Phosphorus Turnover Research Articles

Feedbacks between oceanic redox states and marine productivity: A model perspective focused on benthic phosphorus cycling

A new model for the marine cycles of particulate organic carbon (POC), oxygen, nitrate, and phosphorus has been developed and applied to explore the controls and constraints on marine productivity and nutrient inventories. The coupled benthic‐pelagic model uses a new approach for the simulation of the reactive phosphorus turnover (Preac corresponding to the sum of organic P, authigenic P, and adsorbed phosphate) in marine sediments. The simulated POC/Preac burial ratio in shelf, slope and rise, and deep‐sea sediments increases under strongly reducing conditions in agreement with field observation. The model runs revealed that the spread of anoxia in bottom waters may enhance the productivity of the global ocean by one order of magnitude if sufficient nitrate is provided by N2‐fixation. Thus anoxic bottom waters promote eutrophic conditions and vice versa. Additional model runs showed that the productivity and nutrient inventory of the glacial ocean were probably enhanced due to the falling sea level. Marine regression induced a narrowing of the depositional areas on the continental shelves and thereby an increase in the fraction of POC exported to the deep ocean. The accelerated POC delivery, in turn, decreased the oxygen contents of the deep water and thus favored the release of phosphate from deep‐sea and rise sediments. Enhanced recycling of phosphate at the seafloor promoted further POC export in a positive feedback loop.

Microbial biomass phosphorus turnover in variable-charge soils in China

Turnover of microbial biomass phosphorus (Bp) in three acid red soils (one Arenic aquult and two Plinthic aquults) were investigated by 32P-labeling microorganisms in situ and fumigation–extraction techniques. The turnover rates of Bp in the three red soils were 130, 190, and 217 days, respectively, that is 1.7 to 2.8 times per year. The contents of Bp were 12.2, 17.8, and 31.5 mg kg−1, respectively, for the three soils. Microbial biomass turnover provided a dynamic source of available phosphorus (P) with the size of 2–3 times greater than the Bp. The annual fluxes of P through microbial biomass in these soils could amount to 91 to 146 kg ha−1, which are 3–5 times greater than the amount of P annually removed by the harvested crops. The turnover rate of Bp was greater in the sandy soil than in the other two clayey soils. This was explained by a larger amount of Bp and lower mineralization in the clayey soils, as compared with the sandy soil. Apparently, the turnover of Bp plays a very important role in the supply of plant-available P and ecological cycling of P in the subtropical red soil region.

Hydrodynamic control of nitrogen and phosphorus turnover in an eutrophicated estuary in the Baltic

The turnover of phosphorus and nitrogen have been studied in a low salinity estuary in the Bothnian Sea. The estuary, Gårdsfjärden, has a high loading of nutrients from a pulp and paper mill which supplies the estuary with three times the annual natural input of phosphorus and nitrogen, respectively. The turnover of nutrients was to a great extent determined by hydrodynamic variations. During periods of intense resuspension there was a net export of particulate bound nutrients from the estuary to the sea but since these periods were short there was an overall net retention of particulate nutrients. The estuary was a source for dissolved phosphorus to the sea. The major source of phosphorus export was release of dissolved P from anoxic sediments. Gårdsfjärden was a sink for dissolved nitrogen which most likely escaped the estuary by denitrification. Nitrate was supplied by degradation of particulate organic nitrogen but the main source was import from the sea.

Contribution of cytophaga-like bacteria to the potential of turnover of carbon, nitrogen, and phosphorus by bacteria in the rhizosphere of barley (Hordeum vulgare L.).

