Anti-fungi activity of organic extracts from the tree Fagara monophylla (Rutaceae) in Venezuela. The tree Fagara monophylla ranges throughout Tropical America. The genus Fagara has a diversity of alkaloid compounds with antibiotic properties; nevertheless, there are few reports antifungal activity of its organic compounds. Organic extracts from Venezuelan F. monophylla were tested for antimicrobial activity against Aspergillus terreus, A. flavus, Penicillium digitatum, P. funiculosum, P. citrinum, Paecilomyces and Candida albicans. Minimal Inhibitory Concentration (MIC) was determined. The susceptibility trials of organic fractions (Hex., CH 2 Cl 2 and MeOH) showed that the highest inhibition was presented by MeOH against A. flavus (55 mm), P. digitatum (60 mm), P. funiculosum (56 mm) and C. albicans (26 mm). The activities of MeOH/EtOAc fractions 1 and 2 suggest a combined effect against A. flavus, P. digitatum and P. funiculosum. The MIC of 1 MeOH/ EtOAc subfraction activity was lower against C. albicans (32 µg/ml) and moderate (128 µg/ml) against P. digitatum. This organic extract has a great antifungal potential. The phytochemical proves and TLC testing on the organic extract, and the MeOH/EtOAc subfraction, respectively, indicated the presence of alkaloid compounds.
Fungal and bacterial biomass as indicators of soil C sequestration in savannas soils substituted by pine plantations. A transformation of any natural ecosystem to an agricultural or forest system leads to an important soil modification, not only in the total carbon pool, but also in the carbon associated to the microbial biomass. This way, carbon quantification on soil quality is important for the determination of impacts of agricultural practices and land use changes. The aim of this study was to the determine, through the selective inhibition technique, the fungal and bacterial biomass, and fungal-to-bacterial ratio (F:B) in pine plantations (Pinus caribaea var. hondurensis), to establish if these parameters are sensible indicators of changes in the carbon content in Uverito soils (Venezuela). Furthermore, the inhibitor additivity ratio (IAR) and total combined inhibition (TCI) were carried out to determine if the antibiotics caused non-target inhibition. The quantification of fungal and bacterial biomass was carried out by using of cyloheximide as fungal inhibitor, and streptomycin and chloranphenicol as specific bacterial inhibitors. This research evidences that this land use change exerted a significant effect on soil microbial biomass, and shows that in pine plantations there is a dominance of the fungal component, in contrast to the native savanna, in which the bacterial biomass dominates. The substitution of native savanna by pine plantation in Uverito promotes a major soil carbon sequestration. The values of the inhibitor additivity ratio (IAR) as for native savanna as pine system, were both >1.0. The total combined inhibition (TCI) was smaller in the pine systems, from which it is possible to infer that a high proportion of microbial biomass was affected by the combination of the inhibitors. Rev. Biol. Trop. 58 (3): 977-989. Epub
Substitution of native savanna by Pinus caribaea (Pinaceae) plantations in Venezuela: effect on parameters that indicated changes in soil carbon content. A great extension (615 000 ha) of native savannas of the eastern plains of Venezuela have been replaced by plantations of Pinus caribaea var. hondurensis; however, only scarce information exists about the impact of this land use on carbon dynamics in soils. We studied the effect of temporal variability and the substitution on the total organic carbon (TOC), water-soluble carbon (WSC), microbial biomass C (Cmic), basal respiration (BR), microbial metabolic quotient (qCO 2) and Cmic/Corg ratio. Selected chemical properties and biological parameters of soils were measured under 3 and 29 year old forest plantations of P. caribaea and an adjacent native savanna which was considered the control. At each site, nine soil composite samples were collected (0-10 cm depth). The studied parameters did not show a defined pattern in relation to temporal variability. Higher carbon preservation occurs in soil microbial biomass under pine plantations. The basal respiration rate and qCO 2 suggests that there is a more efficient microbial carbon utilization in the plantations. The Cmic/Corg ratio shows that the microbial biomass has an important stock of soil carbon in pine plantations. The conversion of savannas to pine plantations can increase soil carbon in the eastern plains of Venezuela, but this must be balanced with the ecological importance of natural savannas ecosystems.
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Microbial activity in Eastern Venezuelan savannas turned into grasslands. We studied the effects of season and management practices on chemical properties and biochemical parameters in a typical Ultisol soil of native and introduced pastures of the Eastern savannas of Venezuela. Sseason, soil management, and their interaction, significantly affected chemical properties and biochemical parameters. The total carbon and the water soluble carbon experienced a significant decrease during the wet pereiod. The basal respiration, the arginine ammonification (AA) and the fluoriscein diacetate hydrolysis showed showed a relatively low microbial activity. The transformation of native savannas to pastures systems of B. brizantha and S. capitata increased the organic matter content in soil. The AA and the basal respiration were sensible indicators to estimate changes in soil quality and also reflected the interaction of temporal changes and management practices. Rev. Biol. Trop. 54(2): 273-285. Epub 2006 Jun 01.
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