Wood properties and ring width responses to long-term atmospheric CO2 enrichment in field-grown loblolly pine (Pinus taeda L.)

Loblolly pine (Pinus taeda L.) were grown in the field, under non-limiting nutrient conditions, in open-top chambers for 4 years at ambient CO2 partia l pressures (pCO(2)) and with a CO2-enriched atmosphere (+ 30 Pa pCO(2) com pared to ambient concentration). A third replicate of trees were grown with out chambers at ambient pCO(2). Wood anatomy, wood density and tree ring wi dth were analysed using stem wood samples. No significant differences were observed in the cell wall to cell lumen ratio within the latewood of the th ird growth ring formed in 1994. No significant differences were observed in the density of resin canals or in the ratio of resin canal cross-sectional area to xylem area within the same growth ring. Ring widths were significa ntly wider in the CO2-enrichment treatment for 3 of 4 years compared to the ambient chamber control treatment. Latewood in the 1995 growth ring was si gnificantly wider than that in the ambient control and represented a larger percentage of the total growth-ring width. Carbon dioxide enrichment also significantly increased the total wood specific gravity (determined by disp lacement). However, when determined as total sample wood density by X-ray d ensitometry, the density of enriched samples was not significantly higher t han that of the ambient chamber controls. Only the 1993 growth ring of enri ched trees had a significantly higher maximum latewood density than that of trees grown on non-chambered plots or ambient chambered controls. No signi ficant differences were observed in the minimum earlywood density of indivi dual growth rings between chambered treatments. These results show that the most significant effect of CO2 enrichment on wood production in loblolly p ine is its influence on radial growth, measured as annual tree ring widths. This influence is most pronounced in the first year of growth and decrease s with age.