Showing papers on "Phosphorus published in 1981"

Membrane-Mediated Decrease in Root Exudation Responsible for Phorphorus Inhibition of Vesicular-Arbuscular Mycorrhiza Formation

Abstract: The mechanism responsible for phosphorus inhibition of vesicular-arbuscular mycorrhiza formation in sudangrass (Sorghum vulgare Pers.) was investigated in a phosphorus-deficient sandy soil (0.5 micrograms phosphorus per gram soil) amended with increasing levels of phosphorus as superphosphate (0, 28, 56, 228 micrograms per gram soil). The root phosphorus content of 4-week-old plants was correlated with the amount of phosphorus added to the soil. Root exudation of amino acids and reducing sugars was greater for plants grown in phosphorus-deficient soil than for those grown in the phosphorus-treated soils. The increase in exudation corresponded with changes in membrane permeability of phosphorus-deficient roots, as measured by K+ (86Rb) efflux, rather than with changes in root content of reducing sugars and amino acids. The roots of phosphorus-deficient plants inoculated at 4 weeks with Glomus fasciculatus were 88% infected after 9 weeks as compared to less than 25% infection in phosphorus-sufficient roots; these differences were correlated with root exudation at the time of inoculation. For plants grown in phosphorus-deficient soil, infection by vesicular-arbuscular mycorrhizae increased root phosphorus which resulted in a decrease in root membrane permeability and exudation compared to nonmycorrhizal plants. It is proposed that, under low phosphorus nutrition, increased root membrane permeability leads to net loss of metabolites at sufficient levels to sustain the germination and growth of the mycorrhizal fungus during pre- and postinfection. Subsequently, mycorrhizal infection leads to improvement of root phosphorus nutrition and a reduction in membrane-mediated loss of root metabolites.

A Comparison of the Structure, Primary Productivity, and Transpiration of Cypress Ecosystems in Florida

Abstract: To investigate how inputs of water and nutrients influence the structural and functional characteristics of cypress wetlands, primary productivity, respiration, transpiration, tree growth, biomass, basal area, stem density, standing stocks of phosphorus, and litterfall were measured in several kinds of Florida cypress ecosystems subjected to varying inflows of water and nutrients. A scrub cypress forest, natural and sewage-enriched cypress domes, and a cypress floodplain forest were studied. Floodwaters in these ecosystems ranged from stagnant and phosphorus poor (0.01-0.08 mg P/L) to flowing and phosphorus rich (0.66-5.86 mg P/L). Inputs of total phosphorus transported by water to these forests varied from 0.11 g P m-2 yr-1 in the scrub cypress forest to 1625 g P m-2 yr-1 in the floodplain forest. Phosphorus content of aboveground biomass (ranging from 0.25 to 4.78 g P/M2) appeared to be positively related to phosphorus inputs. Biomass and other structural characteristics of the study sites appeared to be related to stand history rather than to phosphorus inputs. For example, there was little difference in aboveground biomass between natural cypress domes (20.6-26.6 kg/M2), a sewage-enriched dome (21.7 kg/M2), and a floodplain forest (28.4 kg/M2). Aboveground biomass for the scrub cypress forest was low (3.6 kg/ m2). Net daytime photosynthesis (2.1-13.7 g C.m-2 ground surface d-1), plant respiration (0.9-10.9 g C m-2 ground surface .d-1) and an estimate of gross primary productivity increased with increasing inputs of total phosphorus. Aboveground biomass production (sum of wood production, ranging from 44 to 1080 g.m-2 yr-1, and litterfall, ranging from 224 to 941 g m-2 yr-1) increased with increasing total phosphorus inputs in the low range, but biomass production leveled in the high input range. Total water loss from cypress forests increased with increasing P inputs. Mean daily transpiration rates from the scrub cypress forest (1.0 mm) and cypress domes (3.1-3.8 mm) were lower while those from the floodplain forest (5.6 mm) were similar to evaporation rates from open water bodies. Ratios of transpiration to net daytime photosynthesis were also low (156-221 g H20/g organic matter), showing that cypress is efficient in its water use. In cypress domes and scrub cypress forest, where water may be limiting, trees appear to adjust to potential water stress through leaf morphology adaptations and minimum canopy development (leaf area index, LAI = 0.53-3.4 m2/m2). When water is not potentially limiting, as in the floodplain forest, adaptations to conserve water were lacking (e.g., LAI = 8.5 m2/m2). A dome with added sewage effluent had higher leaf biomass, leaf area index, and chlorophyll a content, and more phosphorus stored in leaves than untreated domes. Net primary productivity, litter production, and wood production increased approximately twofold over pre-effluent rates or untreated cypress domes.

