Methane consumption by proteobacterial methanotrophs in boreal spruce phyllosphere activated with methane

<p>Current knowledge on methane (CH<sub>4</sub>) sinks is limited to chemical processes in the atmosphere, and to methanotrophy in forest soils and peatlands. Recent discoveries have indicated that also tree branches, i.e. phyllosphere, may consume atmospheric CH<sub>4</sub>, thus functioning as a novel CH<sub>4</sub> sink. However,  the process is not yet confirmed and the mechanism not resolved.</p><p>Here, we confirm that leaves and needles of boreal trees have the capacity to consume CH<sub>4</sub> with stable isotope enrichment studies in field and laboratory experiments, and that the consumption is a biological process. With molecular analyses, we confirmed that the activity of needle-associated proteobacterial methanotrophs increased sporadically under CH<sub>4</sub> and acetate enrichment. Our results indicate that CH<sub>4</sub> consumption can exist in the tree canopy, which is characterized by interspecies variation, spatial patchiness and small but significant microbial activity.</p><p>This is a novel symbiotic connection between microbes and plant cells, which can enhance overall carbon sequestration in the boreal forests.</p>

Aquatic ecosystems in Miocene western Amazonia – marine ingressions vs. salt leaching

<p>Before the onset of the modern Amazon river system, north-western South America was shaped by an extensive wetland during the Miocene. This ‘Pebas mega-wetland’ kept a well renowned endemic mollusk and ostracod fauna, which initiated a persisting debate about marine ingressions reaching the center of Amazonia at that time. Due to high endemism, uniformitarian principles are hardly applicable to this biota but also other paleontological, sedimentological and geochemical information led to ambiguous paleoenvironmental interpretations. These results are based on ostracod and foraminiferal assemblages and the oxygen and carbon stable isotopy of their biogenic calcite from an outcrop at the cutbank of the Amazon river (NE-Peru, ~55 km S of Iquitos). While ostracods (e.g., <em>Cyprideis</em>) are able to calcify their carapaces along the entire salinity range, at least low saline conditions are a prerequisite for the biomineralization of calcareous foraminiferan tests. Hence, the finding of calcareous foraminifers (<em>Ammonia</em>, <em>Elphidium</em>), associated mainly with brackish water ostracods, indicates the presence of saline waters. In contrast, δ<sup>18</sup>O- and δ<sup>13</sup>C-analyses performed on co-occurring ostracod valves and foraminiferan tests yielded constantly very light ratios. Such values refer to a pure freshwater environment and are incompatible with the interference of isotopically heavier, marine waters or an evaporative stable isotope enrichment. Based on these opposing data, we hypothesize that the Pebas mega-wetland was episodically influenced by mineralized but isotopically light groundwater discharge. Possibly, the resulting specific hydrochemistry contributed not only to the evolution of the endemic Pebasian fauna but also facilitated the sporadic settlement of euryhaline foraminifers, which mimics short-lived marine incursions.</p>

Stable isotope analysis spills the beans about spatial variance in trophic structure in a fish host – parasite system from the Vaal River System, South Africa

BackgroundStable isotope analysis offers a unique tool for comparing trophic interactions and food web architecture in ecosystems. This approach is based on analysis of the stable isotope ratios of carbon (13 C/ 12 C) and nitrogen (15 N/ 14 N) in organisms. Studies comparing stable isotope enrichment in hosts and parasites have shown that parasites are variably enriched in stable isotopes relative to the host.MethodsSharptooth catfish (Clarias gariepinus) were collected from six sites along the Vaal River, South Africa and were assessed for ectoparasites and endoparasites. Lamproglena clariae (Copepoda), Tetracampus ciliotheca and Proteocephalus glanduligerus (Cestoda), and larval Contracaecum sp. (Nematoda) were collected from the gills, intestine and mesenteries, respectively. Signatures of δ 13 C and δ 15 N were analysed in host muscle tissue and parasites using bulk stable isotope analysis.ResultsStable isotope enrichment was variable between parasites and the host fish, with L. clariae and the host sharing similar δ 15 N signatures and the endoparasites being depleted in both δ 13 C and δ 15 N relative to the host. Spatial differences in enrichment of stable isotopes were also identified. Fish and parasites collected from below the Vaal River Barrage were more enriched in the 15 N isotope than hosts and parasites collected from other sites. The opposite was identified for 13 C isotope fractionation.ConclusionDifferences in stable isotope enrichment in parasites infecting C. gariepinus could be related to the feeding strategy of each parasite species collected. Enrichment of δ 15 N in L. clariae would relate to the micropredatory nature of this parasite, which feeds on whole blood of the host fish. Depleted isotope levels in endoparasites could relate to their absorptive feeding strategy on metabolic by-products of the host. Spatial differences in both host and parasite tissues identified likely resulted from differences in the diet of the host and related with availability of prey items for the host fish.

Stable Isotope Marking of Laboratory-Reared Aedes aegypti (Diptera: Culicidae)

The use of stable isotope enrichment to mark mosquitoes has provided a tool to study the biology of vector species. In this study, we evaluated isotopic marking of Aedes aegypti (L.) (Diptera: Culicidae) in a laboratory setting. We determined the optimal dosage for marking adult Ae. aegypti mosquitoes with 13C and 15N. Additionally, Ae. aegypti mosquitoes were single and dually marked with 13C and 15N for up to 60 d postemergence without changes to adult body size or transgenerational marking. This report adds to the growing literature that explores the use of alternative marking methods for ecological and vector biology studies.