Respiration Of Microorganisms Research Articles

Inhibition of activated sludge respiration by sodium azide addition: Effect on rheology and oxygen transfer

Although microorganism respiration inhibition by sodium azide (NaN 3) is used in some studies to identify activated sludge adsorption capacity, little is known about the effect of this compound on the suspension properties. In this study we have investigated the effect of NaN 3 addition on both volumetric oxygen mass transfer coefficient and rheology of activated sludge (AS) suspensions in a 1.9 L bioreactor. The rheological properties (shear thinning one) of AS suspensions with and without NaN 3 addition are measured in situ (triphasic conditions). It appears that NaN 3 addition leads to a deflocculation of AS suspensions and thus a decrease in apparent viscosity. A small amount of suspended solids was added in order to obtain identical apparent viscosities (under 1.2 or 46.3 s −1) for AS suspensions with and without NaN 3 addition. K L a values were then measured in both respiring and non-respiring suspensions for different air flow rates (2, 3 or 4 L/min) and under low or high mechanical shear rate (1.2 or 46.3 s −1). Results show that under high mechanical shear rate, the respiration state for a given air flow rate does not impact the K L a values. On the contrary, under low mechanical shear rate, NaN 3 addition induces an increase of K L a values in comparison with those obtained with the respiring biomass. This effect, for a same apparent viscosity, is attributed to the deflocculation observed in the presence of NaN 3. Indeed, AS with and without NaN 3 addition used for the K L a measurements induce a modification of the floc internal structure, corresponding to smaller floc size in the case of NaN 3 addition.

Carbonate recrystallization in root-free soil and rhizosphere of Triticum aestivum and Lolium perenne estimated by 14C labeling

Under arid and semiarid conditions, pedogenic (secondary) carbonates are formed in soil by precipitation of Ca2+ from soil parent material with dissolved CO2 originating from root and rhizomicrobial respiration. δ13C values of secondary CaCO3 record the photosynthetic pathway of former vegetation and is therefore used as a tool for paleoenvironmental studies. The time scale of pedogenic carbonate formation as well as the influence of several environmental factors are crucial, yet poorly known. We estimated the recrystallization rate of pedogenic carbonate by the 14C isotopic exchange method. 14CO2 was assimilated by plants, respired into the rhizosphere and subsequently incorporated into secondary carbonate by recrystallization of primary loess carbonate. With ascending number of 14CO2 pulses, the amount of rhizosphere 14C recovered in loess CaCO3 increased linearly, leading to recrystallization rates of 3.2 × 10−5 and 2.8 × 10−5 day−1 for wheat and ryegrass, respectively. In loess close to roots, recrystallization rates more than twice as high were obtained. Extrapolating these rates we showed that several hundred years are necessary for complete recrystallization of primary loess CaCO3 in root-free substrate, assuming that both primary and secondary carbonate is recrystallized several times. In contrast, the process probably takes only decades in rhizosphere loess if carbonaceous encrustations form around the root, impeding repeated recrystallization. This indicates the importance of rhizosphere processes (e.g. respiration of roots and microorganisms, exudation) for secondary carbonate formation.

Monitoring fermentation parameters during phytase production in column-type bioreactor using a new data acquisition system

Fermentation parameters for phytase production in column-type bioreactor were monitored using a new data acquisition system. There are a number of studies reporting phytase production in flasks, but a lack of data about microorganism respiration behaviour during phytase production using column bioreactor. The objectives of this work were the monitoration of fermentation parameters during phytase production and its relation with fungal growth and forced air. Phytase production by A. niger FS3 increased with forced air. The O(2) consumption and CO(2) production during solid-state fermentation were monitored by sensors (in the bottom and top of the columns) linked to controllers, recorded by acquisition software and processed by Fersol2(®) software tool. Phytase synthesis was associated with fungal growth. Therefore, phytase could be used to estimate FS3 biomass formed in citric pulp degradation.

