Variations in ergosterol content and ornithine decarboxylase activity of ectomycorrhizal root-soil systems

Influences of soil P fertilization on temporal changes in ergosterol content and ornithine decarboxylase (E.C. 4.1.1.17, ODC) activity were monitored in rhizosphere soil, non-rhizosphere soil and Pinus contorta roots ectomycorrhizal with Hebeloma crustuliniforme grown in a loamy sand. With addition of mycorrhizal inoculum to loamy sand, ODC activity mg^-1 root increased between 10% and 2 fold within 21 weeks of pianting. Inoculation also decreased root mass per seedling. Inoculation increased mycelia mass per root mass by up to 2 fold but no differences were observed for total seedling mass until 35 weeks. Intramatrical mycelia were detrimental to early plant growth, but inoculated seedlings had 1.7 times more root mass and 1.3 times more shoot mass at 35 weeks. Rhizosphere soil contained up to 5 times more mycelia and up to 6 times greater ODC activity than non-rhizosphere soil. Inoculation increased rhizophere metabolic activity and intramatrical mycelia mass. Their sensitivity to fungal inoculation, P fertilization and temporal trends may make the methods useful in studies of rhizosphere ecology and root-microbe relationships.