Effects of endomycorrhizas on the competitive ability of white clover

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Abstract
White clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) were grown spearately and together, at 5 soil P levels, and with or without vesicular-arbuscular myocorrhizas (VAM). At 0 kg P/ha VAM produced a 5-fold increase in total clover dry wt when grown alone and a 40-fold increase when grown with ryegrass. In the absence of ryegrass, total clover dry wt was increased by VAM at 0 and 4 kg P/ha while in the presence of ryegrass, clover P concentrations were depressed and VAM stimulated clover growth at 12 kg P/ha. By the 3rd harvest VAM stimulated clover grown alone at 12 kg P/ha did not significantly stimulate total yield. VAM clover is better equipped than non-mycorrhizal clover to compete with ryegrass for soil P and that inter- and intra-specific competition for soil P resulted in VAM stimulating clover more and at higher soil P levels. Ryegrass displayed a poor response to both P and VAM, which was attributed to N deficiency.