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  • 34.50.H  (1)
  • Microbial biomass carbon  (1)
  • Soil microbial population  (1)
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  • 1
    ISSN: 1432-0789
    Keywords: Key words Mesquite ; Carbon dioxide production ; Nitrogen mineralization ; Microbial biomass carbon ; Nitrous oxide production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In the central highlands of Mexico, the vegetation is dominated by mesquite (Prosopis spp.), a leguminous tree or shrub. An experiment was carried out to investigate how cultivating the land and the disappearance of the natural ecosystem affected the biological functioning of the soil. Soil was sampled from under the canopy of isolated (MESQ treatment) and densely growing mesquite trees (DENS treatment), from the surrounding soil not covered by the canopies of the trees (BARE treatment) and from adjacent land cultivated with maize (ARABLE treatment). Soil was characterized and then incubated aerobically for 39 days at 22±1  °C and CO2, N2O production, microbial biomass C and inorganic N concentrations were monitored. The organic C content was 2.3 times and 1.1 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while microbial biomass C was 3.5 times and 1.3 times greater. The microbial biomass activity as expressed by CO2 production was 5.9 times and 3.9 times greater in the MESQ and the BARE treatments, respectively, than in the ARABLE treatment, while N mineralization, as witnessed by the increase in NO3 – concentrations, was 3.4 times and 1.7 times greater. No significant amounts of N2O were produced in any of the treatments. It was found that cultivating land characterized by the presence of mesquite changed its characteristics profoundly, and even soil not covered by tree canopies had higher microbial biomass C, and C and N mineralization than soil cultivated with maize and beans.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0789
    Keywords: Key words Catclaw ; Carbon dioxide production ; Inorganic N dynamics ; Soil microbial population
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In the central highlands of Mexico, heavily eroded soils are often colonized by catclaw (Mimosa buincifiera): an N2-fixing shrub. An experiment was carried out to investigate how this shrub affected characteristics of the soil and its biological functioning. Soil was sampled from outside and under the canopy of catclaw at three sites characterized by different degrees of erosion and an increase in plant density. The soil microbial biomass C, total amounts of bacteria, fungi, actinomycetes and free-living N2-fixing micro-organisms were measured, while production of CO2 and dynamics of nitrate (NO3 –), nitrite (NO2 –) and ammonium (NH4 +) were monitored in an aerobic incubation at 22±1  °C for 35 days. The C content was 1.6 times greater in the area with the largest density of plants and the least erosion (RECUP) compared with the site with the lowest density and greatest erosion (DEGR), while it was 1.2 times greater under the canopy of the catclaw than outside it (average of the three sites). The incorporation of N into the soil organic matter was greater under the canopy of the catclaw than outside it as the C:N ratio was on average 8.4 and 9. 1, respectively. The microbial biomass C, as a percentage of soil organic matter, was 1.5 times greater in the RECUP than in the DEGR site. Greatest total number of colony-forming bacteria and fungi (mean of organisms found under and outside the canopy) were found in the RECUP treatment and lowest in the DEGR treatment. Free-living N2-fixing organisms and actinomycetes showed opposite trends. Greater total numbers of colony-forming bacteria, fungi, actinomycetes and free-living N2-fixing organisms (mean of the three treatments) were found under the canopy of catclaw than outside of it, Production of CO2 was 1.8 times greater in the RECUP than in the DEGR and 1.6 times greater under the canopy of catclaw than outside. Production of NO3 – was 1.3 times greater in the RECUP than in the DEGR and 3.5 times greater under the canopy of catclaw than outside. There was no significant effect of location or canopy on NO2 – and NH4 + concentrations. It is concluded that the natural vegetation of catclaw increased microbial biomass and soil organic matter content under, but also outside its canopy, and preserved N better, releasing greater amounts of inorganic N upon mineralization. Catclaw can serve as a first colonizer of heavily eroded soil and be replaced by other vegetation, natural or crops, when fertility is restored.
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  • 3
    ISSN: 1434-6079
    Keywords: 34.50.H ; 79.20.N ; 61.14.F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this note we correct previous evidence, according to which a structure, found in double-differential electron distributions induced by ion beam-foil interaction, could be interpreted in terms of Bragg diffraction. We now attribute this structure to a distortion of the electric field of our spectrometer and present distributions taken with a new equipment in which this distortion is eliminated.
    Type of Medium: Electronic Resource
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