Showing papers on "Phosphorus published in 1988"

Exchange of phosphorus across the sediment-water interface

Abstract: In this article, principles of phosphorus retention and phosphorus release at the sediment-water interface in lakes are reviewed. New results and hypotheses are discussed in relation to older models of phosphorus exchange between sediments and water. The fractional composition of sedimentary phosphorus is discussed as a tool for interpretation of different retention mechanisms. Special emphasis is given to the impact of biological, particularly microbial, processes on phosphorus exchange across the sediment-water interface and to the significance of biologically induced CaCO3 precipitation to phosphorus retention in calcareous lakes.

Synthesis of Carbon-Phosphorus Bonds, Second Edition

Abstract: INTRODUCTION Recent Advances in C-P Bond Formation Nomenclature of C-P Compounds Information Sources for C-P Compounds SYNTHESIS OF ORGANOPHOSPHORUS COMPOUNDS FROM ELEMENTAL PHOSPHORUS Introduction Availability of Elemental Phosphorus Attack on Elemental Phosphorus by Nucleophiles Radical Attack on Elemental Phosphorus Direct Addition to P-Systems Oxidative Additions with Olefins Experimental Procedures Summary References C-P BOND FORMATION USING NUCLEOPHILIC TRIVALENT PHOSPHORUS REAGENTS Introduction Substitution Reactions Using Neutral Trivalent Phosphorus Reagents Substitution Reactions Using Anionic Trivalent Phosphorus Reagents Preparations Of A-substituted Phosphoryl Compounds Conjugate Addition Reactions Experimental Procedures References C-P BOND FORMATION VIA DISPLACEMENT, ADDITION, OR REARRANGEMENT Introduction Phosphorus-halogen Compounds Substitution Reactions on Phosphorus-halogen Compounds Using Organometallics and Related Reagents Addition Reactions of P-H Compounds Addition Reactions of P-Cl Compounds Rearrangements Resulting In The Formation Of New P-C Bonds Experimental Procedures References PENTACOORDINATE PHOSPHORUS Introduction General Structure of Pentacoordinate Phosphorus Stable Phosphoranes Carbonnphosphorus Bond Formation Involving Phosphorane Intermediates Experimental Procedures References AROMATIC AND VINYLIC C-P BONDS Introduction Aromatic Carbon-Phosphorus Bond Formation Vinylic Carbon-Phosphorus Bond Formation Experimental Procedures References Index

Phosphorus efficiency of plants. I: External and internal P requirement and P uptake efficiency of different plant species

Abstract: Plant species differ in their P efficiency, i.e. the P content in soil needed to reach their maximum yield. The differences in external P requirements can be attributed to either a lower internal P requirement for optimum growth or higher uptake efficiency of the plant. The objective of this research was to investigate the reasons for different P efficiencies of seven plant species. Onion, ryegrass, wheat, rape, spinach, tomato and bean were grown in a P-deficient subsoil fertilized with 0, 2, 5, 10, 20, 40 and 80mg P 100 g 1. All species showed a strong yield increase due to P fertilization. To reach 80% of maximum yield onion and tomato needed 17 and 11 mg P 100 g-~ respectively, corresponding to a soil solution concentrations of 6.9 and 5.7/~mol P 1 -~, whereas ryegrass, wheat and rape needed about 5mg P 100g 1 corresponding to only 1.4#mol P 1 ~ in soil solution. These differences in external P requirement cannot be explained by differences in their internal P requirement since onion, with the highest external P requirement, only contained 0.14% P in the shoot at 80% of maximum yield, while wheat, as the most P efficient species, contained 0.28%. P efficiency was related to the uptake efficiency of the plant which is determined by both root-shoot ratio and absorption rate per unit of root (influx). Species of low efficiency such as onion, tomato and bean had low influx rates and low root-shoot ratios, whereas species of medium to high efficiency had either high influx rates (rape and spinach) or high root-shoot ratios (ryegrass and wheat). The combination of both high influx rate and high root-shoot ratio was not found in any of the species studied.

