David T. Tissue

Effects of low and elevated CO2 on C3 and C4 annuals

In order study C3 and C4 plant growth in atmospheric CO2 levels ranging from past through predicted future levels, Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) were grown from seed in growth chambers controlled at CO2 partial pressures of 15 Pa (below Pleistocene minimum), 27 Pa (pre-industrial), 35 Pa (current) and 70 Pa (predicted future). After 35 days of growth, CO2 had no effect on the relative growth rate, total biomass or partitioning of biomass in the C4 species. However, the C3 species had greater biomass accumulation with increasing CO2 partial pressure. C3 plants grown in 15 Pa CO2 for 35 days had only 8% of the total biomass of plants grown in 35 Pa CO2, C3 plants had lower relative growth rates and lower specific leaf mass than plants grown in higher CO2 partial pressures, and aborted reproduction. C3 plants grown in 70 Pa CO2 had greater root mass and root-to-shoot ratios than plants grown in lower CO2 partial pressures. These findings, support other studies that show C3 plant growth is more responsive to CO2 partial pressure than C4 plant growth. Differences in growth responses to CO2 levels of the Pleistocene through the future suggest that competitive interactions of C3 and C4 annuals have changed through geologic time. This study also provided evidence that C3 annuals may be operating near a minimum CO2 partial pressure for growth and reproduction at 15 Pa CO2.

Photosynthesis, Nitrogen, Their Adjustment and its Effects on Ecosystem Carbon Gain at Elevated CO{sub 2}l. A Comparison of Loblolly and Ponderosa Pines

A functional understanding of terrestrial ecosystem carbon processes is essential for two reasons. First, carbon flow is a most fundamental aspects of ecosystem function as it mediates most of the energy flow in these systems. Second, carbon flow also mediates the majority of energy flow in the global economy and will do for the foreseeable future. The increased atmospheric carbon dioxide and its inevitable flow through global ecosystems will influence ecosystem processes. There is, of course, great interest in the potential of ecosystems to sequester some of the carbon being loaded into the atmosphere by economic activity.