Effects of mycorrhizal colonization byPaxillus involutuson uptake of Ca and P byPicea abiesandBetula pendulagrown in unlimed and limed peat

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Abstract
Summary: Uptake of P(32P) and Ca(45Ca) by seedlings ofPicea abies(L.) Karst andBetula pendulaRoth, non‐mycorrhizal or mycorrhizal withPaxillus 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 (32P and45Ca) 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(32P) in the unlimed substrate and in the substrate limed to a pH of 5.1. At the highest lime rate, the uptake of P(32P) 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. How‐ever, 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(45Ca) 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.