Prediction of Phosphorus Release Rates from Total and Reductant-Soluble Phosphorus in Anoxic Lake Sediments

Abstract: Release rates of phosphorus from anoxic sediment surfaces in seven North American lakes were determined from core tube incubations. These rates were compared with several P fractions within the 0–5...

The Biogeochemistry of Phosphorus Cycling and Phosphorus Availability Along a Desert Soil Chronosequence

Abstract: The biogeochemistry ofthe weathering, landscape movements, and chemical transformations of phosphorus and its availability to plants were examined in a chrono- sequence of soils developed from quartz monzonite alluvium in southern New Mexico. Total P in the soil profile decreased with increasing soil age and was removed from the ecosystem as readily as the most easily leachable base cations. Although Ca-bound forms of P decreased with increasing soil age, Ca-P remained the single largest fraction of total P in all soils. In contrast, Fe- and Al-bound P was a very small percent of total P in all soils. There was little evidence for the stabilization of P by soil organic matter within this ecosystem; both soil organic P and microbial P represented very small pools of total soil P. Phosphorus availability, measured by in situ resin bags, was not well correlated with soil age or total soil P, and P concentrations in shrub tissues did not reflect changes in forms or total amounts of soil P. The biogeochemical cycle of P in this system differs sharply from that in a more mesic, forested system, where fixation by iron and aluminum oxides and biologic activity play more dominant roles in the conservation of P within the ecosystem.

Phosphorus flux from lake sediments: Effect of epipelic algal oxygen production

Abstract: Previous studies utilizing oxygen-sensitive microelectrodes have demonstrated that as a result of epipelic algal photosynthesis and microbial metabolism, and regardless of the oxygen concentration of the overlying water, sediments within the euphotic zone of lakes undergo marked diel fluctuations in the extent of oxygen penetration. This investigation utilized oxygen-sensitive microelcctrodes, 32P0,3- radiotracer, and a novel flow-through system to examine the effect of epipelic algal photosynthesis on sediment oxygen dynamics and the concomitant pattern of phosphorus release from lake sediments. Epipelic algae mediated release of phosphorus from sediments to overlying water via daily formation and breakdown ofthe oxidized microzone. During illumination, surficial sediments rapidly became oxygenated, and release of phosphorus diffusing from deeper sediment layers was inhibited. During darkness the microzone became anoxic, and phosphorus was released to overlying water at an accelerated rate, producing marked diel fluctuation in efflux rate. Observed patterns of release are consistent with recent evidence for a mechanism consisting of rapid uptake or rclcase of dissolved phosphate by sediment microorganisms in response to respective oxic or anoxic conditions. Microbial metabolism in aquatic sediments regenerates inorganic phosphate that accumulates in interstitial water and forms concentration gradients. Subsequent diffusive transport to overlying water can be retarded by a number of processes that either temporarily or permanently immobilize phosphate. Mortimer (1941, 1942) demonstrated that the presence of an oxidized microzone at the sediment surface inhibited phosphorus release but that a decrease in redox potential of the microzone following the onset of anoxic conditions in the overlying water stimulated the reduction of Fe(III), thus releasing phosphate bound in hydrous oxides and gels at the sediment surface. This key role of oxygen has been substantiated in numerous studies in various lake and sediment types @Lamp-Nielsen 1974; Patrick and Khalid 1974; Frevert 1980). Also identified as factors affecting the rate of P flux from sediments are pH, tem

Phosphorus in soil, water and sediment: an overview

Abstract: The geochemistry, availability and abundance of different forms of phosphorus in soil, water and sediments are reviewed. The present knowledge of phosphorus pathways in ecosystems and their regulation is discussed.

