Effects of soil compaction on phosphorus uptake and growth of Trifolium subterraneum colonized by four species of vesicular–arbuscular mycorrhizal fungi

Abstract

The ability of four species of vesicular–arbuscular mycorrhizal (VAM) fungi to increase phosphorus uptake and growth of clover plants (Trifolium subterraneum L.) at different levels of soil compaction and P application was studied in a pot experiment. Dry matter in the shoots and roots of clover plants decreased with increasing soil compaction. Colonization by Glomus intraradices Schenck & Smith and Glomus sp. City Beach WUM16 increased plant growth and P uptake up to a bulk density of 1·60 Mg m⁻³, although the response was smaller as soil compaction was increased. Glomus etunicatum Becker & Gerdeman and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe had no effect on the shoot d. wt and P uptake when the bulk density of the soil was [ges ]1·40 and [ges ]1·60 Mg m⁻³, respectively. Soil compaction to a bulk density of 1·60 Mg m⁻³ had no effect on the percentage of root length colonized by G. intraradices and Glomus sp. City Beach, but total root length colonized decreased as soil compaction was increased. Decreased P uptake and growth of clover plants colonized by G. intraradices and Glomus sp. City Beach, with increasing soil compaction up to a bulk density of 1·60 Mg m⁻³, was mainly attributed to a significant reduction in total root length colonized and in the hyphal biomass. Soil compaction, which increased bulk density from 1·20 to 1·75 Mg m⁻³, reduced the O₂ content of the soil atmosphere from 0·16 to 0·05 m³ m⁻³. The absence of any observable mycorrhizal growth response to any of the four species of VAM fungi in highly compacted soil (bulk density = 1·75 Mg m⁻³) was attributed to the significant decrease in the O₂ content of the soil atmosphere, change in soil pore size distribution and, presumably, to ethylene production.