The functional potential of bacteria isolated from the rhizosphere of barley (Hordeum vulgare L.) in May, July, and August and cultivated on nutrient-rich substrate (1/10 TSBA) and nutrient-poor substrate (cold soil extract agar) was determined. There was no significant difference in numbers of CFU when counted on nutrient rich or poor substrate. Bacterial numbers increased approximately 3-fold in the rhizosphere soil from May to August but was unchanged in bulk soil over the same period. A total of 4474 randomly isolated bacteria were screened for enzymatic activities involved in carbon turnover (amylase, cellulase, mannanase, xylanase, and chitinase), nitrogen turnover (protease, nitrate and nitrite reductase), and phosphate turnover (phosphatase). In the rhizosphere soil, bacteria carrying C and P turnover enzymes were not stimulated by the growing plant whereas protease and nitrate and nitrite reductase were stimulated by the growing plant. No changes were observed in the bulk soil. Two taxonomic groups were followed: Cytophaga-like bacteria (CLB) and fluorescent pseudomonads, the latter being abundant in the rhizosphere and important contributors to the cycling of organic matter in soil. Unexpectedly in the spring samples, CLB were around 25% of all bacteria isolated, whereas fluorescent pseudomonads made up less than 10%. The relative proportion of these bacterial groups then decreased during the plant growth season but at all times showing a clear rhizosphere effect. Furthermore, up to 70% of the isolates carrying enzymes involved in the turnover of carbon, in the May sample, were identified as CLB, indicating the importance of this group in early colonization of the rhizosphere. The fluorescent pseudomonad group contributed less than 3%.

Rapid biologically mediated oxygen isotope exchange between water and phosphate

In order to better constrain the rate of oxygen isotope exchange between water and phosphate via biochemical reactions a set of controlled experiments were conducted in 1988 at the Aquaculture Plant in Elat, Israel. Different species of algae and other organisms were grown in seawater tanks under controlled conditions, and the water temperature and oxygen isotopic composition (δ18Ow) were monitored. The oxygen isotopic composition of phosphate (δ18Op) in the organisms' food source, tissues, and the δ18Op of dissolved inorganic phosphate (DIP) were measured at different stages of the experiments. Results indicate that intracellular oxygen isotope exchange between phosphorus compounds and water is very rapid and occurs at all levels of the food chain. Through these reactions the soft tissue δ18Op values become 23–26‰ higher than δ18Ow, and δ18Op values of DIP become ∼20‰ higher than δ18Ow. No correlation between δ18Op values and either temperature or P concentrations in these experiments was observed. Our data imply that biogenic recycling and intracellular phosphorus turnover, which involves kinetic fractionation effects, are the major parameters controlling the δ18Op values of P compounds dissolved in aquatic systems. This information is fundamental to any application of δ18Op of dissolved organic or inorganic phosphate to quantify the dynamics of phosphorus cycling in aquatic systems.

POLYPHOSPHATE AND SILICEOUS GRANULES IN THE GAMETOPHYTES OF THE RED ALGA PORPHYRA PURPUREA (BANGIOPHYCEAE)

Variations of the different phosphorylated fractions in tissues of starved and fresh plants of Porphyra purpurea, a representative of the Bangiophyceae, over a 72 hour incubation period in pulse‐enriched seawater (15 μM phosphorus and 25 μM nitrogen) were analyzed and compared to those in Chondrus crispus, a representative of the Florideophyceae, considered the more advanced of the two classes of the Rhodophyta. Differences point towards P. purpurea being a much more metabolically active phosphorus “pump” than C. crispus, with a higher phosphorus turnover rate, in which the orthophosphate fraction is predominant and acid‐soluble and acid‐insoluble polyphosphates are not as significant storage pools. Confirmation of the presence of acid‐insoluble polyphosphates, detected by chemical analyses, in the form of cytoplasmic granules was obtained by transmission electron microscopy and energy dispersive X‐ray microanalysis. The granules in P. purpurea were, however, much smaller (20 to 110 nm in diameter) than those in C. crispus (around 1 μm, but some larger than 2 μm in diameter). Larger granules (290 to 310 nm in diameter) were also observed. Their surface was more uniformly electron‐opaque without the reticulated or globular appearance of typical polyphosphate granules. Energy dispersive X‐ray microanalysis demonstrated that they were siliceous granules. To our knowledge, this is the first report in algae of such structures whose occurrence and metabolic role remain enigmatic.

