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Fig. 1. A systems analysis diagram of the geophysiological feedbacks between plants and CO2. It applies only when times of potential overheating of leaves due to high CO2 levels may have occurred. Arrows originate at causes and end at effects. Arrows with bull's-eyes represent inverse responses. Arrows without bull's-eyes represent direct responses. Letters adjacent to arrows designate paths followed by feedback loops. The time scales over which the paths operate are as follows: a, b, i, k, p, q, s, and u, 100 to 101 years; c and d, 101 to 103 years; f–h, j, m, n, r, and t, 103 to 106 years; e, >106 years.
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Fig. 2. Evolution of the atmosphere and land plants in the Paleozoic. (A) Modeled (
) or paleosol (
) atmospheric CO2 changes during the Late Paleozoic (3). (B) Observed (—) and modeled (––) increase in maximum width of megaphyll leaves (7). (C) Maximum plant height calculated from observed axis diameter of Devonian and Carboniferous vascular plants (18, 21, 32) (r2 = 0.66, P 3), the latter estimated from pyrite burial rates and a Cambrian–Silurian mean molar organic carbon/pyrite sulfur burial ratio of 1.5, assuming no changes in the proportion of burial in euxinic basins or anoxic oceans. Error bars in A indicate the range of uncertainty. The points in B represent the maximum size of megaphyll leaves calculated from fossils for 10-million-year intervals.
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Source: PNAS, February 1, 2005, vol. 102 no. 5, 1302-1305.
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