Annals of Botany

Photosynthetic plasticity and survival across the Triassic-Jurassic boundary

Why did Gingko almost disappear during the Triassic–Jurassic mass extinction when ferns did so well? The answer has relevance for future atmospheric changes.

Investigating the often overlooked evolutionary role of photosynthetic plasticity under fluctuating [O2]:[CO2], Yiotis et al. assess mature plants from two angiosperms, two monilophytes and Ginkgo biloba acclimated to a Triassic-Jurassic boundary (TJB) atmosphere and their photosynthetic plasticity using gas exchange and chlorophyll fluorescence methods.

Schematic model depicting the changes in the energy flows of Ginkgo and ferns when acclimated to TJB atmospheric conditions.
Schematic model depicting the changes in the energy flows of Ginkgo and ferns when acclimated to TJB atmospheric conditions. The thickness of the arrows is representative of the relative magnitude, and the flows that change under low [O2]:[CO2] are outlined with red colour. LHC, light-harvesting complex, EABS, absorbed energy; Q, heat dissipation; J, photosynthetic electron flow; JO, photosynthetic electron flow supporting photorespiratory metabolism; JC, photosynthetic electron supporting photosynthesis; DIo/RC, heat dissipation per reaction centre, Fv/Fm, maximum efficiency of primary photochemistry.

Contrary to monilophytes, Ginkgo photorespires heavily and displays increased heat dissipation and severe photodamage when exposed to a TJB atmosphere. The observed photodamage reflects Ginkgo’s inability to divert photosynthetic electron flow to sinks other than photosynthesis and photorespiration, and provides insights into the underlying mechanism of Ginkgoales’ near extinction and ferns’ proliferation across the TJB.

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Yiotis, C., Evans-Fitz.Gerald, C., & McElwain, J. C. (2017). Differences in the photosynthetic plasticity of ferns and Ginkgo grown in experimentally controlled low [O2]:[CO2] atmospheres may explain their contrasting ecological fate across the Triassic–Jurassic mass extinction boundary. Annals of Botany, 119(8), 1385–1395.