RESUMO
Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4(+)), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2(-) and PO4(3-) are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the future.
Assuntos
Fixação de Nitrogênio , Água do Mar/microbiologia , Archaea/genética , Archaea/isolamento & purificação , Bactérias/genética , Bactérias/isolamento & purificação , Cianobactérias/genética , Cianobactérias/isolamento & purificação , Desnitrificação , Processos Heterotróficos , Nitratos/análise , Fixação de Nitrogênio/genética , Oceanos e Mares , Oxirredutases/classificação , Oxirredutases/genética , Oxigênio/análise , Peru , Filogenia , Proteobactérias/genética , Proteobactérias/isolamento & purificação , Água do Mar/químicaRESUMO
OBJECTIVE: We recently found increased temperature and increased bradycardia and desaturation during skin-to-skin care (SSC). We wanted to determine if these effects were related. STUDY DESIGN: Twenty-two infants (median gestational age at birth 28.5 weeks [range 24-31], median age at study 25.5 days [range 10-60 days], median birth weight 1025 g [range 550-1525 g], median weight at study 1320 g [range 900-2460 g]) underwent three 2-hour recordings of breathing movements, nasal airflow, heart rate, and pulse oximeter saturation (SpO 2 ): at thermoneutrality (TN) during incubator care, at TN during SSC, and at elevated temperature (ET) during incubator care. Core temperature was measured via a rectal probe. Recordings were analyzed for the summed rate of bradycardia and desaturation (heart rate <2/3 of baseline; SpO 2 Assuntos
Apneia/etiologia
, Temperatura Corporal
, Bradicardia/etiologia
, Cuidado do Lactente
, Doenças do Prematuro/etiologia
, Feminino
, Frequência Cardíaca
, Humanos
, Incubadoras para Lactentes
, Lactente
, Recém-Nascido
, Recém-Nascido Prematuro
, Masculino
, Oximetria
, Mecânica Respiratória