Soil respiration across scales: towards an integration of patterns and processes

New Phytologist Forum Editorial The New Phytologist Tansley Medal New Phytologist was founded by Sir Arthur Tansley and was first published in 1902. The long and independent history of the journal has allowed a positive inflow of revenue that is managed by the New Phytologist Trust and which is ploughed back into the scientific community to foster plant science (for a brief history of New Phytologist see Lewis & Ingram, 2002). The Trust currently finances two scientific meetings a year (e.g. Bruns & Kennedy, 2009; Harvey & Strauss, 2009) in addition to providing support for other meetings and activities (see http://www.newphytologist. org). A new innovation from the Trust is an annual com- petition for the New Phytologist Tansley Medal, specifically aimed at plant scientists in the early stages of their career. The plant scientists are required to submit their best research, either as a research article or as a small review, in a global competition for the award of a £2000 prize, in addi- tion to publication of the work and an editorial comment in New Phytologist. Details of the practicalities can be found on the New Phytologist Trust website at http://www. newphytologist.org/tansleymedal.htm. The New Phytologist Tansley Medal competition is a two- round process. In the first round, candidates submit an extended abstract of their work, together with their curricu- lum vitae and a reference from a scientist who has agreed to support the application. The number of applications at this stage is large and they are sifted by two Editors to produce a short list of candidates (seven candidates for the 2009 medal) who progress to the second round. Those who make it to this stage are requested to submit a complete manu- script, which is then peer-reviewed in the usual way. In addition, the Referees and Editors are asked for their assess- ments of the suitability of the manuscript for the Tansley Medal. Two Editors then make the final choice of the medal award. This year we are delighted to award the first Tansley Medal to Steven Spoel from the Institute of Molecular Plant Sciences at the University of Edinburgh, UK, for his paper on Post-translational protein modification as a tool for transcription reprogramming (this issue, pp. 333–339). As the title suggests, the manuscript deals with the control of transcriptional reprogramming. This process contributes to, for example, the co-ordinated changes in gene expression The Authors (2010) Journal compilation New Phytologist Trust (2010) that occur during development or during adaptation to environmental stress. Spoel and his co-authors focus on the contribution that protein modification makes to the control of transcriptional reprogramming. In a lucid and highly accessible account they discuss how the activation and repression of genes can be achieved by phosphorylation, ubiquitinylation, S-nitrosylation and disulphide-bonding of transcriptional activators, co-activators and repressor pro- teins. The Minireview provides examples of how these processes operate and their significance in relatively well- understood systems such as yeast. However, the main focus is on the plant immune response and especially on how modification of the immune co-activator protein NPR1 can control its localization and abundance in plant cells. The result is a highly authoritative review of an emerging topic of fundamental importance to our understanding of plant cell biology. New Phytologist also publishes papers of candidates in the final short list, following successful review. Congratulations are due to these candidates who have provided manuscripts on a wide range of topics in plant sciences and which can be read in this issue. • Ward Capoen, Sesbania rostrata: a case study of natural variation in legume nodulation (pp. 340–345) • Colleen Iversen, Digging deeper: fine-root responses to rising atmospheric CO 2 concentration in forested ecosystems (pp. 346–357) • Katherine McCulloh, Moving water well: comparing hydraulic efficiency in twigs and trunks of coniferous, ring- porous, and diffuse-porous saplings from temperate and tropi- cal forests (pp. 439–450) • Rebecca Mosher, Maternal control of Pol IV-dependent siRNAs in Arabidopsis endosperm (pp. 358–364) • Nicholas Rouhier, Plant glutaredoxins: pivotal players in redox biology and iron–sulfur center assembly (pp. 365–372) Thank you to the many applicants who submitted extended abstracts and also to those Editors and Referees who contributed in full to this first enterprise for the New Phytologist Tansley Medal. F. Ian Woodward Editor-in-Chief, New Phytologist (email f.i.woodward@sheffield.ac.uk) Alistair M. Hetherington Tansley review Editor, New Phytologist (email alistair.hetherington@bristol.ac.uk) New Phytologist (2010) 186: 263–264 263 www.newphytologist.com

Modeling organic transformations by microorganisms of soils in six contrasting ecosystems: Validation of the MOMOS model

The Modeling Organic Transformations by Microorganisms of Soils (MOMOS) model simulates the growth, respiration, and mortality of soil microorganisms as main drivers of the mineralization and humification processes of organic substrates. Originally built and calibrated using data from two high‐altitude sites, the model is now validated with data from a 14C experiment carried out in six contrasting tropical ecosystems covering a large gradient of temperature, rainfall, vegetation, and soil types from 65 to 3968 m asl. MOMOS enabled prediction of a greater number of variables using a lower number of parameter values than for predictions previously published on this experiment. The measured 14C mineralization and transfer into microbial biomass (MB) and humified compartments were accurately modeled using (1) temperature and moisture response functions to daily adjust the model responses to weather conditions and (2) optimization of only one parameter, the respiration rate kresp of soil microorganisms at optimal temperature and moisture. This validates the parameterization and hypotheses of the previous calibration experiment. Climate and microbial respiratory activity, related to soil properties, appear as the main factors that regulate the C cycle. The kresp rate was found to be negatively related to the fine textural fraction of soil and positively related to soil pH, allowing the proposition of two transfer functions that can be helpful to generalize MOMOS application at regional or global scale.

