The influence of elevated carbon dioxide and water availability on herbaceous weed development and growth of transplanted loblolly pine ( Pinus taeda)

Abstract

Loblolly pine ( Pinus taeda L.) seedlings were grown in competition with native weeds using soil and seed bank collected from recently chopped and burned areas near Appomattox, Virginia. One-year-old seedlings were planted and weeds allowed to germinate from the native seed bank while being exposed to CO 2 (ambient and elevated — approximately 700 ppm) and water (water stressed and well watered) treatments for approximately one growing season in a greenhouse. Elevated CO 2 did not influence total weed biomass; however, C 3 weed community development was favored over C 4 weed community development in elevated CO 2 regardless of water availability. This suggests that weed community composition may shift toward C 3 plants in a future elevated CO 2 atmosphere. Pine growth was significantly greater in the well watered and elevated CO 2 treatments compared to the water stressed and ambient treatments, respectively, even though they were competing with native herbaceous weeds for resources. There was a significant water and CO 2 interaction for pine root:shoot ratio. Under elevated CO 2, root:shoot ratio was significantly greater in the water stressed treatment than the well watered treatment. In contrast, there was no significant difference in the root:shoot ratio under the ambient CO 2 treatment for either water treatment. These results suggest that loblolly pine seedlings will respond favorably in an elevated CO 2 atmosphere, even under dry conditions and competing with herbaceous weeds.