Nitrogen isotopes reveal independent origins of N 2 -fixing symbiosis in extant cycad lineages.

Autor: Kipp MA; Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA. michael.kipp@duke.edu.; Virtual Planetary Laboratory, NASA Astrobiology Institute, Seattle, WA, USA. michael.kipp@duke.edu.; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA. michael.kipp@duke.edu.; Division of Earth and Climate Sciences, Nicholas School of the Environment, Duke University, Durham, NC, USA. michael.kipp@duke.edu., Stüeken EE; Virtual Planetary Laboratory, NASA Astrobiology Institute, Seattle, WA, USA.; School of Earth & Environmental Sciences, University of St. Andrews, St. Andrews, UK., Strömberg CAE; Department of Biology, University of Washington, Seattle, WA, USA.; Burke Museum of Natural History and Culture, Seattle, WA, USA., Brightly WH; Department of Biology, University of Washington, Seattle, WA, USA., Arbour VM; Department of Knowledge, Royal BC Museum, Victoria, British Columbia, Canada., Erdei B; Botanical Department, Hungarian Natural History Museum, Budapest, Hungary., Hill RS; School of Biological Sciences and the Environment Institute, University of Adelaide, Adelaide, South Australia, Australia., Johnson KR; Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA., Kvaček J; Department of Palaeontology, National Museum, Prague, Czech Republic., McElwain JC; Department of Botany, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland., Miller IM; National Geographic Society, Washington, DC, USA., Slodownik M; School of Biological Sciences and the Environment Institute, University of Adelaide, Adelaide, South Australia, Australia., Vajda V; Research Division, Swedish Museum of Natural History, Stockholm, Sweden.; Department of Geology, Lund University, Lund, Sweden., Buick R; Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA.; Virtual Planetary Laboratory, NASA Astrobiology Institute, Seattle, WA, USA.
Jazyk: angličtina
Zdroj: Nature ecology & evolution [Nat Ecol Evol] 2024 Jan; Vol. 8 (1), pp. 57-69. Date of Electronic Publication: 2023 Nov 16.
DOI: 10.1038/s41559-023-02251-1
Abstrakt: Cycads are ancient seed plants (gymnosperms) that emerged by the early Permian. Although they were common understory flora and food for dinosaurs in the Mesozoic, their abundance declined markedly in the Cenozoic. Extant cycads persist in restricted populations in tropical and subtropical habitats and, with their conserved morphology, are often called 'living fossils.' All surviving taxa receive nitrogen from symbiotic N 2 -fixing cyanobacteria living in modified roots, suggesting an ancestral origin of this symbiosis. However, such an ancient acquisition is discordant with the abundance of cycads in Mesozoic fossil assemblages, as modern N 2 -fixing symbioses typically occur only in nutrient-poor habitats where advantageous for survival. Here, we use foliar nitrogen isotope ratios-a proxy for N 2 fixation in modern plants-to probe the antiquity of the cycad-cyanobacterial symbiosis. We find that fossilized cycad leaves from two Cenozoic representatives of extant genera have nitrogen isotopic compositions consistent with microbial N 2 fixation. In contrast, all extinct cycad genera have nitrogen isotope ratios that are indistinguishable from co-existing non-cycad plants and generally inconsistent with microbial N 2 fixation, pointing to nitrogen assimilation from soils and not through symbiosis. This pattern indicates that, rather than being ancestral within cycads, N 2 -fixing symbiosis arose independently in the lineages leading to living cycads during or after the Jurassic. The preferential survival of these lineages may therefore reflect the effects of competition with angiosperms and Cenozoic climatic change.
(© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)
Databáze: MEDLINE
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