Showing papers on "Phosphorus published in 2005"

Eutrophication of aquatic ecosystems: Bistability and soil phosphorus

Abstract: Eutrophication (the overenrichment of aquatic ecosystems with nutrients leading to algal blooms and anoxic events) is a persistent condition of surface waters and a widespread environmental problem. Some lakes have recovered after sources of nutrients were reduced. In others, recycling of phosphorus from sediments enriched by years of high nutrient inputs causes lakes to remain eutrophic even after external inputs of phosphorus are decreased. Slow flux of phosphorus from overfertilized soils may be even more important for maintaining eutrophication of lakes in agricultural regions. This type of eutrophication is not reversible unless there are substantial changes in soil management. Technologies for rapidly reducing phosphorus content of overenriched soils, or reducing erosion rates, are needed to improve water quality.

Nature of phosphorus limitation in the ultraoligotrophic eastern Mediterranean.

Abstract: Phosphate addition to surface waters of the ultraoligotrophic, phosphorus-starved eastern Mediterranean in a Lagrangian experiment caused unexpected ecosystem responses. The system exhibited a decline in chlorophyll and an increase in bacterial production and copepod egg abundance. Although nitrogen and phosphorus colimitation hindered phytoplankton growth, phosphorous may have been transferred through the microbial food web to copepods via two, not mutually exclusive, pathways: (i) bypass of the phytoplankton compartment by phosphorus uptake in heterotrophic bacteria and (ii) tunnelling, whereby phosphate luxury consumption rapidly shifts the stoichiometric composition of copepod prey. Copepods may thus be coupled to lower trophic levels through interactions not usually considered.

Root architectural tradeoffs for water and phosphorus acquisition

Abstract: Root architectural traits that increase topsoil foraging are advantageous for phosphorus acquisition but may incur tradeoffs for the acquisition of deep soil resources such as water. To examine this relationship, common bean genotypes contrasting for rooting depth were grown in the field and in the greenhouse with phosphorus stress, water stress and combined phosphorus and water stress. In the greenhouse, water and phosphorus availability were vertically stratified to approximate field conditions, with higher phosphorus in the upper layer and more moisture in the bottom layer. Under phosphorus stress, shallow-rooted genotypes grew best, whereas under drought stress, deep-rooted genotypes grew best. In the combined stress treatment, the best genotype in the greenhouse had a dimorphic root system that permitted vigorous rooting throughout the soil profile. In the field, shallow-rooted genotypes surpassed deep-rooted genotypes under combined stress. This may reflect the importance of early vegetative growth in terminal drought environments. Our results support the hypothesis that root architectural tradeoffs exist for multiple resource acquisition, particularly when resources are differentially localised in the soil profile. Architectural plasticity and root dimorphism achieved through complementary growth of distinct root classes may be important means to optimise acquisition of multiple soil resources.

Rhizoeconomics: Carbon costs of phosphorus acquisition

Abstract: Plants display a wide array of physiological adaptations to low soil phosphorus availability. Here we discuss metabolic and ecological costs associated with these strategies, focusing on the carbon costs of root traits related to phosphorus acquisition in crop plants. We propose that such costs are an important component of adaptation to low phosphorus soils. In common bean, genotypes with superior low phosphorus adaptation express traits that reduce the respiratory burden of root growth, including greater allocation to metabolically inexpensive root classes, such as adventitious roots, and greater formation of cortical aerenchyma, which reduces specific root respiration. Root hair formation increases phosphorus acquisition at minimal carbon cost, but may have other unknown ecological costs. Mycorrhizas and root exudates enhance phosphorus acquisition in some taxa, but at significant carbon cost. Root architectural patterns that enhance topsoil foraging enhance phosphorus acquisition but appear to incur tradeoffs for water acquisition and spatial competition. A better understanding of the metabolic and ecological costs associated with phosphorus acquisition strategies is needed for an intelligent deployment of such traits in crop improvement programs.

