The effect of the storage of soils on their microbial activity has been studied using a microcalorimetric method. Soil samples
were kept in closed polyethene bags at 4°C during 3–6 months. Results show changes in the slope of the differentP−t curves recorded from the samples stored at 4°C. This fact strongly suggest the existence of changes of the microbial activity
of soil as the heat evolution is a direct measurement of the cells metabolic activity. The value of the Peak-time (time in
which the microcalorimetric signal reaches the maximum value) is related with the microbial density of soil samples. This
parameter was affected by the time of storage increasing with time. The total heat evolutionQ(t), of the soil samples amended with glucose calculated from the area limited by the Power-Time curves, also decreases with
the time of storage. The soil that had been stored for 6 months before experiments, showed the lowest valu ofQ(t).
Isothermal microcalorimetry is now established as a useful technique for the characterization of the microbial activity in
soil. A brief summary of publications from this field and of instruments used in such work is presented. Several experimental
parameters that can form important sources for systematic errors are discussed and it is suggested that further method work
is made in this area. In most isothermal microcalorimetric investigations on the microbial activity in soil, the samples are
amended with glucose. It is proposed that cellulose also will be used.
Microcalorimetry was used
to study the seasonal evolution over one year of the microbial activity in
a humic-eutrophic Cambisol soil as a function of its forest cover. The study
was carried out on three soils with identical origin but covered with different
forest species: pine, eucalyptus, and a typical Atlantic-humid riverside forest.
Some other physical, chemical and biological
properties and environmental parameters, mainly humidity and environmental
temperature, were considered to analyze their influence on soil microbial
The study was performed using a microcalorimeter Thermal
Analysis Monitor 2277 in which the experiments were carried out with 1 g soil
samples treated with 1.25 mg glucose g–1
soil. From the measured results it follows that pine forest soil is the least
productive of the three, as it generates an average heat of 2.7 vs. 5.9 J g–1 generated
by the eucalyptus forest soil and 3.1 J g–1
generated by the riverside forest soil. These results are dependent on the
remaining physical, chemical and biological features analysed and because
of this, pine forest soil, with a pH value 3.3 in spring, shows a small capacity
to maintain a stable microbial population which is the lowest of the three
(0.079108 to 0.46108
microorganisms g–1 soil) while riverside
soil microbial population is in the range from 7.9108
to 17108 microorganisms g–1
The potential effect of doxycycline on the microbial activity was investigated in three types of soil. Soil samples were spiked with doxycycline, incubated at 25°C and tested at 0, 2, 4 and 6 days after treatment. The microbiological activity of the soil was characterized by the viable count determined by plate pouring and by the time necessary to reach a defined rate of the redox-potential decrease termed as time to detection (TTD).The viable count of the samples was not changed during the storage. The TTD values, however exhibited a significant increase in the 0.2–1.6 mg/kg doxycycline concentration range compared to the untreated samples indicating concentration-dependent inhibitory effect on microbial activity. The potency of the effect was different in the 3 soil types. To describe the combined effect of the doxycycline concentration and time on the biological activity of one type of soil a mathematical model was constructed and applied.The change of microbial metabolic rate could be measured also without (detectable) change of microbial count when the traditional microbiological methods are not applicable. The applied new redox potential measurement-based method is a simple and useful procedure for the examination of microbial activity of soil and its potential inhibition by antibiotics.
Using TAM III multi-channel calorimetry combined with direct microorganism counting (bacteria, actinomycetes and fungi) under
laboratory conditions, we determined the microbial population count, resistance and activity toward cadmium (Cd(II)) and hexavalent
chromium (Cr(VI)) toxicity in soil. The thermokinetic parameters, which can represent soil microbial activity, were calculated
from power-time curves of soil microbial activity obtained by microcalorimetric measurement. Simultaneous application of the
two methods showed that growth rate constant (k), peak-heat output power (Pmax) and the number of living microorganisms decreased with increasing concentration of Cd and Cr. The accumulation of Cr on
E. coli was conducted by HPLC-ICP-MS. Cr6+ accumulation by Escherichia coli was increased steadily with increasing Cr6+ concentration. The results revealed that the change in some thermo-kinetic parameters could have good corresponding relationship
with metal accumulation. Our work also suggests that microcalorimetry is a fast, simple, more sensitive, on-line and in vitro
method that can be easily performed to study the toxicity of different species of heavy metals on microorganism compared to
other biological methods, and can combine with other analytic methods to study the interaction mechanism between environmental
toxicants and microbes.
Summary Soil productivity and health were analyzed using an experimental procedure designed for this kind of studies. The continuous loss of fertile soil obliged the Food and Agriculture Organization (FAO) to declare soil as an item to be protected as a support of the world society welfare. The procedure here described is in accordance with the premises necessary for a rational and sustainable development of soil and the resources it contains and can be used to study any soil all over the world. The study was carried out using soil microbial population as a bioindicator of soil health. Microbial activity was followed using the microcalorimetric technique. The microcalorimetric study can be complemented through a deep analysis of soil physical, chemical and biological properties together with a study of the environmental properties that have a strong influence on the afore mentioned properties and, thus on the microbial activity in soil. The different properties follow different ASTM, ISS/FAO, USDA, etc. well defined standards. The experimental procedure reported in this work could be very helpful to create a data basis that could be useful to quantify and control soil potentiality or design soil decontamination and recovery systems.
This work is a ‘historical’
revision of the evolution of an experimental procedure developed by Prof.
Lisardo Nez and his research group TERBIPROMAT to study the
sustainability and the soil health state.
From the very beginning,
in 1993, the microbial activity was the main bioindicator selected to analyse
the ‘soil health state’. For this reason, a microcalorimetric
technique was used lately to analyse the influence of different human activities
such as reforestations, agricultural exploitation or pollution on the microbial
activity in different soils. Microcalorimetry is the main scientific technique
used in this research to follow the stimulation of the microbial activity
by addition of glucose. The data obtained were complemented by a study of
physical, chemical and biological parameters of soil and allowed to follow
the microbial activity in soils of Galicia (Spain) along the year.
The final results, still in revision, will be helpful in establishing
a data basis for real maps of the ‘health state’ of different
soils. Such maps could be used to design processes that help us to decide
how we should exploit soils ensuring their sustainability.
OM, microbialactivity and N mineralization (N’DAYEGAMIYE & CÔTÉ, 1989). Negative correlation between net nitrification, MBC, and saccharase were reported, while no significant correlations were found between the other microbiological parameters. An