Uptake and transport of phosphorus by Agrostis capillaris seedlings from rapidly hydrolysed organic sources extracted from32 P-labelled bacterial cultures

Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with³² P labelled phosphate, to produce a uniformly³² P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.     

Mineralization of dissolved organic phosphorus from a shallow eutrophic lake

Release of soluble reactive phosphorus (SRP) from dissolved organic phosphorus (DOP), concentrated by reverse osmosis of water samples from Lough Neagh Northern Ireland, was measured in the presence of enzymes and cultures of lake water bacteria in a basal liquid medium adjusted to the pH of lake water (7.6). No hydrolysis of unfractionated DOP was observed in the presence of alkaline phosphatase but a combination of alkaline phosphatase and phosphodiesterase mineralized 14% of DOP in a 30 day incubation period at 15 °C. A similar amount of mineralization was attained by phytase. Phytase induced the same degree of mineralization in a range of DOP fractions varying from MW > 100 000 to c. 500. A mixed culture of lake water bacteria mineralized 12% of unfractionated DOP. Single cultures of lake water bacteria displayed low mineralizing activity (mean of 49 cultures = 5% DOP hydrolysed). Results indicate that DOP from Lough Neagh in the above molecular weight range is predominantly recalcitrant to bacterial mineralization under natural lake conditions.     

Barley genotypes differ in activity of soluble extracellular phosphatase and depletion of organic phosphorus in the rhizosphere soil

In the present investigation we studied the extent of variation among barley genotypes (Hordeum vulgare L. cv. Alexis, Canut, Digger, Etna, Peel) in their ability: i) to induce activity of soluble extracellular phosphatase in rhizosphere soil. ii) to withdraw bicarbonate extractable organic phosphorus (NaHCO₃-P₀). All the genotypes induced 3–4 times higher phosphatase activities in rhizosphere soil as compared to bulk soil. Among the genotypes, there were significant (p>0.01) differences in soluble extracellular and non-soluble phosphatase activities and depletion of NaHCO₃-P₀ in soil near their root mats. Etna induced highest phosphatase activities and depleted most NaHCO₃-P₀ from the rhizosphere soil. A high correlation (r=0.79) was found between the activity of soluble extracellular phosphatase and the quantity of NaHCO₃-P₀ withdrawn from the rhizosphere soil by the barley genotypes.     

Comprehensive utilization of activated sludge for the preparation of hydrolytic enzymes,polyhydroxyalkanoates, and water-retaining organic fertilizer

The urban wastewater treatment industry produces a large amount of excess activated sludge which is mainly composed of microbial biomass and costly to be disposed. In this research, a comprehensive utilization of activated sludge was developed by sequentially extracting hydrolytic enzymes and polyhydroxyalkanoates (PHAs), and the residue was used to prepare water-retaining organic fertilizer. The sludge was extracted with fourfold H₂O-containing 1% Triton X-100 with the yield of 66.7% protease activity. The enzyme solution was precipitated in 80% acetone and vacuum dried at 40°C at the dried enzyme yield of 2.4?g/kg wet sludge. The enzyme product contains collagenase, lipase, amylase, and cellulase activities, which are good compound enzymes to feed. The PHAs were extracted with 30% sodium hypoclorite:chloroform (1:3). The PHA solution was decolored and dried, and pure white PHAs were obtained at the yield of 70.1?g/kg wet sludge. The residue was used to prepare water-retaining organic fertilizer at the optimal condition. The fertilizer absorbs 131.3-fold distilled water and had good performance in water retention and can effectively slow down the loss of soil moisture when added into soil. This work provides a simple and practical approach for comprehensive utilizing activated sludge with significant economic benefits.     

华南典型树种凋落叶的野外分解和溶解性有机质溶出动态

选用华南亚热带地区常见阔叶树种木荷和针叶树种湿地松的新近凋落叶,在野外分解0、30、60、90、150、210、240、365 d,分析溶出的溶解性有机质(DOM)浓度、组成和性质的变化,以及对土壤可溶性有机碳(DOC)的影响.结果表明: 随着分解的进行,尽管木荷叶片的DOM浓度高于松针,但是2种凋落叶DOM浓度、性质和物质组成变化规律一致;2种凋落叶的DOM浓度均呈下降趋势,芳香化程度和分子量增大,富里酸、腐殖酸类物质逐渐增多,可降解的简单芳烃蛋白(如酪氨酸)逐渐减少.在分解初期,DOM主要由亲水中性和酸性部分组成,易分解、易迁移,对表层土壤DOC影响不显著;在分解后期,DOM主要为腐殖酸和富里酸类物质,吸附性强,表层土壤DOC浓度显著下降.     

