INTERSPECIFIC N-TRANSFER AND PLANT DEVELOPMENT IN A MYCORRHIZAL FIELD-GROWN MIXTURE

In the field, a mycorrhizal mixture of corn and soybean was compared to non-mycorrhizal and to P-compensated plant mixtures. The extent of N-15-transfer from soybean to corn was assessed. Plant development and the competitive relationship between the components of the mixtures were also examined. After having labelled selected soybean plants with isotopic NH4NO3 by feeding roots induced on their stems, a greater amount of N-15-transfer to corn was measured in mycorrhiza inoculated plots than in control plots. The growth of both corn and soybean plants was greatly enhanced when inoculated with Glomus intraradix, and the effect of the fungus could not be replicated by fertilization. Inoculation and P fertilization had similar effects on P, K and Mg uptake by plants, but their effects differed regarding Ca absorption. Inoculation with the mycorrhizal fungus favoured the grass component of the mixture over the legume. Even if more N appeared to be transferred from soybean to corn when plants were mycorrhizal, the nutrient status of the plants suggests that the growth increase can be attributed mainly to a better P uptake by mycorrhizal plants, and that the significance of interspecific mycorrhizae-mediated N-transfer may be limited.