Sergio Feijóo

The effect of soil moisture on soil microbial activity studied by microcalorimetry

Abstract Microcalorimetry has been used to study the effect of moisture on soil microbial activity. Different moisture regimes produce changes on heat flow rate-time curves recorded for soil samples, affecting also certain parameters, such as the total heat evolution Q tot , the microbial growth rate constant μ and growth yield Y , which are calculated by the microcalorimetric method. A positive correlation was found between the percentage humidity, the total heat evolution and the microbial growth rate constant. The values of these parameters decrease with the dryness of the soil. Field capacity moisture appears to be the optimum moisture level for soil microbial activity.

Interpretation of the Metabolic Enthalpy Change, ΔHmet, Calculated for Microbial Growth Reactions in Soils

AbstractThe microcalorimetric method was used to calculate the metabolic enthalpy change per mol of glucose degraded by soil microorganisms, ΔHmet. This parameter has been calculated by microcalorimetry for many organic, inorganic and biochemical reactions, but there is only some information about its quantification for microbial growth reactions in soils. Values of ΔHmet were calculated for different soil samples collected in Galicia (Spain) and Campinas (Săo Paolo, Brazil). Exponential microbial growth was stimulated in all soil samples by the addition of glucose and power-time curves were recorded. Results showed changes in the values of ΔHmet calculated for all the soil samples, suggesting a dependence of this value with the microbial growth rate constant, with the percentage of growth, with the initial number of microorganisms of soil samples, with the quantity of glucose added and with the strain of bacteria growing in soil.The interpretation of variations of ΔHmet provides important qualitative and quantitative information. It reports data that allow to interpret from a qualitative point of view, the increase in biomass as a consequence of the degradation of the organic matter in soil, to understand changes in the percentages of soil organic matter and to know if the microbial population growing in differential soil samples is homogeneous. Therefore, to report that value would be very important in ecological studies, but beforehand, it is necessary to solve some problems that can appear in the experiments done to make the quantification .

A combined mass and energy balance to provide bioindicators of soil microbiological quality.

In this work, a method is proposed to quantify the efficiency of carbon utilization by soil microbes. Microcalorimetry was used to compute the heat yield (Y(Q/X)) of six soil samples collected in the Amazon. A combined mass and energy balance is developed to quantify the enthalpy of the glucose oxidation reaction (Delta(r)H(s)) and the biomass yield (Y(X/S)) from the experimental values of Y(Q/X). Results were compared by graphical analysis to establish the kinetics of the glucose oxidation and the microbial growth reactions in terms of energy dissipation. The correlations found suggest that the measured values for Y(Q/X) and Delta(r)H(s) are biomass yield dependent. The main environmental factors affecting the kinetics of the glucose oxidation and the microbial growth reactions in soils are the initial microbial population and the percentage of nitrogen of the samples. The comparative study among the samples showed that the deforestation of the Primary forests in the Amazon to establish arable lands, affected the efficiency of the carbon utilization by soil microorganisms.

Comparative study of the microbial activity in different soils by the microcalorimetric method

Abstract Microcalorimetry was applied to the study of the microbial activity of four soils with different percentages of organic matter. The qualitative study of the heat flow rate-time curves, recorded from soil samples amended with glucose, showed remarkable differences in the soil microbial activity. In order to show results in a more quantitative way, the total heat evolution, Q tot , the total heat evolution of soil samples amended with glucose, Q tot(glc.) , and the values of peak time and microbial growth rate constant, μ, were calculated from the heat flow rate-time curves recorded from all samples. Values of peak time increased with decreased microbial density and a positive correlation between total heat evolution, Q tot , and percentage of organic matter, was found. Microcalorimetry appears as a suitable technique to carry out both qualitative and quantitative comparative studies of microbial activity in soils.

Microcalorimetric determination of the cell specific heat rate in soils: relationship with the soil microbial population and biophysic significance

Microcalorimetry was applied to study the basal respiration in several soils collected in Galicia (Northwest Spain) and in the Brazilian Amazon. The microbial activity was recorded microcalorimetrically as power–time lines during 24 h. The soil mass specific heat rate JQ/S and the cell specific heat rate JQ/N were calculated, and compared to the microbial population of the soil samples and to the number of microorganisms per organic carbon. Results showed an inverse hyperbolic relation between JQ/N and number of microorganisms of the samples, and between JQ/N and the number of microorganisms per organic carbon. The microcalorimetric indexes of microbial activity were affected by some other soil properties, as percent of carbon, nitrogen, and C/N ratio, as well as by the introduction of agriculture, which affected the microbial population. We believe that the cell specific heat rate can be considered as an index that indicates the efficiency of the energy utilization by soil microorganisms, similarly to the specific respiration activity. The reason of its negative correlation with the microbial density could be attributed to changes in the strategy of the energy utilization by microorganisms in soils.

