Populus tremuloides photosynthesis and crown architecture in response to elevated CO and soil N availability.

We tested the hypothesis that elevated CO would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO. Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides. Rooted cuttings of P.