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This study estimates the carbon stock of Banja Forest which is natural and dry Afromontane forest type in Banja District, northwest of Ethiopia. A systematic sampling method was used to identify each sampling point through the Global Positioning System. A total of 63 plots measuring 20 × 20 m were employed to collect tree species and soil data. Losses on ignition and the Walkley–Black method were used to estimate biomass and soil carbon stock, respectively. The carbon stock of trees was estimated using an allometric equation. The results revealed that the total carbon stock of the forest was 639.87 t/ha whereas trees store 406.47 t/ha, litter, herbs, and grasses (LHGs) 2.58 t/ha and soil 230.82 t/ha (up to 30 cm depth). The carbon pools’ carbon stock variation with altitude and slope gradients were not significant (p > 0.05) which was similar to other previous studies. The Banja Forest is a reservoir of high carbon and thus acts as a great sink of the atmospheric carbon. It can be concluded that the Forest plays a role in climate change mitigation. Hence, it should be integrated with reduced emission from deforestation and degradation (REDD+) and the clean development mechanism (CDM) of the Kyoto Protocol to catch monetary benefits.  相似文献   
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Journal of Soils and Sediments - Precipitation data are an important input variable for soil loss (SL) and sediment export (SE) modeling, although they are rarely available at fine spatial and...  相似文献   
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 A study of the effects of different qualities (fresh and composted) and rates (equivalent to 120, 240, and 360 kg N ha–1) of mustard meal application on wheat yields on humid tropical vertisol was started in 1990 at Ginchi Research Station in Ethiopia. After continuous wheat cropping for 7 years and without any further fertilisation, soil microbial parameters (basal respiration, microbial biomass-C and N, organic-C, and ecophysiological quotients) were studied during one growth period. After 7 years of application, mustard meal still exerted a significant positive effect on microbial biomass, basal respiration, organic-C, Cmic : Nmic ratio, and metabolic quotient (qCO2). Organic-C, qCO2 and Cmic : Nmic ratios were higher for the compost-amended plots than plots amended with fresh mustard meal. Basal respiration, Cmic, and Cmic : Nmic ratio showed a clear seasonality, but only in manured plots. The data indicate shifts in microbial community structure (from bacteria to fungi and from r to K strategists) and suggest positive medium-term effects of mustard meal on humid tropical vertisol biological qualities. Received: 25 May 1999  相似文献   
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An ecological model for transmission of Salmonella enterica in swine production ecosystems was developed, identifying host species, environmental reservoirs, and temporal, spatial, and functional (i.e., stage of production) dimensions. It was hypothesized that transmission was most likely within spatial and functional compartments, between hosts of the same species and abiotic compartments of the same type. Eighteen swine production systems in Illinois, USA, were sampled in four collection cycles (1998, 1999, 2000, 2003). There were 11,873 samples collected, including feces from swine and other mammals and birds, and samples from insects, pen floors, boots, feed, and water. The 460 Salmonella isolates obtained were genotyped using repetitive sequence PCR with three primers—REP, BOX, and ERIC. All isolates from 2000 and 2003 were serotyped, as well as a subsample from 1998 and 1998. Genetic relatedness was estimated from the similarity of fragmentation patterns after gel electrophoresis of PCR products. Cluster analysis identified genetically related isolates. Linking of isolates in tight clusters (similarity ≥85%) was viewed as evidence for transmission. Five farms had a sufficient number of tight clusters for hypothesis testing. The factors most differentiating isolates genetically were farm of origin and time of sampling. Isolates were also differentiated genetically by site, building, room, and pen. There was no consistent association of genotype with stage of production or host/environment reservoir. Serotype analysis confirmed that Salmonella lineages were differentiated by visit and site. Thus, Salmonella transmission was primarily over short distances, i.e., within the same pen or room, with some transmission between rooms and buildings on the same site, but with limited transmission between sites. Transmission was observed across a variety of ecological niches represented by different host species and environmental reservoirs. Genetic differences over time reflected multiple introductions into the ecosystem of different Salmonella genotypes, as well as evolutionary changes within lineages. Intervention strategies to reduce Salmonella prevalence within swine production ecosystems would be best targeted at maintaining spatial barriers to transmission, whereas intervention targeted at specific biological hosts or environmental reservoirs is less likely to be effective.  相似文献   
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Common bean (Phaseolus vulgaris L.) is the most important food legume crop in Africa and Latin America where rainfall pattern is unpredictable. The objectives were to identify better yielding common bean lines with good canning quality under drought, and to identify traits that could be used as selection criteria for evaluating drought‐tolerant genotypes. In all, 35 advanced lines were developed through single seed descent and evaluated with a standard check under drought and irrigated conditions at two locations over 2 years in Ethiopia. Grain yield (GY), pod number per m2, seed number per m2 and seed weight decreased by 56%, 47%, 49% and 14%, respectively, under drought stress. Eight genotypes had better yield with good canning quality under drought compared to the check. Moderate to high proportion of genetic effects were observed under drought conditions for GY and yield components compared to genotype × environment effects. Significant positive correlations between GY and pod harvest index (PHI) in drought suggest that PHI could be used as an indirect selection criterion for common bean improvement.  相似文献   
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Pulsed field gel electrophoresis (PFGE) using restriction enzymes AvrII, SpeI, and XbaI, and repetitive sequence polymerase chain reaction (Rep-PCR) using BOX, ERIC, and REP primers, were compared with respect to their ability to detect genetic differences among 68 Salmonella isolates from nine Illinois swine farms. Both genotyping methods had high reproducibility of fragment numbers (reliability>0.9) and sizes (reliability>0.85), and produced approximately the same number of DNA fragments, but Rep-PCR fragment profiles had considerably greater variation. Genetic distances between isolates were calculated from fragment size matching. There was good agreement between the genetic distance matrices for the composite (3-enzyme and 3-primer) methods (Mantel’s r=0.83). PFGE detected slightly greater variation in genetic distances among isolates, but failed to differentiate seven pairs of isolates, three of which were sampled at least 1 month apart and therefore unlikely to be truly identical genetically. In contrast, Rep-PCR identified no isolates as genetically identical. In cluster analyses based on genetic distances, there were moderate differences between PFGE and Rep-PCR (about 2/3 agreement in tight cluster membership). Both PFGE and Rep-PCR were able to differentiate isolates of the same serotype. However, some serotypes (Agona, Anatum, Derby, Infantis, Worthington) were distributed across clusters. There was less agreement between individual primer/enzyme and composite results for Rep-PCR than for PFGE. This greater independence of results for individual primers for Rep-PCR accounted in part for the greater discriminative ability of the composite method. Both composite methods indicated that most Salmonella transmission occurred within a farm and that there was no preference for transmission between specific ecological compartments. Given the equally high reliability of both genotyping methods, the greater discriminative ability of Rep-PCR recommends it as the preferred method for precise detection of transmission links.  相似文献   
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