Browsing by Subject "Nitrogen"

Now showing 1 - 4 of 4
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    Microbial nitrogen limitation in the mammalian large intestine
    (Springer Nature, 2018-12) Reese, Aspen T.; Pereira, Fátima C.; Schintlmeister, Arno; Berry, David; Wagner, Michael; Hale, Laura P.; Wu, Anchi; Jiang, Sharon; Durand, Heather K.; Zhou, Xiyou; Premont, Richard T.; Diehl, Anna Mae; O'Connell, Thomas M.; Alberts, Susan C.; Kartzinel, Tyler R.; Pringle, Robert M.; Dunn, Robert R.; Wright, Justin P.; David, Lawrence A.; Otolaryngology -- Head and Neck Surgery, School of Medicine
    Resource limitation is a fundamental factor governing the composition and function of ecological communities. However, the role of resource supply in structuring the intestinal microbiome has not been established and represents a challenge for mammals that rely on microbial symbionts for digestion: too little supply might starve the microbiome while too much might starve the host. We present evidence that microbiota occupy a habitat that is limited in total nitrogen supply within the large intestines of 30 mammal species. Lowering dietary protein levels in mice reduced their faecal concentrations of bacteria. A gradient of stoichiometry along the length of the gut was consistent with the hypothesis that intestinal nitrogen limitation results from host absorption of dietary nutrients. Nitrogen availability is also likely to be shaped by host-microbe interactions: levels of host-secreted nitrogen were altered in germ-free mice and when bacterial loads were reduced via experimental antibiotic treatment. Single-cell spectrometry revealed that members of the phylum Bacteroidetes consumed nitrogen in the large intestine more readily than other commensal taxa did. Our findings support a model where nitrogen limitation arises from preferential host use of dietary nutrients. We speculate that this resource limitation could enable hosts to regulate microbial communities in the large intestine. Commensal microbiota may have adapted to nitrogen-limited settings, suggesting one reason why excess dietary protein has been associated with degraded gut-microbial ecosystems.
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    Water and nitrogen availability co-control ecosystem CO2 exchange in a semiarid temperate steppe
    (Springer Nature, 2015-10-23) Zhang, Xiaolin; Tan, Yulian; Li, Ang; Ren, Tingting; Chen, Shiping; Wang, Lixin; Huang, Jianhui; Department of Earth Sciences, School of Science
    Both water and nitrogen (N) availability have significant effects on ecosystem CO2 exchange (ECE), which includes net ecosystem productivity (NEP), ecosystem respiration (ER) and gross ecosystem photosynthesis (GEP). How water and N availability influence ECE in arid and semiarid grasslands is still uncertain. A manipulative experiment with additions of rainfall, snow and N was conducted to test their effects on ECE in a semiarid temperate steppe of northern China for three consecutive years with contrasting natural precipitation. ECE increased with annual precipitation but approached peak values at different precipitation amount. Water addition, especially summer water addition, had significantly positive effects on ECE in years when the natural precipitation was normal or below normal, but showed trivial effect on GEP when the natural precipitation was above normal as effects on ER and NEP offset one another. Nitrogen addition exerted non-significant or negative effects on ECE when precipitation was low but switched to a positive effect when precipitation was high, indicating N effect triggered by water availability. Our results indicate that both water and N availability control ECE and the effects of future precipitation changes and increasing N deposition will depend on how they can change collaboratively in this semiarid steppe ecosystem.