation of peat and organic waste from latrines. Calcium and barium in groundwater come from dissolution of detrital (and possibly pedogenic) carbonate, while magnesium is supplied by both carbonate dissolution and weathering of mica. The 87 Sr/ 86 Sr values of dissolved strontium define a two-component mixing trend between monsoonal rainfall (0.711 6 0.001) and detrital carbonate (,0.735).

Topsoil foraging – an architectural adaptation of plants to low phosphorus availability

Abstract: Low phosphorus availability is a primary constraint to plant productivity in many natural and agricultural ecosystems. Plants display a wide array of adaptive responses to low phosphorus availability that generally serve to enhance phosphorus mobility in the soil and increase its uptake. One set of adaptive responses is the alteration of root architecture to increase phosphorus acquisition from the soil at minimum metabolic cost. In a series of studies with the common bean, work in our laboratory has shown that architectural traits that enhance topsoil foraging appear to be particularly important for genotypic adaptation to low phosphorus soils (‘phosphorus efficiency’). In particular, the gravitropic trajectory of basal roots, adventitious rooting, the dispersion of lateral roots, and the plasticity of these processes in response to phosphorus availability contribute to phosphorus efficiency in this species. These traits enhance the exploration and exploitation of shallow soil horizons, where phosphorus availability is greatest in many soils. Studies with computer models of root architecture show that root systems with enhanced topsoil foraging acquire phosphorus more efficiently than others of equivalent size. Comparisons of contrasting genotypes in controlled environments and in the field show that plants with better topsoil foraging have superior phosphorus acquisition and growth in low phosphorus soils. It appears that many architectural responses to phosphorus stress may be mediated by the plant hormone ethylene. Genetic mapping of these traits shows that they are quantitatively inherited but can be tagged with QTLs that can be used in plant breeding programs. New crop genotypes incorporating these traits have substantially improved yield in low phosphorus soils, and are being deployed in Africa and Latin America.

Biogeochemistry. Phosphorus solubilization in rewetted soils.

Abstract: Biogeochemical cycles are shaped by events that follow soil drying and rewetting Here we show that the process of drying and rapidly rewetting soil increases the amount of water-soluble phosphorus present and that this is predominantly in organic form after having been released from the soil microbial biomass This effect could not only significantly affect phosphorus pollution of waterbodies but might also corrupt results from analyses involving water extraction of dried soils

Regulation of root hair density by phosphorus availability in Arabidopsis thaliana

Abstract: We characterized the response of root hair density to phosphorus (P) availability in Arabidopsis thaliana. Arabidopsis plants were grown aseptically in growth media with varied phosphorus concentrations, ranging from 1 mmol m -3 to 2000 mmol m -3 phosphorus. Root hair density (number of root hairs per mm of root length) was analysed starting at 7 d of growth. Root hair density was highly regulated by phosphorus availability, increasing significantly in roots exposed to low-phosphorus availability. The initial root hairs produced by the radicle were not sensitive to phosphorus availability, but began to respond after 9 d of growth. Root hair density was about five times greater in low phosphorus (1 mmol m -3 ) than in high phosphorus (1000 mmol m -3 ) media. Root hair density decreased logarithmically in response to increasing phosphorus concentrations within that range. Root hair density also increased in response to deficiencies of several other nutrients, but not as strongly as to low phosphorus. Indoleacetic acid (IAA), the auxin transport inhibitor 2(p-chlorophenoxy)-2-methylpropionic acid (CMPA), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and the ethylene synthesis inhibitor aminooxyacetic acid (AOA) all increased root hair density under high phosphorus but had very little effect under low phosphorus. Low phosphorus significantly changed root anatomy, causing a 9% increase in root diameter, a 31% decrease in the cross-sectional area of individual trichoblasts, a 40% decrease in the cross-sectional area of individual atrichoblasts, and 45% more cortical cells in cross-section. The larger number of cortical cells and smaller epidermal cell size in low phosphorus roots increased the number of trichoblast files from eight to 12. Two-thirds of increased root hair density in low phosphorus roots was caused by increased likelihood of trichoblasts to form hairs, and 33% of the increase was accounted for by changes in low phosphorus root anatomy resulting in an increased number of trichoblast files. These results show that phosphorus availability can fundamentally alter root anatomy, leading to changes in root hair density, which are presumably important for phosphorus acquisition.

