MYCORRHIZAL INFECTION OF BETULA PENDULA AND ACER PSEUDOPLATANUS: RELATIONSHIPS WITH SEEDLING GROWTH AND SOIL FACTORS.

Mycorrhizal infection of two-year-old seedlings of Betula pendula Roth, and Acer pseudoplatanus L. was examined in a pot experiment, in relation to several soil variables (pH, organic matter, N, P, K, Ca, Fe, and phosphatase activity), host uptake of 32 P, and plant performance (height and weight), in 25 Cumbrian soils from natural and semi-natural habitats (such as woodland, carr and upland heath). Soils were used in a fresh state to maintain indigenous mycofloras and seedlings were raised from several seed-lots to include possible ecotypic variation. Infection (incidence and intensity) of both 'immature' and 'mature' mycorrhizas was estimated. Most plants were mycorrhizal, ectomycorrhizas occuring on Betula and vesicular-arbuscular (VA) endophytes in Acer. Differences in the degree of infection between soils, but not between seed-lots, were highly significant. Infection of one or both species was highly correlated with several soil factors (pH, organic matter, phosphorus and iron), and with all the plant variables. In Betula, evidence for most of these relationships was obtained only from 'immature' mycorrhizas, suggesting early physiological activity. Mycorrhizas accounted for a small but significant proportion of the variation in growth of both hosts, and soil properties accounted for a high proportion of the variation in both the plant growth and mycorrhizal infection, as shown by multiple regression analyses. Growth of Acer appeared to have a greater influence than soil factors on the variation in VA infection. 'Beading' of Acer roots was negatively correlated with plant weight and soil phosphorus, suggesting a morphological response to P- deficiency. Possible causal relationships between hosts, fungal symbionts and soils are discussed.