Organic phosphorus in the environment

Abstract: Separation, preconcentration and speciation Organic phosphorus speciation in natural waters by mass spectrometry Abiotic degradation of organic phosphorus compounds in the environment Enzymatic hydrolysis of organic phosphorus Abiotic stabilization of organic phosphorus Microbial tumover of phosphorus in soil Organic phosphorus dynamics in tropical agroecosystems Organic phosphorus transfer from terrestrial to aquatic environments Interactions in terrestrial ecosystems Organic phosphorus in the aquatic environment: speciation, transformations and interactions with nutrient cycles

Decoupling of Iron and Phosphate in the Global Ocean

Abstract: [1] We formulate a mechanistic model of the coupled oceanic iron and phosphorus cycles The iron parameterization includes scavenging onto sinking particles, complexation with an organic ligand, and a prescribed aeolian source Export production is limited by the availability of light, phosphate, and iron We implement this biogeochemical scheme in a coarse resolution ocean general circulation model using scavenging rates and conditional stability constants guided by laboratory studies and a suite of box model sensitivity studies The model is able to reproduce the broad regional patterns of iron and phosphorus In particular, the high macronutrient concentrations of the Southern Ocean, tropical Pacific, and subarctic Pacific emerge from the explicit iron limitation of the model In addition, the model also qualitatively reproduces the observed interbasin gradients of deep, dissolved iron with the lowest values in the Southern Ocean The ubiquitous presence of significant amounts of free ligand is also explicitly captured We define a tracer, Fe* which quantifies the degree to which a water mass is iron limited, relative to phosphorus Surface waters in high-nutrient, lowchlorophyll regions have negative Fe* values, indicating Fe limitation The extent of the decoupling of iron and phosphorus is determined by the availability and binding strength of the ligand relative to the scavenging by particulate Global iron concentrations are sensitive to changes in scavenging rate and physical forcing Decreasing the scavenging rate 40% results in � 01 nM increase in dissolved iron in deep waters Forcing the model with weaker wind stresses leads to a decrease in surface [PO4] and [Fe ]i n the Southern Ocean due to a reduction in the upwelling strength

Sediment Depth Attenuation of Biogenic Phosphorus Compounds Measured by 31P NMR

Abstract: Being a major cause of eutrophication and subsequent loss of water quality, the turnover of phosphorus (P) in lake sediments is in need of deeper understanding. A major part of the flux of P to eutrophic lake sediments is organically bound or of biogenic origin. This P is incorporated in a poorly described mixture of autochthonous and allochthonous sediment and forms the primary storage of P available for recycling to the water column, thus regulating lake trophic status. To identify and quantify biogenic sediment P and assess its lability, we analyzed sediment cores from Lake Erken, Sweden, using traditional P fractionation, and in parallel, NaOH extracts were analyzed using 31P NMR. The surface sediments contain orthophosphates (ortho-P) and pyrophosphates (pyro-P), as well as phosphate mono- and diesters. The first group of compounds to disappear with increased sediment depth is pyrophosphate, followed by a steady decline of the different ester compounds. Estimated half-life times of these compound groups are about 10 yr for pyrophosphate and 2 decades for mono- and diesters. Probably, these compounds will be mineralized to ortho-P and is thus potentially available for recycling to the water column, supporting further growth of phytoplankton. In conclusion, 31P NMR is a useful tool to asses the bioavailability of certain P compound groups, and the combination with traditional fractionation techniques makes quantification possible.

Mapping of QTL controlling root hair length in maize (Zea mays L.) under phosphorus deficiency

Abstract: Suboptimal phosphorus availability is a primary constraint for terrestrial plant growth and crop productivity. Root hairs are subcellular extensions from the root epidermis that play an important role in the uptake of immobile nutrients such as phosphorus by increasing soil exploration. The objective of this study was to identify quantitative trait loci for root hair length and plasticity in response to phosphorus stress in maize. Using a cigar roll culture system in a controlled environment, root traits including root hair length, tap root length, root thickness, and root biomass were evaluated in 169 recombinant inbred lines derived from a cross between B73 and Mo17. These parents have contrasting adaptation to low phosphorus availability in the field. The parents segregated for the length of individual root hairs under low phosphorus. Average root hair length (RHL) of RI lines ranged from 0.6 to 3.5 mm with an average of 2.0 mm under fertile conditions, and RHL was increased from 0% to 185% under phosphorus stress. Using composite interval mapping with a LOD threshold of 3.27, one QTL was associated with RHL plasticity, three QTL with RHL under high fertility, and one QTL with root hair length under low phosphorus. These QTL accounted for 12.7%, 31.9%, and 9.6% of phenotypic variation, respectively. No QTL were detected for taproot thickness and root biomass. Six QTL were associated with 53.1% of the total variation for seed phosphorus in the population. Root biomass plasticity was significantly correlated with RHL induced by low phosphorus, taproot length plasticity, and seed phosphorus reserves. Our results suggest that genetic variation in root hair length and plasticity may be an appropriate target for marker aided selection to improve the phosphorus efficiency of maize.

