Mineralization Of Organic Phosphorus Research Articles

Microbial gross organic phosphorus mineralization can be stimulated by root exudates – A 33P isotopic dilution study

Phosphorus (P) is one of the most important nutrients for plant growth. While most studies on microbial P mobilization, i.e. on mineralization of organic P and solubilization of inorganic P, focus on mycorrhiza, P mobilization by non-mycorrhizal microorganisms in soil is little explored. In this study we address the question whether root exudates stimulate organic P mineralization by non-mycorrhizal microorganisms. A 33P isotopic dilution approach was applied to investigate microbial gross P mineralization in top- and subsoil horizons of three forest soils differing in P concentrations (Leptosol, Podzol, and Cambisol). To simulate the effects of root exudates on microbial gross P mineralization, glucose, alanine, and methionine were added in rhizosphere-relevant concentrations (12 mg carbon (C) g−1 soil organic C). Based on 33P isotopic dilution we showed that glucose and alanine addition increased gross P mineralization rates up to a factor of 20 and 31, respectively. In contrast, methionine had little effect on microbial gross P mineralization rates. Phosphatase activity was increased most strongly due to the addition of alanine and glucose by factors of up to 6 and 4, respectively. Fifteen days after addition of artificial root exudates, microbial P concentrations and 33P recovery in the microbial biomass were only slightly and not consistently changed. In conclusion, the results show that alanine and glucose can stimulate microbial gross P mineralization and phosphatase activity, and that structure and stoichiometry of root exudates significantly shape the extent of stimulation of microorganisms. Our study indicates that stimulation of non-mycorrhizal microorganisms by root exudates might be an important strategy of plants to increase the availability of P in soils.

Kinetic parameters of phosphatase: A quantitative synthesis

Phosphatases play an important role in mineralization of organic phosphorus, soil phosphorus availability and global phosphorus cycling. Release of phosphorus in different ecosystems is important for plant growth and microbial function, and may be simulated by modeling organic phosphate mineralization. The half-saturation constant (Km) and the maximum enzyme activity (Vmax) in the Michaelis–Menten equation are the two important kinetic parameters in these models, but their values have not been systematically investigated. In this study, we compiled a database of kinetic parameters of phosphatase from 139 publications, estimated the means, variations and distributions of the kinetic parameters, and tested the differences in kinetic parameters of phosphatases of different types, origins and under different incubation conditions. We also analyzed the activation energy (Ea), temperature sensitivity (Q10), optimum pH (pHopt) and sensitivity of pH (pHsen) of phosphatase activity. Our results indicated that: 1) Both Vmax and Km were log-normal distributed with large variations; 2) There was no significant difference in Km between the acid or alkaline phosphatases, but a significantly higher Vmax for acid phosphatases was found compared with alkaline phosphatases; 3) Km and Vmax varied with the origins of enzymes and under different incubation conditions. Plant originated enzymes had the highest Vmax while soil originated enzymes had the lowest Vmax. Larger variation in Vmax was found among the incubation times than among the incubation temperatures; 4) The mean values of Ea for acid and alkaline phosphatases were 36.30 and 23.61 kJ mol−1, respectively, with an overall mean of 34.40 kJ mol−1. The mean value of estimated pHopt for acid phosphatase was 5.2 while that for alkaline phosphatase was 9.5. The information generated in this study will be useful for phosphorus mineralization modeling and uncertainty analysis.

Impact of sulfate and chloride on sediment phosphorus release in the Yangtze Estuary Reservoir, China

The impact of sulfate (SO4(2-)) and chloride (Cl(-)) on phosphorus (P) release from sediment in the drinking water reservoir of Yangtze River Estuary was studied systematically. A significant correlation between sodium (Na(+)), Cl(-), SO4(2-) and total P was found, suggesting that P was directly or indirectly associated with these ions. SO4(2-) and Cl(-) were important factors that had an impact on P release from the sediment. The results showed that both sulfate and chloride enhanced phosphorus release from sediment. In the sulfate treatment, the decrease of organic phosphorus (OP) suggested that the mineralization of OP enhanced P release from sediment. Phosphonate was the main factor affecting the P release under sulfate condition. In chloride treatment, the sediment composition of iron (Fe), aluminum (Al), calcium (Ca) and magnesium (Mg) increased. The P fractions of Fe/Al-P, Ca-P and OP in sediment also increased. However, the increase of P was unstable after chloride treatment and was easy to release under disturbance. In this study, it was observed that sulfate and chloride could increase the risk of eutrophication in the Yangtze River Estuary drinking water reservoir.