No interactive effects of pesticides and plant diversity on soil microbial biomass and respiration

Non-target effects of pesticides are widespread and potentially modify essential ecosystem processes. Since microorganisms are major soil decomposers driving key processes such as organic matter decomposition, nutrient cycling and, thereby, plant productivity, effects of pesticides on soil microorganisms need to be considered. In the context of the biodiversity–ecosystem functioning debate, the question arises if pesticide effects are modulated by the diversity of the plant community. We applied pesticides (dimethoate, chlorpyrifos and fosthiazate) to plots of the Jena Experiment field site differing in plant diversity, and measured basal respiration, biomass and specific respiration of soil microorganisms. Pesticide applications either increased (chlorpyrifos and fosthiazate) or decreased (dimethoate) soil microbial parameters, but the effects neither varied with plant species nor with plant functional group richness.

가축분뇨처리공정의 자동제어 인자 신뢰성 평가 및 적정 외부탄소원 공급량 지표 확립

다양한 조건하에서 가축분뇨처리공정을 운전하면서 각 자동제어 인자의 반응을 분석하고 ORP, DO, pH(mV)-time profile를 이용한 자동제어 신뢰성을 평가하였다. 또한 무산소 조건에서의 잔존 유기물 및 미생물 자기산화에 의한 탈질율을 고려한 적정 외부탄소원 공급량 지표를 파악하였다. 실험은 45L의 유효용적을 지닌 실험실 규모의 SBR 공정을 이용하여 수행되었다. ORP-와 pH(mV)-, DO-time profile 상에서 완전질산화를 의미하는 NBP가 뚜렷하게 발현하던 중 NH4-N의 낮은 부하와 고농도 NOx-N 함유 폐수의 유입 및 불충분한 무산소 조건 제공이 이루어졌을 때 ORP-와 DO-time profile 상에서 NBP가 사라지기 시작하였으며 NOx-N의 지속적인 증가에 의해 ORP 값의 민감성이 둔화되기 시작하였다. 그러나 pH(mV)-time profile은 항상 일정한 변화패턴을 유지하면서 암모니아성 질소의 완전 질산화가 이루어졌을 때 뚜렷한 NBP를 발현하였다. NOx-N/NH4-N의 비가 80:1 수준까지 높아지는 조건하에서도 pH(mV)- time profile상에서의 이러한 안정적 NBP의 발현은 지속되었으며 발현되는 NBP는 MSC(Moving Slope Change)의 변화 패턴을 추적함에 의해 인식되도록 프로그램 할 수 있었다. pH(mV)-time profile에서의 NBP의 발현과 MSC를 이용한 자동제어시점 인식은 반응조내 NOx-N 농도가 무려 300mg/L 이상의 수준에서도 안정적이었다. 유기물 농도에 따른 자동제어 인자의 반응을 분석한 시험에서도 반응조내 유기물의 농도가 STOC 기준 약 10,000mg/L 수준으로 증가함에도 불구하고 pH(mV)-time profile 상에서의 이러한 NBP 발현은 지속되었으며 고농도 유기물 축적 하에서도 동일한 자동제어 알고리즘이 이용될 수 있음을 알 수 있었다. 잔존 유기물과 미생물 자기산화에 의한 탈질율은 약 0.4mg/L.hr로 분석되었으며 안전지수 0.1을 도입하여 산출된 NOx-N 기준 적정 외부탄소원 공급량은 0.83 STOC/NOx-N으로 파악되었다. Responses of real-time control parameters, such as ORP, DO and pH, to the conditions of biological animal wastewater treatment process were examined to evaluate the stability of real-time control using each parameter. Also an optimum index for supplemental carbon source addition based on NOx-N level was determined under a consideration of denitrification rate by endogenous respiration of microorganism and residual organic matter in liquor. Experiment was performed with lab-scale sequencing batch reactor(SBR) and working volume of the process was 45L. The distinctive nitrogen break point(NBP) on ORP-and DO-time profiles, which mean the termination of nitrification, started disappearing with the maintenance of low NH4-N loading rate. Also the NBP on ORP-and DO-time profiles was no longer observed when high NOx-N was loaded into the reactor, and the sensitivity of ORP became dull with the increase of NOx-N level. However, the distinctive NBP was constantly occurred on pH(mV)-time profile, maintaining unique profile patterns. This stable occurrence of NBP on pH(mV)-time profile was lasted even at very high NOx-N:NH4-N ratio(over 80:1) in reactor, and the specific point could be easily detected by tracking moving slope change(MSC) of the curve. Revelation of NBP on pH(mV)-time profile and recognition of the realtime control point using MSC were stable at a condition of over 300mg/L NOx-N level in reactor. The occurrence of distinctive NBP was persistent on pH(mV)-time profile even at a level of 10,000mg/L STOC(soluble total organic carbon) and the recognition of NBP was feasible by tracing MSC, but that point on ORP and DO-time profiles began to disappear with the increase of STOC level in reactor. The denitrfication rate by endogenous respiration and residual organic matter was about 0.4mg/L.hr., and it was found that 0.83 would be accepted as an index for supplemental carbon source addition when 0.1 of safety factor was applied.

