Journal of Experimental Botany, Vol. 52, No. 357, pp. 801-809,
April 15, 2001
© 2001 Oxford University Press
Original Papers |
The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C4 species
1 Department of Plant Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
2 Blaustein Institute for Desert Research, Ben Gurion University of the Negev, 84990, Israel
Angiosperm plants were grown under either the present day 21 kPa O2 atmosphere or 28 kPa, as estimated for the end-Cretaceous (100–65 MyBP). CO2 was held at different levels, within the 24–60 Pa range, as also estimated for the same period. In C3 Xanthium strumarium and Atriplex prostrata, leaf area and net photosynthesis per unit leaf area, were reduced by the high O2, while the whole-plant respiration/photosynthesis ratio increased. The high O2 effects were strongest under 24 Pa, but still significant under 60 Pa CO2. Growth was reduced by high O2 in these C3 species, but not in Flaveria sp., whether C3, C4, or intermediary grown under light intensities <350 µmol m-2 s-1 PPF. Photosynthesis of C3 Flaveria sp. was reduced by high O2, but only at light intensities >350 µmol m-2 s-1 PPF. It is concluded that the high O2 atmosphere at the end-Cretaceous would have reduced growth of at least some of the vegetation, thus adversely affecting dependent fauna. The weakened biota would have been predisposed to the consequences of volcanism and the K/T boundary bolide impact. Conversely, photosynthesis and growth of C4 Zea mays and Atriplex halimus were little affected by high, 28 kPa, O2. This suggests an environmental driver for the evolution of C4 physiology.
Key words: K/T boundary, extinctions, paleo-atmosphere, oxygen, C4 emergence.