Phytate addition to soil induces changes in the abundance and expression ofBacillusß-propeller phytase genes in the rhizosphere

Phytate-mineralizing rhizobacteria (PMR) perform an essential function for the mineralization of organic phosphorus but little is known about their ecology in soils and rhizosphere. In this study, PCR-based methods were developed for detection and quantification of the Bacillus β-propeller phytase (BPP) gene. Experiments were conducted to monitor the presence and persistence of a phytate-mineralizing strain, Bacillus sp. MQH19, after inoculation of soil microcosms and within the rhizosphere. The occurrence of the BPP gene in natural pasture soils from Chilean Andisols was also examined. The results showed that the Bacillus BPP gene was readily detected in sterile and nonsterile microcosms, and that the quantitative PCR (qPCR) methods could be used to monitor changes in the abundance of the BPP gene over time. Our results also show that the addition of phytate to nonsterile soils induced the expression of the BPP gene in the rhizosphere of ryegrass and the BPP gene was detected in all pasture soils sampled. This study shows that phytate addition soils induced changes in the abundance and expression of Bacillus BPP to genes in the rhizosphere and demonstrates that Bacillus BPP gene is cosmopolitan in pasture soils from Chilean Andisols.

Responses of Soil Microbial Community Structure and Potential Mineralization Processes to Solidago canadensis Invasion

Solidago canadensis is a noxious invasive weed of Eastern China. It is still unclear how its invasion affects the soil microbial community structure and mineralization processes. Therefore, the microbial community structure (assessed by phospholipid fatty acid [PLFA]) and potential mineralization processes associated with its invasion were measured in five field areas in Zhejiang Province, China. Phospholipid fatty acid abundances of bacterial, fungal, actinomycete, two function groups (i.e., Gram-negative bacteria and mycorrhizae), and two ratios for Gram-negative/positive bacterial PLFAs and fungal/bacterial PLFAs were significantly higher in soils invaded by Solidago than in the native soil (P < 0.05), whereas the ratio cy17:0/16:1ω7 decreased (P < 0.05). Ammonification, cellulose, and organic phosphorus mineralization also significantly increased following the invasion of Solidago, respectively, but the nitrification significantly decreased (P < 0.05). Principal components analysis for the PLFA data sets clearly discriminated the native plots from the invaded plots. Redundancy analysis with Monte Carlo permutation tests showed that some PLFAs such as 10:0, 12:0, cy17:0, cy19:0, 16:1ω7, 18:1ω9, 18:1ω7, 18:2ω6, 16:1ω5, 10Me18:0, 10ME17:0, 10Me16:0, 17:1ω8, and 18:0 were strongly correlated with rates of ammonification, nitrification, and cellulose and organic phosphorus decomposition. These results suggest that the invasion-induced changes in soil microbial community structure and nutrient transformation processes (especially nitrification inhibition and ammonification promotion) may be one of the reasons why Solidago becomes predominant in competition with indigenous species for soil nutrients in the invaded ecosystem.