Detection of phosphine: new aspects of the phosphorus cycle in the hydrosphere

Abstract: The role of phosphorus in limiting organic matter production and in causing eutrophication has been in the forefront of hydrobiological research during the past 30–50 yr1–7. Comparing the cycles of major biogenic elements, it is evident that, with the exception of phosphorus, each of them contains gaseous substances (for example, CO2, CH4, O2, N2, NH3, H2S and volatile organic sulphur compounds) which, because of their gaseous state, can leave aquatic systems8–16. We examined the phosphorus cycle of open-air sewage treatment plants and a deficit (∼30–45%) in the phosphorus mass balance was found which cannot be explained by knowledge based on earlier research on this cycle of the hydrosphere. By developing special sampling and analytical methods, we have shown that gases released from the sewage treatment plants and from the sediments of shallow (1–2 m deep) waters contain a reduced, gaseous phosphorus compound: phosphine. According to our measurements and calculations, about 5g of phosphorus per day was released as phosphine from an Imhoff tank settling 2,000 m3 per day of raw sewage. Under laboratory conditions, it was also demonstrated that phosphine is released by bacterial reduction from a medium containing inorganic phosphorus. The phosphorus content of the medium decreases by nearly one half. Our results on the metabolic importance of phosphine formation and release suggest that ∼25–50% of the phosphorus deficit in open-air sewage treatment plants can be explained by the release of phosphine into the atmosphere. These results change our understanding of the aquatic phosphorus cycle; former ideas about the phosphorus budget should be revised.

Nitrogen, phosphorus and organic carbon pools in natural and transplanted marsh soils

Abstract: Total nitrogen, phosphorus and organic carbon were compared in natural and transplanted estuarine marsh soils (top 30 cm) to assess nutrient storage in transplanted marshes. Soils were sampled in five transplanted marshes ranging in age from 1 to 15 yr and in five nearby natural marshes along the North Carolina coast. Dry weight of macroorganic matter (MOM), soil bulk density, pH, humic matter, and extractable P also were measured. Nutrient pools increased with increasing marsh age and hydroperiod. Nitrogen, phosphorus and organic carbon pools were largest in soils of irregularly flooded natural marshes. The contribution of MOM to marsh nutrient reservoirs was 6–45%, 2–22%, and 1–7% of the carbon, nitrogen and phosphorus, respectively. Rates of nutrient accumulation in transplanted marshes ranged from 2.6–10.0, 0.03–1.10, and 84–218 kmol ha−1yr−1 of nitrogen, phosphorus and organic carbon, respectively. Accumulation rates were greater in the irregularly flooded marshes compared to the regularly flooded marshes. Approximately 11 to 12% and 20% of the net primary production of emergent vegetation was buried in sediments of the regularly flooded and irregularly flooded transplanted marshes, respectively. Macroorganic matter nutrient pools develop rapidly in transplanted marshes and may approximate natural marshes within 15 to 30 yr. However, development of soil carbon, nitrogen and phosphorus reservoirs takes considerably longer.

Phosphorus in sediments — speciation and analysis

Abstract: Characterization of sediment phosphorus is commonly based on sequential chemical extractions, in which phosphorus is supposed to be selectively removed from different compounds in the sediments The first extraction schemes were designed to quantify discrete chemical or mineralogical compounds As extraction schemes have been tested on different sediments, several systematic errors have been detected and the schemes have been modified and simplified accordingly Other chemical extractions or treatments have attempted to determine phosphorus bound to particles with a certain strength or binding energy, the purpose being to determine the labile, loosely bound, exchangeable, mobile or algal-available fraction of sediment phosphorus All extraction procedures yield operationally defined fractions and cannot be used for identification of discrete phosphorus compounds The many methodological modifications make it necessary to be cautious when comparing results from the literature in this field

Role of phosphorus and nitrogen in photosynthetic and whole plant carbon gain and nutrient use efficiency in eastern white pine

Abstract: In white pine (Pinus strobus) seedlings grown in five forest soils from New York State, net photosynthetic capacity (Amax) plant-1 was correlated with total foliar N plant-1 (r2=0.57), but was more highly correlated with total foliar P plant-1 (r2=0.82). There was no relationship (r2<0.01) between Amax [g leaf]-1 and foliar N [g leaf]-1 for the pooled data set, but there was a significant (P<0.001), but weak (r2=0.20) positive relationship between Amax [g leaf]-1 and foliar P [g leaf]-1 across all soils. However, within two of the five soils leaf N concentration was a significant (P<0.05) determinant of photosynthetic capacity. Due to differences in soil nutrient availabilities a large range in foliar P:N ratio (0.02–0.15) was observed, and the proportion of leaf P:N appeared to control Amax [g leaf N]-1. Whole plant nitrogen (NUE) and phosphorus (PUE) use efficiencies were well correlated with whole plant P:N ratio. In addition, NUE was well correlated with Amax [g leaf N]-1 and PUE was well correlated with Amax [g leaf P]-1. However, NUE was not well correlated with PUE, and Amax [g leaf N]-1 was not well correlated with Amax [g leaf P]-1. These results indicated that P and/or N limitations were important components of photosynthetic nutrient relations in white pine grown in these five soils and suggest that both P and N and their proportions should be considered in analyses of photosynthesis-nutrient relations.

