Effects of nitrogen on the growth of jack pine competing with Canada blue-joint grass and large-leaved aster

Abstract

Biomass, leaf area, canopy photosynthesis, photosynthetic nitrogen-use efficiency (PNUE), nitrogen-partitioning ratio (NPR: ratio of nitrogen taken up by jack pine relative to two different competitor species), and nitrogen uptake (NU) of jack pine ( Pinus banksiana Lamb.) competing with large-leaved aster ( Aster macrophyllus L.) and Canada blue-joint grass ( Calamagrostis canadensis (Michx.) Beauv.) were examined at three nitrogen levels in a controlled-environment growth chamber. When grown with large-leaved aster, jack pine biomass, photosynthesis and PNUE ( p<0.001) increased as nitrogen level increased. Jack pine biomass, photosynthesis and NPR ( p<0.001) decreased as nitrogen level increased when grown with Canada blue-joint grass. At the lowest nitrogen supply level, jack pine photosynthesis decreased as competitor PNUE increased ( r 2=0.84, p<0.001). Jack pine photosynthesis decreased as NU of large-leaved aster (37.5 mg N l −1: r 2=0.75, p<0.001; 100 mg N l −1: r 2=0.86, p<0.001) and Canada blue-joint grass (37.5 mg N l −1: r 2=0.96, p<0.001; 100 mg N l −1: r 2=0.84, p<0.001) increased. NU and PNUE may play an important role in the outcome of interactions between jack pine seedlings and competing forest vegetation in newly planted stands.