EFFECTS OF 2 AND A HALF YEARS OF ATMOSPHERIC CO-2 ENRICHMENT ON THE ROOT DENSITY DISTRIBUTION OF 3-YEAR-OLD SOUR ORANGE TREES

Eight sour orange trees planted directly into the ground at Phoenix, Arizona, as small seedlings in July 1987 have been enclosed by four clear-plastic-wall, open-top chambers since November of that year, half of which have been continuously supplied with a CO2 enriched atmosphere consisting of an extra 300 cm3 CO2 m-3 of air. Extensive soil coring of the trees' root zones conducted in July 1990 indicated that two and a half years of growth under these conditions produced a fine root biomass enhancement of 175% in the CO2 enriched trees. This growth enhancement is of the same order of magnitude as our previously reported results for net photosynthesis and trunk and branch volumes for these trees.