Ectomycorrhizal rain-forest legumes and soil phosphorus in Korup National Park, Cameroon

Abstract: SUMMARY The mycorrhizal status of a group of caesalpinioid legumes in lowland rain-forest in Korup National Park, SW Cameroon, was examined. Species in ten genera, Anthonotha, Aphanocalyx, Berlinia, Didelotia, Gilbertiodendron, Julbernardia, Microberlinia, Monopetalanthus, Tetraberlinia(tribe Amherstieae) and Afzelia(tribe Detarieae) were ectomycorrhizal. These species were not uniformly distributed in the forest, and three large emergent species Microberlinia bisulcata A. Chev., Tetraberlinia bifoliolata(Harms) Hauman, and T. moreliana Aubr. in particular appear to form groves c. 600 m across. This type of distribution may be related to the ectomycorrhizal habit. A previous large scale enumeration and soil survey on four 5 km transects of plots in the forest, carried out during the wet season, had revealed an association between these ectomycorrhizal legumes and low concentrations ( 5 μg g-1) of extractable phosphorus in the mineral soil. In the current study part of one of the original transects in a low phosphorus area of the forest, where ectomycorrhizal trees comprise 29 % of the basal area, was resampled at the subplot level during the dry season. Whereas in the wet season soil phosphorus had been lower (2·8 μg g-1) within the ectomycorrhizal groves than without (3·8 μg g-1), in the dry season the situation was reversed and the overall concentrations were higher (12·3 and 7·9 μg g-1 respectively). Ordination analysis re-affirmed the association of the three Microberlina/Tetraberlinia species with relatively low concentrations of extractable phosphorus in the wet season but relatively high ones in the dry season. The groves are characterized by high inputs of leaf litter in the dry season, extensive colonization of surface organic matter by ectomycorrhizas and hyphal strands, and high carbon: extractable inorganic phosphorus ratios in the mineral soil in the wet season. These features are discussed in relation to the presumed ability of ectomycorrhizas to utilize organic phosphorus.

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants : I. Wild vs. cultivated oats.

Abstract: We tested the hypothesis that mycorrhizal infection benefits wild plants to a lesser extent than cultivated plants. This hypothesis stems from two observations: (1) mycorrhizal infection improves plant growth primarily by increasing nutrient uptake, and (2) wild plants often possess special adaptations to soil infertility which are less pronounced in modern cultivated plants. In the first experiment, wild (Avena fatua L.) and cultivated (A. sativa L.) oats were grown hydroponically at four different phosphorus levels. Wild oat was less responsive (in shoot dry weight) to increasing phosphorus availability than cultivated oat. In addition, the root: shoot ratio was much more plastic in wild oat (varying from 0.90 in the low phosphorus solution to 0.25 in the high phosphorus solution) than in cultivated oat (varying from 0.44 to 0.17). In the second experiment, mycorrhizal and non-mycorrhizal wild and cultivated oats were grown in a phosphorus-deficient soil. Mycorrhizal infection generally improved the vegetative growth of both wild and cultivated oats. However, infection significantly increased plant lifespan, number of panicles per plant, shoot phosphorus concentration, shoot phosphorus content, duration of flowering, and the mean weight of individual seeds in cultivated oat, while it had a significantly reduced effect, no effect, or a negative effect on these characters for wild oat. Poor positive responsiveness of wild oat in these characters was thus associated with what might be considered to be inherent adaptations to nutrient deficiency: high root: shoot ratio and inherently low growth rate. Infection also increased seed phosphorus content and reproductive allocation.

