Photosynthesis in Seedlings of Six Conifer Species under Natural Environmental Conditions

Highest average daily rates of net photosynthesis in hemlock, grand fir, Sitka spruce, and Douglas—fir occurred at the outer margin of a forest stand. For Scots pine and noble fir highest rates occurred in an open, fully exposed area. The environment at the stand border apparently resulted in more favorable internal water relations. Species which assimilated best under exposed conditions apparently were better able to control moisture loss than were the other species. Species differed in photosynthetic efficiency. Shade—grown seedlings apparently are capable of higher rates of net photosynthesis than sun—grown plants of the same species.