Pigs expressing salivary phytase produce low-phosphorus manure

Abstract: To address the problem of manure-based environmental pollution in the pork industry, we have developed the phytase transgenic pig. The saliva of these pigs contains the enzyme phytase, which allows the pigs to digest the phosphorus in phytate, the most abundant source of phosphorus in the pig diet. Without this enzyme, phytate phosphorus passes undigested into manure to become the single most important manure pollutant of pork production. We show here that salivary phytase provides essentially complete digestion of dietary phytate phosphorus, relieves the requirement for inorganic phosphate supplements, and reduces fecal phosphorus output by up to 75%. These pigs offer a unique biological approach to the management of phosphorus nutrition and environmental pollution in the pork industry.

Temperature effects in treatment wetlands.

Abstract: Several biogeochemical processes that regulate the removal of nutrients in wetlands are affected by temperature, thus influencing the overall treatment efficiency. In this paper, the effects of temperature on carbon, nitrogen, and phosphorus cycling processes in treatment wetlands and their implications to water quality are discussed. Many environmental factors display annual cycles that mediate whole system performance. Water temperature is one of the important cyclic stimuli, but inlet flow rates and concentrations, and several features of the annual biogeochemical cycle, also can contribute to the observed patterns of nutrient and pollutant removal. Atmospheric influences, including rain, evapotranspiration, and water reaeration, also follow seasonal patterns. Processes regulating storages in wetlands are active throughout the year and can act as seasonal reservoirs of nutrients, carbon, and pollutants. Many individual wetland processes, such as microbially mediated reactions, are affected by temperature. Response was much greater to changes at the lower end of the temperature scale (< 15 degrees C) than at the optimal range (20 to 35 degrees C). Processes regulating organic matter decomposition are affected by temperature. Similarly, all nitrogen cycling reactions (mineralization, nitrification, and denitrification) are affected by temperature. The temperature coefficient (theta) varied from 1.05 to 1.37 for carbon and nitrogen cycling processes during isolated conditions. Phosphorus sorption reactions are least affected by temperature, with theta values of 1.03 to 1.12. Physical processes involved in the removal of particulate carbon, nitrogen, and phosphorus are not affected much by temperature. In contrast, observed wetland removals may have different temperature dependence. Design models are oversimplified because of limitations of data for calibration. The result of complex system behavior and the simple model is the need to interpret whole ecosystem data to determine temperature coefficients. Temperature seems to have minimal effect on biochemical oxygen demand (0.900 < theta < 1.015) and phosphorus (0.995 < theta < 1.020) removal, and more significant effect on nitrogen removal (0.988 < theta < 1.16). In colder climates, there may be seasonal slowdown of treatment, which can decrease the overall treatment efficiency of constructed wetlands.

Extracellular secretion of Aspergillus phytase from Arabidopsis roots enables plants to obtain phosphorus from phytate

Abstract: Phosphorus (P) deficiency in soil is a major constraint for agricultural production worldwide. Despite this, most soils contain significant amounts of total soil P that occurs in inorganic and organic fractions and accumulates with phosphorus fertilization. A major component of soil organic phosphorus occurs as phytate. We show that when grown in agar under sterile conditions, Arabidopsis thaliana plants are able to obtain phosphorus from a range of organic phosphorus substrates that would be expected to occur in soil, but have only limited ability to obtain phosphorus directly from phytate. In wild-type plants, phytase constituted less than 0.8% of the total acid phosphomonoesterase activity of root extracts and was not detectable as an extracellular enzyme. By comparison, the growth and phosphorus nutrition of Arabidopsis plants supplied with phytate was improved significantly when the phytase gene (phyA) from Aspergillus niger was introduced. The Aspergillus phytase was only effective when secreted as an extracellular enzyme by inclusion of the signal peptide sequence from the carrot extensin (ex) gene. A 20-fold increase in total root phytase activity in transgenic lines expressing ex::phyA resulted in improved phosphorus nutrition, such that the growth and phosphorus content of the plants was equivalent to control plants supplied with inorganic phosphate. These results show that extracellular phytase activity of plant roots is a significant factor in the utilization of phosphorus from phytate and indicate that opportunity exists for using gene technology to improve the ability of plants to utilize accumulated forms of soil organic phosphorus.

