Phosphorus Uptake (phosphorus + uptake)

Distribution by Scientific Domains

Selected Abstracts


Cécile Jauzein
Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO43,) concentrations in this environment over the 1970,1995 period. To determine if this dinoflagellate species has a competitive advantage in PO43, -limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO43, uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (QP and QC). Shifts in trends of QP/QC and QP per cell (QP·cell,1) along the DR gradient allowed the definition of successive P-stress thresholds for A. catenella cells. The maximal uptake rate of 33PO43, increased strongly with the decrease in DR and the decrease in QP/QC, displaying physiological acclimations to PO43, limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO43, limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO43, threshold between 0.4 and 1 ,M. As lower PO43, concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds. [source]

Phosphorus uptake, not carbon transfer, explains arbuscular mycorrhizal enhancement of Centaurea maculosa in the presence of native grassland species

C. A. Zabinski
Summary 1Previous studies have shown that arbuscular mycorrhizas (AM) enhance the growth of the invasive forb Centaurea maculosa when growing with native grass species. Using 13CO2, we tested the hypothesis that this enhancement is explained by carbon transfer from native species to C. maculosa via mycorrhizal hyphal linkages. 2A C. maculosa plant was paired with one of five native species , three grasses (Festuca idahoensis, Koeleria cristata and Pseudoroegneria spicata) and two forbs (Achillea millefolium and Gaillardia aristata) , in pots that separated the plants with either a mesh barrier (28 µm, excludes fine roots but not hyphae) or a membrane barrier (0·45 µm, excludes roots and hyphae). 313CO2 was added to the atmosphere of either Centaurea or the native species after 20 weeks' growth. A 25 min pulse application was followed by 7 days' growth and subsequent harvest. 4The biomass response of C. maculosa was consistent with previous experiments: C. maculosa was larger when growing in mesh barrier pots, when hyphae were able to access the opposite side of the pot; in mesh barrier pots only, biomass varied with neighbouring species. Native plant biomass did not vary between mesh- vs membrane-barrier pots. 5There was no evidence of carbon transfer, either from the native plant to C. maculosa or in the reverse direction. 6Centaurea maculosa contained significantly more phosphorus in mesh-divided pots, but this depended on the neighbouring plant. The P concentration in C. maculosa was significantly higher in mesh-divided pots when growing with a grass and not a forb. Native species contained more P in mesh-divided pots than membrane-divided pots, and P concentration differed between species (higher in forbs than grasses), but did not vary between mesh- and membrane-divided pots. 7Our study suggests that C. maculosa is able to exploit its mycorrhizal symbiosis more effectively than the native grassland species. The mechanism for this appears to be luxury consumption of P through efficient utilization of extra-radical hyphae, but that effect is dependent on neighbouring species, and occurs when growing with a grass neighbour. 8Although no single study can disprove the carbon-transfer hypothesis, our work suggests that AM-mediated neighbour effects are the result of mycorrhizal networks that increase species' access to P. Whether the synergistic effects of neighbours are due to complementarity of AM fungal symbionts utilized by different plant species, or have to do with the structure of AM networks that develop more extensively with multiple host plants, remains to be investigated. [source]

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Tesfaye Balemi
Abstract Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P-efficient genotypes. Two efficient and two inefficient genotypes were investigated for P-efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P-uptake rate of roots but decreased root-to-shoot ratio, root-hair length, and P-utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot,dry matter yield and relative shoot-growth rate at low P supply, and therefore can be considered as P-efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P-utilization efficiency and that of CIP 384321.3 to both higher P-uptake efficiency in terms of root-to-shoot ratio and intermediate P-utilization efficiency. Phosphorus-efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P-utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P-utilization efficiency. Simulation of P uptake revealed that no other P-mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described. [source]

Identification and comparison of aerobic and denitrifying polyphosphate-accumulating organisms

Raymond J. Zeng
Abstract Two laboratory-scale sequencing batch reactors (SBRs) were operated for enhanced biological phosphorus removal (EBPR) in alternating anaerobic,aerobic or alternating anaerobic,anoxic modes, respectively. Polyphosphate-accumulating organisms (PAOs) were enriched in the anaerobic,aerobic SBR and denitrifying PAOs (DPAOs) were enriched in the anaerobic,aerobic SBR. Fluorescence in situ hybridization (FISH) demonstrated that the well-known PAO, "Candidatus Accumulibacter phosphatis" was abundant in both SBRs, and post-FISH chemical staining with 4,6-diamidino-2-phenylindol (DAPI) confirmed that they accumulated polyphosphate. When the anaerobic,anoxic SBR enriched for DPAOs was converted to anaerobic,aerobic operation, aerobic uptake of phosphorus by the resident microbial community occurred immediately. However, when the anaerobic,aerobic SBR enriched for PAOs was exposed to one cycle with anoxic rather than aerobic conditions, a 5-h lag period elapsed before phosphorus uptake proceeded. This anoxic phosphorus-uptake lag phase was not observed in the subsequent anaerobic,aerobic cycle. These results demonstrate that the PAOs that dominated the anaerobic,aerobic SBR biomass were the same organisms as the DPAOs enriched under anaerobic,anoxic conditions. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 140,148, 2003. [source]