Increased Phosphorus Availability Research Articles

Synthesis and evaluation of a new class of stabilized nano-chlorapatite for Pb immobilization in sediment

During the past years, efforts have been made to deal with the Pb contaminated sediment in Xiawangang River in Hunan province, China, but it remains a serious problem since the smelting pollutants were accumulated. According to previous studies, phosphate showed an effective ability to transfer labile Pb to pyromorphite (Pb5(PO4)3X, X=F, Cl, Br, OH) but its application was limited by its solubility and deliverability. Hence a new class of nano-chlorapatite was synthesized by using sodium dodecyl sulfate (SDS) as a stabilizer and characterized by TEM, FESEM, DLS, FTIR, and EDAX. Results demonstrated that the SDS stabilized nano-chlorapatite (SDS-nClAP) was in spherical or spheroidal shape with a hydrodynamic diameter of 40.4nm. Experimental data suggested that SDS-nClAP was effective in transforming labile Pb to stable fraction with a maximum increase of 38.3%, also the reduction of TCLP-leachable Pb from 0.30 to 0mg/L after 45-d treatment. The increase of available phosphorus in both SDS-nClAP and ClAP treated sediment samples verified dissolution-precipitation mechanism involved in Pb immobilization. Additionally, the increment of organic matter in 10:1 treated samples was approximately 5-fold than that in 2:1 treated samples, which revealed that the micro-organisms may play an important role in it.

Cable Bacteria Control Iron-Phosphorus Dynamics in Sediments of a Coastal Hypoxic Basin.

Phosphorus is an essential nutrient for life. The release of phosphorus from sediments is critical in sustaining phytoplankton growth in many aquatic systems and is pivotal to eutrophication and the development of bottom water hypoxia. Conventionally, sediment phosphorus release is thought to be controlled by changes in iron oxide reduction driven by variations in external environmental factors, such as organic matter input and bottom water oxygen. Here, we show that internal shifts in microbial communities, and specifically the population dynamics of cable bacteria, can also induce strong seasonality in sedimentary iron-phosphorus dynamics. Field observations in a seasonally hypoxic coastal basin demonstrate that the long-range electrogenic metabolism of cable bacteria leads to a dissolution of iron sulfides in winter and spring. Subsequent oxidation of the mobilized ferrous iron with manganese oxides results in a large stock of iron-oxide-bound phosphorus below the oxic zone. In summer, when bottom water hypoxia develops and cable bacteria are undetectable, the phosphorus associated with these iron oxides is released, strongly increasing phosphorus availability in the water column. Future research should elucidate whether formation of iron-oxide-bound phosphorus driven by cable bacteria, as observed in this study, contributes to the seasonality in iron-phosphorus cycling in aquatic sediments worldwide.

Phytase-producing Bacillus sp. inoculation increases phosphorus availability in cattle manure

Organic wastes rich in phosphorus (P) are considered an alternative to decrease the dependence on chemical P fertilization in crops and pastures. Microbial inoculants are being studied as a tool to increase plant P availability in organic wastes. In this study, we explore the effect of inoculation with Bacillus sp. MQH-19 (a native phytase-producing bacterium) on the release of inorganic phosphorus (Pi) in cattle manure with low available P but a high total P content. Bacteria inoculation resulted in a higher release of Pi (8% in NaHCU3 and 13% in NaOH-EDTA extracts) compared with that of uninoculated manure (0.7% in NaHCU3 and 0.1% in NaOH-EDTA extracts). However, a greater amount of Pi was released in inoculated manure supplemented with phytate (47% in NaHCU3 and 117% in NaOH-EDTA extracts) compared with that of uninoculated manure supplemented with phytate (30% in NaHCU3 and 15% in NaOH-EDTA extracts). In addition, the use of denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR) revealed that the bacterial community structure in manure was affected by inoculation and that the prevalence of Bacillus sp. MQH-19 decreased during incubation (6 days). This study demonstrates that Pi availability in cattle manure can be increased by phytase-producing bacteria inoculation. Phytase-producing bacteria inoculation might represent an attractive strategy to increase P availability in agricultural wastes, which are used as organic fertilizers in crops and pastures.