Elevated secretion and action of serum parathyroid hormone in young adults consuming high phosphorus, low calcium diets assembled from common foods.

Abstract: We sought to determine if the high phosphorus, moderately low calcium intake typical of U.S. teenagers and young adults alters parathyroid function as it does in experimental animals. Because those animals ultimately developed osteopenia, it has been suggested that low dietary calcium to phosphorus ratios may reduce peak bone mass and increase susceptibility to osteoporotic fracture later in life. However, it is not known whether PTH secretion or action increases in response to commonly consumed phosphorus-rich, calcium-poor foods. We studied the 24-h mineral and hormonal responses of eight men and eight women, aged 18-25 yr, after 8 days of ingesting a control diet that had calcium (820 mg) and phosphorus (930 mg) contents near the recommended daily intakes, and a test diet with calcium and phosphorus contents (1660 mg phosphorus, 420 mg calcium) typical of current intakes. Both diets were made from common grocery store foods. The 24-h mean serum immunoreactive PTH levels increased in men (11%; P less than 0.006) and women (22%; P less than 0.003) during the test diet. In both sexes, the test diet significantly increased serum phosphorus, plasma 1,25-dihydroxyvitamin D, and urinary hydroxyproline and cAMP excretion; in women only it decreased serum ionized and total calcium levels. Thus, short term ingestion of a diet typifying current levels of calcium and phosphorus intake resulted in elevated serum iPTH levels and indexes of PTH action in young adults.

Response of Anabaena and Synechococcus to manipulation of nitrogen: phosphorus ratios in a lake fertilization experiment

Abstract: Additions of inorganic nitrogen and phosphorus to selected areas of oligotrophic Kennedy Like began in 1978 and resulted in development of late-summer blooms of the nitrogen-fixing cyanobacteria Anabaena circina[is in 1981 and 1982. In subsequent years the blooms were successfully eliminated by increasing the molar N: P ratio of added nutrients to 35:1. The nutrient additions also resulted in dramatic increases in both autotrophic (predominantly Synechococcus sp.) and heterotrophic (bacteria) picoplankton numbers, with respective maxima of 4.0 x 105 ml-] and >4.0 x 10c ml’-’. Chlorophyll concentrations were generally <-2 kg liter–’ during untreated conditions and increased to as much as 50 pg liter’-’ during blooms. In the years following the Anabaena blooms, hypolimnetic nitrate concentrations were significantly higher in the treated basin of the lake than they were in an adjacent untreated basin or than they were before the blooms. Development of nitrogen-fixing cyanobacteria blooms is dependent on both a low N: P supply ratio and a sulllcient phosphorus supply.

Nutrition and growth of birch seedlings at varied relative phosphorus addition rates

Abstract: Birch (Betula pendula Roth.) was investigated under steady state nutrition and growth at different relative addition rates of phosphorus (Rp). Phosphorus deficiency symptoms appeared on the leaves when the internal phosphorus concentration decreased, but disappeared again under steady state nutrition, independent of the stress level. The increased root/shoot ratio and the exploratory type of root systems developed during the adjustment stage remained under steady state conditions. At nonoptimum and close to optimum relative addition rates, independent of the rate, the phosphorus concentration of the culture solution did not exceed 2 μmol dm−3 and was generally < 1 μmol dm−3 immediately after phosphorus additions. The phosphorus concentration just before additions was generally < 0.5 μmol dm−3. The nutrition/growth relationships were similar to those for nitrogen, with relative growth rate (Rg) closely related to the Rp applied and with a strong linear relationship between internal phosphorus concentration and Rg. Regression was much steeper than that for nitrogen. The slope of the optimum nutrition was attained at a lower phosphorus weight proportion to nitrogen (8–10 P: 100 N) than previously estimated (= 13 P: 100 N), but a higher relative phosphorus requirement was observed under stress conditions. Birch seedlings had a strong tendency to consume phosphorus in excess of immediate requirements with a small effect on growth above optimum. This resulted in rapidly decreasing phosphorus productivity (Pp, growth rate per unit of phosphorus) with increasing internal phosphorus concentrations above optimum.

