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Title: TURGOR MAINTENANCE IN ELEVATED CARBON DIOXIDE

Author
item Fiscus, Edwin
item Booker, Fitzgerald
item Flowers, Michael

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 4/8/2003
Publication Date: 7/26/2005
Citation: Fiscus, E.L., Booker, F.L., Flowers, M.D. 2005. Turgor maintenance in elevated carbon dioxide. American Society of Plant Biologists Annual Meeting.

Interpretive Summary:

Technical Abstract: Soybeans were grown in the ground in charcoal-filtered open-top field chambers equipped to control CO2. Seasonal mean CO2 concentrations for the controls and supplemental CO2 treatments were 360 and 700 'l l-1. The center leaflets of the trifoliolates were sampled early in the morning throughout the growing season and subjected to potential-volume analysis. Midday xylem pressure potentials were also measured for a 50-day period during the middle of the season. Ontogenetic changes in most of the parameters were large compared to treatment effects. Analysis showed that although the turgor loss potential in elevated CO2 was reduced by only 12% over the season, the difference was significant and its effect on midday turgor was magnified by an ontogenetic shift in the elevated CO2 treatment which turned a 0.12 MPa difference in midday leaf water potential (MDWP) into a 0.29 MPa midday turgor potential during the sampling period 62 days after planting (DAP). During the sampling period 72 ± 5 DAP those respective values were 0.17 MPa and 0.40 MPa. So, although MDWPs were only modestly higher in the elevated CO2 treatment, that, together with the lower Turgor Loss Potential (TLP), resulted in a substantially larger midday turgor pressure. This increased turgor suggests a larger leaf water buffering capacity and ability for continued tissue expansion even through the most stressful part of the day. Starch content and soluble sugars were increased, on a DW basis, by elevated CO2, while free amino acid concentrations were unaffected. However, as a percentage of the total leaf osmotica, sugars and amino acids increased under elevated CO2. Together, the soluble sugars and amino acids accounted for about 15% of the total osmotica in the CF360 treatment but 10 to 35% in the CF700, differences disappearing at season's end. And, although the fractional increase in sugars as a percentage of the total osmotica was larger, they still constituted a smaller fraction of the total than the free amino acids.