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

Loblolly pine (Pin1r.s tae(/(i L.) seedlings were grown in co~npetition with native weeds using soil and seed bank collected from recently chopped and burned areas near Appornattox, Virginia. One-year-old seedlings were planted and weeds allowed to germinate from the native seed bank while being exposed to COz (ambient and elevated approximately 700 ppm) and water (water stressed and well watered) treatments for approximately one growing season in a greenhouse. Elevated CO, did not influence total weed biomass: however, C, weed community development was favored over C, weed community development in elevated CO, regardless of water availability. This suggests that weed community composition may shift toward C, plar~ts in a future elevated CO, atmosphere. Pine growth was significantly greater in the well watered and elevated CO, 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, interaction for pine root:shoot ratio. Under elevated CO,, root:shoot ratio was significantly greater in the water stressed treatnlent than the well watered treatment. 111 contrast, there was no significallt difference in the root:shoot ratio ~lnder the ambient CO, treatment for either water treatment. These results suggest that loblolly pine seedlings will respond favorably in an elevated COZ atmosphere, even under dry conditions and competing with herbaceous weeds. O 2000 Elsevier Science Ireland Ltd. All rights reserved. K(~j .~~~orl / . s : Biomass; C02; Competition; I-Icrbaceous weeds: Loblolly pine