In order to assess the importance of nutrient uptake and mycorrhizal infection for the establishment of seedlings of pedunculate oak (Quercus robur L.) and silver birch (Betula pendula Roth.), seedlings were grown on two nutrient-poor soils and sequential harvests taken throughout the first growing season. Seedlings were artificially established in two woodland sites and in pots of soil collected from each field site.
The pattern of nutrient depletion from oak cotyledons indicated that the initial N and P contents were completely utilized by the production of the first flush of leaves after 7 wk. Similarly, growth of birth in acid-washed sand ceased after the production of the first pair of leaves. Growth rates of field-grown seedlings were lower than those of pot-grown seedlings in each case, such that pot-grown plants were three times larger than field-grown plants by the final harvest. Nutrient losses in abscised foliage constituted a significant proportion of the total nutrient uptake of both species: between 14 and 35 % of N, P and K was abscised in the case of birch. Taking losses of nutrients in abscised foliage into account, nutrient budgets of field-grown seedlings were either slightly positive, or not significantly greater than zero.
The onset of ectomycorrhizal infection of field-grown plants was 2–4 wk more rapid than that of pot-grown plants; initial infection of field-grown seedlings was observed 3 wk after outplanting. Percentage infection of field-grown seedlings tended to be higher than in pots throughout the growing season, by up to 40%. Different mycorrhizal types displayed contrasting patterns of development: for example, Paxillus involutus (Batsch) Fr. tended to increase rapidly, to maximum percentage infections of over 30 %; whereas Cenococcum geophilum Fr. was consistently recorded at 10% infection. The role of mycorrhizal infection during seedling establishment is discussed in the light of these results.