Effects of soil freezing disturbance on soil solution nitrogen, phosphorus, and carbon chemistry in a northern hardwood ecosystem

Abstract: Reductions in snow cover undera warmer climate may cause soil freezing eventsto become more common in northern temperateecosystems. In this experiment, snow cover wasmanipulated to simulate the late development ofsnowpack and to induce soil freezing. Thismanipulation was used to examine the effects ofsoil freezing disturbance on soil solutionnitrogen (N), phosphorus (P), and carbon (C)chemistry in four experimental stands (twosugar maple and two yellow birch) at theHubbard Brook Experimental Forest (HBEF) in theWhite Mountains of New Hampshire. Soilfreezing enhanced soil solution Nconcentrations and transport from the forestfloor. Nitrate (NO3 −) was thedominant N species mobilized in the forestfloor of sugar maple stands after soilfreezing, while ammonium (NH4 +) anddissolved organic nitrogen (DON) were thedominant forms of N leaching from the forestfloor of treated yellow birch stands. Rates ofN leaching at stands subjected to soil freezingranged from 490 to 4,600 mol ha−1yr−1, significant in comparison to wet Ndeposition (530 mol ha−1 yr−1) andstream NO3 − export (25 mol ha−1yr−1) in this northern forest ecosystem. Soil solution fluxes of Pi from the forestfloor of sugar maple stands after soil freezingranged from 15 to 32 mol ha−1 yr−1;this elevated mobilization of Pi coincidedwith heightened NO3 − leaching. Elevated leaching of Pi from the forestfloor was coupled with enhanced retention ofPi in the mineral soil Bs horizon. Thequantities of Pi mobilized from the forestfloor were significant relative to theavailable P pool (22 mol ha−1) as well asnet P mineralization rates in the forest floor(180 mol ha−1 yr−1). Increased fineroot mortality was likely an important sourceof mobile N and Pi from the forest floor,but other factors (decreased N and P uptake byroots and increased physical disruption of soilaggregates) may also have contributed to theenhanced leaching of nutrients. Microbialmortality did not contribute to the acceleratedN and P leaching after soil freezing. Resultssuggest that soil freezing events may increaserates of N and P loss, with potential effectson soil N and P availability, ecosystemproductivity, as well as surface wateracidification and eutrophication.

Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique?

Abstract: The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree of limitation.

Biomass Production of ‘Alamo’ Switchgrass in Response to Nitrogen, Phosphorus, and Row Spacing

Abstract: Management practices for biomass production of bioenergy grasses may differ from management for forage. Our objective was to determine the yield and stand responses of Alamo' switchgrass (Panicum virgatum L.) to N and P fertilization as affected by row spacing. A combination of five rates each of N and P were applied to plots during 1992 to 1998 at Stephenville, TX and 1993 to 1995 at Beeville, TX. Three row-spacing treatments were applied as subplots. Biomass production was determined each year with a single harvest in late summer. Tiller density and tiller mass were measured during 1993 to 1996 at Stephenville. Biomass production was not influenced by the addition of P. Biomass production response to N at Beeville was greater in narrow rows than wide rows during the establishment year only. Biomass production responses to N were quadratic in 5 of 7 yr at Stephenville and linear at Beeville. A maximum yield of 22.5 Mg ha -1 occurred during 1995 at Stephenville at 168 kg N ha -1 . Lodging occurred at both locations but only at the 224 kg N ha -1 rate. Tiller density and mass increased as row width increased. Tiller mass also increased with increasing N fertility at Stephenville. This response was more important in determining biomass production than was tiller density. Average biomass production at 168 kg N ha -1 yr -1 was 14.5 and 10.7 Mg ha -1 yr -1 at Stephenville and Beeville, respectively. Biomass production without applied N tended to decline over the years. Our data indicated that switchgrass biomass production is sustainable at Stephenville only with the application of at least 168 kg N ha -1 yr -1 , but P application and row spacing are not crucial.

Three years experience of operating and selling recovered struvite from full-scale plant.

