Effect of Pinus sylvestriformis seedlings density on net photosynthetic rate under elevated CO₂

The effect of Pinus sylvestriformis seedlings density on net photosynthetic rate was studied under elevated CO₂. Atmospheric CO₂ concentration was controlled in OTC (Open Top Chamber). The results showed that elevated CO₂ not only made net photosynthetic rates (NPRs) of two Pinus sylvestriformis seedlings densities increased, but also mitigated their intra-specific competition. Meanwhile, the difference of seedling NPRs between 100 and 400 plant·m^-2 under 500 μmol·mol^-1 air CO₂ concentration was less than that under 350 μmol·mol^-1 with the same PAR levels. When air CO₂ concentration reached 700 μmol·mol^-1, the NPRs of seedlings under both planting densities were close to each other with the same PAR levels. The intra-specific competition was minimized under air CO₂ concentration of 700 μmol·mol^-1.