Photosynthesis, nitrogen-use efficiency, and water-use efficiency of jack pine seedlings in competition with four boreal forest plant species

The objective of this study was to understand the mechanism underlying nitr ogen (N) and water competition between jack pine (Pinus banksiana Lamb.) an d four boreal forest species. Large-leaved aster (Aster macrophyllus L.), C anada blue-joint grass (Calamagrostis canadensis (Michx.) Beauv.), tremblin g aspen (Populus tremuloides (Michx.), and red raspberry (Rubus idaeus L.) were planted at a range of densities (0-8 plants/m(2)) with jack pine seedl ings. Net photosynthesis (P-n), nitrogen-use efficiency (NUE), water-use ef ficiency (WUE) of each species were monitored over three consecutive growin g seasons. Changes in available soil N and water were also measured. Jack p ine P-n, NUE, and WUE decreased as competitor density increased, but these effects varied among species (p < 0.001) and over time (p < 0.001). The inf luence of density on jack pine P-n decreased over time for aster and blue-j oint grass and increased over time for aspen and raspberry (p < 0.001). At most sample times, jack pine P-n correlated with available soil N. In contr ast, the correlation between jack pine P-n and soil water was rarely signif icant.