228 research outputs found
Microbial diversity and microbial activity in the rhizosphere
No full textIt is well established that microbial life only occupies a minor volume of soil being localised in hot spots such as the rhizosphere soil (Nannipieri et al., 2003), where microflora has a continuous access to a flow of low and high molecular weight organic substrates derived from roots. This flow, together with specific physical, chemical and biological factors, can markedly affect microbial activity and community structure of the rhizosphere soil
Nannipieri, P., Ascher, J., Ceccherini, M.T., Landi, L., Pietramellara, G. & Renella, G. 2003. Microbial diversity and soil functions. European Journal of Soil Science, 54, 655–670.: Reflections by P. Nannipieri, J. Ascher-Jenull, M. T. Ceccherini, L. Giagnoni, G. Pietramellara & G. Renella
No full textOur review of 2003 discussed the meaning of both microbial diversity and microbial activity at the dawn of the ‘soil omics’ era. It focused on problems with the methods to determine them and on the main ways that soil functions depend on microbial processes. Between 2003 and 2016, the molecular techniques applied in the study of soil microbial diversity have improved markedly. Sequencing techniques today provide accurate estimates of microbial diversity in soil, whereas determining the expression of microbial genes as synthesized proteins is still problematic (Renella et al., 2014a). The assumption was and still is that with a fuller understanding of microbial diversity we might be able to control some soil functions. This is a fallacy because soil functions depend on microbial activity and not only on microbial diversity. A better understanding of the link between microbial diversity and microbial activity might be obtained by an integration of molecular and classical techniques. Sequencing techniques have confirmed the primary role of soil properties in shaping soil microbial diversity and the redundancy of species involved in soil processes such as the mineralization of organic C. Future research should improve techniques for the characterization of soil proteomics, promote the combination of classical and molecular approaches, promote hypothesis‐ more than technology‐driven research and propose molecular markers as indicators of soil quality, for example, the gene copy/gene expression or gene/enzyme activity ratios
Soil Organic Matter in Dryland Ecosystems
No full text<p>Drylands are regions with low rainfall, high temperatures and very high evapotranspiration, as well as limited plant biomass production. Covering more than 45% of the Earth’s land surface and being inhabited by more than 35% of the world population, drylands are of paramount importance for global sustainability. Among the many factors that influence the ability of drylands to provide essential ecosystem services, soil organic matter deserves special attention. This chapter provides an overview of the quantity of soil organic matter in dryland ecosystems, the main factors regulating its formation and conservation, its vulnerability to ongoing global changes, and existing options to preserve or even enhance this essential natural resource.</p>
High Performance Distributed Optical Fiber Sensors based on Raman Scattering
No full textWe present advanced techniques for high performance Raman distributed temperature sensing systems, based on graded index multi-mode and standard single-mode fibers. Advanced coding allows for ultra-long sensing capabilities with meter or sub-meter scale spatial resolution
Nannipieri, P., Ascher, J., Ceccherini, M.T., Landi, L., Pietramellara, G. & Renella, G. 2003. Microbial diversity and soil functions. European Journal of Soil Science, 54, 655-670.: Reflections by P. Nannipieri, J. Ascher-Jenull, M. T. Ceccherini, L. Giagnoni, G. Pietramellara & G. Renella
No full textLandmark papers. Our review discussed the meaning of both microbial diversity and microbial activity at the dawn of the ‘soil omics’ era. It focused on problems with the methods to determine them and on the main ways that soil functions depend on microbial processes. Between 2003 and 2016, the molecular techniques applied in the study of soil microbial diversity have improved markedly. Sequencing techniques today provide accurate estimates of microbial diversity in soil, whereas determining the expression of microbial genes as synthesized proteins is still problematic (Renella et al., 2014a). The assumption was and still is that with a fuller understanding of microbial diversity we might be able to control some soil function
The Seven Grand Questions on Soil Microbiology (Selman A. Waksman, Reexamined by Arthur D. McLaren)
No full textMicrobiology has flourished ever since the discovery and description of microorganisms as agents —invisible to the naked eye —that are ubiquitous and have key capacities of transforming matter and causing disease. A major characteristic of soil as a biological system is the capacity of surface-reactive soil particles to adsorb key biological molecules, such as proteins and nucleic acids. A plethora of nitrogen fixers, ammonia oxidizers, nitrate reducers, sulfate reducers, iron reducers, next to fermenters, and straightforward aerobic organic carbon degraders could be isolated from soil. A large suite of developments with respect to the mechanisms that underlie interactions in soil also aims to unravel the molecular events that trigger particular associative or antagonistic responses. The role of soil organic matter (SOM) as the basis of soil fertility across many soils has been extensively documented. Interactions between SOM and complex human–natural systems require new research into regional and global SOM budgets.<br/
