Accumulation Of Po Research Articles

Conversion of pure Chinese fir plantation to multi-layered mixed plantation increases organic phosphorus accumulation and transformation within soil aggregates

Evaluation of the impacts of environmental factors and microbial communities on soil organic phosphorus (Po) availability is needed to clarify P cycling and regulate plantations productivity. However, the effects on Po accumulation and transformation of converting pure Chinese fir plantation to multi-layered mixed plantation and their regulatory mechanisms remain unclear. The aim of this study was to examine the impacts of the transformation of pure stand of Chinese fir (Cunninghamia lanceolata; PP) to mixed plantation with multiple tree species (C. lanceolata, Castanopsis hystrix, and Michelia hedyosperma; MP) on Po accumulation and transformation within topsoil (0–10 cm) aggregates in subtropical China. Our results showed that the soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH4+-N), and available phosphorus (AP), as well as the carbon‑nitrogen ratio of soil (C/Nsoil) and carbon‑phosphorus ratio of soil (C/Psoil) were significantly higher (P < 0.05) of all aggregates in MP than those in PP. The quantities of soil microbial biomass C, N, P (MBC, MBN, and MBP) in all different aggregates were significantly greater (P < 0.05) in MP than in PP. The phospholipid fatty acid contents related to bacteria, fungi, arbuscular mycorrhizal fungi (AMF), and actinomycetes were significantly greater in all aggregate classes (P < 0.05) in MP relative to PP. The activities of all tested C, N, and P hydrolytic enzymes, as well as labile organic P, moderately labile organic P, moderately resistant organic P, and highly resistant organic P contents, were significantly higher of most aggregate size classes in MP. Finally, redundancy analysis (RDA) suggested that Po fractions were primarily affected by the NH4+-N, litterfall biomass (LF), carbon‑nitrogen ratio of litter (C/Nlitter), SOC and fine root biomass (FR). Our findings suggest that converting pure Chinese fir plantations into multi-layered mixed plantations may represent an effective management strategy for promoting organic P accumulation and transformation by regulating soil and microbial properties in degraded soils of Chinese fir plantations.

Legacy phosphorus in Alabama Hartsells soil after long-term amendment with broiler litter.

Numerous studies have investigated effects of long-term manure application on total phosphorus (P) and inorganic P (Pi ), but few have evaluated soil organic P (Po ). Little is known about crop management effects on Po in soils with varying minerology. In this study, sequential fractionation was used to characterize specific P forms after 25 years of broiler litter (BL) or ammonium nitrate (Con) applications to an Alabama Hartsells soil. Crops (corn [Zea mays L.], soybean [GlycineWilld.], and corn or soybean with a wheat [Triticum aestivum L.] cover crop) were under conventional tillage (CT) or no-tillage (NT). Regardless of crop, tillage, or fertilizer type, the proportion of extractable Pi was relatively stable at 21%-49% at 0-5cm and 25%-45% at 5-10cm. Extractable Pi ranged from 0.69 to 2.4mg g-1 . BL increased total extractable Pi (p≤0.001) at 0-5cm and 5-10cm. Total extractable P was influenced at 0-5cm (p≤0.006) by both tillage and fertilization type, but not at 5-10cm or at either depth in soybean plots. Long-term BL application increased total extractable soil P at 0-5cm. In corn systems, CT did not reduce P loading to topsoil or result in P leaching to lower soil depths, compared to NT. Soybean and soybean-wheat reduced P loading in BL plots, compared to corn and corn-wheat. Soil Po was classed in the order of monoesters >phytate and polyphosphates, where most was extractable with NaOH. BL increased extractable Po in all fractions. Care should be taken when applying BL to highly weathered soils to avoid legacy Po accumulation. Soybean rotations and cover crops could help remediate P-laden soils after repeated BL application.