Abstract: The adoption of phosphorus removal at sewage treatment works (STW) creates two main problems. Firstly large amounts of sludge are produced and secondly the quantity of the effluent deteriorates due to the increase in the phosphorus load of the sidestream. Furthermore, these processes do not remove phosphorus in a form that would enable it to be recycled. Therefore in order to control these process difficulties and produce a recyclable phosphorus product a sidestream struvite crystallisation reactor was developed. The struvite was produced in a fluidised bed reactor using dewatered filtrate from anaerobic sludge digestion. Magnesium hydroxide was added in a magnesium to phosphate ratio of 1 : 1 and the pH was adjusted to between 8.2 – 8.8 with the addition of sodium hydroxide. A retention time of 10 days allowed the growth of pellets between 0.5 – 1.0mm in size. The recovered struvite contained only minute traces of toxic substances and was sold to fertiliser companies for 27,000 yen tonne−1. It is used to...

The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues

Abstract: The flavonol content of Arabidopsis thaliana and tomato seedlings was assessed in conditions of reduced nitrogen or phosphorus availability. In both systems, a significant inverse relationship was observed between nutrient availability and flavonol accumulation, with nitrogen limitation promoting the greatest increase in flavonols. A trial was established to determine the effects of decreased nitrogen and phosphorus availability on the flavonol content of leaf and fruit tissues of tomato plants (Lycopersicon esculentum cv. Chaser) in a commercial situation. Nutrients were supplied by a hydroponic system with nutrient regimes designed to provide the highest and lowest nitrogen and phosphorus levels with which it is possible to support plant growth and fruit set. Fruiting was abundant and tomato fruits were harvested at mature green, breaker and red stages of ripening; leaves were also harvested from the tops of the plants. All tissues were analysed for flavonol content using reversed-phase high-performance liquid chromatography. Flavonol accumulation in the leaves of mature tomato plants was found to increase significantly in response to nitrogen stress, whereas phosphorus deficiency did not elicit this response. Reduced nitrogen availability had no consistent effect on the flavonol content of tomato fruits. Phosphorus deficiency elicited an increase in flavonol content in early stages of ripening. Effects of nutrient stress on the flavonol content of tomato fruits were lost as ripening progressed. The findings suggest that nutrient status may be employed to manipulate the flavonol content of vegetative tissues but cannot be used to elevate the flavonol content of tomato fruit.

Effect of phosphorus availability on basal root shallowness in common bean.

Abstract: Root gravitropism may be an important element of plant response to phosphorus availability because it determines root foraging in fertile topsoil horizons, and thereby phosphorus acquisition. In this study we seek to test this hypothesis in both two dimensional paper growth pouch and three-dimensional solid media of sand and soil cultures. Five common bean (Phaseolus vulgaris L.) genotypes with contrasting adaptation to low phosphorus availability were evaluated in growth pouches over 6 days of growth, and in sand culture and soil culture over 4 weeks of growth. In all three media, phosphorus availability regulated the gravitropic response of basal roots in a genotype-dependent manner. In pouches, sand, and soil, the phosphorus-inefficient genotype DOR 364 had deeper roots with phosphorus stress, whereas the phosphorus-efficient genotype G19833 responded to phosphorus stress by producing shallower roots. Genotypes were most responsive to phosphorus stress in sand culture, where relative root allocation to the 0–3- and 3–6-cm horizons increased 50% with phosphorus stress, and varied 300% (3–6 cm) to 500% (0–3 cm) among genotypes. Our results indicate that (1) phosphorus availability regulates root gravitropic growth in both paper and solid media, (2) responses observed in young seedlings continue throughout vegetative growth, (3) the response of root gravitropism to phosphorus availability varies among genotypes, and (4) genotypic adaptation to low phosphorus availability is correlated with the ability to allocate roots to shallow soil horizons under phosphorus stress.

Root hairs confer a competitive advantage under low phosphorus availability

Abstract: Root hairs are presumably important in the acquisition of immobile soil resources such as phosphorus. The density and length of root hairs vary substantially within and between species, and are highly regulated by soil phosphorus availability, which suggests that at high nutrient availability, root hairs may have a neutral or negative impact on fitness. We used a root-hairless mutant of the small herbaceous dicot Arabidopsis thaliana to assess the effect of root hairs on plant competition under contrasting phosphorus regimes. Wildtype plants were grown with hairless plants in a replacement series design at high (60 μm phosphate in soil solution) and low (1 μm phosphate in soil solution) phosphorus availability. At high phosphorus availability, wildtype and mutant plants were equal in growth, phosphorus acquisition, fecundity and relative crowding coefficient (RCC). At low phosphorus availability, hairless plants accumulated less biomass and phosphorus, and produced less seed when planted with wildtype plants. Wildtype plants were unaffected by the presence of hairless plants in mixed genotype plantings. Wildtype plants had RCC values greater than one while hairless plants had RCC values less than one. We conclude that root hairs increase the competitiveness of plants under low phosphorus availability but do not reduce growth or competitiveness under high phosphorus availability.

