THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE V. THE EFFECTS OF MYCORRHIZAL INFECTION, SOIL TYPE AND PARTIAL SOIL‐STERILIZATION (BY GAMMA‐IRRADIATION) ON GROWTH OF CRANBERRY (VACCINIUM MACROCARPON AIT.)

Abstract

SUMMARYVacdnium 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 y-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. j-1 -i 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.

The Biology of Mycorrhiza in the Ericaceae

“…The results of the present study therefore support the suggestion of Stribley et al (1975) that mycorrhizas directly aid uptake of nitrogen by ericaceous plants. In a current experiment, nitrogen-15 is being used to investigate the relative importance of inorganic and organic sources of nitrogen in the nutrition of mycorrhizal plants of Calluna and Vaccinium growing on heathland soils.…”

“…The characteristics of this program and the symbols and contractions used in discussing the quantities computed have been described by Stribley et al (1975). The following growth functions were computed for each treatment and harvest: (i) root/shoot ratio RJS^ where R^ is root dry weight and 6"^ is shoot dry weight, (ii) percentage content of nitrogen (dry weight basis) and (iii) specific absorption rate for nitrogen on the basis of root dry weight i/i?^.…”

“…Mycorrhiza may have participated directly by efficiently absorbing inorganic nitrogen present at low coneentration or by providing access to a source of nitrogen (possibly organic) not available to uninfected roots (Stribley and Read, 1974b). On the other hand, it may be that mycorrhiza operated indirectly by improving the general physiological condition of the host plant through enhanced uptake of some other deficient nutrient, such as phosphorus.…”

“…Mycorrhizal infection of ericaceous plants can increase the efficiency with which roots of the host plant absorb nitrogen from heathland soils of low fertility (Stribley, Read and Hunt, 1975). Mycorrhiza may have participated directly by efficiently absorbing inorganic nitrogen present at low coneentration or by providing access to a source of nitrogen (possibly organic) not available to uninfected roots (Stribley and Read, 1974b).…”

Vesicular‐arbuscular Mycorrhiza in Natural Vegetation Systems

“…It therefore seems likely that the responses to irradiation are largely due to nutrient release. Stribley, Read and Hunt (1975) have shown that nutrient release is particularly marked in organic soils and that nitrogen and phosphorus are the principle elements concerned. Nitrogen release can be sustained for about 20 weeks following re-introduction of micro-organisms into irradiated soil.…”