Growth, Dry Matter Partitioning and Photosynthesis in North American Ginseng Seedlings

North American ginseng seedlings (Panax quinquefolius L.) were grown in pots in heated greenhouses, in a cool greenhouse, or in the field, in 11 experiments at various times over 16 years. Crop establishment, dry matter partitioning, photosynthesis, radiation use efficiency and carbon budget were measured and/or calculated in some years. Once the seedling canopy, of about $20\;cm^2$ per seedling, and a leaf area index of 0.37, was established, about 40 days after germination, full canopy display lasted about 87 days. Only 16.6% of the incoming solar radiation was intercepted by the crop, the remainder falling on the mulched soil surface. Total and root dry matter accumulations in the cool greenhouse and in the field were about double that in the heated greenhouses. Partitioning of dry matter to roots (economic yield or harvest index) in the cool greenhouse and in the field was 73% whereas it was 62.5% in the heated greenhouses. The relationship between root dry matter and radiation interception during the full canopy period was linear with growth efficiencies of $2.92\;mg\;MJ^{-1}$ at 4.8% of incoming radiation and $0.30\;mg\;MJ^{-1}$ at 68% of incoming radiation. A photosynthetic rate of $0.39\;g\;m^{-2}\;h^{-1}$ was attained at light saturation of about $150\;{\mu}mol\;m^{-2}\;s^{-1}$ (7.5% of full sunlight); dark respiration was $0.03\;g\;m^{-2}\;h^{-1}$, about 8.5% of maximum assimilation rate. Estimates of dry matter accumulation by growth analysis and by $CO_2$ uptake were similar, 6.21 vs. 7.62 mg $CO_2$, despite several assumptions in $CO_2$ uptake calculations.