菌丝室接种解磷细菌Bacillus megateriumC4对土壤有机磷矿化和植物吸收的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 菌丝室接种解磷细菌Bacillus megaterium C4对土壤有机磷矿化和植物吸收的影响 DOI: 10.5846/stxb201106170826 作者: 作者单位: 中国农业大学,中国农业大学,中国农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31071871,30890132) The effects of inoculation with phosphate solubilizing bacteria Bacillus megaterium C4 in the AM fungal hyphosphere on soil organic phosphorus mineralization and plant uptake Author: Affiliation: China Agriculture University,China Agriculture University,China Agriculture University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过30 μm尼龙网将根盒分成根室和菌丝室,菌丝室中的低磷土壤施加75 mg P /kg土壤的植酸钙,研究了菌丝室土壤中丛枝菌根(AM)真菌Glomus intraradices和解磷细菌Bacillus megaterium C4对有机磷的矿化和吸收。结果表明,在试验条件下,植酸钙的溶解性很低,对土壤溶液有机磷的贡献不大。接种解磷细菌C4提高了土壤中磷酸酶的活性,减少了土壤中有机磷的含量。但是,由于存在解磷细菌与AM真菌对磷的竞争,解磷细菌矿化出的磷大部分被自身利用,AM真菌的生长受到抑制,解磷细菌对植物磷营养的改善没有表现出显著的贡献。 Abstract:To study the interactions between arbuscular mycorrhizal (AM) fungus and phosphate solubilizing bacteria (PSB) and their effects on soil organic phosphorus (P) utilization in the hyphal compartment soil, maize (Zea myas L.) plants were grown 8 weeks in sterilized soil (brunisolic soil) in a two compartmented rhizoboxes. The rhizobox was composed of a compartment for root growth (root compartment) and a compartment separated from the root compartment by 30 μm nylon mesh, which can allow the fungal hyphae penetration but prevent the root from growing through (hyphal compartment). Glomus intraradices was inoculated in root compartment of all rhizoboxes. PSB Bacillus megaterium C4 at the concentration of 108 CFU/mL were inoculated in the hyphal compartment. Each rhizobox received 20 mg P/kg of KH2PO4 in the root compartment and 75 mg P/kg of phytin in the hyphal compartment. The results showed that inoculation with PSB C4 in the hyphal compartment soil had no significant influence on mycorrhizal colonization but decreased hyphal length density. The pH in AM treatment was higher than that in the control treatment but close to C4 treatment. The phosphatase activity in AM treatment was similar to the control treatment but significantly lower than that in C4 treatment. NaHCO3 extractable organic and inorganic P contents in AM treatment were similar to those in the control treatment. But both of them decreased significantly in C4 treatment. The biomass and P content of maize in AM treatment were much higher than those in the control treatment, but similar to C4 treatment. The results showed that NaHCO3 extractable organic P content in the hyphal compartment after experiment was 4.4 mg P/kg in the control treatment which was close to the initial soil content of 3.9 mg P/kg. Neither inoculation with AM fungus nor PSB C4 increased the P content, indicating that the solubility of phytin under the experimental condition was lower and didn't have significant contribution to the soil effective organic P. By supplying NO3--N in the hyphal compartment soil, AM fungi raised soil pH but had no influence on the phoshpatase activity. Inoculation with C4 increased phosphatase activity but didn't change soil pH, indicating that C4 added the mount of phosphatase in the hyphal compartment soil. The NaHCO3 extractable organic P content in C4 treatment was much lower than that in AM treatment. NaHCO3 extractable inorganic P content in the C4 treatment soil was also significantly lower than that in the AM treatment but the total P content of maize didn't increase. The hyphal length density decreased after inoculation with C4, and the number of C4 was 5×106 CFU/g soil, indicating that the soil must have provided it with P. So the bacterium C4 immobilized part of soil P to decrease the P uptake by AM fungal hyphae. As a result, the hyphae length density may decrease and P uptake of maize may not increase after inoculation with PSB C4. 参考文献 相似文献 引证文献

Actinomicetos mineralizadores de fosfato involucrados en la interacción radical de Glomus sp. - trébol blanco.

