Showing papers on "Phosphorus published in 1973"

Phosphate flow into mycorrhizal roots

Abstract: Ectotrophic mycorrhizas have been studied intensively and their value to some tree species is well known. Endotrophic mycorrhizas have received less attention and their potential value to plants has only been fully substantiated within the last 12 years. Responses of the host to mycorrhizal infection seem always to be associated with improved phosphorus nutrition of the plant. The mechanism whereby this occurs is considered. There is evidence that the ultimate limitation on phosphorus uptake by a simple cylindrical root is the diffusion impedance in the soil around it, and that widely spreading hyphae effectively short-circuit this impedance. Some data on hyphal length, and estimated net flux of phosphorus through the hyphae are given, with a discussion of possible mechanisms driving this flux.

Effects of phosphorus deficiency on the photosynthesis and respiration of leaves of sugar beet.

Abstract: Phosphorus deficiency was induced in sugar beet plants (Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO2 and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO2 fixation of 125 ng CO2 cm−2 sec−1 at saturating irradiance, 25 C, and an ambient CO2 concentration of about 250 μl l−1. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO2 uptake, photorespiratory evolution of CO2 into CO2-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance (rm) which increased from 2.4 to 4.9 sec cm−1, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance (rl′) from 0.3 to 0.9 sec cm−1, as well as further increases in rm to 8.5 sec cm−1. Leaf diffusion resistance (rl′) was increased greatly by low P at low but not at high irradiance, rl′ for plants at low P reaching values as high as 9 sec cm−1.

Molecular Basis of Flame Inhibition.

Abstract: The role played by inorganic chemical additives in fire retardancy and flame inhibition is considered. Particular attention is given to the molecular level aspects of commercially important systems containing compounds of antimony, halogens, and phosphorus. The flame inhibiting function of metal containing additives is also discussed.

Output of phosphorus, dissolved organic carbon, and fine particulate carbon from hubbard brook watersheds1

Abstract: The output of phosphorus, dissolved organic carbon (DOC), and fine particulate organic carbon (FPOC) was measured in two watersheds of the Hubbard Brook Experimental Forest, New Hampshire. One watershed had a cover of birch, beech, and maple; the other had been denuded of trees and regrowth prevented. Concentrations of DOC and dissolved plus fine particulate P changed little with changes in flow. Concentrations of FPOC, however, were strongly dependent on flow and most of the FPOC was exported during a few periods of high runoff. Deforestation caused higher runoff (by 26%), but also greatly increased erosion. Thus, DOC and FPOC output was similar in the two watersheds while the loss of large particulate phosphorus, mostly as inorganic bedload, increased 12 times in the treated watershed. With a rainwater input of 100 g P ha−1, there was an annual net gain of 87 g P in the undisturbed watershed and a net loss of 104 g P in the disturbed watershed. In view of the large amounts of phosphorus cycling in the natural forest (e.g. some 1,900 g P ha−1 in annual leaf fall alone) this ecosystem is strongly conserving phosphorus.

Phosphorus dynamics in lake water.

Abstract: An exchange mechanism exists in lake water between phosphate and plankton, but the excretion of an organic phosphorus compound by the plankton is also a significant process. It results in the extracellular formation of a colloidal substance, and most of the nonparticulate phosphorus in lake water is in this form.

Characteristics of phosphorus deficiency in anabaena1

Abstract: SUMMARY Several aspects of the metabolism and composition of a strain of Anabaena have been studied during phosphorus deficiency. The effects of medium composition, substrate concentration, temperature, pH, and illumination on alkaline phosphatase activity and phosphate uptake have been examined. Of particular interest among these results was the dependence of maximum alkaline phosphatase activity on Ca and of phosphate uptake on Mg. Depletion of dissolved phosphate from the culture medium runs accompanied by a marked increase in alkaline phosphatase activity, initial rate of phosphate uptake, and total amount of phosphate taken up to satisfaction of the phosphorus debt. Readdition of phosphate to a phosphorus-deficient culture resulted in a rapid decline in the ability to take up phosphate but no loss of alkaline phosphatase beyond dilution of activity already present. Entry into phophorus deficiency was accompanied by a loss of heterocysts, a decline in chlorophyll a, protein, RNA, and cellular phosphorus, and an increase in carbohydrate per unit dry weight. The possible use of these changes as physiological indicators of phosphorus limitation in natural situations is discussed.

Effect of aluminium on the growth chemical composition of some tropical and temperate pasture legumes

Abstract: The effects of aluminium (0, 0.5, 1.0, 2.0 p.p.m.) on the dry matter production (tops and roots) and chemical composition of five tropical and six temperate pasture legumes grown in a cultu1.e solution containing 2 p.p.m. phosphorus were ascertained. The tolerances of the tropical species to aluminium were in the order Desmodiunz uncinatum = Macroptilium latlzyyuoides = Lotonis bainesii = Stylosanthes humilis = Glycine wightii > Medicago sativa, and temperate species in the order Trifolium rueppellianum= Trifolium sernipilosum > Trifolium repens = Medicago scutellata = Medicago truncatula = Medicago sativa. In the tolerant species the yield of plant material from the 0.5 p.p.m. aluminium treatment was greater than from the control. The top/root weight ratios of the tolerant species were unaffected by treatment; the ratios of the sensitive species were reduced. The effect of aluminium treatment on aluminium, nitrogen, phosphorus, potassium, calcium, magnesium, and sodium concentrations in the plants are given. The principal nutrients to be affected were calcium and phosphorus. Aluminium treatment reduced the calcium concentrations in the tops of all species and there were reciprocal relationships between calcium, magnesium, and potassium concentrations. In the sensitive species aluminium treatment reduced phosphorus in the plant tops and roots; in some of the tolerant species the intermediate aluminium treatment increased the phosphorus concentration in the plant tops; however, the high aluminium treatment reduced the phosphorus concentration.