Ecological significance of phosphomonoesters and phosphomonoesterase activity in a small Mediterranean river and its estuary

In 1998, the concentration of phosphomonoesters, a biologically available fraction of the dissolved organic phosphorus pool, was measured along Palmones River (a small Mediterranean river in Southern Spain) and its estuary. Due to the extremely low phosphomonoester concentration in the river (usually under detection limits by analytical procedures), a method using chromatographic cartridges to concentrate this compound was used. Phosphomonoester concentration was usually in the nanomolar range, although values up to 6 m were measured in a sampling station near an effluent of domestic sewage and a cellulose pulp plant. Concentrations were always lower than the dissolved reactive phosphorus (mostly orthophosphate). Phosphomonoesters represented a variable percentage of the dissolved organic phosphorus, from negligible percentages up to 56%. Besides, a highly significant correlation between these two phosphorus fractions was found.In addition, phosphomonoesterase (alkaline phosphatase) activity was measured in the water and macrophytobenthos (both algae and aquatic phanerogams) along the river and the estuary. In water, most of the phosphatase activity upstream was regarded as soluble. This was confirmed by the difficulty of performing kinetic studies in the unfiltered samples. On the contrary, the phosphomonoesterase activity in the estuary was attributed to different size fractions, suggesting that phosphomonoesters are used actively as a phosphate source by bacteria and phytoplankton, with relative contributions depending on the sampling period.     

The winter and summer partitioning of dissolved nitrogen and phosphorus. Observations across the Irish Sea during 1997 and 1998

Winter and summer water column profiles from a transect co-inciding with the 54° N parallel across the Irish Sea were examined for relationships between the fractions of total dissolved nitrogen and phosphorus. Inorganic nitrogen and phosphorus gave the expected seasonal variation. As inorganic nitrogen concentrations decreased during the summer, dissolved organic nitrogen concentrations increased. Dissolved organic phosphorus showed little seasonal variation and formed a smaller fraction of the total dissolved pool compared to nitrogen. Winter inorganic nitrogen and phosphorus salinity relationships were conservative: winter organic nitrogen and phosphorus salinity relationships were not conservative. In the winter, dissolved organic nitrogen and phosphorus formed a significant fraction of the total dissolved pool.     

模拟氮沉降对低磷胁迫下马尾松不同家系根系分泌和磷效率的影响

近年来大气氮(N)沉降的增加, 导致森林土壤中有效N含量增加、N:P发生改变, 研究N沉降对低磷(P)胁迫下林木根系分泌和P效率的影响具有重要意义。该文以马尾松(Pinus massoniana)家系作为试验材料, 设置模拟N沉降与同质低P (介质表层与深层均缺P)、异质低P (介质表层P丰富、深层缺P)耦合的二年生盆栽实验, 系统研究了模拟N沉降对低P胁迫下马尾松根系分泌性酸性磷酸酶(APase)活性、有机酸分泌以及P效率的影响。结果表明: (1)同质低P和异质低P下, 模拟N沉降均显著提高了植株N:P化学计量比、增加了P素的相对匮乏程度, 从而诱导根系增加了APase和有机酸的分泌, 而同质低P比异质低P下增加幅度更大, 其中有机酸分泌均与马尾松生长呈正相关关系, 而APase活性与P效率相关性较小; (2)同质低P下, N沉降虽然增加了根系分泌, 但未提高马尾松P素吸收和生长量, 其原因在于, 同质低P下植株N:P过高, 因而植株对N沉降敏感性低; 在异质低P下, 植株表现为N、P共同限制, 因而对N敏感性较高, N沉降增加了根系分泌, 同时提高了N和P吸收效率、增加了生物量; (3)马尾松根系分泌对模拟N沉降的响应存在较大的家系差异。同质低P下, 家系71×20的有机酸分泌和生物量对N沉降的响应幅度较大; 异质低P下, 家系36×29、71×20和73×23对N沉降的响应幅度较大。     

Dissolved organic matter and phosphorus leached from fresh and 'terrestrially' aged river red gum leaves: implications for assessing river–floodplain interactions

