Effects of CO2 enrichment on growth of Liquidambarstyraciflua and Pinustaeda seedlings under different irradiance levels

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Abstract
Mathematical growth analysis techniques were used to assess the effects of atmospheric CO2 enrichment on growth and biomass partitioning of L. styraciflua L. (sweetgum) and P. taeda L. (loblolly pine) seedlings. Plants were grown from seed under high (1000 .mu.mol .cntdot. m-2 .cntdot. s-1) and low (250 .mu.mol .cntdot. m-2 .cntdot. s-1) photosynthetic photon flux density at CO2 concentrations of 350, 675, and 1000 .mu.l .cntdot. l-1 for 84 or 112-113 days. Elevated atmospheric CO2 concentration significantly increased height, leaf area, basal stem diameter and total dry wt of sweetgum seedlings grown under high irradiance and to a lesser extent under low irradiance. Increases in dry matter accumulation were associated with early CO2 enhancement of net assimilation rate, but increases in amount of leaf surface area contributed more towards maintenance of larger size as seedlings aged. For sweetgum seedings in particular, reduction of growth by low irradiance under normal atmospheric CO2 was compensated for by growing plants with elevated CO2. In contrast, elevated CO2 concentration produced no significant increase in growth of loblolly pine seedlings.