Effects of disturbance on phosphorus turnover and plankton dynamics

In coastal lagoons, one common type of anthropogenic disturbance is opening of the sand barriers that isolate these lagoons from the sea. We investigated how a disturbance caused by an artificial opening of the sand barrier affects phytoplankton and bacterioplankton dynamics and alkaline phosphatase activities (APA) in a Brazilian coastal lagoon. We propose an index of potential phosphorus turnover time (PPTT) calculated as the ratio of total phosphorus (TP) and APA in an attempt to quantify the effect of disturbances on phosphorus recycling within the plankton community. Opening the harrier caused increased phytoplankton biomass, TP concentrations, APA and PPTT, and decreased bacteria to phytoplankton biomass ratio. PPTT is easily calculated and may be used to detect plankton responses to anthropogenic disturbances.

Intracellular phosphorus pool of the cyanobacteriumSpirulina platensis

An intracellular phosphorus pool in a monoculture of the cyanobacteriumSpirulina platensis was assessed using radioactive and nonradioactive phosphorus. The derived dependence of specific growth rate on the intracellular content of mineral phosphorus can be presented in the form of the Droop equation. It was found that the stage of replenishment of the intracellular phosphorus pool may affect the phosphorus turnover estimation in aquatic environments from the results of short-term measurements of phosphorus uptake

Variability of inorganic and organic phosphorus turnover rates in the coastal ocean

Phosphorus is an essential nutrient in pelagic marine ecosystems. Phosphorus cycling in the upper ocean is, however, poorly understood, and few studies have directly investigated the biological utilization of this essential element1,2,3,4. Here, we have determined in situ phosphorus-turnover rates in a coastal marine environment by measuring the activities of two cosmogenic radionuclides (32P and 33P, with half lives of 14.3 and 25.3 days, respectively) in dissolved inorganic, dissolved organic and total particulate phosphorus pools over a seasonal cycle. Phosphorus turnover rates within dissolved and particulate pools are rapid and vary over seasonal timescales, suggesting that low phosphorus concentrations can support relatively high primary production. Furthermore, picoplankton, such as bacteria, appear preferentially to utilize certain dissolved organic phosphorus compounds to obtain other associated nutrients, such as carbon and nitrogen. It seems that the significance of the roles of both dissolved inorganic and organic phosphorus in supporting primary production—and, hence, CO2 uptake and particulate organic carbon export—has been hitherto underestimated.

Utilization of Substitutable Carbon and Phosphorus Sources by the Mixotrophic Chrysophyte Ochromonas Sp

In laboratory experiments, I studied the influences of bacterial density and light on the ingestion and growth rates, pigment contents, and the carbon and phosphorus turnover rates of the mixotrophic flagellate Ochromonas sp. The investigated strain is a bacterivorous flagellate that can enhance its photosynthetic apparatus and grow phototrophically when bacterial densities are low. This was also evident from significantly higher chlorophyll $a$ contents during active photosynthetic growth phases. Moderate phototrophic growth should be possible even if bacteria were absent. Bacterial ingestion rates increased hyperbolically with bacterial density, and there was no difference between light— and dark—adapted cells. Ochromonas released soluble reactive phosphorus (SRP) when growth was predominantly phagotrophic, but it took up SRP when growth was phototrophic. The mixotrophic strategy in Ochromonas appears to be bound up with costs and trade—offs: Ochromonas needs high bacterial densities to reach maximum growth rates, its basic metabolic costs are higher than for obligately phagotrophic flagellates, and its phototrophic growth rates are lower than for obligately phototrophic phytoplankton of comparable size.

Effects of Biomass, Light, and Grazing on Phosphorus Cycling in Stream Periphyton Communities