1. The rates of leaching, speciation and bioavailability of dissolved organic matter (DOM) and dissolved phosphorus (P) leached from fresh leaves of the river redgum, Eucalyptus camaldulensis Dehnh, were compared to those from leaves which had been aged on the flood plain for 5_months. The DOM and P leaching rates from microbially inhibited aged leaves were first-order with respect to leaf quantity. The kinetics of DOM and P leaching from fresh leaves were more complex; DOM leaching from fresh leaves appeared to be self-inhibitory, while P leaching from leaves was potentially enzymatically mediated.
2. The speciation and microbial bioavailability of DOM from fresh and aged leaves were completely different. At lower leaf biomass, almost all the DOM from fresh leaves was utilized by an introduced microbial consortium; at higher biomass, microbial utilization appeared to be nutrient limited. Conversely, only about 30% of the DOM leached from aged leaves was utilized by the introduced microbial consortium during the course of the experiment. The difference in microbial utilization could be a result of changes in DOM speciation as a consequence of terrestrial ageing.
3. Weak-anion exchange chromatograms of microbially inhibited fresh leaf extracts showed numerous (unassigned) DOM peaks, most of which could be used by the microbial consortium present. The weak-anion exchange chromatograms of sterile aged leaves showed only three broad peaks and a number of smaller spikes. Only one of the broad peaks could be utilized by the microbial consortium.
4. Phosphorus speciation was also determined by weak-anion exchange chromatography. Most of the P leached from both fresh and aged leaves was free orthophosphate, and therefore, readily available. Two organic-P species leached from microbially inhibited fresh leaves were also found to be readily available to the microbiota.     

有机酸对土壤无机态磷转化和速效磷的影响

土壤有效磷含量低是影响作物生产的重要限制因素之一.作物根分泌活化难溶性磷的有机酸对改善其磷素营养具有重要意义.采用张守敬和Jackson无机磷分级方法,以湖北省3种pH值土壤为材料,加入不同磷源和有机酸,经过室温培养后,测定速效磷含量和无机磷组分的变化.结果表明:施磷显著提高了土壤中速效磷含量,中性土、酸性土Fe-P和Al-P含量大幅上升, Fe-P占增加量的50%以上,而碱性土Ca-P含量显著增加.加施有机酸使中性土速效磷含量增多,除苹果酸处理的变幅较小外,草酸和柠檬酸的加入速效磷显著增加.由于有机酸的作用,中性土Al-P含量下降,Ca-P含量上升,变幅大小依次为草酸＞柠檬酸＞苹果酸;酸性土中Al-P含量呈下降趋势,碱性土中Ca-P含量有不同程度的减少,3种土壤中O-P含量均有所增加.说明有机酸活化的磷主要来源于中性土和酸性土Al-P、Fe-P及碱性土Ca-P中的磷,同时有机酸能够促进土壤中闭蓄态磷(O-P)的形成与积累.     

亚热带森林不同植物及器官来源的可溶性有机质输入对土壤激发效应的影响及其作用机理

外源有机物的输入可以通过正负激发效应影响土壤有机碳(SOC)的矿化。然而, 当前的研究较少考虑不同植物及器官来源可溶性有机质(DOM)输入对土壤激发效应的影响及其作用机理。该研究以武夷山森林土壤为研究对象, 以室内培养的方式向土壤中添加¹³C标记青冈(Cyclobalanopsis glauca)、杉木(Cunninghamia lanceolata)、木莲(Manglietia fordiana)和相思(Acacia confusa)这4种植物的根和叶来源DOM, 研究不同植物及器官来源DOM输入对土壤激发效应的影响及其作用机理。主要结果: 不同植物及器官来源DOM添加初期加快了SOC的矿化, 呈现正激发效应, 随后转为负激发效应。从整个培养期(90天)的累积激发效应来看, DOM的输入均抑制了SOC的矿化, 使其矿化量减少22%-49%, 其中青冈根DOM输入使SOC的矿化量减少最多, 而由木莲叶DOM输入减少的SOC矿化量最少。DOM输入引起的土壤激发效应强度受不同植物器官影响明显, 具体表现在植物根来源DOM输入所引起的土壤激发效应强度显著高于植物叶来源DOM输入所引起的激发效应强度(相思除外)。DOM的输入总体上提高了土壤微生物生物量碳(MBC)含量、土壤β-葡萄糖苷酶活性、纤维素酶活性以及土壤有效氮含量, 而对微生物群落组成无明显影响。从结构方程模型来看, DOM输入所引起的土壤激发效应主要受土壤微生物对外源碳的利用(¹³C-MBC)、纤维素酶活性以及土壤有效氮含量的影响, 这些因子的变化可解释植物叶来源DOM和根来源DOM添加处理下土壤激发效应变化的68%和86%。该研究结果表明在土壤氮充足的条件下, DOM的输入可以通过提高微生物生物量、土壤酶活性来加快分解所添加的外源有机物, 从而减少了对SOC的分解。因此, 在该研究中“底物优先利用”是土壤激发效应的主要作用机理。     

Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd initially insoil-solution system form. Critical concentrations of DOM (DOMnp) were obtained where the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOMnp promoted atrazine sorption on soils (Kd* ＞ Kd), whereas the presence of DOM with concentrations higher than DOMnp tended to inhibit atrazine sorption (Kd* ＜ Kd). Interestingly, DOMnp for tested soils was negatively correlated to the soil organic carbon content, and the maximum of Kd*/Kd (i.e.Kmax) correlated positively with the maximum of DOM sorption on soil (Xmax). Further investigations showed that the presence of hydrophobic fraction of DOM evidently promoted the atrazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the atrazine sorption. Interactions of soil surfaces with DOM and its fractions were suggested to be the major processes determining atrazine sorption on soils. The results of this work provide a reference to the agricultural use of organic amendment such as sewage sludge for improving the availability of atrazine in soils.     

Effects of dissolved organic matter from sewage sludge on the atrazine sorption by soils

The effects of dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge, on the sorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine) by soils were studied using a batch equilibrium technique. Six paddy soils, chosen so as to have different organic carbon contents, were experimented in this investigation. Atrazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd initially increased and decreased thereafter with increasing DOM concentrations of 0-60 mg DOC ·L-1 in soil-solution system form. Critical concentrations of DOM (DOMnp) were obtained where the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOMnp promoted atrazine sorption on soils (Kd* > Kd), whereas the presence of DOM with concentrations higher than DOMnp tended to inhibit atrazine sorption (Kd* < Kd). Interestingly, DOMnp for     

Concentrations and controls of dissolved organic matter in a constricted-channel region of the Ohio River

A 12-month study was conducted to measure the concentrations ofdissolved organic matter (DOC, TDN, TDP) in four sites within a119 km long reach of the Ohio River, near Louisville, KY. In thisstudy we test whether specific geomorphological and biologicalfactors influenced variations in dissolved organic matter.Concentrations of DOC in the river averaged 1200mol/L, and varied by nearly two orders of magnitudeseasonally (mean DOC during base flow 620 mol/L).Peak periods for DOC at all sites were during April–May. Thesite nearest a navigation dam (deeper, lower current velocities)had significantly lower concentrations of TDN and greater C:Nratios than upstream sites. The largest tributary entering thisreach (Kentucky River) had no significant effect on levels of DOMin the main river, despite having significantly greaterconcentrations of TDN and lower levels of DOC during most monthsof the year. Concentrations of DOC, TDN, and TDP were notsignificantly different in littoral and pelagic habitats at allsites studied, suggesting little floodplain influence on DOM inthis constricted-channel section of the Ohio River. C:N ratios ofDOM in the Ohio were significantly different among seasons; C:Nexceeded or equaled Redfield ratios in summer and fall (6 to 10),but were below Redfield (1.8 to 3.0) during winter and spring.Regression models suggest that total phytoplankton densities andflow conditions are the two most important factors regulating DOMin this very large river.     

Characterization and origin of polar dissolved organic matter from the Great Salt Lake

Polar dissolved organic matter (DOM) was isolated from a surface-water sample from the Great Salt Lake by separating it from colloidal organic matter by membrane dialysis, from less-polar DOM fractions by resin sorbents, and from inorganic salts by a combination of sodium cation exchange followed by precipitation of sodium salts by acetic acid during evaporative concentration. Polar DOM was the most abundant DOM fraction, accounting for 56% of the isolated DOM. Colloidal organic matter was ¹⁴C-age dated to be about 100% modern carbon and all of the DOM fractions were ¹⁴C-age dated to be between 94 and 95% modern carbon. Average structural models of each DOM fraction were derived that incorporated quantitative elemental and infrared, ¹³C-NMR, and electrospray/mass spectrometric data. The polar DOM model consisted of open-chain N-acetyl hydroxy carboxylic acids likely derived from N-acetyl heteropolysaccharides that constituted the colloidal organic matter. The less polar DOM fraction models consisted of aliphatic alicyclic ring structures substituted with carboxyl, hydroxyl, ether, ester, and methyl groups. These ring structures had characteristics similar to terpenoid precursors. All DOM fractions in the Great Salt Lake are derived from algae and bacteria that dominate DOM inputs in this lake.     

