A PLAUSIBLE MECHANISM FOR INTERNAL GAS TRANSPORT IN LYCOPSIDS

Acropetal gas phase carbon dioxide transport, basipetal oxygen transport and net fixation of sedimentary carbon has been observed in many extant species of Isoëtes, one of the modern relatives of the group of lycopsids that grew to tree stature and dominated coal swamps in the late Paleozoic. It has been suggested that this organized gas transport in aerenchyma connecting buried and photosynthetic organs constitutes an adaptive metabolic strategy associated with the high oxygen/low carbon dioxide atmosphere of the late Carboniferous and early Permian. Here we show that diffusion alone is too slow to account for the observed transport rates, and illustrate how a model of temperature-derived convection can lead to net gas transport on a diurnal timescale. Combined with a source-sink effect of metabolic oxygen consumption and photosynthetic carbon dioxide production, this process could lead to an amount of within-plant recycling of sedimentary carbon that would have been significant at the eco-system scale and may have affected the global carbon cycle in the late Paleozoic.