Photosynthetic response of lake plankton to nutrient enrichment: A test for nutrient limitation

Abstract: Measurements of carbon uptake by lake plankton at different levels of added phosphorus reveal some phytoplankton strategies that contribute to their survival in low-nutrient waters. Nutrient-deficient populations seem to temporarily reduce, rather than enhance, photosynthesis when phosphorus becomes available. This contradicts the basic hypothesis of the 14C bioassay used to determine “limiting” nutrients in natural waters. The reduction of carbon uptake rate continues until either the nutrient addition is taken up or no further storage is possible; at this time carbon upake may be enhanced. Concurrent measurements of phosphorus uptake showed no light response unless the plankton were exposed to significant phosphorus concentrations in the dark for several hours. Phytoplankton seem to be adapted for and dependent upon intermittent events exposing them to nutrient-enriched water. The ability of phosphate-depleted plankton to take up phosphate in excess of their growth requirements was used to develop an index for phosphate deficiency. To normalize for different biomass levels, the optimum photosynthetic rate was divided by the maximum uptake velocity giving a range for the C:P maximum uptake from 1.2 to 206 for plankton samples of varying phosphate deficiency.

Involvement of Phosphorus in Nitrogen Fixation by Subterranean Clover (Trifolium subterraneum L.)

Abstract: Effects of phosphorus supply on nodulation and nitrogen fixation in subterranean clover paralleled those on growth and occurred only after, or at the same time as, growth responses. However, correcting phosphorus deficiency increased nitrogen concentrations in tops as well as weight of tops. Effects of vesicular-arbuscular (VA) mycorrhizas on growth, nodulation and nitrogen fixation operated through effects on phosphorus nutrition of the host. Inoculation with a VA mycorrhizal fungus only stimulated nodulation and nitrogen fixation when insufficient phosphorus was applied for maximum growth of the non-mycorrhizal plant. Phosphorus concentrations in nodules greatly exceeded those in either tops or roots in both mycorrhizal and non-mycorrhizal plants and with phosphorus levels ranging from severely deficient to luxury supply for plant growth. Nitrogen applied after nitrogen fixation had commenced increased fresh weight of tops to a greater extent where phosphorus was non-limiting to growth. This positive interaction between nitrogen and phosphorus on the growth of nodulated nitrogen-fixing subterranean clover suggests that phosphorus deficiency does not limit growth in legumes by decreasing nitrogen fixation. It is concluded that increasing phosphorus supply increases nitrogen fixation in subterranean clover by stimulating host plant growth rather than by effects on either rhizobial growth and survival or on nodule formation and function.

Urinary Calcium and Calcium Balance in Young Men as Affected by Level of Protein and Phosphorus Intake

Abstract: Eight young adult males were subjects in a 51-day metabolic study conducted to examine the effects of level of protein and of phosphorus intake on urinary calcium and calcium balance. Two levels of protein (50-150 g) were given at each of two levels of phosphorus intake (1,010 and 2,525 mg). Dietary calcium and magnesium were maintained at 500 and 350 mg, respectively. Raising the protein intake from 50 to 150 g caused a calciuresis at both phosphorus intakes, but the actual increase in urinary calcium was 71 mg/day greater at the low than at the high phosphorus intake and calcium balance was changed from 24 to -116 mg/day at the low phosphorus intake and from 8 to -25 mg/day at the high. When the phosphorus intake was raised, urinary calcium decreased from 156 to 93 mg/day at the low protein intake and from 334 to 200 mg/day at the high protein intake and the markedly negative calcium balance found at the high protein intake was greatly improved. Simultaneous increases in protein and phosphorus intakes caused a 28% increase in urinary calcium whereas the increase in protein intake alone caused a 115% increase.

