RESUMEN
Non-predatory mortality of zooplankton provides an abundant, yet, little studied source of high quality labile organic matter (LOM) in aquatic ecosystems. Using laboratory microcosms, we followed the decomposition of organic carbon of fresh 13 C-labelled Daphnia carcasses by natural bacterioplankton. The experimental setup comprised blank microcosms, that is, artificial lake water without any organic matter additions (B), and microcosms either amended with natural humic matter (H), fresh Daphnia carcasses (D) or both, that is, humic matter and Daphnia carcasses (HD). Most of the carcass carbon was consumed and respired by the bacterial community within 15 days of incubation. A shift in the bacterial community composition shaped by labile carcass carbon and by humic matter was observed. Nevertheless, we did not observe a quantitative change in humic matter degradation by heterotrophic bacteria in the presence of LOM derived from carcasses. However, carcasses were the main factor driving the bacterial community composition suggesting that the presence of large quantities of dead zooplankton might affect the carbon cycling in aquatic ecosystems. Our results imply that organic matter derived from zooplankton carcasses is efficiently remineralized by a highly specific bacterial community, but does not interfere with the bacterial turnover of more refractory humic matter.
Asunto(s)
Bacterias/metabolismo , Ciclo del Carbono , Daphnia/química , Agua Dulce/microbiología , Zooplancton/química , Animales , Bacterias/clasificación , Bacterias/crecimiento & desarrollo , Bacterias/aislamiento & purificación , Carbono/metabolismo , Daphnia/metabolismo , Daphnia/microbiología , Ecosistema , Procesos Heterotróficos , Zooplancton/metabolismo , Zooplancton/microbiologíaRESUMEN
The biodiversity of bacterial communities along the Yenisei River at section c. 1800 km was studied using next-generation sequencing of 16S rRNA genes and common biodiversity indices. Overall, 3022 unique operational taxonomic units were identified. Actinobacteria and Proteobacteria were the dominant phyla at all sampling sites. The highest alpha-diversity values were found in the middle section of the studied river. The beta-diversity of bacterial assemblages in the river was related to the surrounding landscape (biome): three distinctly different bacterial assemblages occurred in sections of the river, situated in mountain taiga, plain taiga and in a region of permafrost, covered by forest-tundra and tundra. Tributaries arising from these different landscapes likely contributed substantially to the variations of Yenisei bacterial communities. In contrast to a prediction of the river continuum concept, the proportion of photoautotrophic Cyanobacteria in bacterial assemblages did not increase downstream, but peaked at the middle section.