The influence of periphyton biomass, irradiance, and herbivory by snails on phosphorus turnover in stream periphyton communities was examined over a 15-d experimental period. A 2 × 2 × 2 factorial design was employed with each treatment combination replicated twice. Percent increase in periphyton biomass was greater under: low vs. high initial biomass; high vs. low light levels; and no-snail vs. snail-present conditions. Significant interactions among main effects revealed that the percent increase in biomass in the low initial biomass treatment was greater when snails were absent, whereas the effect of light was greater when snails were present. Phosphorus turnover from the mat was significantly greater under low than high initial biomass levels and snail-present vs. no-snail conditions. Grazing removed periphyton biomass from the substrates, resulting in increased P turnover because of physical and consumptive losses. In the absence of snails, initial biomass level had surprisingly little effect on P turnover. We suspect that biomass accrued rapidly in the absence of snails, thereby blurring the distinction between low and high biomass treatments by day 15. However, in the presence of snails, P turnover rate was significantly lower in communities with high initial biomass. Despite the fact that lower irradiance resulted in significantly lower metabolic rates of periphyton, irradiance had no significant effect on P turnover. These results suggest that internal cycling provides an important source of nutrients in periphyton communities with high biomass and that grazing promotes nutrient turnover in periphyton, regardless of biomass level.

Estimation of phosphorus metabolic rates of Daphnia galeata using a three-compartment model

A compartment model to estimate the different phosphorus metabolic rates in Daphnia galeata is presented. The model has three compartments: gut, metabolic pool and structural pool. Existing two-compartment models used for carbon and phosphorus turnover in Daphnia do not allow estimation of ingestion and egestion rates. We extended existing two-compartment models with one more compartment, the gut, which allowed us to estimate both the ingestion and the egestion rates. Parameters of the model are estimated from a single experiment of feeding unlabelled Daphnia with P-32-labelled Scenedesmus obliquus. Separate experiments with juvenile and adult daphnids were carried out in order to compare their metabolisms. This model permits a reliable estimation of the different metabolic rates of Daphnia in a single experiment and discriminates clearly between animals of different sizes. [KEYWORDS: Scenedesmus-acutus; food; zooplankton; release; assimilation; ingestion; quality; carbon; dependence; nitrogen]

Nitrogen and phosphorus turnover in some benthic marine invertebrates: implications for the use of C:N ratios to assess food quality

The present study was designed to measure the relative turnover of nitrogen and phosphorus during a standard period of metabolism among several co-occurring species of benthic invertebrates: chitons (Poneroplax albida Blainville 1825); albalones (Haliotis roei Gray, 1826); gastropods [Turbo (ninella) torquatus Gmelin, 1791]; ascidians [Herdmania momus (Savigny)]; and sponges (Aplysina sp. and Iotrochata baculifera Ridley, 1884). Five of the six species (collected at Wreck Rock, Western Australia in 1985) exhibited a high turnover of phosphorus (P) relative to nitrogen (N). In contrast to N, P turnover was related to the concentration of P in body tissues. A relatively high demand for P in the diet is required to support the observed rapid turnover of P with respect to N. This observation suggests that the evaluation of potential foods would be better accomplished by the measurement of the C:P or the N:P ratio, rather than the commonly used C:N ratio.

Physiological and community responses of summer plankton to nutrient manipulation in the Gulf of Finland (Baltic Sea) with special reference to phosphorus

Abstract Summer plankton communities from two locations in the central and western Gulf of Finland (Stns LL6 and JML, respectively), characterized by different nutrient dynamics, were manipulated with nitrogen and phosphorus additions in the laboratory. The aim was to study whether these populations would show indices of different phosphorus physiology or community structure. We were especially interested to determine whether the growth of diazotrophic filamentous cyanobacteria could be stimulated by phosphorus additions. No growth of these species was observed with daily addition of nutrients. The most evident population response was that of the small-size fraction organisms ( < 10 µm) in both experiments to N + P additions. In the size fraction > 10 µm the species favored by the nutrient additions were Dictyosphaerium subsolitarium van Goor in the central part and Snowella sp. in the western part of the Gulf. Phosphorus turnover rates measured by 32P-uptake were faster in the control and N-supplemented samples, as well in the exp-LL6 sample with N + P addition. The behaviour of the alkaline phosphatase activity was best explained by the ambient DIN : DIP ratio. The PN : PP ratios in exp-LL6 indicated more phosphorus deficiency than in exp-JML. Our conclusion is that there was difference in both population dynamics and biochemical indices between the central and western sea areas showing more signs of phosphorus deficiency in the central area of the Gulf.