The objective of this work was to determine the capacity of actinomicetes for organic phosphorus mineralization and their rhyzospereinteraction with mycorrhiza of Trifolium repens L. (whiteclover). In January 2009, at the laboratory of the Unidad deInvestigaciones Agropecuarias (UNIDIA) of the Pontifi ciaUniversidad Javeriana, Bogotá, Colombia, the phosphataseactivity of Streptomyces sp. (strain MCR9), Streptomycessp. (strain MCR26) and Thermobifi da sp. (strain MCR24)were determined using the p-nitrofenil phosphate technique.Thermobifi da sp. (strain MCR24) showed the lowest activity.Inoculation of actinomycetes alone resulted in higher valuesof inorganic soil P, while leaf P content was higher when coinoculationof actinomycete-Glomus sp. occurred, with theexception of the strain Thermobifi da sp. (strain MCR24). Coinoculation with actynomicetes and Glomus sp. stimulatedbiomass production and colonization percent. Actynomicetesare sinergistic with Glomus sp., resulting in benefi ts for theplant and the mycorrhiza. Analysis of variance and “t” testsALS (P&lt;0,05) were conducted to compare the treatments.The relation between the degree of mycorrhization plant dryweight was determined by the “r” correlation coeffi cient, andplants associated with microorganisms was higher than 70%.

Phosphate geochemistry, mineralization processes, and Thioploca distribution in shelf sediments off central Chile

Sediments underlying the major costal upwelling systems of the world oceans are hot-spots of modern formation of hydroxyapatites, often associated with benthic communities of large, nitrate-accumulating sulfur bacteria. We studied the association between phosphate release, organic phosphorus mineralization, and occurrence of dense communities of the filamentous sulfur bacteria, Thioploca spp., on the continental shelf off central Chile during the austral summer when high phytoplankton productivity and anoxic bottom water prevailed. Freshly deposited phytodetritus stimulated extremely high sulfate reduction rates, which supported a large Thioploca community of up to 100 g biomass per m 2. Effective bacterial sulfide uptake kept the sulfide concentration low, which enabled the accumulation of free iron, thus demonstrating intensive iron reduction concurrent with sulfate reduction. Phosphate released to the pore water reached 100–300 μM peak concentrations within the uppermost 0–5 cm and phosphate was lost to the overlying anoxic water column. The large phosphate release was not directly related to the presence of Thioploca but was rather the result of a high deposition and mineralization rate of fresh organic detritus. Although the pore water was super–saturated with respect to hydroxyapatite, this mineral was only a minor P-component in the sediment. Most solid-phase phosphate was bound to iron.

Changes of Available Phosphorus and phosphatase activity in the rhizosphere of some field and vegetation crops in the fast growth stage

A large proportion of P is found in organic forms. Phosphatase, plays an essential role in the mineralization of organic phosphorus. Agronomy species can affect phosphatase activity in rhizosphere. The aim ofour study was to determine the effects of some agronomy species (Gramineae, Leguminose, Solanaceae, Labiatae, Cruciferae, Umbellifera, Alliaceae) on phosphatase activity in their rhizosphere. The agronomy species were planted in a semiarid soil in the pots under greenhouse condition. Phosphatase activity in the rhizosphere of any species was studied at middle of their growth. Phosphatase activity was greatly enhanced in the rhizosphere of all species. Alkaline phosphatase activity increased 102-325% and acid phosphatase activity increased 205-455% in the rhizosphere soil compared to the non-rhizosphere soil. This suggests that agronomy species actively promote rhizosphere phosphatase activity either directly by secretion or indirectly by stimulation of microbial activity and/or by depletion of Pi. There were significant differences between phosphatase activities in rhizosphere of plant species. The highest and lowest means of alkaline phosphatase activity were found in rhizosphere of Trifolium repens andOcimum basilicum respectively. The highest and lowest means of acid phosphatase activity were found in rhizosphere of Triticum aestium and Cicer arietinum respectively.