Mineral limitation of zooplankton: stoichiometric constraints and optimal foraging

Abstract: Nutritional deficiencies are a very common phenomenon, and consumers generally face food that is not optimally suited for their needs. Especially herbivores are habitually confronted with food of inferior quality, usually a result of too-low nutrient concentrations in plant material. Waterfleas of the genus Daphnia are good model organisms to study the effect of inferior quality food, and how animals deal with this. We tested the effect of algae to which we had given different phosphorus contents on both life history and feeding parameters of Daphnia magna. Phosphorus content of the algae strongly af- fected both the growth rate and the feeding activity of the daphniids. Feeding activity increased with declining food quality (increase in C:P ratio of the algae), whereas growth rates were maximal at intermediate C:P levels. We conclude that the direct limitation of phosphorus is a very important factor determining food quality for zooplankters. Daphniids counterbalanced lower P content of their food by spending more C (energy) on acquiring this limiting resource. This implies that when Daphnia are given phosphorus-limited food both the addition of phosphorus and the addition of carbon (energy) should increase the growth rate of the animals (co-limitation). The influence of the phosphorus content of the food on the feeding activity of Daphnia offers a mechanistic explanation for the observed homeostasis in daphniids.

Attenuation of phosphate starvation responses by phosphite in Arabidopsis.

Abstract: When inorganic phosphate is limiting, Arabidopsis has the facultative ability to metabolize exogenous nucleic acid substrates, which we utilized previously to identify insensitive phosphate starvation response mutants in a conditional genetic screen. In this study, we examined the effect of the phosphate analog, phosphite (Phi), on molecular and morphological responses to phosphate starvation. Phi significantly inhibited plant growth on phosphate-sufficient (2 mM) and nucleic acid-containing (2 mM phosphorus) media at concentrations higher than 2.5 mM. However, with respect to suppressing typical responses to phosphate limitation, Phi effects were very similar to those of phosphate. Phosphate starvation responses, which we examined and found to be almost identically affected by both anions, included changes in: (a) the root-to-shoot ratio; (b) root hair formation; (c) anthocyanin accumulation; (d) the activities of phosphate starvation-inducible nucleolytic enzymes, including ribonuclease, phosphodiesterase, and acid phosphatase; and (e) steady-state mRNA levels of phosphate starvation-inducible genes. It is important that induction of primary auxin response genes by indole-3-acetic acid in the presence of growth-inhibitory Phi concentrations suggests that Phi selectively inhibits phosphate starvation responses. Thus, the use of Phi may allow further dissection of phosphate signaling by genetic selection for constitutive phosphate starvation response mutants on media containing organophosphates as the only source of phosphorus.

Phosphorus sorption characteristics of estuarine sediments under different redox conditions.

Abstract: Phosphorus (P) plays a major role in eutrophication of aquatic systems. Estuarine sediments could function as sources or sinks for P to the overlying water column depending upon their physico-chemical characteristics. Understanding of P sorption phenomena in estuarine sediments is important in regulating the P availability in estuaries. Phosphorus sorption characteristics of sediments from the Indian River Lagoon, Florida, USA, were determined to examine the role of selected physico-chemical properties of the sediments on soluble reactive P status in estuary water. Mean equilibrium P concentrations (EPCo) of 0.75 mg L(-1) and mean P sorption maxima (Smax) of 32.2 mg kg(-1) were obtained under anaerobic conditions, compared with EPCo of 0.05 mg L(-1) and Smax of 132.7 mg kg(-1) under aerobic conditions. The higher EPCo values under anaerobic conditions and the greater Smax values under aerobic conditions were associated with amorphous and poorly crystalline iron. These results suggest that sediments enriched with amorphous and poorly crystalline forms of iron act as an excellent reservoir for P by adsorbing excessive P in aerobic sediment zones and releasing it upon burial under anaerobic conditions. This study also indicates that P compounds in sediments independently maintain equilibrium with P in solutions. Thus, heterogeneous systems like soil and sediment simply behave as a mixture of homogeneous surfaces as far as their P sorption characteristics are concerned, and hence can be successfully described by the Langmuir and Freundlich models.

