Arbuscular mycorrhizal induced changes to plant growth and root system morphology in Prunus cerasifera

We compared root system morphogenesis of micropropagated transplants of Prunus cerasifera L. inoculated with either of the arbuscular mycorrhizal (AM) fungi Glomus mosseae or Glomus intraradices or with the ericoid mycorrhizal species Hymenoscyphus ericae. All plants were grown in sand culture, irrigated with a nutrient solution that included a soluble source of phosphorus, for 75 days after transplanting. Arbuscular mycorrhizal colonization increased both the survival and growth (by over 100%) of transplants compared with either uninoculated controls or transplants inoculated with H. ericae. Arbuscular mycorrhizal colonization increased root, stem and leaf weights, leaf area, root length and specific leaf area, and it decreased root length/leaf area ratio, root/shoot weight ratio and specific root length. Both uptake of phosphorus and its concentration in leaves were increased by AM infection, although the time course of the relationships between intensity of AM infection and E nutrition were complex and suggested a role for factors other than nutrition. The time course for the development of infection varied. It was most rapid with G. mosseae, but it was ultimately higher with G. intraradices. None of the treatments significantly affected the lengths a adventitious roots or the first-, second- or third-order lateral that developed from them. Arbuscular mycorrhizal colonization increased the intensity of branching in all root orders with the effect being most obvious on first-order lateral roots where the number of branches increased from under 100 to over 300 branches m-1. As a result, although first-order laterals made up 55% of the root systems of control plants, the comparable value was 36% in AM-infected plants. In contrast, second-c der laterals represented 25% of control root systems, but 50 of AM-colonized root systems. Glomus intraradices but n G. mosseae increased root diameter. Anatomical studies vealed no changes in the overall form of the root tip, although there were changes in the diameter of the root cap, cell numbers and cell size. Hymenoscyphus ericae increased the duration of the metaphase index. Both AM fungal treatments increased the concentrations of soluble proteins in root extracts and modified the protein profiles by the elimination and addition of protein bands detected by PAGE analysis. We conclude that AM fungal inoculation influenced processes in the root system at different levels, but not all effects were due to improved P nutrition or increased physiological age.