Quantifying gross mineralisation of P in dead soil organic matter: Testing an isotopic dilution method

Gross mineralisation of organic phosphorus (P) may play a key role in soil P availability to plants and in P cycling. The challenge for studying P availability is to accurately quantify the two main biological processes involved (mineralisation of microbial P and gross mineralisation of P in dead soil organic matter F MDSOM) separately. However, distinguishing between the two processes can be extremely difficult using the usual isotopic dilution methods. Our objective was to test the basic assumption of another isotopic method — homogeneous labelling of all exchangeable pools of phosphate ions (iP in soil solution, microbial biomass P, and iP sorbed to the solid phase) — that would allow direct quantification of F MDSOM separately from the mineralisation of microbial P. To favour homogeneous labelling, we incubated for a long period a low P-sorbing soil with a low fraction of inorganic P (6% of total P). The soil was labelled with 33P at constant soil respiration in an incubator at 20 °C, and then specific activities of solution ionic P ( SA W) and of microbial P ( SA MB) were monitored for 154 days. A batch experiment with 32P-labelled soil was used to model the exchange reactions with the solid constituents. The results showed that SA W and SA MB converged after 83 days and that the small reactions between solution and sorbed ionic P did not significantly affect values of SA W and SA MB. Beyond day 83 the homogeneous labelling of solution ionic P and microbial P was not strictly maintained (divergence between SA W and SA MB; homogeneous labelling assumption invalidated). However, the combined pool of the two remained at the same SA level. This alternative approach enabled us to evaluate F MDSOM through both pools of ionic P in solution and microbial P. Comparing this result with previous measurements of the biological processes on the same soil showed that gross fluxes of mineralised P were likely to include a larger proportion of what was mineralised P from microbial biomass rather than mineralised P from dead soil organic matter. Thus, the method tested here could avoid any erroneous interpretations when attributing the gross organic P mineralisation flux to any defined biological process. Moreover, quantifying the mineralisation fluxes correctly and separately would enable a better understanding of the biological processes and possible assessment of the changes in P cycling in a changing environment.

Long-term organic phosphorus mineralization in Spodosols under forests and its relation to carbon and nitrogen mineralization

Abstract In forest soils where a large fraction of total phosphorus (P) is in organic forms, soil micro-organisms play a major role in the P cycle and plant availability since they mediate organic P transformations. However, the correct assessment of organic P mineralization is usually a challenging task because mineralized P is rapidly sorbed and most mineralization fluxes are very weak. The objectives of the present work were to quantify in five forest Spodosols at soil depths of 0–15 cm net mineralization of total organic P and the resulting increase in plant available inorganic P and to verify whether net or gross P mineralization could be estimated using the C or N mineralization rates. Net mineralization of total organic P was derived from the net changes in microbial P and gross mineralization of P in dead soil organic matter. We studied very low P-sorbing soils enabling us to use lower extractants to assess the change in total inorganic P as a result of gross mineralization of P in dead soil organic matter. In addition, to enable detection of gross mineralization of P in dead soil organic matter, a long-term incubation (517 days) experiment was carried out. At the beginning of the experiment, total P contents of the soils were very low (19–51 μg g−1) and were essentially present as organic P (17–44 μg g−1, 85–91%) or microbial P (6–14 μg g−1; 24–39%). Conversely, the initial contents of inorganic P were low (2–7 μg g−1; 9–15%). The net changes in the pool size of microbial P during the 517 days of incubation (4–8 μg g−1) and the amounts of P resulting from gross mineralization of dead soil organic matter (0.001–0.018 μg g−1 day−1; 0.4–9.5 μg g−1 for the entire incubation period) were considerable compared to the initial amounts of organic P and also when compared to the initial diffusive iP fraction (

수질예측을 위한 WASP7 모형 매개변수의 추정

The objective of this study is analysis of Andong-Dam lake water quality with water quality model. Model parameters of the WASP applied to Lake Andong-Dam were estimated. The methodology is based on grouping water quality constituents and relevant parameters and successively estimating parameters by a trial-and-error procedure. Water qualify system for modeling consisted of BOD, DO, T-N, T-P. The results of water quality modelling using WASP. T-N was maximum affected by K71C(Organic nitrogen mineralization rate) parameter. T-P was maximum affected by K83C(Dissolved organic phosphorus mineralization) parameter, and It did not show a difference almost from the parameter of others and it omitted. BOD was maximum affected by Temperature parameter, it was visible of the reaction due to the KDC(Deoxygenation rate) in afterwords, and it did not show a difference from the parameter of others and it omitted. DO was maximum affect by Temperature parameter, and It did not show a difference almost from the parameter of others and it omitted. The parameter which it presumes from the this study uses a water quality modeling and Actual value and the result with which it compares, error rate the parameter presumption which is appropriate with 1% interior and exterior is investigated, It will reach and it uses and it will be able to apply to the suitable parameter in water quality modelling of the objective area which can be feeded by it becomes.