Comparative assessment of microbial enzyme activity with compost and sewage sludge amendment

Changes in soil microbial activities were investigated to examine the effect of aerobically digested sewage sludge (SS) and compared with compost under incubation conditions over 63 days. Sandy soil was amended with 0.25, 0.5, 1.0 and 1.5 % w/w of compost and sewage sludge. Enzyme activity (dehydrogenase, alkaline phosphatase, acid phosphatase, phytase and urease) were examined at an interval of 3, 7, 14, 21, 28, 42 and 63 days. At the end of the experiment the change in organic carbon, nitrogen, potassium and phosphorus was also recorded.Results indicated that enzyme activities were substantially enhanced in presence of both amendments for first few days and the higher increases were measured at 1.5% of compost and sewage sludge amendment. Then an overall decrease in enzyme activity was recorded. Both the amendments also significantly increased the organic carbon, nitrogen and potassium of the soil while increase in available phosphorus was only recorded in treatment receiving compost. The present experiment indicated that addition of compost and sewage sludge have positive effect on soil microbial activity and can be safely used as soil amendment without having any adverse effect. Though, a previous examination of sewage sludge to be used must be made for heavy metals and pathogens.

Phosphate solubilization and promotion of maize growth by Penicillium oxalicum P4 and Aspergillus niger P85 in a calcareous soil.

Alternative tactics for improving phosphorus nutrition in crop production are needed in China and elsewhere, as the overapplication of phosphatic fertilizers can adversely impact agricultural sustainability. Penicillium oxalicum P4 and Aspergillus niger P85 were isolated from a calcareous soil in China that had been exposed to excessive application of phosphatic fertilizer for decades. Each isolate excreted a number of organic acids into, acidified, and solubilized phosphorus in a synthetic broth containing insoluble tricalcium phosphate or rock phosphate. Isolate P4, applied as a seed treatment, increased maize fresh mass per plant when rock phosphate was added to the calcareous soil in greenhouse pot studies. Isolate P85 did not increase maize fresh mass per plant but did significantly increase total phosphorus per plant when rock phosphate was added. Significant increases in 7 and 4 organic acids were detected in soil in association with isolates P4 and P85, respectively, relative to the soil-only control. The quantity and (or) number of organic acids produced by these isolates increased when rock phosphate was added to the soil. Both isolates also significantly increased available phosphorus in soil in the presence of added rock phosphate and effectively colonized the maize rhizosphere. Studies reported here indicate that isolate P4 is adapted to and capable of promoting maize growth in a calcareous soil. Plant-growth promotion by this isolate is likely due, at least in part, to increased phosphorus availability resulting from the excretion of organic acids into, and the resulting acidification of, this soil.

Lignite amendment has limited impacts on soil microbial communities and mineral nitrogen availability

The application of lignite (brown coal) as a soil amendment has been shown to provide a number of benefits under certain circumstances, including increased cation exchange capacity, increased phosphorus availability and reduced heavy metal availability. However, there is also evidence that some lignites can have negative impacts on soil biology, with very little known about how lignite affects soil nitrogen (N) dynamics and microbial activity. We conducted a microcosm experiment to assess the influence of lignite from Victoria, Australia, and the same lignite in combination with urea, on soil microbial community composition, biomass, activity and nitrogen cycling. Extractable NO3− and NH4+, microbial biomass, phospholipid fatty acids (PLFAs), microbial respiration and enzymes activities were measured over a 120-day incubation period. The lignite had minor effects on inorganic N concentration in different soil types with or without urea application. Lignite reduced the total CO2 emissions from soil over the incubation period, primarily by inhibiting respiration shortly after application. Changes to total microbial biomass were negligible, but shifts in the soil microbial community caused by lignite or urea application were detected up to 60 days after treatment. During this time, periodic increases in peroxidase and phenol oxidase activities in lignite-treated soils were also observed, but changes in dehydrogenase activities were only apparent in urea-treated soils. Our results indicate that raw Victorian lignite has only a minor, temporary impact on soil microbial activity, community composition and N-cycling and does not increase CO2 emissions over a short time period of investigation. More research is now needed to determine potential longer-term impacts at the field scale.