Biodegradability of fecal nitrogen in composting process

Biodegradability of fecal nitrogen was studied in composting process. Fecal nitrogen was subdivided into two fractions: a type originally inert in biological activity (N XI), and a slowly biodegradable one (N XS). During the composting process, an inert type of organic matter (N XIB) was reproduced by endogenous respiration of heterotrophic microorganism. Evaluations for fecal nitrogen formed a conclusion of 75% (N XS) and 25% (N XI), respectively. It was estimated that the N XIB could be 9% of initial fecal nitrogen. Thus, approximately 34% (N XI + N XIB) of initial fecal nitrogen remained in the composting material (mixture of sawdust and feces) as biologically inert type of organic nitrogen.

Effects of short-chain chlorinated paraffins on soil organisms

Despite the fact that chlorinated paraffins have been produced in relatively large amounts, and high concentrations have been found in sewage sludge applied to soils, there is little information on their concentrations in soils and the effect on soil organisms. The aim of this study was to investigate the toxicity of chlorinated paraffins in soils. The effects of short-chain chlorinated paraffins (64% chlorine content) on invertebrates ( Eisenia fetida, Folsomia candida, Enchytraeus albidus, Enchytraeus crypticus, Caenorhabditis elegans) and substrate-induced respiration of indigenous microorganisms were studied. Differences were found in the sensitivity of the tested organisms to short-chain chlorinated paraffins. F. candida was identified as the most sensitive organism with LC 50 and EC 50 values of 5733 and 1230 mg/kg, respectively. Toxicity results were compared with available studies and the predicted no effect concentration (PNEC) of 5.28 mg/kg was estimated for the soil environment, based on our data.

Contribution of plant root respiration to the CO2 emission from soil

The respiration activity of roots was studied in field experiments on gray forest and soddy-podzolic soils and under cropland and natural vegetation. It was shown that the contribution of roots to the CO2 emission from the soil surface depends significantly on the method of determination. The contributions of fine and coarse roots to the total root respiration were approximately similar in forest ecosystems. The use of the method of substrate-induced respiration made it possible to obtain the best estimates of the contributions of root respiration and respiration of microorganisms. The application of glucose in the form of a dry mixture with sand or talc instead of in the water-soluble form appeared to be the optimal procedure for determining the root respiration under field moisture conditions.

Contribution of rhizomicrobial and root respiration to the CO2 emission from soil (A review)

Separate determination of root respiration and rhizomicrobial respiration is one of the most interesting, important, and methodologically complicated problems in the study of the carbon budget in soils and the subdivision of the CO2 emission from soils into separate fluxes. In this review, we compare the main principles, the advantages and disadvantages, and the results obtained by the methods of component integration, substrate-induced respiration, respiratory capacity, girdling, isotope dilution, model rhizodeposition, modeling of the 14CO2 efflux dynamics, exudates elution, and the δ13C measurements of the microbial biomass and CO2. Summarizing the results of the determinations performed by these methods, we argue that about 40% of the rhizosphere CO2 efflux is due to root respiration and about 60% of this efflux is due to the respiration of microorganisms decomposing root exudates.

