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UV-B absorbing compounds in Pinus spp. pollen indicate plastic responses to solar radiation
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  • Mari JokerudOrcid,
  • Alistair Seddon,
  • Joseph Chipperfield,
  • Katherine Willis,
  • Vigdis Vandvik
Mari Jokerud
Orcid
Norwegian Institute for Nature Research, Norwegian Institute for Nature Research (NINA)
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Alistair Seddon
University of Bergen
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Joseph Chipperfield
Norwegian Institute for Nature Research
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Katherine Willis
University of Oxford
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Vigdis Vandvik
University of Bergen
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Peer review status:IN REVISION

12 Mar 2020Submitted to Ecology and Evolution
13 Mar 2020Assigned to Editor
13 Mar 2020Submission Checks Completed
25 Mar 2020Reviewer(s) Assigned
27 May 2020Review(s) Completed, Editorial Evaluation Pending
28 May 2020Editorial Decision: Revise Minor

Abstract

1. The abundance of UV-B absorbing compounds (for example p-Coumaric acid, pCA) within pollen-grain sporopollenin has been proposed as a proxy for reconstructing past changes in surface solar radiation, but drivers of the variation of these compounds in pollen grains remains poorly understood. 2. One important consideration is that the physiological response that results in the production and timing of pCA in pollen remains poorly understood. This calls for studies that explicitly tests the temporal resolution and plasticity of the response of pCA in pollen under field conditions. 3. To address this, we conducted two parallel experiments. First, we measured pCA in four Pinus spp. from Geneva in two consecutive years to investigate the impact of natural variation in ambient solar radiation, and differences in responses between species. Second, we covered pollen cones on Pinus sylvestris trees in Bergen with 90% shading cloth one month before dehiscence and compared the amount of pCA in pollen from shaded and sun-exposed cones from the same tree. 4. Between years, in Geneva, Pinus spp. produced 31% more pCA in 2014 than in 2013, with higher levels of solar radiation also observed in 2014. pCA content also showed strong species-level variation, largely reflecting differences in pollen size between species. Experimentally shaded Pinus sylvestris pollen produced 21% less pCA than fully exposed pollen. 5. Our work demonstrates a plastic response in the production of UV absorbing compounds (pCA) to inter-annual and experimentally induced variation in ambient solar radiation in Pinus spp. pollen. This supports pCA as a highly responsive proxy for early-season solar radiation. We also find strong species-level variation in pCA content in pine pollen, likely related to pollen grain size, which should be accounted for in reconstructions from sites with multiple Pinus species present.