Topsoil foraging and phosphorus acquisition efficiency in maize (Zea mays)

Abstract: In soybean and common bean, enhanced topsoil foraging permitted by shallow root architectures is advantageous for phosphorus acquisition from stratified soils. The importance of this phenomenon in graminaceous crops, which have different root architecture and morphology from legumes, is unclear. In this study we evaluated the importance of shallow roots for phosphorus acquisition in maize (Zea mays L.). In a field study, maize genotypes with shallower roots had greater growth in low phosphorus soil than deep-rooted genotypes. For physiological analysis, four maize genotypes differing in root shallowness in the field were grown in solid media with stratified phosphorus availability in a controlled environment. Of the four genotypes, one shallow and one deep genotype were also inoculated with arbuscular mycorrhiza (AM). Shallower genotypes had significantly greater growth and phosphorus accumulation compared with deeper genotypes at low phosphorus availability. Mycorrhizal colonisation altered root shallowness under low phosphorus conditions, increasing shallowness substantially in a deep-rooted genotype but slightly decreasing shallowness in a shallow-rooted genotype. Mycorrhizal colonisation increased phosphorus acquisition under low phosphorus availability. Respiration costs of roots and shoots of phosphorus-efficient genotypes were significantly lower under low phosphorus conditions compared with inefficient genotypes. The physiological efficiency of phosphorus acquisition, expressed as root respiration per unit of phosphorus acquisition, was greater in shallow rooted genotypes. Our results demonstrate that genetic variation for root shallowness exists in maize, that phosphorus and AM can modulate root shallowness independently, and that a shallower root system is beneficial for plant performance in maize at low phosphorus availability. We propose that root architectural traits that enhance topsoil foraging are important traits for improved phosphorus acquisition efficiency of annual grain crops such as maize in addition to legumes.

Aluminum control of phosphorus sorption by lake sediments.

Abstract: Release of reactive (phosphate-like) phosphorus (P) from freshwater sediments represents a significant internal P source for many lakes. Hypolimnetic P release occurs under reducing conditions that cause reductive dissolution of ferric hydroxide [Fe(OH)3]. This hypolimnetic P release may be naturally low or artificially reduced by sediment with naturally high or artificially elevated concentrations of aluminum hydroxide [Al(OH)3]. We presentfield and laboratory data for a common extraction analysis of sediments from 43 lakes differing in trophic status, pH regime, climate, and P loading. The results indicate that a simple sequential extraction of sediment may be a useful predictor of sediment's ability to release P. Sequential extractions of sediment P, Al, and Fe by water (H2O), bicarbonate-dithionite (BD), and NaOH (at 25 degrees C) showed that negligible amounts of P would be released from lake sediments during hypolimnetic anoxia if either (1) the molar Al(NaOH-25):Fe(BD) ratio is > 3 or (2) the molar Al(NaOH-25):P(H2O+BD) ratio is > 25. These ratios can be used as operational targets for estimation of sediment P release potential and Al dosing of P-rich sediment to prevent hypolimnetic P release under anoxic conditions.

Soluble nitrogen and phosphorus excretion of exotic freshwater mussels (Dreissena spp.): potential impacts for nutrient remineralisation in western Lake Erie

