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TECHNICAL REPORTS

Effects of Elevated Atmospheric CO₂ on Invasive Plants: Comparison of Purple and Yellow Nutsedge (Cyperus rotundus L. and C. esculentus L.)

^a USDA-ARS National Soil Dynamics Lab., 411 S. Donahue Drive, Auburn, AL 36832
^b School of Forestry and Wildlife Sciences, Auburn Univ., Auburn University, AL 36849

^* Corresponding author (hrogers{at}ars.usda.gov).

Received for publication March 28, 2007. The rise in atmospheric CO₂ concentration coupled with its direct, often positive, effect on the growth of plants raises the question of the response of invasive plants to elevated atmospheric CO₂ levels. Response of two invasive weeds [purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.)] to CO₂ enrichment was tested. Plants were exposed to ambient (375 µmol mol^–1) or elevated CO₂ (ambient + 200 µmol mol^–1) for 71 d in open top chambers. Photosynthetic rate did not differ between CO₂ treatments for either species. Conductance was lower in purple nutsedge and tended to be lower in yellow nutsedge. Purple nutsedge had higher instantaneous water use efficiency; a similar trend was noted for yellow nutsedge. Purple nutsedge had greater leaf area, root length and numbers of tubers and tended to have more tillers under high CO₂. In yellow nutsedge, only tuber number increased under CO₂ enrichment. Leaf dry weight was greater for both species when grown under elevated CO₂. Only purple nutsedge made seed heads; CO₂ level did not change seed head dry weight. Root dry weight increased under the high CO₂ treatment for purple nutsedge only, but tuber dry weight increased for both. Total dry weight of both species increased at elevated CO₂. Purple nutsedge (under elevated CO₂) tended to increase allocation belowground, which led to greater root-to-shoot ratio (R:S); R:S of yellow nutsedge was unaffected by CO₂ enrichment. Findings suggest both species, purple more than yellow nutsedge, may be more invasive in a future high-CO₂ world.

Abbreviations: OTC, open-top chamber • WUE, water use efficiency