The influence of lead on the respiration and biomass of microorganisms in gray forest soil in a long-term field experiment

The effects of lead oxide and lead nitrate on soil microorganisms were studied in a field experiment. As soon as the soil was treated with lead, a response of the microbial community was expressed in the higher rate of the basal respiration irrespectively of the dose and form of the lead compounds applied. At the same time, the microbial biomass decreased in the variants contaminated with 100–1000 mg Pb/kg. The long-lasting influence of lead lowered the basal respiration and the microbial biomass in the variant with the application of 400–1000 mg Pb/kg in the form of nitrate and 1000 mg Pb/kg as oxide. The experiments proved that the content of mobile lead in the soil, irrespectively of the form and solubility of the lead compounds, controls the functional relationship between the effect of the lead and the microbiological indices of the soil. The suppression of the soil microbial activity by more than 25% took place when the mobile lead content exceeded 170 mg Pb/kg.

Eco-toxicological studies of diesel and biodiesel fuels in aerated soil

The goal of this study was to compare diesel fuel to biodiesel fuel by determining the toxicity of analyzed materials and by quantitatively evaluating the microbial transformation of these materials in non-adapted aerated soil. The toxicity levels were determined by measuring the respiration of soil microorganisms as well as the activity of soil dehydrogenases. The quantitative evaluation of biotransformation of analyzed materials was based on the principle of balancing carbon in the following final products: (a) carbon dioxide; (b) humus compounds; (c) the remainder of non-biodegraded analyzed material; and (d) intermediate biodegradation products and the biomass of microorganisms. The results of these studies indicate that diesel fuel has toxic properties at concentrations above 3% (w/w), while biodiesel fuel has none up to a concentration of 12% (w/w). The diesel fuel is more resistant to biodegradation and produces more humus products. The biodiesel is easily biotransformed.

Biodegradability of chlorinated solvents and related chlorinated aliphatic compounds

The biodegradability of chlorinated methanes, chlorinated ethanes, chlorinated ethenes, chlorofluorocarbons (CFCs), chlorinated acetic acids, chlorinated propanoids and chlorinated butadienes was evaluated based on literature data. Evidence for the biodegradation of compounds in all of the compound categories evaluated has been reported. A broad range of chlorinated aliphatic structures are susceptible to biodegradation under a variety of physiological and redox conditions. Microbial biodegradation of a wide variety of chlorinated aliphatic compounds was shown to occur under five physiological conditions. However, any given physiological condition could only act upon a subset of the chlorinated compounds. Firstly, chlorinated compounds are used as an electron donor and carbon source under aerobic conditions. Secondly, chlorinated compounds are cometabolized under aerobic conditions while the microorganisms are growing (or otherwise already have grown) on another primary substrate. Thirdly, chlorinated compounds are also degraded under anaerobic conditions in which they are utilized as an electron donor and carbon source. Fourthly, chlorinated compounds can serve as an electron acceptor to support respiration of anaerobic microorganisms utilizing simple electron donating substrates. Lastly chlorinated compounds are subject to anaerobic cometabolism becoming biotransformed while the microorganisms grow on other primary substrate or electron acceptor. The literature survey demonstrates that, in many cases, chlorinated compounds are completely mineralised to benign end products. Additionally, biodegradation can occur rapidly. Growth rates exceeding 1 d-1 were observed for many compounds. Most compound categories include chlorinated structures that are used to support microbial growth. Growth can be due to the use of the chlorinated compound as an electron donor or alternatively to the use of the chlorinated compound as an electron acceptor (halorespiration). Biodegradation linked to growth is important, since under such conditions, rates of degradation will increase as the microbial population (biocatalyst) increases. Combinations of redox conditions are favorable for the biodegradation of highly chlorinated structures that are recalcitrant to degradation under aerobic conditions. However, under anaerobic conditions, highly chlorinated structures are partially dehalogenated to lower chlorinated counterparts. The lower chlorinated compounds are subsequently more readily mineralized under aerobic conditions.

