Investigating peste des petits ruminants (PPR) in naturally infected goats and sheep in Anseba Region,Eritrea, by reverse transcription polymerase chain reaction (RT-PCR)     

Oshiek  A. A.  Abdelkadir  M. W.  Mihreteab  Bereket  Mengesha  S. B.  Teklay  G. H.  Yemane  H.  Mesfun  H. G.  Efrem  G. H.  Njeumi  F. 《Tropical animal health and production》2018,50(4):915-920

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Soil respiration characteristics of tropical soils from agricultural and forestry land-uses at Wondo Genet (Ethiopia) in response to C, N and P amendments     

Tesfay Teklay  Anders Nordgren 《Soil biology & biochemistry》2006,38(1):125-133

In most parts of tropical Africa, conversion of forests into agricultural lands is often accompanied by drastic changes in soil properties. However, little study has been done to examine changes in biological properties of soils from different land-uses in response to addition of C and nutrients. We conducted this study with the aim of investigating nutrient limitations for microbial activity in soils from agricultural (farm) and forest land-uses at Wondo Genet (Ethiopia) after amendment with C and limiting nutrients. We measured CO₂ respiration rates from the soils incubated in the laboratory before and after addition of glucose-C together with N and/or P in excess and/or limiting amounts. Based on the respiration kinetics, we determined the basal respiration (BR), substrate-induced respiration (SIR), specific-microbial growth rate (μ), respiration maxima (R_max), % of glucose-C respired, and microbially available N and P in the soils. We found that N was more limiting than P for the micro-biota in the soils considered, suggesting the presence of ample amounts of indigenous P that could be extracted by the micro-biota, if provided with C. Addition of P resulted in a respiration pattern with two peaks, presumably reflecting different N pools being available over time. The SIR, Respiration maxima, μ and microbially available P were higher in soils from the farm, while %C respired was higher in the forest, suggesting increased C costs for micro-biota to be able to utilize nutrients that are strongly bound to organic-matter or clay minerals. Depending on land-use, about 49-69% of added glucose-C was respired during two and a half weeks time, but differences between N or P additions were not significant. The correlation between soil physical and chemical properties and respiration parameters, however, depended on whether N or P was limiting. We concluded that examining the soil respiration kinetics could provide vital information on nutritional status of micro-organisms under different land-uses and on potential availability of nutrients to plants.  相似文献   

The amount of recycled crust in sources of mantle-derived melts   总被引：5，自引：0，他引：5  

Sobolev AV  Hofmann AW  Kuzmin DV  Yaxley GM  Arndt NT  Chung SL  Danyushevsky LV  Elliott T  Frey FA  Garcia MO  Gurenko AA  Kamenetsky VS  Kerr AC  Krivolutskaya NA  Matvienkov VV  Nikogosian IK  Rocholl A  Sigurdsson IA  Sushchevskaya NM  Teklay M 《Science (New York, N.Y.)》2007,316(5823):412-417

Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts (10 to 30%), ocean island and continental basalts (many >60%), and komatiites (20 to 30%). These results imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting.  相似文献   

Temporal changes in soil carbon and nitrogen storage in a hybrid poplar chronosequence in northern Alberta     

Tesfay Teklay  Scott X. Chang   《Geoderma》2008,144(3-4):613-619

Sequestering C in biomass and soils in hybrid poplar plantations can help mitigate global climate change caused by the rising atmospheric CO₂ concentration. However, the impact of the establishment of hybrid poplar plantations on C and N storage and dynamics is poorly understood. We studied the distribution and temporal changes of C and N in soil organic matter (SOM) density fractions in 2-, 5-, 11-, and 13-year-old (age as in 2006) hybrid poplar stands that form a chronosequence by sampling the plantations in both 2004 and 2006. Sodium polytungstate (SPT, density = 1.6 g mL^- 1) was used to fractionate the soil into light (LF, density < 1.6 g mL^- 1), occluded light (LFo, density < 1.6 g mL^- 1) and heavy fractions (HF density > 1.6 g mL^- 1). The results showed that C and N concentrations (g kg^- 1 of fraction) in the SOM density fractions decreased in the order of LFo > LF > HF, while the C/N ratio was in the order of LF > LFo > HF. The amount of C and N stored in the LF, LFo and HF fractions and bulk soil in the top 10 cm of soil was: 149-504, 70-336, 1380-2876 and 1617-3776 g m^- 2, respectively, for C, and 6-26, 3-20, 149-271 and 152-299 g m^- 2, respectively, for N. From 2004 to 2006, C and N storage decreased in the LF and LFo fractions but increased in the HF fraction in the youngest stand. However, stand-age effects were likely muted by high inherent soil variability among the stands. Carbon storage in the light fraction was responsive in the short term to hybrid poplar plantation establishment.  相似文献   

Decomposition of leaves from two indigenous trees of contrasting qualities under shaded-coffee and agricultural land-uses during the dry season at Wondo Genet, Ethiopia     

Tesfay Teklay  Anders Malmer 《Soil biology & biochemistry》2004,36(5):777-786

To explore the potential of trees and shrubs on farmlands on traditional systems in southern Ethiopia, mineralization of macronutrients and loss of organics from leaves of Cordia africana and Albizia gummifera were studied under shaded-coffee and agricultural land-uses during the dry season. Leaves in litterbags were incorporated at 15 cm depth in soil under both land uses and residues were recovered after 2, 4, 8, 12 and 16 weeks. Contents of macronutrients and organics in initial and recovered residues were measured. Single- or double-exponential decay or quadratic functions were fitted to describe patterns of decay or release of various leaf constituents. The two species differed significantly (P<0.05) with respect to contents of ash, N, P, K, cellulose (CEL), lignin (LG), total soluble polyphenols (PL), and condensed tannins (CT). Cordia had higher content of ash, K, P, CEL, LG and a higher C-to-N ratio while Albizia had higher contents of N, PL, CT and a higher C-to-P ratio. Albizia had significantly greater mass loss, N loss and release of CT than Cordia. N was immobilized for the first 4 weeks in most treatments. Across land uses and species, mass loss rates varied from −0.023 week⁻¹ in Cordia to −0.034 week⁻¹ in Albizia (R²>0.70). Higher rate of release of CT seems to have facilitated decomposition in Albizia despite higher initial PL and CT in the leaves of this species. There was no significant land-use effect on any of the variables considered. It was concluded that under drier conditions, tree cover might not affect decomposition, and that organic residues with high content of polyphenols, particularly condensed tannins could decompose faster than those with lower content. This suggests that indigenous tree species with high concentrations of tannins, supposedly considered to be of ‘poor quality’, might still be quite useful as an organic input for improving soil fertility and productivity in the tropics.  相似文献