The effect of psychrotrophic bacteria isolated from the root zone of winter wheat on selected biotic and abiotic factors

Abstract The roots of winter wheat plants, cv. Mikon, grown in 45-year monoculture, were analysed in the study. Twenty-two bacterial isolates obtained from the rhizosphere, rhizoplane, and endorhizosphere that were capable of growth at 8°C and at 28°C, were selected for further analysis. The isolated psychrotrophs accounted for 25% of all bacteria present in the wheat rhizosphere and capable of growth at 8°C. Psychrotrophic bacteria were analysed at a temperature of 10°C and 28°C to determine their ability to inhibit the growth of pathogenic fungi, solubilise mineral phosphates, and to determine their ability to degrade chitin and cellulose. Similarity between the isolates was determined by Enterobacterial Repetitive Intergenic Consensus – Polymerase Chain Reaction (ERIC-PCR) and Random Amplification of Polymorphic DNA – Polymerase Chain Reaction (RAPD-PCR). The majority of isolated psychrotrophs inhibited the growth of pathogenic fungi and solubilised mineral phosphates at both incubation temperatures. Psychrotrophic bacteria exerted a two-fold stronger inhibitory effect on mycelial growth at 10°C than at 28°C. The growth of Fusarium culmorum and F. oxysporum was inhibited to the highest extent at 10°C and at 28°C, respectively. Phosphate solubilisation rates were higher at 28°C, particularly in the rhizosphere. Regardless of temperature, the bacteria exhibited low chitin-degrading potential, and none of the isolates was capable of degrading cellulose. A high similarity between the selected psychrotrophs was revealed by ERIC-PCR and RAPD- -PCR analyses. Based on RAPD-PCR, the analysed population was divided into a group of isolates obtained from the rhizosphere, and two groups comprising representatives of both the rhizoplane and the endorhizosphere. Due to their ability to grow over a wide temperature range and increase phosphorus availability to plants, and their antagonism against pathogens, psychrotrophic bacteria can be used to improve the growth and yield of cereal crops.

Role of plant growth promoting rhizobacteria in modulating the efficiency of poultry litter composting with rock phosphate and its effect on growth and yield of wheat.

The present study was aimed to evaluate the role of Plant Growth Promoting Rhizobacteria (PGPR) in P solubilisation from rock phosphate through composting with poultry litter, and further to study the effects of prepared enriched composts on growth, yield, and phosphorus uptake of wheat crop. Various phosphorus-enriched composts were prepared from rock phosphate and poultry litter (1:10) with and without inoculation of plant growth promoting rhizobacterias (Pseudomonas sp. and Proteus sp.). Results showed that the rock-phosphate-added poultry litter had higher total phosphorus, available (Mehlic-3 extracted) phosphorus, microbial biomass (carbon and phosphorus), and lower total organic carbon, total nitrogen, and carbon/nitrogen ratio over poultry litter alone. Inoculation of Pseudomonas sp. with rock phosphate-added poultry litter showed maximum increase in available phosphorus (41% of total phosphorus) followed by Proteus sp. inoculation (30% of total phosphorus) over uninoculated treatment (23% of total phosphorus) on the 120th day of composting. Microbial biomass (carbon and phosphorus) increased up to Day 45 and tended to decrease till the 120th day of composting, irrespective of the treatments. However, in pot experiments, wheat seeds receiving inoculation with plant growth promoting rhizobacterias, subsequently treated with rock phosphate-enriched compost proved highly stimulatory to plant height, phosphorus uptake, grain yield, and seed phosphorus content over uninoculated untreated control. The plant growth promoting rhizobacterias inoculation can be a sustainable source releasing phosphorus from low grade rock phosphate through composting and application of rock phosphate-enriched compost can be an alternative to chemical fertilisers for better crop production.

Phytoplankton and Macrophyte Response to Increased Phosphorus Availability Enhanced by Rainfall Quantity

Rainfall patterns are becoming more extreme in the northeastern US and are expected to intensify with an increase in extreme precipitation events and a greater frequency of short-term drought. In Northwest Bay, an undeveloped, primarily forested sub-watershed of Lake George, NY, stream discharge and phosphorus loading in 2006 exceeded that of 2007 by more than 3-fold due to unusually heavy rainfall in 2006 and below average rainfall in 2007. The additional phosphorus loading to the open water positively influenced chlorophyll concentrations in 2006, while porewater soluble phosphorus significantly correlated to precipitation in both 2006 and 2007. The elevated porewater concentrations in early summer of 2006 provided a nutrient advantage that resulted in tissue phosphorus in 3 macrophyte species to more than double while no change in nitrogen or carbon was detected. It is believed that the heavy late spring/early summer rainfall in 2006 saturated soils creating additional stormwater run-off and increasing groundwater seepage that supplied ample phosphorus resulting in enhanced phytoplankton biomass and macrophyte uptake of phosphorus.

