Schwendemann, Andrew B. .
Permian photosynthetic pathways: form, function, and stable carbon isotopes of Antarctic Glossopteris leaves.
The climatic conditions of the Permian are analogous to those thought to have shaped the evolution of the C4 photosynthetic pathway in the Oligocene. The C4 pathway has evolved independently in more than 45 lineages of angiosperms as a response to low CO2 levels. Generalized photosynthesis models of C3 plants in low CO2–high O2 climates show a 60–80% decrease in photosynthetic rate. C4 plants, however, are able to concentrate CO2 in cells, thereby reducing photorespiration. It is feasible that the low CO2–high O2 concentrations of the Permian could have prompted a C4 pathway to evolve 200+ million years earlier than typically assumed. Until the Permian, leaves with anastomosing venation patterns were relatively rare in the fossil record and the evolution of such patterns has been linked with declines in atmospheric CO2 concentration. Increasing leaf venation density is one way in which a plant can concentrate CO2 for use in the carbon fixation stage of photosynthesis. Permian Gondwana floras are composed mainly of glossopterid seed ferns, an enigmatic group. The lateral veins of Glossopteris leaves repeatedly dichotomize and anastomose, forming a reticulate venation pattern. The existence of a C4 photosynthetic pathway in Glossopteris will be examined, tested, and discussed in two ways. First, methods utilizing documented anatomical relationships in extant plants are applied to permineralized Glossopteris leaves to determine if there is anatomical evidence for a C4 pathway in the Permian. Secondly, it has also been demonstrated that Kranz anatomy is not required for terrestrial C4 photosynthesis in extant plants. As such, stable carbon isotope analysis of fossil plant tissue will be presented for evidence of a C3 or C4 pathway that is independent of anatomical evidence. The scope of photosynthetic pathway diversity in the Permian will be discussed with respect to Permian climate, optimized photosynthetic capacity for leaves in such a climate, and the potential limits to photosynthetic pathway diversity in the Permian.
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1 - University of Kansas, Department of Ecology & Evolutionary Biology, Natural History Museum and Biodiversity Research Center, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 555B/Convention Center
Date: Monday, August 2nd, 2010
Time: 9:00 AM