Do ectomycorrhizas affect boron uptake in Betula pendula?

The role of mycorrhizas in the uptake of boron (B) is still poorly known; it has been suggested that ectomycorrhizas (ECM) may either increase B uptake or sequester B in forms unavailable for plants. We examined whether ECM infection affects the B uptake compared with nonmycorrhizal plants and whether two ECM fungal species differ in this respect. We inoculated silver birch (Betula pendula Roth) seedlings with either Paxillus involutus (Batsch) Fr. or Laccaria sp. Seedlings were fertilized with a complete nutrient solution including B. The whole-plant specific B uptake rates were slightly higher in Laccaria-inoculated seedlings than in noninoculated seedlings. Laccaria seedlings accumulated B transiently in their roots, which led to an increase in the specific leaf uptake rate of B in a later phase. Colonization of seedlings by Paxillus was low, and this fungus did not affect B uptake or allocation. The main result was that mycorrhizas did not affect B uptake and translocation negatively. An ability to accumulate B in mycorrhizas transiently might even make plants more tolerant to temporary B deficiency as they are not so strictly dependent on a continuous external B supply. However, the possibility of retention at very low B availability remains to be studied.