Context effects in the auditory identification of Spanish fricatives /f/ and /θ/: Hyper and Hypospeech

Twenty‐eight subjects heard 40 Spanish words in which the initial fricative was /f/ or /θ/, combined with vowels /e/ and /u/. Ten words were used for each particular combination (2 fricatives×2 vowels ×10 words). Two forms of speech (Hypo and Hyperspeech) and four conditions were considered: (1) Isolated fricative segment; (2) fricative segment + 51.2 ms of the following vowel; (3) fricative + whole following vowel; (4) whole word. The statistical analysis showed that, despite their differences in production and acoustic characteristics, isolated fricative segments were equally recognized in Hypo and Hyperspeech (cond. 1). Including the vowel ( conditions 2 and 3) significantly improved recognition of both fricatives for both forms of speech, except for the combination /f/+/e/: While fricative identification improves slightly in Hyperspeech, in Hypospeech, recognition decreases with respect to cond. (1). For this particular combination, an acceptable recognition rate is only achieved in the whole word con...

Perceptual effects of coarticulation in fricatives

The perceptual interaction between the consonant and the vowel in fricative+vowel syllables is evaluated. A set of conflicting cue stimuli was used to measure the relative importance of: (a) the influence of the vowel in the previous consonant, and (b) the influence of the fricative in the following vowel. It is concluded that the perceptual interaction between the consonant and the vowel in fricative-vowel syllables can not be explained only by the coarticulatory influence of the consonant or vowel on adjacent segments. The influence of the vowel in the previous fricative is perceptually irrelevant, while the influence of the fricative in the following vowel is more important for the identification of //spl theta// and /f/ than for /s/ and //spl int//. Actually it is perceptually irrelevant for //spl int// and a little important for /s/. Besides the influence of the fricative in the following vowel is notably dependent on the particular vowel.

Influence of frequency range in the perceptual recognition of fricatives

The objective of this paper is to study the importance of various frequency bands for the identification of fricatives. Tokens were CV syllables formed by the combination of the Galician fricatives /θ,f,s,∫/ and the vowels /a,e,i,o,u/ which were pronounced in Hyperspeech form by a man and a woman. Tokens were sampled at 32 kHz and low‐pass filtered with cutoff frequencies of 11, 8, 5.5, 4, and 3 kHz. Thus, the total number of tokens was 240=4 fricatives× 5 vowels× 2 sexes× 6 frequencies. Thirty‐seven listeners carried out the perceptual experiments in two conditions: (1) whole fricative noise plus 100 ms of the following vowel, and (2) whole fricative noise. The results of the perceptual experiments show that as the cutoff frequency is lowered, (a) /s/ tends to be recognized as /θ/ in both conditions; (b) the fricative noise of /θ/ tends to be recognized as /f/, and (c) recognition of /f/ and /∫/ is affected to a lesser extent. Results suggest the importance of low‐frequency energy in the characterization...

Effect of soil storage at 4 °C on the calorespirometric measurements of soil microbial metabolism

Soil samples must usually be stored for a time between collection and measurements of microbial metabolic properties. However, little is known about the influence of storage conditions on microbial metabolism when studied by calorespirometry. Calorespirometry measures the heat rate and the CO2 rate of microbial metabolism, where the ratio of heat and CO2 released, the calorespirometric ratio, informs about the nature of substrates being used by microorganisms. Application to soil microbiology is very recent, and little is known about the influence of the common soil preparation practices between collection and analysis on the calorespirometric measurements. For these reasons, the effect of storage at 4 °C on the microbial metabolism was determined by calorespirometry. Results show CO2 production rate decreases with storage time while the evolution of metabolic heat rate is more stable. The calorespirometric ratio increases with storage time in soil samples with organic matter characterized by lower carbohydrate contribution to the total carbon and higher aromaticity and is unaffected in soil samples with lower carbohydrates in the organic matter and higher aromaticity. Therefore, the calorespirometric ratio values may vary for the same soil sample, such that the soil organic matter properties, as well as the time stored at 4 °C, must be considered in interpreting calorespirometric data on soils.

Computer analysis of speech intelligibility in classrooms.

The objective of this research is to study the relationship between classroom characteristics and speech intelligibility in order to optimize the amount of acoustic treatment and its position in the room. A rectangular shaped room was modeled with the ULYSSESS acoustic analysis software. Total sound level, first reflections, the difference between direct and reflected sound, reverberation time, ALCONs, and STI were calculated. The amount of absorption treatment and its position in the room, as well as the number of people in the room, were the variables studied. Results show that the amount of absorption treatment and the number of people in the room were much more important than the position of both the absorbent materials and the students to obtain good intelligibility scores. Nevertheless, for similar intelligibility scores, overall sound level is higher when the amount of absorbent material is controlled, allowing the listeners in the rear to benefit from higher speech levels. A reduction of 78% in th...