Effects of elevated atmospheric CO2 on invasive plants:: Comparison of purple and yellow nutsedge (Cyperus rotundus L. and C. esculentus L.)

The rise in atmospheric CO2 concentration coupled with its direct, often positive, effect on the growth of plants 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 mu mol mol(-1)) or elevated CO2 (ambient + 200 mu mol 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 a location belowground, which led to greater rout-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.