In situ stabilization of soil lead using phosphorus.

Abstract: In situ stabilization of Pb-contaminated soils can be accomplished by adding phosphorus. The standard remediation procedure of soil removal and replacement currently used in residential areas is costly and disruptive. This study was carried out to evaluate the influence of P and other soil amendments on five metal-contaminated soils and mine wastes. Seven treatments were used: unamended control; 2,500 mg of P/kg as triple superphosphate (TSP), phosphate rock (PR), acetic acid followed by TSP, and phosphoric acid (PA); and 5,000 mg of P/kg as TSP or PR. A significant reduction in bioavailable Pb, as determined by the physiologically based extraction test (PBET), compared with the control upon addition of P was observed in all materials tested. Increasing the amount of P added from 2,500 to 5,000 mg/kg also resulted in a significantly greater reduction in bioavailable Pb. Phosphate rock was equally or more effective than TSP or PA in reducing bioavailable Pb in four out of five soils tested. Preacidification produced significantly lower bioavailable Pb compared with the same amount of P from TSP or PR in only one material. Reductions in Pb bioavailability as measured by PBET were evident 3 d after treatment, and it may indicate that the reactions between soil Pb and P occurred in situ or during the PBET. No further reductions were noted over 365 d. X-ray diffraction data suggested the formation of pyromorphite-like minerals induced by P additions. This study suggests that P addition reduced bioavailable Pb by PBET and has potential for in situ remediation of Pb-contaminated soils.

Phosphorus cycling in UK agriculture and implications for phosphorus loss from soil

Abstract: . Phosphorus (P) use in UK agriculture is reviewed and a P balance sheet presented. The productive grassland and arable area has accumulated an average P surplus of c. 1000 kg ha–1 over the last 65 years. Over the period 1935–1970, the annual P surplus more than doubled due to an increase in animal numbers and associated requirements for inorganic fertilizers and livestock feeds. Since 1970, surplus P has declined by c. 40% as crop yields and P offtake have continued to increase while fertilizer and manure P inputs have remained relatively constant. In 1993, P use efficiency (P imports/P exports) in UK agriculture was estimated at 25% leading to an average annual surplus of 15 kg P ha–1 yr–1, although the latter has since decreased slightly due to reduced fertilizer use. Intensification and specialization of agriculture has also increased the range in P surpluses that are likely between livestock and arable dominated systems. The largest P surpluses occur in the relatively limited areas of arable soils which receive manure from intensive pig and poultry units, whilst farms without manure inputs generate only small surpluses, or are in balance. The cumulative P surplus has led to a build-up of soil total and easily-exchangeable P, especially in areas receiving both fertilizers and manures. Fundamental differences in P use efficiency, surplus P accumulation and the potential for P loss to water, exist between arable and grassland farms and it is important to separate these, due to the marked regionalization of UK agriculture. More judicial use of feeds and fertilizers is required to further reduce the P surplus and minimize the long-term risk of water eutrophication.

Effect of grazing and nutrient supply on periphyton biomass and nutrient stoichiometry in habitats of different productivity

Abstract: The impact of grazing and nutrient supply on epilithic periphyton was investigated in factorial field experiments in four seasons at three Swedish sites of different productivity and herbivore composition (Lake Limmaren, Lake Erken, and Vaddo ¨, a low salinity coastal site). Nutrient supply was enhanced by a granulose fertilizer containing nitrogen (N) and phosphorus (P), and grazer density was manipulated by exclusion cages. Algal biomass was increased by nutrient enrichment and reduced by grazer presence, but effects were highly variable between sites and seasons. Generally, grazers had stronger effects on algal biomass than nutrient enrichment, but there was no overriding effect of either grazing or nutrients. This indicated a simultaneous top-down and bottom-up control of algal biomass. Taxonomic composition of the periphyton was more affected by grazer presence than by nutrients. Internal nutrient ratios of the algae indicated N limitation at two of the sites. At all sites, the content of N and P in the periphytic assemblage was enhanced by the experimental nutrient enrichment, resulting in decreased C : N and C : P ratios. The presence of herbivores also increased periphytic nutrient content (decreased N : P and C : P ratios) in some experiments, suggesting an increase in algal P due to excretion. The effect strength of grazers and nutrients on periphyton was affected by different abiotic characteristics such as light availability, nutrient concen- trations, and temperature. However, single environmental characteristics were not sufficient to explain the relative importance of grazing and nutrients.

