Vaccinium macrocarpon was grown in open pots for 20 weeks on three heathland soils of decreasing fertility. Interactions between the effects of mycorrhizal infection, soil type and partial soil-sterilization (by γ-radiation) were studied by the calculation of various growth-functions from fitted curves.
Mycorrhizal infection increased whole-plant dry weight and relative growth-rate but decreased the root/shoot ratio of plants grown on two of the irradiated soils. These plants contained a greater percentage of nitrogen and had higher specific absorption rates for N than uninfected controls.
The fertility of each soil was increased by partial sterilization. On one irradiated soil, mycorrhizal infection was without effect: all plants grew rapidly and had large specific absorption rates which were associated with a large net mineralization of NH4+-N.
Changes in the values of growth-functions with time occurred in most treatments and were especially marked in plants grown on the irradiated soil with marked mineralization of NH4+-N. The importance of these ontogenetic variations is considered in relation to other experiments on the response of higher plants to mycorrhizal infection.