Mycorrhizal status of Pinus sylvestris L. nursery stock in Poland as influenced by nitrogen fertilization

Indigenous mycorrhizal colonisation of one (1/0) and two (2/0) year old Scots pine (Pinus sylvestris L.) seedlings from forest nurseries situated in the north-west part of Poland was investigated. Seedlings were fertilized after a schedule designed to satisfy their requirements which resulted from soil analysis of each nursery. In autumn needle nitrogen concentration and mycorrhizal status were estimated. As a rule seedlings 1/0 obtained high doses of fertilizers, and their needle nitrogen concentration highly exceeded the recommended optimal level above which mycorrhiza formation is greatly restricted. Highly negative correlation was found between the nitrogen status of foliage and mycorrhizal quantitative and qualitative colonisation estimated in the abundance class of 0-5. When internal nitrogen level was low, several ectomycorrhizal morphotypes were found on roots of tested plants. Excessive nitrogen fertilization decreased root ramification pattern and along with increased pH promoted ectendomycorrhizal symbiosis. Two-year-old seedlings (2/0) were characterised by significantly lower nitrogen concentration in the needles which resulted in much higher ectomycorrhizal colonisation. Ectendomycorrhizal symbiosis in the case of 2/0 seedlings was scarce. The results indicate that natural colonisation in nurseries is dependent on the soil management practices, especially nitrogen fertilization. Optimalization of nitrogen fertilization may intensify ectomycorrhizal colonisation of the nursery stock from indigenous fungal species and improve the growth of Scots pine seedlings in bare-root nurseries and plantations.