Clean rain promotes fine root growth and soil respiration in a Norway spruce forest

AbstractSoil acidification and N saturation are considered to affect the decomposition of soil organic matter as well as growth and mortality of fine roots in many forest soils. Here we report from a field experiment where ‘clean rain’ has been applied to the soil for about 10 years under a roofed plot of a 71‐year‐old Norway spruce plantation at Solling, Central Germany. Reduced amounts of protons (−78%), sulphate (−53%), ammonium (−86%), and nitrate (−49%) were sprayed on the soil surface of the clean rain plot between 1992 and 2001. In an adjacent roofed control plot, throughfall was collected and immediately re‐sprinkled below the roof construction without any chemical manipulation. One year before the clean rain treatment started, live and dead fine root masses (≤2 mm) were determined from undisturbed soil cores down to 40 cm mineral soil depth. Total live fine root mass was significantly lower in the clean rain plot than in the control plot. After the first sampling, the soil holes were refilled with quartz sand and repeatedly sampled in June 1992, June 1996, and October 2001. There were no differences in live and dead fine root masses between the plots in 1992 and 1996. In 2001, both live and dead fine root masses of the clean rain plot were about twice as high as in the control plot, indicating that fine root growth recovered in the mineral soil following 10 years of clean rain treatment. Moreover, the clean rain treatment significantly reduced the total N concentrations of live fine roots and 1‐year‐old needles. Our results suggest that the reduced N input promoted fine root growth to compensate N deficiency. Reduced Al concentration in soil solution may have contributed to the recovery of fine root growth, however, the toxicity of Al species is largely unknown. Mean annual soil respiration rate was 24% higher in the period from 2000 to 2001, indicating that the clean rain treatment increased respiration of roots and heterotrophic microorganisms within the rhizosphere. Laboratory incubation of samples from the organic horizon and the top mineral soil revealed no differences between the plots in the decay rate of soil organic matter. Our results suggest that strong reductions in atmospheric N deposition from about 30 to 10 kg N ha−1 yr−1 and decreasing acid stress can have beneficial effects on growth of fine roots in the mineral soil within a decade. We conclude that biological recovery under reduced atmospheric loads can affect the nutrient and carbon budget of spruce soils in the long run.

Actual Problems of Physiology of Microorganisms

Physiology of microorganisms is traditionally considered as one of branches of microbiology. Fundamental works in this field, the last of which were written almost 40 years ago, included such issues, as chemical composition, physico-chemical properties, metabolism, respiration, reproduction, and growth of microorganisms. For the last few decades, the main efforts of scientists in these fields were concentrated on decoding molecular-genetic mechanisms underlying functioning of microbial cells. At the same time, the accumulated scientific data in adjacent fields of biological science require insistently the necessity of new understanding and systematization of results of study of processes of vital activity of all species of living organisms, based on general integrative physiological principles. By the present time, it has been convincingly proved that the existence of higher organisms is impossible without constant interaction with the world of microbes and, hence, physiology of human, animals or plants is inextricably connected with physiological processes of their inhabiting microorganisms. In the present work the main actual problems of modern physiology of microorganisms are considered, and the necessity of separation of this branch of knowledge as an autonomous part of physiology is emphasized.

Performance of a pilot scale membrane bioreactor coupled with SBR (SM-SBR) - experiences in seasonal temperature changes

The submerged membrane bioreactor is one of the recent technologies for domestic wastewater treatment. In this study, the performance of the pilot-scale submerged membrane bioreactor coupled with sequencing batch reactor (SM-SBR) was investigated. The reactor was operated in sequencing batch modes with a 3-hour cycles consisting of anoxic and aerobic conditions to treat organics, nitrogen and phosphorus. Despite large fluctuations in influent conditions, COD removal was found to be higher than 95%. Sufficient nitrification was obtained within a few weeks after start-up and during the stable period. Moreover, complete nitrification occurred despite of short aeration time. Total nitrogen (TN) removal efficiency was up to 85%. The insufficient organic loading caused by the membrane fouling led to the increase of HRT, leading to endogenous respiration and/or deactivation of nitrifying microorganisms. DGGE patterns confirmed the shift in microbial community structure. The ammonia-oxidizers (i.e. Nitrospira) became dominant in the mixed liquor during long-term operations. Nitrification and denitrification processes were greatly affected by the temperature, while organic removal and phosphorus removal efficiencies were relatively stable below 15°C.