Available content, surface runoff and leaching of phosphorus forms in a typic hapludalf treated with organic and mineral nutrient sources

The application of animal manure to soil can increase phosphorus availability to plants and enhance transfer of the nutrient solution drained from the soil surface or leached into the soil profile. The aim of this study was to evaluate the effect of successive applications of organic and mineral nutrient sources on the available content, surface runoff and leaching of P forms in a Typic Hapludalf in no-tillage systems. Experiment 1 was set up in 2004 in the experimental area of UFSM, in Santa Maria (RS, Brazil). The treatments consisted of: control (without nutrient application) and application of pig slurry (PS), pig deep-litter (PL), cattle slurry (CS), and mineral fertilizers (NPK). The rates were determined to meet the N crop requirements of no-tillage black oat and maize, grown in the 2010/2011 growing season. The soil solution was collected after each event (rain + runoff or leaching) and the soluble, particulate and total P contents were measured. In November 2008, soil was collected in 2 cm intervals to a depth of 20 cm, in 5 cm intervals to a depth of 40 cm, and in 10 cm intervals to a depth of 70 cm. The soil was dried and ground, and P determined after extraction by anion exchange resin (AER). In experiment 2, samples collected from the Typic Hapludalf near experiment 1 were incubated for 20, 35, 58, 73 and 123 days after applying the following treatments: soil, soil + PS, soil + PL, soil + CS and soil + NPK. Thereafter, the soil was sampled and P was analyzed by AER. The applications of nutrient sources over the years led to an increase in available P and its migration in the soil profile. This led to P transfer via surface runoff and leaching, with the largest transfer being observed in PS and PL treatments, in which most P was applied. The soil available P and P transfer via surface runoff were correlated with the amounts applied, regardless of the P source. However, P transfer by leaching was not correlated with the applied nutrient amount, but rather with the solution amount leached in the soil profile.

The involvement of expansins in responses to phosphorus availability in wheat, and its potentials in improving phosphorus efficiency of plants

Phosphorus (P) is a critical macronutrient required for numerous functions in plants and is one of the limiting factors for plant growth. Phosphate availability has a strong effect on root system architecture. Expansins are encoded by a superfamily of genes that are organized into four families, and growing evidence has demonstrated that expansins are involved in almost all aspects of plant development, especially root development. In the current study, we demonstrate that expansins may be involved in increasing phosphorus availability by regulating the growth and development of plant roots. Multiple expansins (five α- and nine β-expansin genes) were up- or down-regulated in response to phosphorus and showed different expression patterns in wheat. Meanwhile, the expression level of TaEXPB23 was up-regulated at excess-P condition, suggesting the involvement of TaEXPB23 in phosphorus adaptability. Overexpression of the TaEXPB23 resulted in improved phenotypes, particularly improved root system architecture, as indicated by the increased number of lateral roots in transgenic tobacco plants under excess-P and low-P conditions. Thus, these transgenic plants maintained better photosynthetic gas exchange ability than the control under both P-sufficient and P-deficient conditions.

Mixed plantations can promote microbial integration and soil nitrate increases with changes in the N cycling genes

Mixed-species plantations of Eucalyptus and legume trees can symbiotically fix nitrogen and potentially improve the soil quality and biomass productivity compared with a conventional Eucalyptus monoculture. In this study, we evaluated changes in the structure and abundance of different microbial groups and nitrogen cycle genes in mixed and pure plantations of Acacia mangium and Eucalyptus urograndis in an experimental area in southeastern Brazil. Soil samples (0–10 cm) collected in two- and three-year-old stands were submitted to chemical characterization and molecular analyses using DGGE and real time-PCR for bacteria (16S rRNA), fungi (ITS), and genes involved in nitrogen cycling (nirK, amoA, nifH). The mixed plantation did not significantly change general soil fertility or total soil C and N content compared with the Eucalyptus monoculture. However, there was a significant increase in available phosphorus and soil nitrate content in both the A. mangium and mixed-species treatments. The multivariate ordination of the DGGE profiles of bacteria, fungi and archaea groups showed distinct community structures in each treatment. Significant differences in the abundance of copies of the target genes were found for fungi, with higher values in the Eucalyptus followed by the mixed and A. mangium plantations. The analysis of nitrogen cycle genes showed no clear difference in the communities of nitrogen fixing bacteria or nitrifying archaea among treatments. The nitrification activity was dominated by archaea because it was not possible to detect the presence of bacterial nitrifiers; the denitrifier community had a distinct profile in the Eucalyptus monoculture. The abundance of archaeal amoA and nirK genes suggests that the A. mangium treatment had higher nitrification and lower denitrification than the other treatments, which would explain the higher soil nitrate levels found in pure A. mangium treatments. Our data suggest that mixed plantations of E. urograndis and A. mangium result in a distinct microbial community relative to the respective monocultures with positive effects on soil phosphorus and nitrate content, which potentially reduces the need for anthropogenic fertilization.

Effects of microbial inoculations on soil chemical, biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P2O5:K2O (NPK) rate (50:25:50 kg ha−1) significantly increased soil available nitrogen (142.81 kg ha−1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha−1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g−1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g−1 soil h−1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g−1 soil) and β-glucosidase activity (48.82 μg PNP g−1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g−1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.

Biological Stoichiometry in Tumor Micro-environments

Tumors can be viewed as evolving ecological systems, in which heterogeneous populations of cancer cells compete with each other and somatic cells for space and nutrients within the ecosystem of the human body. According to the growth rate hypothesis (GRH), increased phosphorus availability in an ecosystem, such as the tumor micro-environment, may promote selection within the tumor for a more proliferative and thus potentially more malignant phenotype. The applicability of the GRH to tumor growth is evaluated using a mathematical model, which suggests that limiting phosphorus availability might promote intercellular competition within a tumor, and thereby delay disease progression. It is also shown that a tumor can respond differently to changes in its micro-environment depending on the initial distribution of clones within the tumor, regardless of its initial size. This suggests that composition of the tumor as a whole needs to be evaluated in order to maximize the efficacy of therapy.

Effects of superficial liming and silicate application on soil fertility and crop yield under rotation

Soil acidity and low natural fertility are the main problems for grain production in Brazilian ‘cerrado’. Although lime has been the most applied source for soil correction, silicate may be an alternative material due to its lower solubility and Si supply, which is beneficial to several crops. This work aimed to evaluate the efficiency of superficial liming and calcium/magnesium silicate application on soil chemical attributes, plant nutrition, yield components and final yield of a soybean/white oat/maize/bean rotation under no-tillage system in a dry-winter region. The experiment was conducted under no tillage system in a deep acid clayey Rhodic Hapludox, Botucatu-SP, Brazil. The design was the completely randomized block with sixteen replications. Treatments consisted of two sources for soil acidity correction (dolomitic lime: ECC=90%, CaO=36% and MgO=12%; calcium/magnesium silicate: ECC=80%, CaO=34%, MgO=10% and SiO2=22%) applied in October 2006 to raise base saturation up to 70% and a control, with no soil correction. Soybean and white oat were sown in 2006/2007 as the main crop and off-season, respectively. Maize and bean were cropped in the next year (2007/2008). Products from silicate dissociation reach deeper soil layers after 18months from the application, compared to liming. Additionally, silicate is more efficient than lime to increasing phosphorus availability and reducing toxic aluminum. Such benefits in soil chemical attributes were only evidenced during bean cropping, when grain yield was higher after silicate application comparatively to liming. Both correction sources were improved mineral nutrition of all the other crops, mainly Ca and Mg levels and agronomical characteristics, reflecting in higher yield.

Influence of phosphocompost application on phosphorus availability and uptake by maize grown in red soil of Ishigaki Island, Japan

Phospho compost application is important with respect to soil fertility and plant nutrition. Therefore, the objective was to evaluate the influence of phospho compost application on P availability and uptake by maize in red soil. The phosphorus applied in the form of phospho compost, as compare to rock phosphate and super phosphate at a rate of 50 and 100 mg P2O5 Kg-1 soil. The application was done as spot and mix application. Results indicate that, spot application of 100 mg P2O5 kg-1 soil as phospho compost (b) registered significantly higher P uptake (2.1 and 5.31 mg·pot-1) and available soil P (19.1 and 21.0 mg·kg-1) as compare to Rock Phosphate alone (0.60 and 0.97 mg·pot-1) and (5.6 and 6.0 mg·kg-1) at 30 and 60 day after sowing, respectively. The probable chelating effect from phospho composting increased the phosphorus use efficiency and resulted into higher relative agronomic efficiency in phospho compost (b) spot application (40%) over mix application (15%). The dry matter yield had positive and significant correlation with available P in soil and P uptake by maize plants at 30 and 60 day after sowing. Results concluded that phospho compost enriched with FYM was most effective in increasing phosphorus availability in red soil and increasing dry matter yield of maize plants.

Massive uprooting ofLittorella uniflora(L.) Asch. during a storm event and its relation to sediment and plant characteristics

During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), growing on sediments with a high organic matter content. Normally, uprooting of the relative buoyant L.uniflora is prevented by an extensive root system, expressed as a high R:S. This was studied by sampling floating and still rooted L.uniflora plants, as well as sediment and sediment pore water, along a gradient of increasing sediment organic matter content. Increasing organic matter content was related to increasing L.uniflora shoot biomass and consequently decreasing R:S. Furthermore, the results indicated that uprooting indeed occurred in plants growing on very organic sediments and was related to a low R:S. The increased shoot biomass on more organic sediments could be related to increased sediment pore water total inorganic carbon (TIC; mainly CO2 ) availability. Additionally, increased phosphorus availability could also have played a role. The disappearance of L.uniflora might lead to higher nutrient availability in the sediments. It is suggested that this could eventually promote the expansion of faster-growing macrophytes.

Nitrogen, phosphorus and light effects on growth and allocation of biomass and nutrients in wild rice

Separating plastic from ontogenetic and growth-limiting responses of plants to changes in resource availability can be challenging because there are a total of eight combinations of these three types of responses. These can, however, be uniquely distinguished on plots of root:shoot ratios against total biomass through time. We used this approach to separate ontogenetic, plastic, and growth-limiting responses of wild rice (Zizania palustris L.) to changes in nitrogen, phosphorus, and light availabilities. Relative growth rate was limited primarily by nitrogen but responded to increased light and phosphorus after nitrogen limitations were alleviated. Nitrogen addition increased relative growth rate because it simultaneously increased unit leaf rate, specific leaf area, and leaf weight ratio. Increased light did not change relative growth rate because decreased specific leaf area and leaf weight ratio compensated the increased unit leaf rate. Phosphorus did not change either relative growth rate or its underlying components. Plants responded ontogenetically to increased nitrogen and light availabilities by accelerating their developmental rate, and plastically by decreasing or increasing their root:shoot ratios, respectively. Plants did not respond either ontogenetically or plastically to increased phosphorus availability. Ontogenetic changes in growth can be separated from plastic and growth-limiting responses by plotting root:shoot ratio against total biomass in the context of the eight possible responses identified above, and also by examining how the underlying components of relative growth rate respond.

Modeling an Improvement in Phosphorus Utilization in Tropical Agriculture

Studies of Terra Preta soils have generated interest in recreating their fertility elsewhere. Much of the research has focused on soil amendment charcoal (“biochar”). Terra Preta also contains bone fragments, producing a high concentration of phosphorus. Some forecast worldwide declines in phosphorus supplies, and better agricultural system management is required to improve phosphorus use efficiency. A conceptual model is offered to consider the influence of charcoal on bioavailability of phosphorus. The model describes a system where improvements in the chemical and biological condition of the soil result in increased phosphorus availability and cycling. Mechanisms of phosphorus/charcoal interaction are considered, and an assessment is made of the potential impact on African subsistence agriculture from the incorporation of biogenic, allogenic phosphorus through biochar.

Seasonality of Aulacoseira ambigua abundance and filament length: biogeochemical implications

Aulacoseira ambigua abundance and filament length were measured weekly during spring and autumn bloom periods in Trout Lake, Wisconsin, USA. In addition, several chemical and biological variables thought to influ- ence A. ambigua growth were assessed. Results of the field-based observations were complimented with controlled laboratory experiments to evaluate the effects of phosphorus availability on A. ambigua growth. Relative to the au- tumn bloom period, A. ambigua colonies were generally larger and more abundant in spring prior to the termination of the bloom in June. Chlorophyll-a concentrations indicated that other phytoplankton were also more abundant dur- ing the spring bloom. Batch culture experiments indicated that increased phosphorus availability during the spring bloom contributed to the seasonal increase in A. ambigua filament length and abundance. Increase in A. ambigua fila- ment length in response to increased phosphorus availability is discussed as a mechanism that may increase nutrient removal through sedimentation and subsequently decrease the efficiency of nutrient regeneration in higher productiv- ity lakes.