Movements of Phosphorus Between its Biologically Important Forms in Lake Water

Abstract: A model consistent with the kinetics of phosphorus in epilimnetic lake water was developed. Adding 32PO4 to lake water and separating the major forms of dissolved phosphorus by Sephadex gel filtrat...

Plant growth responses to vesicular‐arbuscular mycorrhiza v. phosphate uptake by three plant species from p‐deficient soils labelled with 32p

Abstract: Summary The uptake of phosphorus from 32P-labelled soil solution by three plant species, with and without mycorrhiza, was measured. All soils contained very little CaCl2- and NaHCO3-soluble phosphorus. In two soils the specific activity of phosphorus taken up by mycorrhizal and non-mycorrhizal Melinis minutiflora was very similar, indicating that even in very P-deficient soils mycorrhizal plants used the same source of phosphate as non-mycorrhizal. In two other soils non-mycorrhizal Paspalum notatum and Centrosema pebescens contained no 32P activity, suggesting that they had not taken up any soil phosphorus, whereas mycorrhizal plants of both species contained 32P activity and grew much better. It is suggested that non-mycorrhizal roots of some plant species do not utilize phosphate present at extremely low concentrations in the soil solution, but that mycorrhizal roots or fungal hyphae do. The implications of this finding for the mechanism of phosphate uptake by VA mycorrhiza are discussed.

The Effect of Cold Shock and Freeze-Thawing on Release of Phospholipids by Ram, Bull, and Boar Spermatozoa

Abstract: The effects of cold shock and freeze-thawing on the release of total phospholipids phosphorus and of specific phospholipids from ram, bull, and boar spermatozoa are examined. Species differences are apparent, both in the absolute amount of total phospholipids released and in the conditions required to effect a loss of individual phospholipids. The phosphoglycerides most affected by the temperature treatment are choline plasmalogen, phosphatidyl choline, and phosphat idyl ethanolamine. The loss of phospholipids is most specific in boar spermatozoa. Bull spermatozoa suffer a greater overall and more general breakdown of phospholipids, indicating disruption of the cell structure. This is in contrast to the more specific phospholipid losses from ram and boar spermatozoa, which may indicate a more localized region of damage and release of material, possibly acrosomal. The loss of phospholipid may be correlated with the species differences in the fertility of the frozen spermatozoa.

Phosphorus Losses from Four Agricultural Watersheds on Missouri Valley Loess

Abstract: Phosphorus losses from four field-size experimental watersheds at Treynor, Iowa, were measured during 1969, 1970, and 1971. A contour-planted corn watershed and a pasture watershed were fertilized at the recommended P rate (39 kg/ha). A level-terraced and a second contour-planted corn watershed were fertilized at 2.5 times this rate. At the high level of P fertilization, phosphorus loss by surface runoff from the contour-planted corn watershed was 0.495 kg/ha in 1969, 1.034 kg/ha in 1970, and 2.130 kg/ha in 1971. Level terraces greatly reduced P loss by reducing runoff and erosion. Water samples for all runoff events taken above the overfall of each watershed gully contained considerably more inorganic P in solution than samples taken at the weir site, 70 to 230 m downstream. This reduction in solution P was caused by the adsorption of P by the additional suspended soil material entering the stream from gully erosion.

Intestinal Calcium Transport: Stimulation by Low Phosphorus Diets

Abstract: Rats maintained on a low phosphorus diet supplemented with 25-hydroxyvitamin D(3) show high intestinal calcium transport activity as compared to rats similarly treated but fed a diet containing adequate phosphorus. This increased transport activity is correlated with an increased biosynthesis of 1,25-dihydroxyvitamin D(3), the probable metabolically active form of the vitamin in the intestine.

Uptake of phosphorus and potassium in relation to root growth and root density

Abstract: This paper provides some quantitative data on the relationship between the rate of uptake of phosphorus and potassium from soil and the amount of root, root density and rate of root growth. Three experiments were conducted with winter wheat, all grown in the same soil. Root growth and density were manipulated in three ways: (1) by root pruning; (2) by a split-root technique; (3) by growing plants in different soil volumes. Root lengths as well as weights were determined. Potassium uptake per unit amount of root was generally lower the higher the root density, suggesting that roots were competing with each other for potassium even at the lowest density. In contrast, phosphorus uptake showed a good correlation with root growth irrespective of root density or plant age. Phosphorus uptake during a period was more closely and consistently correlated with root growth during that period than with the total amount of root on the plant. The results can be explained in terms of ion supply to the root surface, taking into account the diffusion coefficients of the ions and the approximate distances between neighbouring roots.

The characterization of soluble phosphorus released by limnetic zooplankton1

Abstract: Three rapid techniques were used to characterize the main forms of soluble phosphate released by Daphnia rosea. Uniformly 32P-labeled laboratory animals were transferred to nonradioactive water and most of the soluble radiophosphorus was shown to be similar to PO4 in anion exchange, in gel filtration chromatography, and in a kinetic analysis of incorporation by natural seston. In addition, Diaptomus minutus was labeled in situ with 32P and its release products compared to PO4 by gel filtration. This analysis and those using Daphnia indicated that the released soluble phosphorus was about 90% orthophosphate. However, molybdate analyses of the soluble phosphates released in a 10-hr experiment showed them to be only 60% orthophosphate. Net reuptake of orthophosphate was insufficient to account for this discrepancy. Recycling of phosphorus is postulated in longer experiments, which leads to a substantial underestimate of the orthophosphate release.