Effects of mycorrhizal colonization by Paxillus involutus on uptake of Ca and P by Picea abies and Betula pendula grown in unlimed and limed peat

Uptake of P(P-32) and Ca(Ca-45) by seedlings of Picea abies (L.) Karst and Betula pendula Roth, non-mycorrhizal or mycorrhizal with Paxillus involutus (Batsch: Fr) Fr. was studied. Seedlings were grown in unamended peat (pH 4.0) or in peat limed (CaO) to pH 5.1 or 6.1. A double-labelled (P-32 and Ca-45) complete nutrient solution was added to the peat 7 wk after planting. An 8 d period was allowed for uptake of the isotopes before the seedlings were harvested. Mycorrhizal colonization clearly increased the uptake of P(P-32) in the unlimed substrate and in the substrate limed to a pH of 5.1. At the highest lime rate, the uptake of P(P-32) was greatly reduced in both mycorrhizal and non-mycorrhizal seedlings. The difference in P uptake between mycorrhizal and non-mycorrhizal seedlings was small at this lime rate. The mycorrhizal colonization of the roots was not affected by liming. However, it is possible that the mycelial growth into the substrate was inhibited. The reduction in uptake could thus be an effect of a lower availability of P in combination with a decreased fungal uptake surface at the highest lime rate. The mycorrhizal effect on uptake of Ca was much smaller than its effect on uptake of P. Mycorrhizal colonization increased the Ca(Ca-45) uptake in the unlimed treatment, where the Ca content in the substrate was very small. In the limed substrates the uptake of Ca was as high or higher in the non-mycorrhizal than in the mycorrhizal seedlings.