Investigation of the parameters affecting the separation of bacterial enzymes from cell debris by tangential flow filtration

The effect of organism, enzyme, method of cell breakage and membrane characteristics on the separation of bacterial enzymes from cell debris by tangential flow filtration has been studied. The effectiveness of separation was assessed by process time, enzyme yield and specific activity, and turbidity of the filtrate. For a particular organism and enzyme, method of cell breakage and membrane characteristics significantly influenced separation performance, though results indicate that it is not yet possible to optimize all aspects of performance simultaneously.     

Preferential utilization of organic and inorganic sources of phosphorus by wheat plant

On soils of low P supply organic P (Po) makes up a similar or even larger part in soil solution than inorganic P (Pi). The ability of wheat (Triticum aestivum L., cv. Star) plants to hydrolyze and absorb this Po in comparison to similar concentrations of Pi was studied. Four concentration levels of Pi and Po were obtained by extracting two soils with deionized water in a ratio of 1:1 and concentrating the resulting filtrate by freeze drying to different degrees. The concentration of Pi varied between 5 and 36 μM and Po between 3 and 22 μM. Wheat seedlings were grown in these solutions for 12 and 24 h and acid and alkaline phosphatase activity determined. The reduction of Po concentration in solution expressed on a root length basis gave the rate of Po hydrolysis and the reduction in concentration of Pi and Po gave the P inflow into the roots. No alkaline phosphatase activity was detected. The activity of wheat root acid phosphatase increased with Po concentration in solution. Phosphorus uptake was 2 to 6 fold higher from Pi than from Po at similar concentrations of both. The rate of uptake from Pi, the inflow, as well as the rate of hydrolysis of Po increased linearly with concentration but at similar concentration the inflow was 2 to 4 times higher than the rate of Po hydrolysis. Results suggest that plants can utilize Po after hydrolysis by phosphatase, but Pi is more important and preferentially used by plants; Po may be essential for plant nutrition especially in high P-fixing soils.     

Release and bioavailability of dissolved organic matter from floodplain litter: influence of origin and oxygen levels

1. We determined the rate of release and microbial uptake of dissolved organic carbon (DOC) leached from three components (leaves, bark and twigs) of river red gum ( Eucalyptus camaldulensis ) forest litter originating from different parts of a floodplain and under different oxygen levels.
2. Preliminary experiments showed that substantially more DOC was released from leaves than from bark or twigs; there was relatively little DOC release from coarse particulate matter or soil.
3. Both the amount of DOC released from each litter component and the amount metabolized by the microbial community were independent of position on the flood-plain or amount of oxygen available to microbes.
4. Although the bioavailability of DOC was independent of oxygen concentration, the microbial utilization of DOC under aerobic and anaerobic conditions differed. Under aerobic conditions, leaves were colonized by fungi, while bacteria were dominant under anoxic conditions.
5. Phospholipid fatty acid profiles of the microbial communities growing on leaf extracts showed that different microbial communities developed in each oxygen concentration treatment suggesting that, irrespective of flood conditions, a microbial community will develop to utilize a significant proportion of the DOC leached from litter.     

A comparison of phosphorus and DOC leachates from different types of leaf litter in an urban environment

1. The leaching rates of filterable reactive phosphorus (FRP) and dissolved organic carbon (DOC) from five leaf litter types commonly occurring in urban environments in Mediterranean regions of Southern Australia were compared. The relative composition, bioavailability and oxygen demand of this DOC were also assessed. Four tree species were assessed, including the native river red gum (Eucalyptus camaldulensis) and three introduced deciduous species, the English elm (Ulmus procera), London plane (Platanus acerifolia) and white poplar (Populus alba). Grass cuttings (mixed species) were selected as a common garden waste. 2. Except for English elm, the majority of FRP and DOC was released within the first 48 h. Grass cuttings released the highest amount of FRP with white poplar releasing the most DOC. Species that released relatively high amounts of DOC (white poplar, English elm, river red gum) released relatively low amounts of FRP. Conversely, species that released relatively low amounts of DOC (grass cuttings and London plane) tended to release relatively high amounts of FRP. 3. Analysis of DOC composition, combined with the differing oxygen demand and DOC depletion curves, demonstrated that there were substantial differences in the DOC leached from the leaf litter of the different species. Biochemical oxygen demand and the biodegradability of the DOC was positively correlated with the proportion of hydrophilic and hydrophobic acids present in the leachate. 4. These results demonstrate that simple measurements of nutrient release per gram of leaf litter would be insufficient to predict the ecological impact on receiving waters resulting from changes in dominant vegetation. Furthermore, the use of traps to prevent particulate leaf material from entering streams may have limited potential for reducing the load of dissolved nutrients. We conclude that any changes to vegetation type which substantially alter the timing of leaf fall or the composition of leaf leachates should be avoided.