Effects of Various Nitrogen Loads on the Nitrate Reductase Acitvity in Roots and Mycorrhizas of Norway Spruce Seedlings : Root - Soil Interactions in Trees

2000

S. 43-48

14 Lit.Ang.

Unselbständiges Werk

200083817

Nitrate reductase activity (NRA, in vivo-assay) was measured from mycorrhizal and non-mycorrhizal roots and from excised mycorrhizas of Norway spruce (Picea abies) seedlings. Seedlings were grown in a greenhouse and were either non-mycorrhizal controls or inoculated with the mycorrhizal fungi (Hebeloma crustuliniforme or Laccaria biocolor. Nitrogen was applied as nitrate or ammonium in loads of 50, 100 or 800 kg N/hay. Comparing the loads of 100 kg N/hay nitrate versus ammonium, NRA in the roots was significantly enhanced with nitrate. Increasing nitrate loads led to a 3-4 fold enhance of the NRA in non-mycorrhizal and in mycorrhizal roots. The inoculation with the mycorrhizal fungi however, reduced the NRA significantly at all nitrate treatments, and the reductions were higher in roots associated with H. crustuliniforme than in roots associated with L. bicolor. In excised mycorrhizas, loads of 100 k N/hay nitrate versus ammonium enhanced NR significantly. Increasing nitrate loads enhanced the NRA in excised mycorrhizas 2-6-fold. L. biocolor- compared to H. crustuliniforme-mycorrhizas had higher NRA at all nitrate loads except at 800 kg N/hay. While L. biocolor-mycorrhizas had the highest NRA at a nitrate load of 50 kg N/hay, H. crustuliniforme-mycorrhizas showed it at 800 kg N/hay. According to our results, the inoculation with mycorrhizal fungi led to a reduction of the NRA in roots, indicating an efficient uptake of nitrate by the extraradical mycelia, supporting the hypothesis that nutrient acquisition is improved by mycorrhizal fungi.