The dynamics of phosphorus in turbid estuarine systems: Example of the Gironde estuary (France)

Suspended particles and surface waters were collected in the Gironde estuary (southwestern France) along the salinity gradient. Dissolved inorganic phosphorus (DIP) was analyzed in the filtered surface waters. The suspended particles were sequentially leached to determine five fractions of phosphorus: exchangeable or loosely sorbed P, reactive Fe‐bound P, refractory Fe oxide‐bound P, P associated with apatite and carbonates, and organic P. Experiments were conducted to determine the effects of temperature, salinity, and DIP concentration on phosphorus sorption/desorption processes. The concentration and distribution of particulate phosphorus was homogeneous along the salinity gradient of the estuary, whereas it was variable in time and space in the freshwater part. DIP showed a rapid desorption of loosely sorbed P at low salinities. Desorption depended on suspended particle concentration, but not on DIP concentration. At high suspended particle concentrations, some exchangeable P remained linked to particles, until suspended particle concentration decreased downstream of the estuary. This delayed desorption of bioavailable P occurs in waters in which the penetration of light is sufficient to support photosynthesis and probably plays a major role in primary production at high salinities. Mineralization of organic phosphorus also releases available phosphorus, but this process is slow relative to the water residence time in the estuary. The budget of DIP, the loss of particulate P from the organic fraction, and the water residence time suggest that the dynamics of P in the Gironde estuary is well explained by the two processes of P release from particles to waters without P uptake.

Measuring rates of gross and net mineralisation of organic phosphorus in soils

The isotopic dilution method developed by Oehl et al. [2001b. Organic phosphorus mineralisation studies using isotopic dilution techniques. Soil Science Society of America Journal 65, 780–787] to measure gross mineralisation of soil organic phosphorus (P) was tested on a range of low-P sorbing soils. This isotopic dilution method relies on accurate prediction of radiolabel behaviour due to soil physicochemical processes. Based on experimental validation of the extrapolation for isotopic dilution due to physicochemical processes using autoclaved soils, a simple power function was used for extrapolation rather than the more complex equation used in the original method. For several soils, however, a potential overestimation of gross mineralisation by 0.1–2.0 mg P kg −1 d −1 was revealed. In addition, the detection limit of P mineralisation ranged between 0.6 and 2.6 mg P kg −1 d −1. The method is likely to be at the detection limit for soils that are high in available P and low in biological activity. The method was modified with respect to the extrapolation and successfully applied to a soil with relatively high microbial P (18 mg P kg −1) and soil respiration rates (29 mg C kg −1 d −1), revealing gross mineralisation rates of organic P of 0.9–1.2 mg P kg −1 d −1. Measurement of uptake of 32P by the microbial biomass allowed derivation of a net organic P mineralisation rate of 0.5–0.9 mg P kg −1 d −1.

A time-dynamic phosphorus model for the profundal sediments of Lake Erken, Sweden

Phosphorus profiles in core samples from Lake Erken (Sweden) sediments are combined with a seasonal study of surficial sediments and pore water measurements to develop a model of the phosphorus dynamics in these sediments. Phosphorus is divided into four functional groups: inert phosphorus, organic phosphorus, phosphorus sorbed to iron and phosphorus dissolved in pore water. The model includes processes of sedimentation, burial, chemical equilibrium between dissolved phosphorus and phosphorus sorbed to iron, mineralization of organic phosphorus and vertical diffusion. The model is shown to produce reasonable profiles of concentrations of the four forms of phosphorus in the sediment compared with empirical data. About 50% of the settled phosphorus is eventually buried, and the rest is released to the overlying water column. The amount of phosphorus released is sensitive to temperature and oxygen concentration in the bottom water. Extrapolating the results to the whole area of sediment accumulation is not straightforward, but we suggest that around 3.0 tons of phosphorus is released annually from the profundal sediments of Lake Erken. Year to year variations in internal loading were related to the anoxic area, and we suggest that a shift in the sediment-water equilibrium of P due to an expected increase in temperature may result in increasing phosphorus concentration in the water column.

