Batches of freshly fallen Metasequoia glyptostroboides litter were subjected to one of 12 degradation regimes varying in temperature, pH, and oxygen availability for a three-month decay period. The regimes were intended to simulate possible conditions prevailing during the first winter following the autumnal leaf fall for the Metasequoia dominated forests of Axel Heiberg Island ca. 45 Ma. The decayed leaves were examined by transmission electron microscopy to quantify the extent and quality of chloroplast preservation. The best preservation of chloroplast membranes was observed at pH 8.5 and at 10°C, although it was found that rapidly freezing samples also reliably preserved ultrastructural chloroplast features with a high degree of fidelity to the living state. The results from this study suggest that the ambient water chemistry of the depositional environment in the Eocene floodplain forests of Axel Heiberg Island could have been basic, and maintained by a natural carbonate buffering system, but they also demonstrate that the preservation of chloroplast features can occur under varying environmental conditions.

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