Effects of various amounts and forms of inorganic nitrogen on mycorrhizal Norway spruce seedlings.

BRUNNER, IVANO & SABINE BRODBECK.

Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), CH-8903 Birmensdorf, SWITZERLAND.

Mycorrhizal Norway spruce (Picea abies) seedlings were grown under greenhouse conditions in rootrainers with a peat-vermiculite mixture under various N-regimes. In a first experiment, NH₄NO₃ was applied in concentrations corresponding to 0, 50, 100, 400, 800, and 1600 kg/ha to seedlings inoculated with Hebeloma crustuliniforme or Cenococcum geophilum. In a second experiment, KNO₃ or NH₄Cl were applied in amounts of 0, 50 (only KNO₃), 100, and 800 kg/ha to either non-mycorrhizal control seedlings or seedlings inoculated with H. crustuliniforme, Laccaria bicolor, or C. geophilum. After six months, plants were harvested, and biomass and mycorrhization (% mycorrhizal root tips of the total number of root tips) were recorded. The results showed that with increasing N-supply the total biomass doubled in maximum. At the highest N-amounts total biomass remained on the level of control plants. In addition, inoculations with fungal mycelia of H. crustuliniforme or L. bicolor significantly enhanced the total biomass compared to non-inoculated plants at 100 and 800 kg/ha N using KNO₃ or NH₄Cl. The mycorrhization of seedlings inoculated with H. crustuliniforme and L. bicolor decreased from 100% to approximate 50% above 100 kg/ha N, independently on the N-form. The mycorrhization of seedlings inoculated with C. geophilum decreased from 8-35% to approximate 2-5% at 50 or 100 kg/ha N and to 0% above 100 kg/ha N. Further results are provided on the contents of the major nutrient elements in roots and shoots. To give additional information on the N-metabolism within the roots, a novel approach will be presented using quantitative RT-PCR to determine mRNA levels of the plant nitrate reductase.