Communications Project

Document Type:Master's Thesis
Name:Michael Joseph Gavazzi
Title:The Influence of Elevated Carbon Dioxide and Water Availability on Herbaceous Weed Development and Planted Loblolly Pine (Pinus taeda) and Coppice Sweetgum (Liquidambar styraciflua) Growth
Degree:Master of Science
Committee Chair: Dr. John R. Seiler
Committee Members:Dr. Wallace M. Aust
Dr. Shepard M. Zedaker
Keywords:loblolly pine, sweetgum, carbon dioxide, herbaceous weed community,biomass, competition
Date of defense:May 4,1998
Availability:Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.


Loblolly pine (Pinus taeda) and coppiced sweetgum (Liquidambar styraciflua) seedlings were grown in competition with a native weed community using soil and seed bank collected near Appomattox, Virginia. Seedlings and weeds were exposed to CO2 (ambient and elevated) and water (water stressed and well watered) treatments for approximately one growing season in closed top chambers.

Weed growth had an effect on tree growth, but the amount of variation in tree biomass explained by weed biomass was very low. It appears that the tree seedlings benefited more from available resources than the herbaceous weeds. The influence of competition with loblolly pine and elevated CO2 did not have an influence on total weed biomass; however, it did favor C3 weed community development regardless of water availability. This suggests that weed community composition may shift toward C3 plants in a future elevated CO2 atmosphere.

Loblolly pine height, diameter, needle, shoot and total biomass were significantly greater in the well watered treatment than the water stressed treatment. Pine root, needle, shoot and total biomass were significantly greater in the elevated treatment than the ambient treatment. While not significant, root biomass of water stressed pine seedlings was 63% greater in the elevated CO2 treatment than the ambient treatment. There was a significant water and CO2 interaction for pine root:shoot ratio. Under elevated CO2, root:shoot ratio was significantly greater in the water stressed treatment than the well watered treatment. In contrast, root:shoot ratio in the ambient treatment was nearly identical under both water treatments. These results indicate that loblolly pine will respond favorably in an elevated CO2 atmosphere, even under dry conditions.

The coppiced sweetgum seedlings responded favorably to well watered conditions with significant increases in leaf area, specific leaf area, leaf, shoot and total biomass compared to water stressed conditions. Leaf, root, shoot+stump and total biomass of sweetgum significantly increased and specific leaf area decreased under elevated CO2 compared to ambient CO2, but differences were smaller than previous findings. This indicates that coppicing may dampen the growth response to elevated CO2, at least in the initial growth stage after coppicing.

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