Effect of light, nitrogen fertilization, and mycorrhizal fungi on growth and photosynthesis of lodgepole pine seedlings

Abstract

Seedlings of lodgepole pine (Pinuscontorta Dougl.) were grown for 10 weeks without eetomycorrhizae in the greenhouse at three levels of irradiance (low, medium, and high) and ammonium nitrate (3, 62, and 248 ppm N). At 10 weeks, inoculation with either Pisolithustinctorius (Pers.) Coker and Couch or Suillusgranulatus (L. ex Fr.) O. Kuntze was superimposed on light and nitrogen treatments, and the seedlings were grown for an additional 6 weeks. Mycorrhiza formation increased with increase in irradiance, while fertilization with 62 ppm N resulted in greater mycorrhiza formation than either 3 or 248 ppm N. Further, inoculated plants had significantly greater biomass and took up more phosphorus than nonmycorrhizal seedlings. Inoculation with P. tinctorius and S. granulatus resulted in photosynthetic rates of 1.87 and 1.85 mg CO₂•dm⁻²•h⁻¹, respectively, significantly greater than nonmycorrhizal plants (1.41 mg CO₂•dm⁻²•h⁻¹). Although the increase in growth of the mycorrhizal seedlings was associated with increased photosynthesis, the magnitude of this response depended on specific combinations of irradiance and nitrogen fertilization. These results emphasize the importance of interactions among irradiance, nitrogen fertilization, and mycorrhiza development in the growth of containerized seedlings.