Coastal wetlands provide valuable ecosystem services that are increasingly threatened by anthropogenic activities1. The atmospheric carbon dioxide (CO2) concentration has increased from 280 ppm to 404 ppm since the Industrial Revolution and is projected to exceed 900 ppm by 2100 (ref. 2). In terrestrial ecosystems, elevated CO2 typically stimulates C3 plant photosynthesis and primary productivity leading to an increase in plant size3. However, compared with woody plants or crops4, the morphological responses of clonal non-woody plants to elevated CO2 have rarely been examined. We show that 30 years of experimental CO2 enrichment in a brackish marsh increased primary productivity and stem density but decreased stem diameter and height of the dominant clonal species Schoenoplectus americanus. Smaller, denser stems were associated with the expansion of roots and rhizomes to alleviate nitrogen (N) limitation as evidenced by high N immobilization in live tissue and litter, high tissue C:N ratio and low available porewater N. Changes in morphology and tissue chemistry induced by elevated CO2 were reversed by N addition. We demonstrate that morphological responses to CO2 and N supply in a clonal plant species influences the capacity of marshes to gain elevation at rates that keep pace with rising sea levels.
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Morphometric and derived biomass data from the experiments are posted on the Global Change Research Wetland website (http://serc.si.edu/gcrew/data) and all data are available from the corresponding authors upon request.
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We thank B. Drake for conceiving the original study and leading it until 2010 and G. Peresta for operating the experiment and leading the annual census for nearly all of the 30-year record. We also thank J. Duls, A. Peresta, A. Cawood and the hundreds of volunteers who helped collect data during annual censuses. D. Whigham, T. Jordan, C. Gallegos, J. O’Neill, C. Zhu and H. Guo provided insights or contextual data. This research was supported by the DOE-TES programme (grant no. DE-SC0008339), the NSF-LTREB programme (grant nos. DEB-0950080 and DEB-1457100), the Maryland Sea Grant programme (grant no. SA7528114-WW) and the Thousand Young Talents Program of Yunnan Province.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Ming Nie and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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