Dietary microbial phytase supplementation and the utilization of phosphorus, trace minerals and protein by rainbow trout [Oncorhynchus mykiss (Walbaum)] fed soybean meal‐based diets

Abstract: Effects of thermal and enzymatic treatments of soybean meal on apparent absorption of total phosphorus, phytate phosphorus, nitrogen (protein), ash, calcium, magnesium, copper, iron, manganese, strontium and zinc were examined using rainbow trout, Oncorhynchus mykiss (Walbaum), as the test species. Absorption of the test nutrients was estimated using yttrium as an inert non-absorbable indicator. Thermal treatments (microwaving, dry roasting, steam heating, cooking) had no measurable effect on the apparent absorption of phosphorus and other minerals. Phytase supplementation increased the apparent absorption of phosphorus, nitrogen (protein), ash, calcium, magnesium, copper, iron, strontium and zinc in low-ash diets containing soybean meal, but had little effect in high-ash diets containing both soybean and fish meal. In low-ash diets, the apparent absorption of phosphorus increased in accord with the level of phytase added to the diet, from 27% (no phytase added) up to 90% (phytase added, 4000 units kg−1 diet) or 93% (predigested with phytase, 200 units kg−1 soybean meal). In high-ash diets, dietary acidification with citric acid decreased the effect of phytase, whereas in low-ash diets, acidification markedly increased the effect of the enzyme. Excretion of phosphorus in the faeces of fish fed a low-ash diet containing phytase-treated soybean meal was 0.32 g per kg diet consumed, a 95%−98% reduction compared with phosphorus excretion by fish consuming commercial trout feeds.

The effect of phosphorus availability on the carbon economy of contrasting common bean (Phaseolus vulgaris L.) genotypes

Abstract: A common response to low phosphorus availability is increased relative biomass allocation to roots. The resulting increase in root:shoot ratio presumably enhances phosphorus acquisition, but may also reduce growth rates by diverting carbon to the production of heterotrophic rather than photosynthetic tissues. To assess the importance of increased carbon allocation to roots for the adaptation of plants to low P availability, carbon budgets were constructed for four common bean genotypes with contrasting adaptation to low phosphorus availability in the field ("phosphorus efficiency"). Solid-phase-buffered silica sand provided low (1 microM), medium (10 microM), and high (30 microM) phosphorus availability. Compared to the high phosphorus treatment, plant growth was reduced by 20% by medium phosphorus availability and by more than 90% by low phosphorus availability. Low phosphorus plants utilized a significantly larger fraction of their daytime net carbon assimilation on root respiration (c. 40%) compared to medium and high phosphorus plants (c. 20%). No significant difference was found among genotypes in this respect. Genotypes also had similar rates of P absorption per unit root weight and plant growth per unit of P absorbed. However, P-efficient genotypes allocated a larger fraction of their biomass to root growth, especially under low P conditions. Efficient genotypes had lower rates of root respiration than inefficient genotypes, which enabled them to maintain greater root biomass allocation than inefficient genotypes without increasing overall root carbon costs.

