Finnish Forest Research Institute  Metla

Media release 29.09.2005

Mounding provides favourable conditions for mycorrhizal fungi

Boreal forest trees always form a partnership with fungi, producing structures called mycorrhizae. The mycorrhizae found in the main tree species in Finland form ectomycorrhizae (ECM) on the root tips. The ECM colonization affects the host plant by increasing the root-absorbing area and by providing protection against root pathogens. The results of this Metla study indicated that when seedlings were planted on mounded spots, root growth and ramification were significantly increased and seedling mortality was clearly decreased. Mounding caused a slight increase in the degree of mycorrhizal colonization and changed the ratio between the different strains of mycorrhizal fungi. Root tip samples were DNA tested and classified based on the colour and texture; the results showed that mounding had no effect on the total number of ECM strains.

Nutrient uptake by forest trees is critically dependent on the type of fungi the tree is associated with. In boreal forests the ECM diversity, i.e. the number of fungal species forming mycorrhizal symbioses, is considerable, as many as thousands. The degree of mycorrhizal colonization and the ECM diversity in nursery seedlings may have an effect on regeneration results after planting. The number of ECM strains has previously been reported to decrease after clearcutting.

During the research, one- and two-year-old container seedlings were planted on both mounded and untreated spots in two forest clearcut sites in central Finland . The effects of mounding were studied during two years after outplanting. The height and root growth of the seedlings was measured and the degree of ECM colonization and the number of mycorrhizal strains were assessed.

The results indicate that the mycorrhizae originating from the nursery have an impact on seedling growth at least one growing season after outplanting. It is possible that ECM colonization enhanced root growth and ramification after planting on mounds, even though the improved temperature, water and nutrient conditions as a consequence of mounding were the most likely main factors causing seedling growth. However, knowledge of fungal mycorrhizae is still insufficient and needs to be studied further. In a parallel Metla research project, attempts are being made to identify mycorrhizal fungi capable of surviving and competing for living space both in nursery and after-planting forest conditions and guaranteeing successful early development for seedlings.

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