SPECIFICITY OF INTERPLANT CYCLING OF PHOSPHORUS - THE ROLE OF MYCORRHIZAS

The cycling of nutrients from dying roots of one plant (the 'donor') to other intact plants (the 'receivers') was examined in a series of pot experiments. In each pot receiver plants formed either the same or a different type of mycorrhiza as the donor plant and was therefore respectively either capable or incapable of forming mycorrhizal hyphal links to the donor. There was a preferential transfer of P-32 from the dying roots of the vesicular-arbuscular mycorrhizal (VAM) Lolium perenne to VAM-infected trees Acer pseudoplatanus and Fraxinus excelsior compared to the ectomycorrhizal (ECM) Larix eurolepis, this despite an apparently greater competitive ability of L. eurolepis to obtain P-32 from the soil. Following the death of L. perenne roots there was also an increase in total P in the VAM tree receiver. These findings could not be explained by similarities in rooting distribution of the VAM-infected plants. In a similar study of the transfer of P-32 between heathland plants there was a preferential cycling of P-32 from one ericoid mycorrhizal Calluna vulgaris to another rather than to the VAM Molinia caerulea. In contrast, when P-32 was supplied directly to the soil, M. caerulea obtained significantly more P-32 than C. vulgaris. These results are discussed in relation to the potential role of interplant mycorrhizal links in the cycling of nutrients within partially closed cycles and the implications that this might have for species balance in plant communities.