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51.
OLEG V. MENYAILO BRUCE A. HUNGATE WOLF-RAINER ABRAHAM RALF CONRAD 《Global Change Biology》2008,14(10):2405-2419
Forest ecosystems assimilate more CO2 from the atmosphere and store more carbon in woody biomass than most nonforest ecosystems, indicating strong potential for afforestation to serve as a carbon management tool. However, converting grasslands to forests could affect ecosystem–atmosphere exchanges of other greenhouse gases, such as nitrous oxide and methane (CH4), effects that are rarely considered. Here, we show that afforestation on a well-aerated grassland in Siberia reduces soil CH4 uptake by a factor of 3 after 35 years of tree growth. The decline in CH4 oxidation was observed both in the field and in laboratory incubation studies under controlled environmental conditions, suggesting that not only physical but also biological factors are responsible for the observed effect. Using incubation experiments with 13CH4 and tracking 13C incorporation into bacterial phospholipid fatty acid (PLFA), we found that, at low CH4 concentrations, most of the 13C was incorporated into only two PLFAs, 18 : 1ω7 and 16 : 0. High CH4 concentration increased total 13C incorporation and the number of PLFA peaks that became labeled, suggesting that the microbial assemblage oxidizing CH4 shifts with ambient CH4 concentration. Forests and grasslands exhibited similar labeling profiles for the high-affinity methanotrophs, suggesting that largely the same general groups of methanotrophs were active in both ecosystems. Both PLFA concentration and labeling patterns indicate a threefold decline in the biomass of active methanotrophs due to afforestation, but little change in the methanotroph community. Because the grassland consumed CH4 at a rate five times higher than forest soils under laboratory conditions, we concluded that not only biomass but also cell-specific activity was higher in grassland than in afforested plots. While the decline in biomass of active methanotrophs can be explained by site preparation (plowing), inorganic N (especially NH4+) could be responsible for the change in cell-specific activity. Overall, the negative effect of afforestation of upland grassland on soil CH4 uptake can be largely explained by the reduction in biomass and to a lesser extent by reduced cell-specific activity of CH4-oxidizing bacteria. 相似文献
52.
RALF BRITZ 《Zoological Journal of the Linnean Society》1994,112(4):491-508
The anatomy of the anabantoid fish Luciocephalus is reinvestigated and the ontogeny of certain character complexes is described for the first time. Luciocephalus possesses the following previously unrecognized or equivocally interpreted anatomical characters: a clearly separate ectopterygoid bone, pharyngeal processes of the basioccipital, a toothless pharyngeal process of the parasphenoid, an infrapharyngobranchial I and an endoskeletal mental ossification. In addition, aspects of the ontogeny of the hyopalatine arch in the belontiids Belontia, Trichogaster and Ctenops are described. Species of these three genera all possess an ectopterygoid bone previously thought to be lacking in the family Belontiidae. The significance of the results for reconstructing interrelationships of the anabantoid families and the phylogenetic position of Luciocephalus is discussed. A revised hypothesis of anabantoid intrarelationships is presented. Four synapomorphic characters indicate that Luciocephalus is more closely related to the Belontiidae (including Osphronemus) rather than forming the sister group of all other anabantoids. 相似文献