Research ArticlePLANT SCIENCES

UV-B–induced forest sterility: Implications of ozone shield failure in Earth’s largest extinction

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Science Advances  07 Feb 2018:
Vol. 4, no. 2, e1700618
DOI: 10.1126/sciadv.1700618
  • Fig. 1 Normal and malformed bisaccate pollen.

    (A to H) Fossilized pollen of end-Permian gymnosperms from the Guodikeng Formation, Dalongkou section, North China (A to G) and Nedubrovo, Russia (H). (A) Alisporites sp., bisaccate. (B) Bisaccate indet., possibly taeniate with asymmetric sacci. (C) Klausipollenites sp., trisaccate. (D to F) Alisporites sp., trisaccate. (G) K. schaubergeri, tetrasaccate dyad. (H) K. schaubergeri, fused pollen including a trisaccate. (I to P) Pollen of modern pine (P. mugo Columnaris) irradiated with modeled end-Permian UV-B regimes. (I) Bisaccate. (J) Trisaccate grain with enlarged saccus. (K) Trisaccate grain with enlarged saccus. (L) Trisaccate grain with fused sacci. (M) Trisaccate grain. (N) Tetrasaccate grain. (O) Tetrasaccate dyad. (P) Fused grains, one trisaccate. See Supplementary Text for details and image credits.

  • Fig. 2 Paleogeographic distribution of Permian-Triassic palynomorph sequences featuring forest decline and/or pollen malformations.

    Gymnosperm turnover documented directly (A to K and S) and indirectly through sequences displaying gymnosperm recovery following lycopsid spore spikes (L to N and T). (A) East Greenland (2). (B) Southern Barents Sea (66). (C) North Italy (26). (D) Southwest China (21, 67). (E) Israel (23). (F) Madagascar (68). (G) Pakistan (22, 69). (H) Antarctica (25). (I) Australia (70). (J) South Africa (71). (K) Norway and central Barents Sea (9, 72). (L) Western Poland (24). (M) North China (73). (N) South Tibet (74). (O) South Africa (10). (P) Nedubrovo, Russia (5). (Q) North China (5). (R) Ireland (75). (S) South India (11), and (T) Argentina (76). Late Permian paleogeographic reconstruction adapted from Scotese (77).

  • Fig. 3 UV-B impacts on malformed pollen production in pines (P. mugo).

    Boxplots representing malformation frequencies of individual trees in control and three modeled end-Permian UV-B regimes. Y axis: Malformation frequency: Percent malformed grains (n = 600 grains per cone, eight cones per tree, three trees per treatment). X axis: UV-B treatment (kJ m−2 day−1)BE: Treatments correspond to growth chamber control (0) and end-Permian modeled (54, 75, and 93) UV-B regimes. The dashed line indicates 3% malformation frequency of stressed trees in nature (5). See results in table S1 and summary in table S2 for two–mixed-factor nested ANOVA.

  • Fig. 4 Ovulate cone developmental stages in (P. mugo).

    (A) Schematic of ovulate cone developmental stages in P. mugo. Stage descriptions: (1 to 2) Bud enclosing cone expands. (3) Cone emergence from bud scales. (4) Cone extends. (4L) Extension is completed, but ovuliferous scales (purple) are not fully opened. (5E) Ovuliferous scales perpendicular to cone axis—enabling pollen access to ovules. (5L) Ovuliferous scales swell, intercepting pollination. (6) Ovuliferous scales swollen completely, blocking pollen access to ovules (63). (B) Images of select ovulate cones from each treatment showing a typical developmental stage ~70 to 76 days following emergence. Treatments correspond to growth chamber control (0), outdoor ambient (7.2), and end-Permian modeled (54, 75, and 93) UV-B regimes. See Supplementary Text for details.

  • Fig. 5 UV-B impacts on ovulate cone survivorship in pine (P. mugo).

    Bubble chart displaying P. mugo ‘Columnaris’ ovulate cone survivorship by displaying the percentages of cones reaching their furthest developmental stage per treatment population (n = 48 to 60). See table S4 for ovulate cone data.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/e1700618/DC1

    Supplementary Text

    fig. S1. BE UV-B fluxes versus distance from UV-B lamps in growth chamber experiments.

    fig. S2. Pollen cone subsampling strategy.

    fig. S3. Sample size and accuracy of malformed pollen frequency determination.

    table S1. Results of a two–mixed-factor nested ANOVA of malformed pollen frequencies.

    table S2. Summary of a pairwise, two–mixed-factor nested ANOVA of malformed pollen frequencies.

    table S3. Pollen malformation frequencies, percentages, and index per tree.

    table S4. Ovulate cone survivorship across treatments.

    table S5. Temperature settings during growth chamber experiment.

    table S6. Photoperiod settings during growth chamber experiment.

    References (7880)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Text
    • fig. S1. BE UV-B fluxes versus distance from UV-B lamps in growth chamber experiments.
    • fig. S2. Pollen cone subsampling strategy.
    • fig. S3. Sample size and accuracy of malformed pollen frequency determination.
    • table S1. Results of a two–mixed-factor nested ANOVA of malformed pollen frequencies.
    • table S2. Summary of a pairwise, two–mixed-factor nested ANOVA of malformed pollen frequencies.
    • table S3. Pollen malformation frequencies, percentages, and index per tree.
    • table S4. Ovulate cone survivorship across treatments.
    • table S5. Temperature settings during growth chamber experiment.
    • table S6. Photoperiod settings during growth chamber experiment.
    • References (78–80)

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