Effects of Canada bluejoint grass competition, nitrogen fertilization, and litter layer removal on soil nitrogen processes and tree growth

The mechanisms of Canada bluejoint grass (Calamagrostis canadensis (Michx.) Beauv.) competition is not well understood. I examined the effects of competition, N fertilization, and litter layer removal on soil N processes and the growth of planted white spruce (Picea glauca (Moench.) Voss). Weed and litter removal increased soil temperature and net N mineralization and nitrification rates. Litter removal increased litter decomposition rates, probably due to increased soil temperature. Weed control significantly increased tree diameter growth, and foliar N concentration and content. Mineral N supply rates and tree diameter growth were positively related in the field experiment. I conclude that weed control and litter removal had positive effects on increasing N availability and applying N fertilizer without weed control was inefficient in improving tree growth. A complimentary growth chamber experiment showed that sufficient moisture availability might enhance the competitiveness of bluejoint for limited N.