The influence of animals on phosphorus cycling in lake ecosystems

Abstract: Aquatic animals directly influence the cycling of phosphorus in lakes through feeding and excretion Traditionally, animals (zooplankton, benthic invertebrates and fish) have been assigned only minor roles in the process of freshwater phosphorus cycling They were regarded as consumers without much regulating influence Today there is growing evidence that animals, predators and herbivores, directly or indirectly can control biomass of primary producers and internal cycling of phosphorus

Rice cultivar evaluation for phosphorus use efficiency

Abstract: Phosphorus deficiency is one of the most growth-limiting factors in acid soils in various parts of the world. The objective of this study was to screen 25 rice cultivars (Oryza sativa L.) at low, medium, and high levels of soil P. Number of tillers, root length, plant height, root dry weight and shoot dry weight were related to tissue P concentrations, P uptake and P-use efficiency. Shoot weight was found to be the plant parameter most sensitive to P deficiency. Significant cultivar differences in P use efficiency were found. Phosphorus use efficiency was higher in roots than shoots and decreased with increasing levels of soil P. Positive correlations were found among growth parameters such as plant height, tillers, root and shoot weight, and P content of roots and shoots. These results indicate selection of rice cultivars for satisfactory performance under low P availability can be carried out using shoot and root dry weight as criteria.

Phosphorus cycling in wheat-pasture rotations. II. The role of the microbial biomass in phosphorus cycling.

Abstract: The incorporation of phosphorus derived from fertilizer and plant residues into the soil microbial biomass was studied under field conditions by using isotopic double labelling. The 33P-labelled medic residues (Medicago truncatula cv. Paraggio) and 32P-labelled fertilizer were added to a solonized brown soil (Calcixerollic xerochrept) before sowing of a wheat crop ( Triticum aestivum cv. Warigal). Amounts of 31P, 32P and 33P in the microbial biomass were determined at 0, 7, 18, 32, 46, 61, 81 and 95 days after sowing of the wheat. Throughout the experiment, amounts of 31P in the microbial biomass were closely related to gravimetric soil water content, with a large and rapid increase in the amount of 3 1 ~ in the microbial biomass being observed in the first 7 days after wetting of the (initially) dry soil. Due to banding of the fertilizer at sowing, little (<5%) of the 32P was recovered in the microbial biomass throughout the experiment. Of the 33P applied in the medic residues, 22-28% was recovered in the microbial biomass. Most of the P taken up by the microbial biomass was derived from native soil P (i.e. not added that season).

Phosphorus and nitrogen limitation of phytoplankton in the inner Oslofjord (Norway)

Abstract: Several criteria of potential phosphorus and nitrogen limitation were applied throughout 1986 to the phytoplankton of the inner Oslofjord, a brackish-marine fjord in southeastern Norway. The criteria were hased on information on concentrations and distribution of nutrients, on analyses of the carbon (C), nitrogen (N), and phosphorus (P) content of particulate matter in the water column, and on results of deck experiments on the plankton. Indications of nutrient limitation were obtained from seasonal trends in C:N, C:P and N:P ratios, as well as from further shifts in these ratios in plankton kept in a container on deck for 24 hours. Nitrogen limitation was also deduced from an increase in the uptake capacity for ammonium in plankton during 24 hours of containment, and phosphorus limitation from an increase in alkaline phosphatase activity. During diatom blooms. a lowering of the ratio of light to dark rates of nitrate uptake provided one further test for nitrogen limitation. Two other tests (a st...

Eutrophication of Buttermilk Bay, a cape cod coastal embayment: Concentrations of nutrients and watershed nutrient budgets

Abstract: Nutrient concentrations in Buttermilk Bay, a coastal embayment on the northern end of Buzzards Bay, MA, are higher in the nearshore where salinities are lower. This pattern suggests that freshwater sources may contribute significantly to nutrient inputs into Buttermilk Bay. To evaluate the relative importance of the various sources we estimated inputs of nutrients by each major source into the watershed and into the bay itself. Septic systems contributed about 40% of the nitrogen and phosphorus entering the watershed, with precipitation and fertilizer use adding the remainder. Groundwater transported over 85% of the nitrogen and 75% of the phosphorus entering the bay. Most nutrients entering the watershed failed to reach the bay; uptake by forests, soils, denitrification, and adsorption intercepted two-thirds of the nitrogen and nine-tenths of the phosphorus that entered the watershed. The nutrients that did reach the bay most likely originated from subsoil injections into groundwater by septic tanks, plus some leaching of fertilizers.

