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

Although Siberian Trap volcanism is considered a primary driver of the largest extinction in Earth history, the end-Permian crisis, the relationship between these events remains unclear. However, malformations in fossilized gymnosperm pollen from the extinction interval suggest biological stress coinciding with pulsed forest decline. These grains are hypothesized to have been caused by enhanced ultraviolet-B (UV-B) irradiation from volcanism-induced ozone shield deterioration. We tested this proposed mechanism by observing the effects of inferred end-Permian UV-B regimes on pollen development and reproductive success in living conifers. We find that pollen malformation frequencies increase fivefold under high UV-B intensities. Surprisingly, all trees survived but were sterilized under enhanced UV-B. These results support the hypothesis that heightened UV-B stress could have contributed not only to pollen malformation production but also to deforestation during Permian-Triassic crisis intervals. By reducing the fertility of several widespread gymnosperm lineages, pulsed ozone shield weakening could have induced repeated terrestrial biosphere destabilization and food web collapse without exerting a direct "kill" mechanism on land plants or animals. These findings challenge the paradigm that mass extinctions require kill mechanisms and suggest that modern conifer forests may be considerably more vulnerable to anthropogenic ozone layer depletion than expected.

Applying morphometrics to early land plant systematics: a new Leclercqia (Lycopsida) species from Washington State, USA.

PREMISE OF THE STUDY: Early land plant fossils can be challenging to interpret due to their morphological simplicity and often fragmentary nature. Morphometric techniques using commonly preserved characters might increase diagnostic value of such material. To evaluate the utility of morphometrics in assessing morphospecies boundaries in the Devonian, we compared degrees of variation within the cosmopolitan lycopsid genus Leclercqia with that of living relatives (Lycopodium-Spinulum spp.) Of particular interest was determining whether a new morphotype of Leclercqia from the Middle Devonian Chilliwack flora of Washington State fell within or outside the range of variation of previously described species. METHODS: Morphological variation of Leclercqia was assessed across the geographic range of the genus using six vegetative and three reproductive characters. The new morphotype and two previously described species (L. complexa, L. andrewsii) were compared using linear discriminant analysis (LDA). Extant Lycopodium-Spinulum species and variants were similarly analyzed to assess inter- vs. intraspecific variation in living lycopsids. KEY RESULTS: The LDA comparisons of Lycopodium-Spinulum yielded notable morphological disparity between species but substantial overlap between intraspecific variants. Among the fossils, LDA separates the new morphotype, Leclercqia complexa, and L. andrewsii to a similar degree as Lycopodium and Spinulum species. Based on these results and further study, we describe a new species of Leclercqia: Leclercqia scolopendra Benca et Strömberg sp. nov. CONCLUSIONS: Morphometric analyses can aid in informing taxonomic assignment of fragmentary early land plant fossils using readily preserved features, even in the absence of reproductive structures. Applications of this approach to the Chilliwack flora suggest Leclercqia displayed greater morphological variation, taxonomic diversity, and biogeographic extent than previously thought.