Effect of Green Manure Addition on Soil Organic Phosphorus Mineralisation

The mineralization of organic forms of phosphorus (P) in soil contributes significantly to plant P uptake, although quantification of organic P mineralisation has been impeded by methodological difficulties. An isotopic dilution method, based on tracer kinetic theory, was used to study the organic P flux rates for unamended and green manure amended soil in an incubation experiment carried out over 35 days. Firstly, the specific activity (SA) between two points of time as affected by dominant biological processes (under conditions of constant soil respiration rates) was determined in a series of successive labelling incubation experiments. Secondly, the instantaneous specific activity (instSA) between two points of time was also determined by shaking an unlabelled soil with 33P, i.e. soil samples that were not labelled with 33P, but kept under conditions identical to the labelled soil samples. This gives the net size of the exchangeable inorganic P pool in the labelling experiments at two points of time during incubation. The SA dilution in the labelling experiments at a constant exchangeable inorganic P pool between two times was attributed to the release of non-labelled inorganic P from the organic P pool by mineralisation. The daily gross organic P mineralisation rates for the 21 days of incubation were 0.06 and 0.27 mg P kg−1 day−1 for unamended and green manure amended soils, respectively. The study demonstrated that green manure amendment contributed to an overall increase in soil P availability through enhanced organic P mineralisation.

Mineralization of Soil Organic Phosphorus Caused by Drying and Rewetting: Isotopic Exchange Study

A radioisotope glasshouse experiment was carried out using 32P to investigate the cause of increased extractable P concentrations induced by drying and rewetting of soil, and lime-induced decrease in P extractability. An acid soil from the South Island of New Zealand was used. Air-drying and rewetting decreased activity and specific activity of 32P of both the soil and plant extracts. This finding indicated that the increased extractability of P following air-drying and rewetting of soil resulted mainly from net mineralization of soil organic P. Liming decreased the activity and specific activity of 32P in soil extracts, and this was attributed to the formation of calcium phosphate compounds in the limed soil treatments. In contrast, the activity and specific activity of 32P in plant samples were significantly (p

Implications of soil organic carbon and the biogeochemistry of iron and aluminum on soil phosphorus distribution in flooded forests of the lower Orinoco River, Venezuela

Relationships among soil phosphorus distribution, soil organic carbon and biogeochemistry of iron and aluminum were studied along a flooded forest gradient of the Mapire river, Venezuela. Soil samples were collected during the dry season in three zones subjected to different flooding intensity: MAX inundated 8 months per year, MED inundated 5 months per year, and MIN inundated 2 months per year. Total labile phosphorus (resin + bicarbonate extractable fractions) was significantly higher in MIN than in MAX. The longer non-flooding period in MIN probably allowed a higher accumulation of microbial biomass in soils of this zone and consequently a greater release of the bicarbonate organic fraction. The moderately labile phosphorus fraction associated with the chemisorbed phosphorus on amorphous and some crystalline aluminum and iron was significantly lower in MAX than in MIN following the same tendency observed for crystalline iron oxides. This result allowed us to hypothesize that the combined effect of a long flood period and a high soil organic carbon content in the MAX, could be appropriate conditions for microbial reduction of stable forms of iron. The ratio of soil organic carbon to total organic phosphorus decreased from MAX to MIN, indicating higher mineralization of organic phosphorus in MIN. Our results suggests two distinct flood-dependent mechanisms operating for phosphorus release along the gradient. In MAX mineralization process appears to be limited, while microbial mineral dissolution appears to be an important source of phosphorus. In MIN supply of phosphorus is associated with the stability of soil organic matter.