Consequences of phosphate imbalance.

Abstract: Phosphorus is the sixth most abundant element in the body after oxygen, hydrogen, carbon, nitrogen, and calcium. It comprises about 1% of the total body weight of humans. Eighty-five percent of it is stored in the bone in the form of hydroxyapatite crystal; 14% is in the soft tissues in the form of energy-storing bonds with nucleotides (ATP, GTP), nucleic acids in chromosomes and ribosomes, 2,3-DPG in the red blood cells, and phospholipids in the cells' membranes. Less than 1% is in the extracellular fluids. Phosphate balance is maintained by multiple systems. The gut is responsible for the absorption of two thirds of the 4-30 mg/kg/day of phosphate intake. Absorption sites are all along the gut; in humans the most active site is the jejunum. The kidney filters 90% of the plasma phosphate and reabsorbs it in the tubuli. In states of hypophosphatemia the kidney can reabsorb the filtered phosphates very efficiently, reducing the amount excreted in the urine virtually to zero. The healthy kidney can excrete high loads of phosphate and rid the body of phosphate overload. Through the vitamin D-PTH axis the endocrine system regulates the phosphate balance by influencing the kidney, gut, and bone. Other hormones, including thyroid, insulin, glucagon, glucocorticosteroid, and thyrocalcitonin, play a lesser role in regulation of phosphate metabolism. Because of the complex control of phosphate homeostasis, various clinical conditions may lead to hypophosphatemia. These include nutritional repletion, gastrointestinal malabsorption, use of phosphate binders, starvation, diabetes mellitus, and increased urinary losses due to tubular dysfunction. The clinical picture of phosphate depletion is manifested in different organs and is due mainly to the fall in intracellular levels of ATP and decreased availability of oxygen to the tissues, secondary to 2,3-DPG depletion. The various manifestations of phosphate depletion are listed in Table 2. The treatment of hypophosphatemia consists of administering enteral or parenteral phosphate salts. An important aspect of dealing with the potentially serious effects of phosphate depletion is to prevent the depletion from happening in the first place. Hyperphosphatemia can occur in renal failure, hemolysis, tumor lysis syndrome, and rhabdomyolysis. The treatment of hyperphosphatemia usually consists of fluid administration (in the absence of kidney failure). In chronic hyperphosphatemia, phosphate binders such as aluminum and magnesium salts can reduce the phosphate load. The use of these phosphate binders is limited by their potential side effects.

Phosphorus transformations in the epilimnion of humic lakes: abiotic interactions between dissolved humic materials and phosphate

Abstract: SUMMARY. 1. Sephadex gel filtration of filtered water from small, Finnish forest lakes demonstrated abiotic movement of 33P from added PO4 to two higher molecular weight fractions. This movement was most pronounced in waters with high humic content which also had high iron content. The two fractions which took up 13P had nominal molecular weights of > 100,000 and 10,000-20,000. 2. An equilibrium existed between free PO4 and the two fractions. However, one fraction, at least, appeared to exist in two phases, with one phase in rapid equilibrium with free PO4 but the other in only slow equilibrium. 3. Additions of ferric iron up to 1 mg Fe l−1 to the filtered lake water stimulated movement from free PO4, provided high concentrations of humic materials were present. In the absence of humic materials even 0.1 mg Fe 1−1 would precipitate all added 33PO4. 4. The high molecular weight P was only partially reactive with standard molybdate reagents. Exposure of the high molecular weight P to sunlight caused a small release of PO4 under the experimental conditions employed. 5. Possible implications for biological phosphorus demand of such sequestration of free PO4 by humic materials in combination with iron are discussed.

Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status

Abstract: Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen + phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments (within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments) was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams.