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Leaf water relations in epiphytic ferns are driven by drought avoidance rather than tolerance mechanisms
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  • Courtney Campany,
  • Jarmila Pittermann,
  • Alex Baer,
  • Helen Holmlund,
  • Eric Schuettpelz,
  • Klaus Mehltreter,
  • James (Eddie) Watkins
Courtney Campany
Shepherd University
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Jarmila Pittermann
University of California Santa Cruz
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Alex Baer
University of California Santa Cruz
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Helen Holmlund
Pepperdine University
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Eric Schuettpelz
Smithsonian Institution
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Klaus Mehltreter
Instituto de Ecologia
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James (Eddie) Watkins
Colgate University
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Abstract

Opportunistic diversification has allowed ferns to radiate into epiphytic niches in angiosperm dominated landscapes. However, our understanding of how ecophysiological function allowed establishment in the canopy and the potential transitionary role of the hemi-epiphytic life form remain unclear. Here, we surveyed 39 fern species in Costa Rican tropical forests to explore epiphytic trait divergence in a phylogenetic context. We examined leaf responses to water deficits in terrestrial, hemi-epiphytic, and epiphytic ferns and related these findings to functional traits that regulate leaf water status. Epiphytic ferns had reduced xylem area (-63%), shorter stipe lengths (-56%), thicker laminae (+41%), and reduced stomatal density (-46%) compared to terrestrial ferns. Epiphytic ferns exhibited similar turgor loss points, higher osmotic potential at saturation, and lower tissue capacitance after turgor loss than terrestrial ferns. Overall, hemi-epiphytic ferns exhibited traits that share characteristics of both terrestrial and epiphytic species. Our findings clearly demonstrate the prevalence of water conservatism in both epiphytic and hemi-epiphytic ferns, via selection for anatomical and structural traits that avoid leaf water stress. Even with likely canalized physiological function, adaptations for drought avoidance have allowed epiphytic ferns to successfully endure the stresses of the canopy habitat.

Peer review status:ACCEPTED

31 Jan 2021Submitted to Plant, Cell & Environment
02 Feb 2021Submission Checks Completed
02 Feb 2021Assigned to Editor
04 Feb 2021Reviewer(s) Assigned
13 Feb 2021Review(s) Completed, Editorial Evaluation Pending
16 Feb 2021Editorial Decision: Revise Minor
21 Feb 20211st Revision Received
23 Feb 2021Submission Checks Completed
23 Feb 2021Assigned to Editor
23 Feb 2021Review(s) Completed, Editorial Evaluation Pending
23 Feb 2021Editorial Decision: Accept