The Biology of Mycorrhiza in the Ericaceae

Abstract

SUMMARY Mycorrhizal and non‐mycorrhizal plants of Vaccinium macrocarpon were grown in a controlled environment for 12 weeks on sand supplied with five different concentrations of ammonium nitrogen in a logarithmically increasing series ranging from 1.0 to 56.0 parts/106. All plants received a full complement of other mineral elements essential to growth. Interactions between the effects of mycorrhizal infection and nitrogen concentration were studied through the calculation of various growth‐functions. With increasing concentrations of ammonium nitrogen, uninfected plants showed significant increases in whole‐plant dry weight, percentage nitrogen content and specific absorption rate for N accompanied by decreases in root/shoot ratio and the value of the allometric constant k (the ratio of the logarithmic growth‐rates of root and shoot). Mycorrhizal infection induced similar changes at intermediate levels of nitrogen supply but did not affect seedlings grown under the highest and lowest concentrations of nitrogen used. Differences due to infection were generally smaller than those between uninfected plants from successive nitrogen treatments. The implications of these results are discussed in relation to the significance of mycorrhiza in the nitrogen nutrition of ericaceous plants in their natural habitats.

Ecology of Mycorrhizae and Mycorrhizal Fungi

“…Ericoid mycorrhizae also form less readily when P and N are abundantly supplied (Morrison, 1957;Burgeff, 1961;Stribley and Read, 1976), but Morrison reported that very high applications of P to Pernettya macrostigma stunted root growth, resulting in atypical but intense infection.…”

Ultrastructural Aspects of Endomycorrhiza in the Ericaceae

“…Most of the information concerning the physiology of ericoid mycorrhizae has been obtained using plants infected with known mycorrhizal fungi under aseptic or axenic conditions (Pearson and Read, 1973b;Stribley and Read, 1975, 1976, 1980Bradley, Burt and Read, 1981). However, before extrapolating results to the field situation it is necessary to ensure that the mycorrhizae synthesized under controlled conditions are morphologically comparable to the natural associations.…”

INFLOW OF PHOSPHATE INTO MYCORRHIZAL AND NON‐MYCORRHIZAL PLANTS OF TRIFOLIUM SUBTERRANEUM AT DIFFERENT LEVELS OF SOIL PHOSPHATE

“…Mycorrhizal infection of the plants resulted in a further increase of uptake at intermediate levels of nitrogen (2-7, 7-5, and 20-5 fig N g'^) but not at 1 or 56 fig N g~^ in sand. Plant growth and concentration of N in the tissues was increased in mycorrhizal plantŝ t 2-7 and 7-5/tg N g"^ (Stribley and Read, 1976). Uptake of phosphate by •Tiycorrhizal onions (Sanders and Tinker, 1973;Sanders et al, 1977) and subter-ranean clover (Smith, Nicholas and Smith, 1979) has been measured on the basis of root length (inflow: moles P absorbed per unit root length per unit time, Brewster and Tinker, 1972) and is considerably greater than uptake into uninfected plants in the soils used but the influence of different levels of phosphate was not studied in these experiments.…”