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Effects of Elevated CO2 in Dry Loess Grassland Species
Szente, K., Nagy, Z. and Tuba, Z.  1998.  Enhanced water use efficiency in dry loess grassland species grown at elevated air CO2 concentration.  Photosynthetica 35: 637-640.

What was done
The authors grew four perennial C3 plants (two grasses and two broad-leaved species) common to loess grasslands of Budapest in open-top chambers with atmospheric CO2 concentrations of 350 or 700 ppm for 231 days to determine the effects of elevated CO2 on photosynthesis, transpiration, and water-use efficiency in these species that often experience hot dry summer growing conditions.

What was learned
Elevated CO2 significantly enhanced rates of net photosynthesis in all species studied, with the two grasses and the two broad-leaved species exhibiting average increases of 136 and 486%, respectively.  Elevated CO2 increased transpiration rates for one grass and one broad-leaved species, while it caused no change in the rate of water loss from the remaining species.  However, elevated CO2 significantly increased the water-use efficiency of every species examined.  The two grasses, for example, exhibited an average increase in water-use efficiency of 72%, while the broad-leaved species displayed an average increase of 366%, primarily due to the tremendous CO2-induced photosynthetic stimulation they experienced.

What it means
As the CO2 content of the air increases, species common to dry loess grasslands near Budapest will likely experience significant increases in photosynthesis.  Although some of these species may also experience greater transpirational water loss, they should all, nonetheless, exhibit tremendous increases in water-use efficiency, with broad-leaved species displaying larger increases than narrow-leaved grasses.  Such increases in water-use efficiency will allow these perennial species to better cope with the dry hot summers characteristic of this region.

Reviewed 1 March 1999