Abstract: SUMMARY 1. Recent increases in phytoplankton biomass and the recurrence of cyanobacterial blooms in western Lake Erie, concomitant with a shift from a community dominated by zebra mussels (Dreissena polymorpha) to one dominated by quagga mussels (D. bugensis), led us to test for differences in ammonia-nitrogen and phosphate-phosphorus excretion rates of these two species of invasive molluscs. 2. We found significant differences in excretion rate both between size classes within a taxon and between taxa, with zebra mussels generally having greater nutrient excretion rates than quagga mussels. Combining measured excretion rates with measurements of mussel soft-tissue dry weight and shell length, we developed nutrient excretion equations allowing estimation of nutrient excretion by dreissenids. 3. Comparing dreissenid ammonia and phosphate excretion with that of the crustacean zooplankton, we demonstrated that the mussels add to nitrogen and phosphorus remineralisation, shortening nitrogen and phosphorus turnover times, and, importantly, modify the nitrogen and phosphorus cycles in Lake Erie. The increased nutrient flux from dreissenids may facilitate phytoplankton growth and cyanobacterial blooms in well-mixed and/or shallow areas of western Lake Erie.

Does high nitrogen loading prevent clear-water conditions in shallow lakes at moderately high phosphorus concentrations?

Abstract: Summary 1. The effect of total nitrogen (TN) and phosphorus (TP) loading on trophic structure and water clarity was studied during summer in 24 field enclosures fixed in, and kept open to, the sediment in a shallow lake. The experiment involved a control treatment and five treatments to which nutrients were added: (i) high phosphorus, (ii) moderate nitrogen, (iii) high nitrogen, (iv) high phosphorus and moderate nitrogen and (v) high phosphorus and high nitrogen. To reduce zooplankton grazers, 1+ fish (Perca fluviatilis L.) were stocked in all enclosures at a density of 3.7 individuals m−2. 2. With the addition of phosphorus, chlorophyll a and the total biovolume of phytoplankton rose significantly at moderate and high nitrogen. Cyanobacteria or chlorophytes dominated in all enclosures to which we added phosphorus as well as in the high nitrogen treatment, while cryptophytes dominated in the moderate nitrogen enclosures and the controls. 3. At the end of the experiment, the biomass of the submerged macrophytes Elodea canadensis and Potamogeton sp. was significantly lower in the dual treatments (TN, TP) than in single nutrient treatments and controls and the water clarity declined. The shift to a turbid state with low plant coverage occurred at TN >2 mg N L−1 and TP >0.13–0.2 mg P L−1. These results concur with a survey of Danish shallow lakes, showing that high macrophyte coverage occurred only when summer mean TN was below 2 mg N L−1, irrespective of the concentration of TP, which ranged between 0.03 and 1.2 mg P L−1. 4. Zooplankton biomass and the zooplankton : phytoplankton biomass ratio, and probably also the grazing pressure on phytoplankton, remained overall low in all treatments, reflecting the high fish abundance chosen for the experiment. We saw no response to nutrition addition in total zooplankton biomass, indicating that the loss of plants and a shift to the turbid state did not result from changes in zooplankton grazing. Shading by phytoplankton and periphyton was probably the key factor. 5. Nitrogen may play a far more important role than previously appreciated in the loss of submerged macrophytes at increased nutrient loading and for the delay in the re-establishment of the nutrient loading reduction. We cannot yet specify, however, a threshold value for N that would cause a shift to a turbid state as it may vary with fish density and climatic conditions. However, the focus should be widened to use control of both N and P in the restoration of eutrophic shallow lakes.

n-type doping of (001)-oriented single-crystalline diamond by phosphorus

Abstract: n-type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350cm2∕Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.

The Phosphorus Cycle

Abstract: Publisher Summary The chapter focuses on the biochemical processes by which phosphorus is incorporated into cells and those processes responsible for both phosphorus release and phosphorus sequestration in nature. Phosphorus is a vital functional and structural component of all living organisms. It occurs universally in living cells as phosphate in essential biomolecules such as nucleic acids (DNA and RNA), in energy transfer systems (NAD(P)H and ATP), and in cell membranes (phospholipids). Many of the biochemical processes are microbially mediated, and the chapter highlights the role of microbes in the phosphorus cycle. Microorganisms with active membrane-transport systems regulate the acquisition of phosphate from the environment, such as the Pts phosphate transport system of Escherichia coli. Microbial processes largely control the mobilization and immobilization of phosphorus in aquatic environments. Organic-bound phosphorus is partly assimilated and partly released as dissolved inorganic phosphorus (DIP) by the heterotrophic microbial community during organic matter mineralization. The chapter compares and contrasts phosphorus cycling in a number of representative freshwater and marine systems.