The seasonal dynamics of amino acids and other nutrients in Alaskan Arctic tundra soils

Past research strongly indicates the importance of amino acids in the N economy of the Arctic tundra, but little is known about the seasonal dynamics of amino acids in tundra soils. We repeatedly sampled soils from tussock, shrub, and wet sedge tundra communities in the summers of 2000 and 2001 and extracted them with water (H2O) and potassium sulfate (K2SO4) to determine the seasonal dynamics of soil amino acids, ammonium (NH4+), nitrate (NO3−), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), and phosphate (PO42−). In the H2O extractions mean concentrations of total free amino acids (TFAA) were higher than NH4+ in all soils but shrub. TFAA and NH4+ were highest in wet sedge and tussock soils and lowest in shrub soil. The most predominant amino acids were alanine, arginine, glycine, serine, and threonine. None of the highest amino acids were significantly different than NH4+ in any soil but shrub, in which NH4+ was significantly higher than all of the highest individual amino acids. Mean NO3− concentrations were not significantly different from mean TFAA and NH4+ concentrations in any soil but tussock, where NO3− was significantly higher than NH4+. In all soils amino acid and NH4+ concentrations dropped to barely detectable levels in the middle of July, suggesting intense competition for N at the height of the growing season. In all soils but tussock, amino acid and NH4+ concentrations rebounded in August as the end of the Arctic growing season approached and plant N demand decreased. This pattern suggests that low N concentrations in tundra soils at the height of the growing season are likely the result of an increase in soil N uptake associated with the peak in plant growth, either directly by roots or indirectly by microbes fueled by increased root C inputs in mid-July. As N availability decreased in July, PO42− concentrations in the K2SO4 extractions increased dramatically in all soils but shrub, where there was a comparable increase in PO42− later in the growing season. Previous research suggests that these increases in PO42− concentrations are due to the mineralization of organic phosphorus by phosphatase enzymes associated with soil microbes and plant roots, and that they may have been caused by an increase in organic P availability.

Short term effects of radiata pine and selected pasture species on soil organic phosphorus mineralisation

Silvopastoral systems comprise part of the continued expansion of conifer plantings on grassland in New Zealand. Greater understanding of the short term dynamics of soil organic P in such systems will further our knowledge about soil carbon and phosphorus relationships which will enable improved nutrient management in the field. A glasshouse experiment was carried out to examine the short-term effects (36 weeks) of combinations of radiata pine (Pinus radiata), lucerne (Medicago sativa L.) and perennial ryegrass (Lolium perenne L.) grown in the same soil type with a range of carbon (C) and phosphorus (P) levels on plant P uptake and the specific mineralisation rate (SMR). The SMR is defined as net mineralisation rate (i.e. gross mineralisation less microbial and geochemical uptake) and calculated from organic P decline as a percentage of organic P in the original soil before planting. This included an investigation of the effect of tree ectomycorrhizal (EM) hyphae on soil organic P. Plant P uptake was positively correlated with water soluble organic carbon (WSOC) and SMR, which in turn was closely related to soil C levels. The soils with high WSOC and C levels (which also contained high levels of labile inorganic and organic P) enabled high P uptake. Although P uptake was the greatest under radiata pine, the trees tended to deplete inorganic P to a lesser extent than the forages. When tree and forage species were combined, P uptake by forages was similar to when the forages were grown alone. The various soil and plant treatments significantly affected SMR. The two low C soils, showed the greatest organic P mineralisation while a high C soil, which contained significant levels of bicarbonate extracted inorganic P at planting and was under a long established undisturbed pasture, showed the least mineralisation. Trees grown alone showed the greatest SMR, EM hyphae and trees with lucerne were slightly lower than trees alone, while the forages showed the lowest SMR. The findings of this study showed that changes in organic P are strongly influenced by interactions between plant species (radiata pine, lucerne, ryegrass) and soil properties as determined by land use and management.