EFFECT OF THE ARBUSCULAR MYCORRHIZAL FUNGUS GLOMUS-FASCICULATUM ON THE UPTAKE OF AMINO NITROGEN BY LOLIUM-PERENNE

The ability of ryegrass (Lolium perenne L.) to take up and utilize asp artic acid (Asp) and serine (Ser), and the effect of colonization of t he roots by the arbuscular mycorrhizal (AM) fungus Glomus fasciculatum (Thax. sensu Gerd.) were studied. The seedlings were grown under cont rolled conditions in a series of micro-lysimeters. All plants were fed with a nutrient solution containing either nitrate, Asp or Ser as the sole N source. After 49 d, they were supplied with N-15 labelled nitr ate, Asp or Ser for 1 h and harvested. AM colonization increased the g rowth and total N content of the plants in all cases. Similarly, the a mount of Asp or Ser taken up was higher in AM than in control plants. There were no differences in biomass production between the nitrate an d Ser-fed plants. However uptake rates were lower for Ser than for nit rate. Growth of the Asp-fed plants was significantly less than the oth er two treatments, and uptake of N-15-Asp was lower than uptake of N-1 5-Ser. Analysis of N-15 incorporation into the amino acids extracted f rom the roots suggests the hydrolysis of Ser followed by re-assimilati on of the resulting ammonia via the GS-GOGAT cycle. There were no diff erences in the patterns of accumulation of amino acids in the root-zon e of control and AM-ryegrass. The implication of these results for the pathway of nitrogen transfer between plants is discussed.