Summer internal phosphorus supplies in Shagawa Lake, Minnesota

Abstract: Phosphorus budget calculations for Shagawa Lake show that significant increases in lake P during July and August 1971-1975 originated from within the lake basin. Mass increases of 2,000-2,900 kg (3550 pgeliter-‘) were measured, corresponding to internal supply rates of 240-680 kg* wk-’ over a 3-9-week interval. After anaerobi : conditions developed in late June, release from the profundal zone sediments contributed :ignificant amounts of P to lake water. Sediment chemical properties were determined to estimate: the size of the P reservoir in the profundal zone (at water depths > 6.5 m). The P content of the surficial profundal zone sediments was 0.2-0.5% (dry wt) and a significant fraction \fas potentially mobile (NaOH extractable). We calculate that the upper 10 cm of these sediments contain 50,000 kg of potentially mobile P, of which a small fraction is released each summer. Although external sources of phosphorus have been reduced by about 80%, the feedback ofP from the sediments is supporting the productivity of Shagawa Lake and may continue to do so for many years.

Chlorophyll-phosphorus relations in individual lakes. Their importance to lake restoration strategies.

Abstract: The response of algal biomass to nutrient reduction is critically evaluated in 16 north temperate lakes by using data from the literature. The analysis confirms that reductions in total phosphorus concentration in the lakes are typically accompanied by consistent declines in chlorophyll. The data also suggest that this response can be expected whether a lake is phosphorus or nitrogen limited, although the magnitude of the response may differ. This is in contrast to the conclusion of a recent report which suggests that a threshold response is involved. Furthermore, the responses of some lakes appear unique and may not be accurately predicted by using current global eutrophication models. Modifications of these models to account for additional factors are urged, in order that these prediction errors may be decreased in the future.

The Sorption of Soluble Phosphorus by Soil Material during Transport in Runoff from Cropped and Grassed Watersheds 1

Abstract: The adsorption of soluble P by surface soil and suspended sediment material during transport in surface runoff under field and simulated laborato ry conditions was investigated. The soluble P concentration of surface runoff from several Southern Plains cropped and grassed watersheds decreased with an increase in sediment concentration. A linear inverse relationship between soluble P and sediment concentration was significant over a wide range in sediment concentration. The slope values of the relationship were similar for different watersheds on the same major soil type. Using soil from these watersheds in simulated surface runoff, sorption of soluble P added in rainfall was found to occur during transport. The magnitude of this sorption was more closely related to the sorptive capacity of the sediment in the surface runoff than to that of the surface soil material. The results suggest that for unfertilized watersheds and for watersheds where fertilizer P is incorporated into the surface soil, away from the zone of immediate removal in surface runoff, the leaching of P from the vegetative cover can contribute significant amounts of soluble P to runoff, and that soil material may act as a P sink rather than a P source. Additional Index Words: surface runoff, sediment. Sharpley, A. N., R. G. Menzel, S. J. Smith, E. D. Rhoades, and A. E. Olness, 1981. The sorption of soluble phosphorus by soil material during transport in runoff from cropped and grassed watersheds. J. Environ. Qual. 10:211-215. The importance of phosphorus (P) in increasing the rate of biomass production in surface waters from agricultural watersheds is well recognized (Keup, 1968; Ryden et al., 1973; Viets, 1975). Because of the appreciably greater availability of soluble P than sediment-P to aquatic organisms (Syers et al., 1973; Porter, 1975), transformations between soluble and sediment-bound P during transport in runoff are important in determining the short-term potential of runoff for increasing algal growth. Leaching of plant material by rainfall, dissolution of fertilizer material, and desorption of soil P by runoff water can contribute substantial amounts of P to runoff water (Timmons et al., 1970; Schuman et al., 1973; Romkens and Nelson, 1974). However, Burwell et al. (1974) suggested that part of the P released to runoff can be readsorbed by soil material during transport. Furthermore, several studies have attributed observed decreases in the soluble P concentration of stream water, during movement from agricultural watersheds, to sorption by suspended sediment and exposed stream bank material (Wang and Evans, 1970; Taylor and Kunishi, 1971; Sharpley and Syers, 1979). The selective erosion of fine particles, which have a greater capacity 'Contribution from the Dep. of Agron., Oklahoma Agric. Exp. Stn., Oklahoma State Univ., Stillwater, OK 74074, in cooperation with Southern Plains Watershed and Water Qual. Lab., USDA-SEA, Durant, OK 74701. Journal Series no. 3796. Received 23 July 1980. 'Soil Chemists, except E. D. Rhoades, Agricultural Engineer. Address, USDA-SEA, Durant, Okla. Last author's present address is USDA-SEA, Morris, Minn. to sorb P during runoff (Schuman et al., 1976; Menzel, 1980; Sharpley, 1980), enhances sorption of P during transport. Little information is available, however, on the extent and rate to which sorption occurs under field or laboratory conditions. This paper reports on an investigation of the relationship between soluble P and suspended sediment concentrations in runoff from several Southern Plains cropped and grassed watersheds and the sorption of P by soil material from the watersheds. EXPERIMENTAL PROCEDURE Watershed Description Characteristics of the four cropped and seven grassed watersheds used in the study are presented in Table 1. Boundaries of the cropped watersheds were defined by man-made berms, and those of the grassed watersheds by ridges and natural boundaries. The continuously grazed watersheds, R-7 and R-8, were overgrazed, which produced poor vegetative ground cover and allowed active gullying. Similarly, the grassed watershed, W-2, was actively eroding from a large gulley. The amounts of fertilizer P applied to the watersheds are presented in