Quantitative assessment of hydrolase production and persistence in soil
No full textThe aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated by adding glucose and nitrogen. Glucose mineralization was monitored by CO2-C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t H and Pe = (r / H)Δt, respectively, where H indicates the peak value of each measured hydrolase activity, t H is the time of the peak value, r indicates the residual activity value, and Δt is the time interval t r - t H, where t r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation at the enzyme molecular level
Modern soil microbiology
No full textIn the ten years since the publication of Modern Soil Microbiology, the study of soil microbiology has significantly changed, both in the understanding of the diversity and function of soil microbial communities and in research methods. Ideal for students in a variety of disciplines, this second edition provides a cutting-edge examination of a fascinating discipline that encompasses ecology, physiology, genetics, molecular biology, and biotechnology, and makes use of biochemical and biophysical approaches. The chapters cover topics ranging from the fundamental to the applied and describe the use of advanced methods that have provided a great thrust to the discipline of soil microbiology. Using the latest molecular analyses, they integrate principles of soil microbiology with novel insights into the physiology of soil microorganisms. The authors discuss the soil and rhizosphere as habitats for microorganisms, then go on to describe the different microbial groups, their adaptive responses, and their respective processes in interactive and functional terms. The book highlights a range of applied aspects of soil microbiology, including the nature of disease-suppressive soils, the use of biological control agents, biopesticides and bioremediation agents, and the need for correct statistics and experimentation in the analyses of the data obtained from soil systems.</p
Impact of Loss variations on Double-Ended Distributed Temperature Sensors Based on Raman Anti-Stokes Signal Only
No full textWe present a theoretical and experimental analysis
of the sensing capabilities of Raman-based distributed tempera-
ture optical Þber sensor (RDTS) systems using only the anti-Stokes (AS) component in loop conÞguration. In particular, the effects of time- and wavelength-dependent losses on the sensor performance are thoroughly investigated under different experimental condi tions. As expected from the developed theory, experimental results demonstrate that using the loop AS-light only approach in RDT systems can correct the impact of local and wavelength-dependent losses on the final temperature measurements, with the simple use of an internal calibration Þber spool at a known temperature value. Signal-to-noise ratio and temperature resolution analyses of the AS-only RDTS point out an improved temperature resolution in comparison to standard RDTS systems in loop conÞguration
Distribution of microbial communities in a forest soil profile investigated by microbial biomass, soil respiration and DGGE of total and extracellular DNA
No full textAbstract
We studied the distribution of the indigenous bacterial and fungal communities in a forest soil profile. The composition of bacterial and fungal communities was assessed by denaturing gradient gel electrophoresis (DGGE) of total and extracellular DNA extracted from all the soil horizons. Microbial biomass C and basal respiration were also measured to assess changes in both microbial biomass and activity throughout the soil profile. The 16S rDNA-DGGE revealed composite banding patterns reflecting the high bacterial diversity as expected for a forest soil, whereas 18S rDNA-DGGE analysis showed a certain stability and a lower diversity in the fungal communities. The banding patterns of the different horizons reflected changes in the microbial community structure with increasing depth. In particular, the DGGE analysis evidenced complex banding patterns for the upper A1 and A2 horizons, and a less diverse microflora in the deeper horizons. The low diversity and the presence of specific microbial communities in the B horizons, and in particular in the deeper ones, can be attributed to the selective environment represented by this portion of the soil profile. The eubacterial profiles obtained from the extracellular DNA revealed the presence of some bands not present in the total DNA patterns. This could be interpreted as the remainders of bacteria not any more present in the soil because of changes of edaphic conditions and consequent shifting in the microbial composition. These characteristic bands, present in all the horizons with the exception of the A1, should support the concept that the extracellular DNA is able to persist within the soil. Furthermore, the comparison between the total and extracellular 16S rDNA-DGGE profiles suggested a downwards movement of the extracellular DNA
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