Effect of VA mycorrhizas on phosphorus uptake and growth of white clover (Trifolium repensL.) growing in association with ryegrass (Lolium perenneL)

Abstract

Abstract In a phosphorus‐deficient soil, vesicular‐arbuscular mycorrhizas (VAM) helped white clover to compete more effectively with ryegrass for phosphate, resulting in better phosphate acquisition by mycorrhizal clover than non‐mycorrhizal clover. The benefit was greatest when competition from ryegrass was severe. Mycorrhizal clover did not grow much faster than non‐mycorrhizal clover, probably because of competition for light from neighbouring ryegrasses. When the soil was fertilised with phosphate, clover and ryegrass yields increased, and non‐mycorrhizal clover plants outyielded mycorrhizal plants. Similar parasitic effects of VAM have been recorded before. It is concluded that the presence of VAM linkages between clover and grass roots will probably negate any benefits to clover of the introduction of elite VAM fungi to pasture soils. Genetic manipulation of a host plant's response to VAM, may be a more profitable way of improving the phosphate nutrition of white clover in mixed swards.