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Low Phosphorus Concentration (low + phosphorus_concentration)
Selected AbstractsLow molecular weight organic acids and fatty acids in root exudates of two Lupinus cultivars at flowering and fruiting stagesPHYTOCHEMICAL ANALYSIS, Issue 5 2001J. A. Lucas García Abstract Low molecular weight organic acids (LOAs) and fatty acids in root exudates of two lupin cultivars, Lupinus albus cv. Multolupa and L. luteus cv. Tremosilla, were determined at flowering and fruiting stages. LOAs were analysed by capillary electrophoresis. Acetic and citric acids were the most abundant, especially the latter in L. luteus at the flowering stage (5922.79,µg/g dry root). The significant decrease in acid content of both cultivars from flowering to fruiting stages was also striking. The highest levels of acetic acid were detected in L. luteus at fruiting stage (1542.03,µg/g dry root). The significant citrate production in L. luteus could be related to the low phosphorus concentration in the studied soils but not to proteoid roots, which were detected only in L. albus. The source of the LOAs detected in these exudates is also discussed, since they may be produced either by the plant or by the associated rhizobacteria. The profile of phospholipid fatty acids was determined by high-resolution GC. A high level of 18:2,6 (a fatty acid specific to fungi) was found in exudates of L. luteus (a mycorrhizal plant) in contrast to L. albus (a non-mycorrhizal plant). Copyright © 2001 John Wiley & Sons, Ltd. [source] Phosphorus sources and availability modify growth and distribution of root clusters and nodules of native Australian legumesPLANT CELL & ENVIRONMENT, Issue 7 2002M. A. Adams Abstract A variety of native Western Australian legumes produced root clusters in sand culture confirming field and published observations. In general, these legumes grew equally well when supplied with organic or inorganic sources of phosphorus. The nitrogen content of shoots and roots varied little among treatments for all species, however, phosphorus content was always greater in plants supplied with inositol-P. The plasticity of root growth in response to localized placement of organic and inorganic sources of phosphorus was demonstrated using a simple ,split root' technique. Total root dry weight was, on average, more than doubled in P-amended sand when compared with non-amended sand. Root clusters tended to be produced in areas of relatively high phosphorus concentration and nodules in areas of low phosphorus concentration. Levels of phosphorus in lateral roots grown in P-amended sand were significantly different from lateral roots grown in the corresponding non-amended sand. Growth increases averaging 70% for white sand to over 100% for yellow sand indicated a large degree of ,plasticity' in roots under conditions of heterogeneous supply of phosphorus. Spatially exclusive development of organs for the acquisition of nutrients is discussed in relation to requirements for carbon in organ production and maintenance. [source] Nutrient requirements of ephemeral plant species from wet, mesotrophic soilsJOURNAL OF VEGETATION SCIENCE, Issue 3 2001Emiel; Brouwer van der Meijden (1996) Abstract. Nanocyperion plant communities occur on wet, more or less nutrient-poor and sparsely vegetated soils in temperate climates and are characterized by tiny, very shortlived plant species. Most of these have become locally extinct. It is generally assumed that drainage and eutrophication were the most important reasons for this decrease. However, chemical analysis of soil pore water from plots on growth sites of these ephemerals showed that phosphorus availability was relatively high. In a greenhouse experiment, the growth of ephemeral species was strongly limited by the amount of available phosphorus, whereas there was little or no limitation to the growth of other plant species from this habitat. At low phosphorus concentrations, the ephemeral species reached their reproductive phase within the same period, but showed a strong reduction in the amount of flowers that were produced. We concluded that ephemeral species in particular require a minimum amount of phosphorus for reproduction. Other species on nutrient-poor, wet soils have a longer life span and can postpone flowering in nutrient-poor soils. In contrast to other short-lived plant species from the same habitat, the growth of ephemeral species was barely stimulated by enhanced nitrogen availability. Apparently, the ephemerals are adapted to low nitrogen concentrations. The occurrence on nitrogen-poor and relatively phosphorus-rich soils suggests that this community may be very sensitive to nitrogen deposition. Reduced phosphorus availability below the minimum requirements of ephemerals, for example after acidification or the exclusion of human activities, has possibly contributed to the decrease of ephemeral plant species. [source] Modelling the reciprocal water exchange between a river (Havel) and a lake (Tegeler See) during spring and autumn overturnsLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 3 2000Karl-Erich Lindenschmidt Abstract A finite volume computer model (current flow and transport) was used to simulate the reciprocal water exchange between a river (Havel) and a lake (Tegeler See) appendaged to the river in Berlin, Germany. The discretization of the model control volume is 2-D along the plane of the water surface, which restricts the modelling to time periods of complete overturn. The finite volume method does, however, allow a depth to be given for each volume cell. A k -, turbulence submodel was integrated into the model to calculate the distinct dispersion coefficients for each volume cell. As current flow measurements were unavailable, the model was verified indirectly by the transport simulation of dissolved chloride, a conservative substance. The results show that the Havel contributes up to 30% of the total inflow to Tegeler See when it is overturned. As the Havel is more heavily polluted with respect to phosphorus loading, this has negative implications to the water quality of Tegeler See. Suggestions are given for controlling the Havel inflow amount by increasing the output of the phosphate elimination facility, the second main inflow to Tegeler See. Its output has very low phosphorus concentrations and serves as a flushing function. [source] | ||||||||||