Phosphorus Requirements of Soybean and Cowpea as Affected by Mode of N Nutrition1

Abstract: A field experiment was conducted on a tropical soil (Humoxic Tropohumult) with a high P sorption capacity to compare the critical external and internal P require ments of soybean (Glycine max (L) Merr.) and cowpea (Vigna unguiculata () Walp.) as affected by the predominant mode of N nutrition during crop growth. The experiment had a split-plot design with two N-level subplots established within each of six Plevel mainplots. Phosphorus treatment ranged from 0.0015 (unamended soil) to 0.08 (1,880 kg P/ha) µg P/ml in 0.01M CaCl2 solutions equilibrated with soil for 6 days. Nitrogen levels were either deficient (plants primarily dependent on N fixation) or sufficient (N fertilizer supplied at rates sufficient to satisfy the crop N requirement). Nitrogen-fixing soybeans required 750 kg P/ha to obtain a 900/. relative yield which was 320 kg P/ha more than that required by N-supplied plants to obtain a comparable relative yield. The P concentration of N-fixing soybean plants was significantly lower than that of Nsupplied plants at all levels of applied P fertilizer. The external P requirement and tissue P concentration of cowpea were unaffected by soil N level. The data show that cowpea was more tolerant of P stress than soybean, especially when dependent on N fixation. The cowpea cultivar grown without P or N fertilizer yielded 72% of the maximum yield obtained at optimum P levels while the comparable relative yield for the soybean cultivar was 28%. We conclude that (i) some N-fixing grain legumes can make respectable yields with little or no P fertilizer while others might not and, (ii) screening N-fixing grain legumes for tolerance to nutrient stress should be conducted on N-deficient soil to insure that nutritional requirements are assessed for the N-fixing plant, especially on the highly weathered soils of the tropics.

Influence of soil inoculation with vesicular-arbuscular mycorrhiza and a phosphate-dissolving bacterium on plant growth and 32P-uptake

Abstract: The influence of inoculation of soil with a vesicular-arbuscular mycorrhizal fungus (Glomus fasciculatus) and a phosphate-dissolving bacterium (Bacillus circulans) on phosphate solubilization, growth of finger millet (Eleusine coracana) and phosphorus uptake from 32P-labelled tricalcium phosphate and superphosphate were studied. The mycorrhizal plants produced more dry matter and removed more 32P from the soil than non-mycorrhizal plants, but did not show increased 32P activity per unit plant mass. The 30 mm NH4F-HCl extractable 32P (available 32P) in soil, plant 32P activity and total P uptake were enhanced by soil inoculation with the bacterium. In the treatment receiving both inocula a synergistic effect was recorded with increased P uptake and dry matter production.

Effect of phosphorus and zinc on the growth and phosphorus, zinc, copper, iron and manganese nutrition of rice

Abstract: A greenhouse experiment was conducted to study the effect of phosphorus and zinc application, in three lowland alluvial rice soils (Haplustalf) on the growth of rice and the concentration of phosphorus, zinc, copper, iron and manganese in shoots and roots. The results showed that application of phosphorus and zinc significantly increased the dry matter yield of shoots, grains and roots. Application of phosphorus caused a decrease in the concentration of zinc, copper, iron and manganese both in shoots and roots. Application of zinc also similarly lowered the concentration of phosphorus, copper and iron, but increased that of manganese in shoots and roots. The decrease in the concentration of the elements in the shoots was not due to dilution effect or to the reduced rate of translocation of the elements from the roots to tops. This has been attributed more to the changes in the availability of the elements in soil resulting from the application of phosphorus and zinc.

Influence of age, sex and calcium and phosphorus levels on the mechanical properties of various bones in swine.

