1,721,264 research outputs found
Cadmium and zinc toxicity to soil microbial biomass and activity
No full textThe effects of sewage sludge selectively enriched with zinc at the maximum perrniued
level and cadmium at concentration four times the current EU limits on microbial biomass
and activity were tested using soils under different management in a laboratory incubation
experiment. The microbial biomass and activity and the heavy metal mobility were measured
over a period of six months. The resuits showed that neither zinc at the maximum permitted
level nor the cadmium at concentrations as high as four times the curent EU limits may have
major adverse effects on the microbial biomass and respiration of soils
Fresh additions of heavy metals do not model long-term effects on microbial biomass and activity
No full textPrevious work has reported adverse effects of long-term exposures of heavy metals (e.g. Cu, Ni, Cd and Zn) on soil microbial biomass (up to 50% decrease) and microbial activity at metal concentrations around current European Union permitted limits. Our aim was to see if we could model such changes in short-term (up to 50 days) laboratory incubations where soils were given a single pulse of metal salts. Such additions, however, caused only small changes in the measured variables. It was concluded that such short-term incubations are a poor model of changes in microbial biomass or activity due to chronic exposure to metals
Microbial biomass dynamics in recently air-dried and rewetted soils compared to others stored air-dry for up to 103 years
No full textThe activity of microorganisms and the availability of composting substrates for decomposition are seriously affected by drying and rewetting cycles. We have measured microbial biomass C (BC) and ninhydrin reactive N (BNIN) of samples of composting material taken at different times from a pile of ligno-cellulosic wastes. Dynamics of these two parameters in control samples that were kept continuously moist were compared with those of samples of the same material that had been subjected to drying and rewetting. The study was also performed on soils to investigate analogies and differences of behaviour of microbial biomass in such different substrates. Moist samples from 10 soils with different organic C content (6.6-41.9 g kg-1 soil) were analyzed for their BC and BNIN content. The soils were then air-dried, rewetted and incubated at 25°C for 10 days. On days 1, 3, 6 and 10 of incubation, samples were analyzed for BC and BNIN content. Compost samples from different composting stages of a mixture of cotton carding and yard wastes were air-dried, rewetted and incubated at 25°C for 12 days, together with the corresponding moist samples (control). On days 1, 5 and 12 of incubation period, samples were analyzed for BC and BNIN content. The regression coefficient between BC and BNIN for all the compost data (continuously moist and rewetted) was 21.4 (r = 0.89 P < 0.001), very close to values normally found in soils, confirming the reliability of microbial biomass measurements performed on composting substrates. Soil drying caused on average a decrease in the size of microbial biomass with respect to moist samples of 13% for BC and 30% for BNIN. BC and BNIN of moist and rewetted soil samples were always significantly correlated. Microbial biomass contentof rewetted compost samples up to 19 days from the beginning of the process were significantly different, but highly correlated with moist controls. No significant differences between moist and rewetted samples (RW) were found in samples collected during the maturing and curing phases. The different response to drying of soils and compost could be related to the greater increase of new available substrate in compost with respect to soil following the drying-rewetting treatment. Dynamics of BC/BNIN ratio in compost was coherent with the normal trend observed in the composition of microbial community during the process, from prevailing bacteria and actinomycetes to prevailing fungi. © 2002 Elsevier Science B.V. All rights reserved
Stato metabolico e resilienza della biomassa microbica del suolo a seguito di riforestazione
No full textTemperature changes and the ATP concentration of the soil microbial biomass
Full text linkTwo soils from temperate sites (UK; arable and grassland) were incubated aerobically at 0, 5, 15 or 258C for up to 23 days.
During this period both soils were analysed for soil microbial biomass carbon (biomass C) and adenosine 5' triphosphate
contents (ATP). Biomass C did not change signi®cantly in either soil at any temperature throughout, except during days 0 to 1
in the grassland soil. Soil ATP contents increased slowly throughout the 23 days of incubation, from 2.2 to a maximum of 3.1
nmol ATP g
ÿ1 soil in the arable soil (a 40% increase) and from 6.2 to a maximum of 11.2 nmol ATP g
ÿ1 soil in the grassland
soil (an increase of 81%), both at 258C. Since biomass C did not change either with increasing temperature or increasing time of
incubation, it was concluded that an increase in ATP was either due to an increase in adenylate energy charge or de novo
synthesis of ATP, or both. During the incubation, biomass ATP concentrations ranged from about 5 to 12 mmol ATP g
ÿ1
biomass C but trends between biomass ATP and incubation temperatures were not very obvious until about day 13. On day 23,
biomass ATP concentrations were positively and linearly related to temperature: (mmol ATP g
ÿ1 biomass C = 6.9820.35 +
0.13420.023 T0 (r 2 = 0.77) with no signi®cant di erence in the slope between the grassland and arable soils. At 258C the
biomass ATP concentration was 10.3 mmol g
ÿ1 biomass C, remarkably close to many other published values. It was concluded
that, although the biomass increased its ATP concentration in response to increasing temperature, the increase was
comparatively small. Also, at all temperatures tested, the biomass maintained its ATP concentration within the range commonly
reported for micro-organisms growing expontentially in vitro. This is despite the fact that the biomass normally exhibits other
features more typical of a ``resting'' or dormant population Ð a paradox which still is not resolved
Measurement of ATP in soil: correcting for incomplete recovery
No full textMartens [Soil Biol. Biochem. 33 (2001) 701] recently reported that Jenkinson and Oades [Soil Biol. Biochem. II (1979) 193] method for measuring adenosine 5′ triphosphate (ATP) in soil leads to serious underestimations. We have now compared the Jenkinson and Oades extraction technique, which corrects for incomplete extraction of ATP by reference to a 'spike' of added ATP, with a sequential extraction procedure as used by Martens. Measurements of the ATP contents of four soils by the two procedures showed no significant differences, in contrast to Martens' finding
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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