Phosphorus Limitation of Microbial Processes in Moist Tropical Forests: Evidence from Short-term Laboratory Incubations and Field Studies

Although there is a widespread belief that phosphorus (P) limits basic ecosystem processes in moist tropical forests, direct tests of this supposition are rare. At the same time, it is generally believed that P does not limit soil microorganism respiration or growth in terrestrial ecosystems. We used natural gradients in P fertility created by soils of varying age underlying tropical rain forests in southwestern Costa Rica, combined with direct manipulations of carbon (C) and P supply, to test the effects of P availability on the decomposition of multiple forms of C, including dissolved organic carbon (DOC) and soil organic carbon (SOC). Results from a combination of laboratory and field experiments suggest that C decomposition in old, highly weathered oxisol soils is strongly constrained by P availability. In addition, P additions to these soils (no C added) also revealed that microbial utilization of at least labile fractions of SOC was also P limited. To our knowledge, this is the first direct evidence of P limitation of microbial processes in tropical rain forest soil. We suggest that P limitation of microbial decomposition may have profound implications for C cycling in moist tropical forests, including their potential response to increasing atmospheric carbon dioxide. Furthermore, this site is still relatively rich in P when compared to many other tropical forests on old soils; thus, we believe that P limitation of soil microorganisms throughout the humid tropics is a possibility.

Qualitative reasoning and integrated management of the quality of stored grain: a promising new approach

Grain quality maintenance has traditionally been the responsibility of grain storekeepers who rely on measurements of grain or its milled products and on implicit knowledge gained through scientific results, common sense and job experience. Thus, managers of grain stores must comprehend the ecological, economic and technical consequences of their actions. Practical application of available knowledge by a grain-store manager may be greatly enhanced by the combination of fundamental concepts from stored-grain ecosystems with principles of expert systems (ES). The ES are computer programs with the capacity to mimic the reasoning logic of human experts when solving complex problems. They have been available as aids for stored-grain management for about a decade. The existing systems that focus mainly on pest management issues are briefly reviewed in the introductory part. Today, there is increasing pressure on the grain-handling industry to manage not only pests but also a broader range of parameters involved in grain quality maintenance. The implementation of a new type of ES to manage grain quality parameters during storage through an integrated qualitative approach is presented. In practice, most of the existing basic knowledge on progressive changes in grain quality attributes can be approximated by the statement of an initial state of quality and predictive models using only three variables: storage duration, grain temperature and water activity (or related moisture content). Combinations of qualitative variables through a logical decision network, predicting changes in different aspects of quality, may enable the prediction of quality from the initial diagnosis. Such a rule-based reasoning approach called “qualitative reasoning” has recently been developed as a decision support tool, starting from the diagnosis of quality attributes of a grain batch upon delivery at a grain store and anticipating the changes that will occur during the storage period. The new approach, based on high level reasoning methods and using a knowledge base (KB) of interactive rules about grain quality changes, is briefly presented. The implementation of this KB has focused on attributes that change very early in unsafe storage conditions such as germination capacity, micro-organism respiration, dry matter loss, visible moulding appearance, pest dynamics, cooling aeration effects and efficacy of residual protectants. Available models that may be introduced into the KB of the system have been reviewed. Most of the parameters of predictive models can be obtained by computation of existing experimental data. The prototype testing indicates that the system may give reliable quality diagnosis and prediction of optimal storage with a level of expertise and advice comparable to human experts. The additional work needed to extend the scope and domain of applicability of this new generation of ES is discussed. The procedure of qualitative reasoning applied to the whole grain ecosystem is shown to be a promising tool for detecting the weaknesses of basic knowledge about changes in cereal quality during storage.

Microorganisms’ activity and energy fluxes in lake Varese (Italy): a field method

Microorganisms are fundamental components of energy fluxes in aquatic ecosystems. Interest in plankton production and respiration has recently stimulated exploration of the use of electron transfer system (ETS) activity in oceanography and limnology. If we consider microorganism production (MP) and microorganism respiration (MR), due to aerobic and anaerobic metabolism, microorganism growth efficiency can be defined as MGE=MP/(MP+MR). In order to calculate MGE, we measured independently the two components of ETS (photosynthesis electron transfer system activity (PETS) and respiration electron transfer system activity (RETS)) during an annual cycle using a portable biosensor microorganisms amperometric detector system (MiDAS) on the site. MGE was calculated in samples collected from the photic and aphotic zones and the superficial sediment and ranged between 0.60 and 0.45 and dropped to 0.15 at the end of the summer. This substantial decrease is probably due to the prevalence of the anaerobic–heterotrophic metabolism after a pronounced state of anoxia during the summer algal bloom.