Thermal effects

Thermal effects

The turnover of river-transported iron, phosphorus and organic carbon in the �re estuary, northern Sweden

The turnover of river-transported iron, phosphorus and organic carbon in the �re estuary, northern Sweden

Effect of temperature on carbon, nitrogen and phosphorus turnover by the solitary ascidian Herdmania momus (Savigny)

Abstract The relationship between the C to N to P composition ratio (C:N:P) of three diets and metabolic C:N:P turnover of a solitary ascidian, Herdmania momus (Savigny), was examined after a retention period of 89 days in two temperature regimes. The three diets (particles derived from fresh kelp, aged kelp particles, and phytoplankton) caused significant variation in respiration rates, C and P content of faeces and N stored in tissues. Temperature regime ( ambient= 16.6−19.5°C; heated= 21°C) caused significant variation in phosphate excretion rate, N content of faeces and internal organs, the RQ, and P stored in tissues. There was no interaction between diet and temperature. The individuals which were retained in heated water had significantly higher N turnover with increased temperature was substantiated by a preliminary comparison of metabolic characteristics of H. momus from two latitudes on the Western Australian coast. Environmental temperature can change the turnover of N with respect to P, and thus the relative requirements for these two elements by this marine heterotroph. The metabolic demands for N and P by H. momus are predicted to vary with local climate, with a lower N and higher P demand as latitude increases.

Phosphorus Pool Sizes and Fluxes in the Epilinnnion of a Mesotrophic Lake

A plausible budget for phosphorus fluxes between different size/functional groups was constructed for the early summer epilimnetic plankton of Jacks Lake, Ontario. Consideration of the complex interactions at the base of the food web, particularly the ability of nanoplankton to graze on picoplankton, helped to resolve the question of phosphate uptake by bacteria versus algae. While the concentration of phosphate we estimated with column chromatography was lower than chemical detection limits, it was still too high to reconcile with our other measurements and we conclude that actual phosphate concentrations may be less than 1 nM. Some microplankton were shown to liberate dissolved phosphate and organic phosphorus when lake water is filtered. The phosphorus content and turnover of major ciliate, rotifer, and crustacean zooplankton were determined and the importance of these compartments as phosphorus sources and sinks was included in the epilimnetic model.

Mineralization of phosphorus by faecal phosphatases of some earthworms of Indian tropics

The casts of earthworms contain greater amounts of extractable inorganic phosphate than underlying soils. Casts contain higher phosphatase activity than that occurs in undigested soil, which increases the inorganic phosphorus released by mineralization. Of the 4 species compared,Perionyx excavatus showed a higher faecal phosphatase activity. Composition of casts vary with species. pH increases and nutrients accumulate in worm-activated soils. Based on the data on surface cast production, it is estimated that grasslands around Bangalore show a phosphorus turnover of about 55 kg ha−1 y−1, and the woodlands, 38 kg ha−1 y−1.

Biogeochemical cycling constraints on stream ecosystem recovery

In systems where production is limited by the availability of a nutrient, nutrient input to and recycling within the system is related to the resilience, or speed of recovery, of a system to its steady state following a disturbance. In particular, it is shown that the return timeT s of the system to steady state, or the inverse of the resilience, is approximately equal to the mean turnover time of the limiting nutrient in the system. From this relationship, it is possible to understand and predict how various properties of food webs and their environments affect resilience. These properties include nutrient input rate, loss rate, size of the detritus compartment, and trophic structure. The effects of these properties on resilience are described by using simple mathematical models. To test model predictions, experimental studies of the response of periphyton-dominated stream ecosystems to disturbance are being conducted on a set of laboratory streams in which nutrient inputs and grazing intensity are regulated at different levels. In streams without snail grazers (low-grazed streams), 90% recirculation of stream water to reduce nutrient inputs resulted in longer turnover times (T r ) of phosphorus within the stream compared with once-through flow. However, in streams with snail grazers (high-grazed streams), there were no differences in phosphorus turnover time between once-through and partially recirculated treatments. Results on the rate of recovery of periphyton from a flood/scour disturbance to each stream partially support the model prediction of a positive relationship between ecosystem return time (T s ) and nutrient turnover time (T r ) within the streams.