Abstract: Seventy-two 4-week-old pigs were randomly assigned by sex (gilts, barrows, boars) to two dietary treatments and four age periods for determinations of the effects of age, sex and Ca and P levels on the mechanical properties of various bones in swine. Pigs were individually fed diets containing either. months after the initiation of the trial. The femur (Fem), humerus (Hum), third and fourth metacarpal (3Me, 4Me), third and fourth metatarsal (3MT, 4MT), third rib (Rib) and thoracic vertibrae were collected at each age period for mechanical tests and determination of percentage of ash. Bending moment, ultimate stress, yield stress and modulus of elasticity were determined by a flexure test in which the bone was treated as a simply supported , centrally-loaded beam (three-point loading). Bending moment of bones from boars was similar to that of bones from gilts or barrows. When expressed as force per unit area, the ultimate stress of bones from boars was less than that of bones from gilts or barrows. Percentage of ash did not differ significantly between sexes, but tended to be lower in bones from boars than in bones from gilts or barrows. Bones from pigs fed T2 had a higher bending moment than bones from pigs fed T1, regardless of age. At A1, the Fem, Hum and Rib of pigs 1Published as Paper No. 6094-, Journal Ser., Ne-braska Agr. Exp. Sta. a Dept. of Anita. Sci. Acknowledgment is made to Chuck Clanton for assistance with engineering equations and to Cecilia Stodd and Mary Barnes for laboratory assistance. fed T2 were able to withstand a greater stress than the same bones of pigs fed T1. At A3 and AS, the ultimate stress of all bones increased with increasing levels of dietary Ca,P. At A7, the Fem, 4MT and Rib failed to show a response to increased levels of Ca, P.

Preventing phosphorus losses during perchloric acid digestion of sodium bicarbonate soil extracts

Abstract: Between 10 and 40% of P was lost during perchloric acid digestion of NaHCO3 soil extracts for measurement of organic P. This observation was confirmed by 32P tracer experiments. Addition of MgCl2 prevented P loss, reduced variability of replicate determinations and ensured virtually 100% recovery of P added to NaHCO3 solution and NaHCO3 soil extracts before digestion. Losses were due both to P volatilisation and conversion of P to forms other than ortho-P in the digestion mixture.

Nitrogen and phosphorus dynamics in hot desert streams of Southwestern U.S.A.

Abstract: Nitrogen to phosphorus ratios and concentrations of nitrate and soluble reactive phosphate are presented for an array of Southwestern streams as evidence that nitrogen is the limiting nutrient where such limitation occurs. Nitrate uptake in sections of intermittent streams was attributable to autotrophic activity. Uptake of soluble reactive phosphate was unrelated to any indicator of autotrophic activity, thus concentrations of this nutrient in desert and semi-desert stream waters may be controlled by other factors.

Nitrogen and Phosphorus Nutrition of Cladophora in the Peel-Harvey Estuarine System, Western Australia

Abstract: Cladophora aff. albida, a nuisance benthic alga, appears to store nutrients during winter and spring, periods of high nutrient input, for use in summer and autumn. Tissue nutrient values were usually above the critical concentrations of 21 mg per g dry weight for N and always below the critical concentration of 33 mg per g dry weight for P. Nutrient sources are surface sediments and decomposing Cladophora and phytoplankton. The few weeks of high river flow in winter do not allow the Cladophora to reach full storage potential of nutrients. Phosphorus regulation may be an important factor in control of this alga in the estuary.

Protein-induced hypercalciuria.

Abstract: Under controlled dietary conditions the level of dietary protein has a profound and sustained effect on urinary calcium and calcium retention of man. Young adults achieve calcium balance at low intakes of 500 mg calcium and 700 to 1,000 mg phosphorus when protein intake is 50 g. Large calcium losses occur at the same calcium and phosphorus intakes when the protein intake is increased approximately threefold. The protein-induced hypercalciuria is due mainly to a decrease in fractional renal tubular reabsorption of calcium, although an increase in glomerular filtration rate is also involved. The changes in kidney function appear to result from the catabolism of excess dietary sulfur amino acids to sulfate and the subsequent excretion of sulfate in the urine. An increase in both protein and phosphorus intakes has a much less dramatic effect on urinary calcium and calcium retention than an increase in protein intake alone. An increase in dietary phosphorus greatly reduces urinary calcium by increasing the fractional renal tubular reabsorption of calcium. It appears therefore that high protein intakes may increase the requirements for both calcium and phosphorus.