Growth and phosphorus inflows of Trifolium repens L. with a range of indigenous vesicular-arbuscular mycorrhizal infection levels under field conditions.

Abstract

Since vesicular-arbuscular mycorrhizas (VAM) are believed to play a fundamental role in phosphorus (P) uptake for many plant species, an experiment was performed to test the hypothesis that rates of P uptake per unit root length (P inflow) should be proportional to the extent of infection. Plants of Trifolium repens L. were grown in pots containing different proportions of sterile and non-sterile soil in radially arranged rooting compartments and transplanted with a consequent range of mycorrhizal infection into the field at a hay meadow of moderate P fertility. Even though plant growth in the field was exponential, plants with greater proportions of their root systems infected did not have higher P inflows or dry matter production. For much of the experiment P inflows were below the levels at which it would be necessary to invoke mycorrhizally assisted uptake. It is suggested that for Trifolium repens, even while the plant is growing actively in the field, VAM do not always function mutualistically.