Rapid incidental phosphorus transfers from grassland

Abstract: In Britain, frequent rainfall means that there is a high potential for rapid, direct (incidental) losses of phosphorus (P) to occur after fertilizer or manure application. However, despite the known contribution of P to the eutrophication of water bodies in Britain, such incidental transfers have received little experimental attention. To rectify this, we used lysimeter plots (each 3 × 10 m) to investigate incidental transfers in a composite of overland and lateral subsurface flow (0–27 cm) following the application of different P sources. The treatments used were triple super phosphate (TSP), dairy slurry (Slurry), an equal mix of TSP plus slurry (TSP + Slurry), and no P (Zero P). The treatments were applied to wet soil at a rate of 29 kg ha−1 In the following 169 h, 48.8 mm rainfall (intensity ≤3 mm h−1) resulted in total phosphorus (TP) exports between 1.8 and 2.3 kg ha−1 A single 4-h period (with overland flow) accounted for 33 to 46% of overall loads from the P-amended treatments. Concentrations in discharge from TSP + Slurry and TSP peaked at 11000 μg TP L−1 (67–68% as reactive P 0.45 μm) and 20% as RP < 0.45 Even in subsurface flow, concentrations exceeded 3000 μg TP L−1 for all P-amended treatments. Incidental TP concentrations in plot discharge were up to 110-fold higher than those considered eutrophic in inland waters. We suggest that targeting short-term management decisions for P applications is the most immediately viable method to mitigate P loss and benefit the environment.

Phosphorus-carbon heterocyclic chemistry : the rise of a new domain

Abstract: Section Headings. The Birth of a New Domain. Three Membered Rings. Phosphiranes and Phosphirenes. Diphosphiranes and Diphosphirenes. Four Membered Rings. Phosphetanes - Early Studies. Four-Membered Rings with one Phosphorus Atom. Diphosphetanes, Dihydrodiphosphetes, and Diphosphetes. Five Membered Rings. Phospholanes and Phospholenes. Phospholes: Early literature 1953-1994. Phospholes: Recent literature 1994-1999. Heterophospholes. Six Membered Rings. Phosphinanes, Dihydro-and Tetrahydro-phosphinines. Phosphinines. Six-Membered Rings with Two or more Heteroatoms with at least One Phosphorus Atom. Macro-, Poly- and Spiro-Heterocycles. Macro- and Spiro-Heterocycles. Bicyclic and Polycyclic Systems with a Ring Junction Phosphorus Atom. Compounds with Phosphorus at the Spiro Position. Applications of Phosphorus Heterocycles in Homogeneous Catalysis. Author Index.

Particulate phosphorus and sediment in surface runoff and drainflow from clayey soils.

Abstract: Recent work has shown that a significant portion of the total loss of phosphorus (P) from agricultural soils may occur via subsurface drainflow. The aim of this study was to compare the concentrations of different P forms in surface and subsurface runoff, and to assess the potential algal availability of particulate phosphorus (PP) in runoff waters. The material consisted of 91 water-sample pairs (surface runoff vs. subsurface drainage waters) from two artificially drained clayey soils (a Typic Cryaquept and an Aeric Cryaquept) and was analyzed for total suspended solids (TSS), total phosphorus (TP), dissolved molybdate-reactive phosphorus (DRP), and anion exchange resin-extractable phosphorus (AER-P). On the basis of these determinations, we calculated the concentrations of PP, desorbable particulate phosphorus (PPi), and particulate unavailable (nondesorbable) phosphorus (PUP). Some water samples and the soils were also analyzed for 137Cs activity and particle-size distribution. The major P fraction in the waters studied was PP and, on average, only 7% of it was desorbable by AER. However, a mean of 47% of potentially bioavailable P (AER-P) consisted of PPi. The suspended soil material carried by drainflow contained as much PPi (47-79 mg kg-1) as did the surface runoff sediment (45-82 mg kg-1). The runoff sediments were enriched in clay-sized particles and 137Cs by a factor of about two relative to the surface soils. Our results show that desorbable PP derived from topsoil may be as important a contributor to potentially algal-available P as DRP in both surface and subsurface runoff from clayey soils.

Characterization of phosphorus-poisoned automotive exhaust catalysts

Abstract: Oil-derived contaminants on light-off catalysts from high mileage taxis were characterized by a variety of physical and chemical methods. The contaminants (mostly phosphates) deposit in a strong axial gradient from the front to the back of the monolithic catalyst channels. Two major forms of phosphorus contamination were observed: (1) an overlayer of Zn, Ca, and Mg phosphates, and (2) aluminum phosphate within the washcoat. The data also suggest the formation of cerium(III) phosphate. Laboratory catalytic reaction measurements on core samples from the taxi catalysts confirm a strong deactivating effect due to the phosphorus contamination. The activity improves dramatically after removing phosphorus via an oxalic acid wash.