Poster: Global Change

Abs # 72: Turgor maintenance in elevated CO₂

Presenter:	Fiscus, Edwin L., edfiscus01@sprynet.com
Authors	Fiscus, Edwin L. (A)   Booker, Fitzgerald L. (A)   Flowers, Michael  (A)
Affiliations:	(A): USDA-ARS Air Quality - Plant Growth and Development Unit

Soybean (cv. Essex) was grown in open-top field chambers supplied with charcoal-filtered air and treated with 360 (CF360) or 700 (CF700) mmol CO₂ mol^-1. Leaves from each CO₂ treatment were subjected to potential-volume analysis, midday xylem pressure potential measurements, and the determination of starch, soluble sugars, and free amino acids. Ontogenetic changes in most of the parameters were large compared to treatment effects. Analysis showed that although the turgor loss potential (TLP) in CF700 was reduced by only 12% over the season, its effect on midday turgor was magnified by an ontogenetic shift that turned a 0.12 MPa difference in midday leaf water potential (MDWP) into a 0.29 MPa midday turgor potential at 62 days after planting (DAP). At 72.5 DAP those respective values were 0.17 MPa and 0.40 MPa. So, although MDWPs were only modestly higher in CF700, that, together with the lower 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 significantly increased, on a dry weight basis in CF700 compared to CF360. Free amino acid concentrations were unaffected by CO₂ treatments. However, as a percentage of the total leaf osmotica, sugars and amino acids increased in CF700 compared to CF360. Together, the soluble sugars and amino acids accounted for about 15% of the total osmotica in CF360 but 10 to 35% in CF700, with 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.