The impact of elevated carbon dioxide on the branch growth of loblolly pine as influenced by water and nutrition

Branches of field grown loblolly pine trees growing under four different water and fertility regimes were exposed continuously to three different CO[sub 2] environments for a growing season. There were four trees in each of the soil regimes (control, fertilized, irrigated, and fertilized and irrigated). Three branches on each tree were individually enclosed in chambers containing CO[sub 2] environments of ambient, ambient plus 175ppm, or ambient plus 350ppm. Data were collected on terminal extension, diameter, needle length, needle number, and needle longevity. The positive impact of elevated CO[sub 2] was greatest on both of the irrigated treatments. In the plus 175ppm and plus 350ppm environments, respectively, the growth increases were 9% and 23% for the fertilized and irrigated trees and 41% and 59% for the irrigated only trees. There was no apparent impact of CO[sub 2] on needle number or needle longevity.