Microorganisms drive stabilization and accumulation of organic phosphorus: An incubation experiment

At the earliest stage of pedogenesis, microorganisms are the main biological drivers of nutrient transformation and mobilization from rock minerals. However, this driving process is not yet well understood despite its importance for the formation and fertility of soil. The aim of this study was to determine the microbial accumulation of organic phosphorus (Po) and microbial release of bioavailable phosphorus (bio-P) from rock minerals and to analyse which factors control these processes. We hypothesized that microorganisms contribute to stabilization and accumulation of Po. For this purpose, we carried out a series of incubation experiments with model soils (with soil Po removed) and soil extracts of natural soil from the earliest stage of pedogenesis in the newest retreat area of the Hailuogou glacier. A modified Hedley fractionation method was used to characterize the P forms in soils. Microbial synthesis of Po was clearly observed in this study. In view of the fact that carbon (C) and nitrogen (N) are the main energy and material sources of microorganisms and that their stoichiometry plays an important role in microbial metabolism, we hypothesized that the C and N (ratio and level) play a regulatory role in microbial transformation of P. Therefore, the different C/N gradients were constructed in our incubation experiments. Results showed addition of C and N resulted in an accumulation of stable Po and decrease in pH in soils. These results suggest that not all microbial biomass P is easily degraded. Along two C/N ratio gradients (same ratio but keeping C vs N constant), opposite patterns of total Po (TPo) changes was observed. Opposite patterns were also observed for bio-P along the two C/N ratio gradients. Regardless of the C/N ratio, high CN additions always led to lower TPo accumulations, higher bio-P releases and higher phosphatase activity compared to low CN additions. We conclude that microbial synthesis of Po contributed to the P fractions in soil stable residual pools and that microbial release of bioavailable P was driven by two modes (i.e., N-driven mode and C-driven mode). Our study highlights that microorganisms drive the accumulation of soil Po during the earliest stage of pedogenesis in our study area.

Mixture of N2-fixing tree species promotes organic phosphorus accumulation and transformation in topsoil aggregates in a degraded karst region of subtropical China

Many studies have shown that introducing N2-fixing tree species into plantations can increase soil nitrogen (N) availability, via biological N2 fixation and faster N cycling. However, the effects and regulatory mechanisms of N2-fixing tree species in planting single species vs a combination of two species on phosphorus (P) accumulation and transformation in degraded karst soils remain poorly understood and appear site-dependent. This study aimed to determine the effects of introducing N2-fixing tree species (via single species vs a combination of two species) into a degraded karst region on organic phosphorus (Po) accumulation and transformation in topsoil aggregates. A comparative experiment was performed involving 8-year-old pure plantations of Dalbergia odorifera (PD) and Acrocarpus fraxinifolius (PA), a mixed plantation of Dalbergia odorifera and Acrocarpus fraxinifolius (MP), and an adjacent natural weed field (no trees, CK) in Mashan, Guangxi, subtropical China. The results showed that the contents of soil organic carbon (SOC), nitrate nitrogen (NO3−-N), available phosphorus (AP) and C:N ratios in bulk soil and aggregates, increased significantly (P < 0.05) in MP compared to CK. The levels of soil microbial biomass N (MBN) and microbial biomass P (MBP) in bulk and aggregate soils increased significantly (P < 0.05), except for micro-aggregates (<0.25 mm) in MP samples. In contrast, no significant differences of MBN or MBP were found among PD, PA and CK plots in bulk and most aggregate soils. The phospholipid fatty acid (PLFA) contents of all microbes, bacteria, fungi, arbuscular mycorrhizal (AM) fungi and actinomycetes were also significantly higher (P < 0.05) in MP than those in CK and PD in bulk and most aggregate soils. Labile Po and highly resistant Po, and the activities of all tested N and P hydrolytic enzymes, improved in bulk soil and most aggregate size classes in all forest types, especially in MP samples. Finally, redundancy analysis (RDA) indicated that Po fractions were primarily driven by alkaline phosphatase (ALP), MBN and AM. Our findings suggest that introducing N2-fixing tree species (especially MP) may be an effective method for increasing N availability and AM colonization of roots, and thereby promoting Po accumulation and transformation in degraded karst regions of southwest China.

Organic phosphorus forms in a tropical sandy soil after application of organic residues of different quality

The addition of organic materials can improve soil fertility and phosphorus availability in agricultural soils. However, knowledge of organic P (Po) forms in soils with the incorporation of different quality residues is limited. This study investigated Po forms and determined the relationship between Po and soil properties in tropical sandy soils after application of local organic residues of different qualities, including groundnut stover (GN), tamarind leaf litter (TM), dipterocarp leaf litter (DP), and rice straw (RS). The Po forms were determined using a sequential extraction procedure and 31P nuclear magnetic resonance (NMR) spectroscopy. Addition of residues, regardless of quality, had little effect on total Po accumulation, but it affected soil Po forms. Labile Po was a dominant form after incorporating high-quality residue (high nitrogen, low lignin, and low polyphenols) (e.g., GN), whereas nonlabile humic-Po and residual Po were dominant forms in soils treated with lower-quality residue with low N, high lignin, and high polyphenols (e.g., TM, DP, and RS). Using 31P NMR spectroscopy, orthophosphate and phosphate monoester (mono-P) were the major forms of inorganic P and organic P in all residue-treated soils, respectively. High-quality residue incorporation increased diester, DNA, and teichoic acid. The results showed that phosphonate occurred in GN soil because of acidic conditions occurring when GN was applied. The Po forms in lower-quality residue additions were dominated by mono-P because these residues had elevated contents of lignin and polyphenols, which has the potential to produce humic substances that form complexes with soil minerals. Furthermore, the nonlabile Po had a positive association with available P in tropical sandy soils.

Lime-Induced pH Elevation Influences Phosphorus Biochemical Processes and Dynamics in the Rhizosphere of Lupinus polyphyllus and Lupinus angustifolius

The biochemical drivers of phosphorus (P) availability and cycling are sensitive to changes in soil pH. However, reports of lime-induced pH modification effects on P availability are (1) inconsistent, (2) focused mainly on chemical changes, and (3) often limited to the bulk soil. Using lupin as an indicator species, we aimed to evaluate the effects of lime-induced soil pH change, from 5.3 to 6.0, on biochemical processes responsible for P mobilization and dynamics in the rhizosphere of two different lupin species. Indicator species, blue lupin (Lupinus angustifolius) and Russell lupin (Lupinus polyphyllus), were grown in a P-deficient acid grassland soil without P inputs for 11 weeks in a glasshouse. The rhizosphere soils were analyzed for enzyme activity, microbial P, and carboxylates. Both bulk and rhizosphere soils were analyzed for P fractions, exchangeable aluminum (Al), and pH. Plant yields and shoot P uptake were measured. Labile inorganic P (Pi) increased in the rhizospheres of both lupin species, likely due to Pi desorption combined with labile organic P (Po) mineralization, induced by rhizosphere pH elevation after liming. Soil pH increase promoted microbial P immobilization and reduced phosphomonoesterase activity in the rhizosphere, leading to an accumulation of Po mainly as moderately labile and stable Po forms. Total carboxylate concentration (TCC) increased with soil pH increase. Variation in shoot P uptake was mostly explained by TCC. These results indicate that (1) lime application strongly affects P biochemical processes and dynamics in the rhizosphere of lupins. (2) Russell lupin utilizes less P than blue lupin and is unresponsive to liming.

Composting with biochar or woody peat addition reduces phosphorus bioavailability

Biochar and woody peat have been recognized as an additive to reduce carbon and nitrogen loss during composting. Yet little is known about their influences on the transformation of phosphorus (P) fractions in composting. This study investigated the quantitative and qualitative changes in different P forms during composting with adding biochar or woody peat using sequential extraction and P K-edge X-ray absorption near-edge structure (XANES). The results showed that compost products from the treatment with adding woody peat had a higher HA/FA (the ratio of humic acid to fulvic acid) compared to biochar treatment and the control, suggesting that the addition of woody peat might benefit the humification process of composting. Sequential extraction and XANES illustrated that adding biochar or woody peat limited the P availability. Biochar increased the proportion of Pi and woody peat decreased the conversion from Po to Pi compared to the control. Structural equation modeling and redundancy analysis suggested that biochar improved the refractory P based on the indirect effects of NH4+-N by regulating microbial community, while woody peat was beneficial for Po accumulation by affecting humic acid. Taken together, this research provides basis for regulating the nutrient level of carbon, nitrogen, and phosphorus in composts and reducing environmental risks.

A 2000-year record of phosphorus forms and accumulation in peatland of the Greater Khingan Mountains in Northeast China: Paleoenvironmental implications

To investigate the connection of phosphorus (P) forms with peatland succession and history of fire in Tuqiang peatland, a 57 cm peat core was sampled with high-resolution (1-cm intervals) in the north of the Great Khingan mountain (Northeast China). AMS 14C dating techniques combined with sequential chemical extraction was used to determine and calculate the accumulation rates of phosphorus fractions. Phosphorus forms were mainly composed with NaOH-Po, hot concentrated HCl–P (conc. HCl–P) and residual-P. Active phosphorus pools were enriched in the top 8–10 cm of the peat surface. The concentrations of organic phosphorus forms and residual-P were generally high during 1200 to 500 cal yr BP, and the accumulation rate of that gradually decreased since 1600 cal yr BP. Both of concentration and accumulation of organic phosphorus decreased after 600 cal yr BP. The accumulation rate of organic phosphorus forms significantly corresponded with peat development frequency, pollen records and other paleo evidence. The concentration and accumulation of organic phosphorus, especially NaOH-Po, was positively connected with concentration of pollen and Cyperaceae, and decreased when relative abundance of moss or shrubs occurred. Fire changed the vegetation community, decreased the concentration and accumulation of Po, and reduced inactive Po/Pi at the same time. Fire events could also leave geochemical evidence on peat. It is necessary to consider the both changes of inactive Po/Pi and organic phosphorus accumulation rate when reflected the fire history by phosphorus in core.

Distribution of Soil Phosphorus Fractions as a Function of Long-Term Soil Tillage and Phosphate Fertilization Management

The forms in which phosphorus (P) accumulates in soils are dependent on management practices, fertilizer sources, and methods of application, which may promote distinct P solubility and plant uptake. We aimed here to evaluate how soil tillage and phosphate fertilization strategies affected soil P fractions over 17 years and to identify best management practices for improving labile P fractions. The experiment was conducted in a very clayey Rhodic Ferralsol (Oxisol) with initially very low P availability, during 17 years under soybean and corn, fertilized with 35 kg P ha?1 year?1 . Treatments were two soil management systems (CT-conventional tillage and NT-no-till) and four phosphate fertilization strategies (TSP ? triple superphosphate or RRP ? reactive rock phosphate, applied to the crop furrow or broadcast). Soil samples were taken at five depth layers, and organic (Po), inorganic (Pi), and total P (Pt) were determined by Hedley?s sequential fractionation. CT resulted in a more homogeneous distribution of Pi fractions throughout the soil profile, while under NT there was a steep depth gradient characterized by Pi accumulation in the fertilizer application zone. NT resulted in accumulation of Pi in more labile fractions and higher accumulation of Po physically protected by aggregation, both compared to CT. Also, under NT with RRP, there was a great accumulation of Pi associated with calcium (HCl Pi) compared to TSP, especially when the fertilizer was broadcast applied. An accumulation of Po down to 20 cm (CT) and 10 cm (NT) was also detected, compared to Cerrado natural soil. NT and RRP positively affected legacy P fractions and can be recommended as strategies to improve P fertilizer use efficiency. Keywords: no-tillage, P fractionation, legacy P, P source, P distribution

The potential role of sediment organic phosphorus in algal growth in a low nutrient lake

The role of sediment–bound organic phosphorus (Po) as an additional nutrient source is a component of internal P budgets in lake system that is usually neglected. Here we examined the relative importance of sediment Po to internal P load and the role of bioavailable Po in algal growth in Lake Erhai, China. Lake Erhai sediment extractable Po accounted for 11–43% (27% average) of extractable total P, and bioavailable Po accounted for 21–66% (40%) of Po. The massive storage of bioavailable Po represents an important form of available P, essential to internal loads. The bioavailable Po includes mainnly labile monoester P and diester P was identified in the sequential extractions by H2O, NaHCO3, NaOH, and HCl. 40% of H2O−Po, 39% of NaHCO3−Po, 43% of NaOH−Po, and 56% of HCl−Po can be hydrolyzed to labile monoester and diester P, suggesting that the bioavailability of Po fractions was in decreasing order as follows: HCl−Po > NaOH−Po > H2O−Po > NaHCO3−Po. It is implied that traditional sequential fractionation of Po might overestimate the availability of labile Po in sediments. Furthermore, analysis of the environmental processes of bioavailable Po showed that the stabler structure of dissloved organic matter (DOM) alleviated the degradation and release of diester P, abundant alkaline phosphatase due to higher algal biomass promoted the degradation of diester P. The stability of DOM structure and the degradation of diester P might responsible for the spatial differences of labile monoester P. The biogeochemical cycle of bioavailable Po replenishs available P pools in overlying water and further facilitate algal growth during the algal blooms. Therefore, to control the algal blooms in Lake Erhai, an effective action is urgently required to reduce the accumulation of Po in sediments and interrupt the supply cycle of bioavailable Po to algal growth.

Nitrogen application favors soil organic phosphorus accumulation in calcareous vegetable fields

Understanding soil P transformation is critical to optimizing P supply to crops while minimizing P loss to water. Nitrogen application in agricultural fields can cause acidification, changing soil chemistry and altering P cycling. In a calcareous vegetable field in China, 13 years of N application (1172 kg N ha−1 year−1) significantly decreased soil pH, CaCO3, and Mehlich-3 extractable (M3) Mg and increased M3-Fe and M3-Al. Nitrogen addition also increased microbial biomass C (MBC), decreased alkaline phosphomonoesterase (ALP) activity, and changed the total bacterial and phoD-harboring bacterial community composition. Soil total P, Olsen-P, and M3-P were not affected by N fertilization, but there were significant increases in soil total organic P (Po), NaOH-extractable Po, and the proportion of orthophosphate diesters. Redundancy analysis showed that soil pH, organic C, CaCO3, and ALP activity had significant effects on the compositions of soil P form (P < 0.05) and could explain 36.4, 13.3, 27.5, and 10.6% of the total variances observed in the composition of P forms. This suggests that soil acidification from N application in this P-rich calcareous soil altered soil abiotic P cycling processes through increasing the chemical adsorption of Po by Fe and Al. It also altered biotic P cycling processes by increasing microbial P uptake and immobilization and decreasing P biochemical mineralization, resulting in Po accumulation.

Soil organic phosphorus transformations during 2000 years of paddy-rice and non-paddy management in the Yangtze River Delta, China

The contents and properties of soil organic phosphorus (Po) largely drive ecosystem productivity with increasing development of natural soil. We hypothesized that soil Po would initially increase with paddy management and then would persist under steady-state conditions. We analyzed soils from a 2000-year chronosequence of a rice-wheat rotation and an adjacent non-paddy 700-year chronosequence in Bay of Hangzhou (China) for their Po composition using solution 31P-NMR after NaOH-EDTA extraction. Land reclamation promoted Po accumulation in both paddy and non-paddy topsoils (depths ≤ 18 cm) until steady-state equilibria were reached within 200 years of land use. Greater Po concentrations were found, however, in the non-paddy subsoils than in those under paddy management. Apparently, the formation of a dense paddy plough pan hindered long-term Po accumulation in the paddy subsoil. The surface soils showed higher proportions of orthophosphate diesters under paddy than under non-paddy management, likely reflecting suppressed decomposition of crop residues despite elevated microbial P compounds stocks under anaerobic paddy-rice management. Intriguingly, the composition of Po was remarkably stable after 194-years of paddy management and 144-years of non-paddy management, suggesting novel steady-state equilibria of P dynamics had been reached in these man-made ecosystems after less than two centuries.

210Po accumulation by components of the Black Sea ecosystem

The naturally occurring radionuclide 210 Po was determined in different components of the Black Sea ecosystem. The specific activity of 210 Po in water in the open part of the sea was about 1Bq ⋅ m-3 . The range of 210 Po specific activity in bottom sediments was 4.5–500 Bq ⋅ kg-1 dry weight depending on their type, area and depth of collection. The highest values were found in the NW part of the Black Sea. Sediment distribution coefficients (Kd) of 210 Po for bottom sediments, calculated on a dry weight basis, varied from 0.5 × 104 to 5 × 105 . The levels of 210 Po specific activity in molluscs and pelagic fishes anchovy and sprat were the highest among the investigated species of the Black Sea biota. Concentration factors (CF) of 210 Po, estimated on a wet weight basis, reached 1.5 × 103 for macrophytes, 4 × 103 for total zooplankton, 103 –104 for the entire fishes depending on their ecological groups affiliation and (0.7–6.0) × 104 for molluscs. So, the ability of the Black Sea biota to accumulate the natural radionuclide 210 Po is comparable with that of similar species from others marine and oceanic areas.

Introduction of a plasmid-encoded phoA gene for constitutive overproduction of alkaline phosphatase in three subsurface Pseudomonas isolates

Three bacterial isolates, Pseudomonas fluorescens F1, Pseudomonas rhodesiae R1 and Pseudomonas veronii V1 were genetically modified by introduction of a plasmid, pJH123, with a phoA hybrid gene that directed constitutive overproduction of the enzyme alkaline phosphatase. The presence of the plasmid in the bacterial hosts elevated extracytoplasmic alkaline phosphatase production from 100- to 820-fold. The growth and survival of the plasmid-bearing hosts in sterilized soil slurries was comparable to parental control strains. In the absence of antibiotic selection, pJH123 was maintained in two of the three hosts ( P. fluorescens F1 and P. veronii V1) during incubation in minimal medium. The effects of the genetically enhanced pseudomonads on the liberation of inorganic phosphate (PO 4 3−) were determined in sterilized soil slurries following the addition of an organophosphorus compound, glycerol-3-phosphate. A significant accumulation of PO 4 3− was measured in soil slurries amended with 10 mM glycerol-3-phosphate and any of the three phosphatase-enhanced pseudomonad isolates. In contrast, soil slurries containing unmodified parental strains did not exhibit significant PO 4 3− accumulation. Two of the three enhanced phosphate-liberating strains released sufficient PO 4 3− that cell-free supernatants from sterilized soil slurry incubations removed significant amounts of uranium (as much as 69%) from solution.

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean-wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO3 extractable P (Olsen-P) and determined the changes in soil inorganic P (Pi) and organic P (Po) caused by a yearly dose of 52 kg P ha—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean-wheat system on Vertisol. In general, the contents of Olsen-P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen-P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen-P by 1 mg kg—1 was 10.5 kg ha—1 without manure and application of 8 t manure reduced it to 8.3 kg ha—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO3-Pi and Po) and moderately labile (NaOH-Pi and Po) fractions linearly and manure application enhanced accumulation of Po. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, Pt). Excess fertilizer P application in presence of manure led to increased levels of Olsen-P in both topsoil and subsoil. In accordance, the recovery of Pt from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.

Utilisation of inorganic and organic soil phosphorus in a hill country soil

Changes in phosphorus (P) fractions of unfertilised and fertilised (superphosphate) soil were investigated over five years at a hill country site near Te Kuiti. Only soil inorganic P (Pi) reserves were utilised for plant uptake when superphosphate was withheld at the site. Immobilisation of P as soil organic P (PO) contributed to depletion of the soil Pi reserves during the first two years of this trial. Where superphosphate was applied, immobilisation of P as PO amounted to about 25% of applied P during the five years measurements were made. Changes in soil P fractions indicated that all forms of soil Pi were utilised when superphosphate was withheld. These included readily available Pi, Al- Pi, Fe-Pi, and residual phosphate rock from previous fertiliser applications. Depletion of the phosphate rock residues in the soil also occurred where superphosphate was applied and appears to have been completed within about two years. The phosphate rock residues had probably accumulated because of the relatively high amounts of unacidulated phosphate rock in superphosphate manufactured before 1983. Accumulation of Po associated with humic acid, or adsorbed on surfaces of hy drous oxides of Al and Fe, occurred in both fertilised and unfertilised soils. The more labile forms of PO also increased in the fertilised soil. Keywords inorganic phosphorus, organic phosphorus, phosphorus immobilisation, soil phosphorus, soil phosphorus fractions, soil phosphorus utilisation.

Somatomedin-C Synergizes with Follicle-Stimulating Hormone in the Acquisition of Progestin Biosynthetic Capacity by Cultured Rat Granulosa Cells*

We have recently shown that nanomolar concentrations of somatomedin-C (Sm-C), are capable of enhancing the FSH-mediated (but not basal) accumulation of progesterone (Po) by cultured rat granulosa cells. To further characterize this direct cytodifferentiative effect of Sm-C, granulosa cells from immature, hypophysectomized, diethylstilbestrol-treated rats were cultured under serum-free conditions for up to 96 h. Concurrent treatment with highly purified Sm-C (50 ng/ml) produced 10.2- and 3.6-fold increments in the FSH (20 ng/ml)-stimulated accumulation of Po and 20 alpha-hydroxy-4-pregnen-3-one, respectively. Sm-C-augmented Po biosynthesis was dose- and time dependent, but was independent of the FSH dose employed. Significantly, this effect of Sm-C could not be accounted for by enhancement of cellular viability or plating efficiency, nor by an increase in the number of cells, or their DNA synthesis. Furthermore, specific inhibition of DNA synthesis with cytosine-1-beta-D-arabinofuranoside was without significant effect on the ability of SM-C to enhance FSH-supported Po biosynthesis. Insulin, like Sm-C, also synergized with FSH in the induction of Po biosynthesis. However, insulin [ED50 = 19.2 +/- 1.6 (SE) micrograms/ml] was approximately 4800-fold less potent than Sm-C [ED50 = 4.0 +/- 0.3 (SE) ng/ml] in this regard, and exerted little or no effect at concentrations presumed to saturate the putative high affinity granulosa cell insulin receptor. Although maximal stimulatory doses of Sm-C (75 ng/ml) or insulin (100 micrograms/ml) produced comparable increments in FSH-supported Po biosynthesis, combined treatment with maximal doses of both peptides did not prove additive. Pertinently, the direct cytodifferentiative effect of Sm-C is exerted at (nanomolar) concentrations compatible with its receptor-binding affinity as observed in all other cell types studied. Thus, Sm-C is not likely to be acting through the putative high affinity insulin receptor but rather through its own high affinity recognition sites. Similarly, the cytodifferentiative action of high dose insulin may reflect the consequences of its cross-interaction with the putative Sm-C, rather than the insulin receptor. These findings are in keeping with the suggestion that the granulosa cell may be the site of Sm-C reception and action and that Sm-C of intraovarian or circulatory origin may participate in the differentiation, as well as replication, of the developing granulosa cell.

Phenol oxidase activity and pigment synthesis in conidiospores of Penicillium cyclopium

AbstractPhenol oxidase (PO)Abbreviations: CH cycloheximide, DIECA diethyldithiocarbamate sodium salt, h p. i. hours after inoculation, NL nutrient solution, PAA polyacrylamide, PDA p‐phenylenediamine dihydrochloride, PO phenol oxidase of Penicillium cycillium belongs to the laccases (E. C. 1. 14.18.1). By PAA‐gel electrophoresis three forms of the enzym were detected. Most of the PO in emerged sporulating cultures accumulates in the cell wall of the conidiospores. However, a high percentage is not bound to the wall constituents and can be easily removed with aqueous solutions. This soluble fraction was 570‐fold enriched by (NH4)2SO4‐precipitation, followed by chromatography on sephadex G 200 and on hydroxylapatite‐cellulose.The necessity of PO for conidiospore pigmentation was shown by means of suspended spores whose rates of pigment accumulation resemble those of conidia maturing in situ. Pigmentation is stopped if PO is inhibited by diethyldithiocarbamate. This corresponds of the fact that in strains with heavily pigmented conidiospores PO acitivity is much higher than in strains with weakly pigmented or unpigmented spores. Also the time course of PO accumulation in the latter strains is different from that of the former. Furthermore, in mutant res‐eth 1 which has unpigmented conidiospores, PO isoenzyme no. 3 could not be detected.