ROOT HAIR LENGTH DETERMINES BENEFICIAL EFFECT OF A GLOMUS SPECIES ON SHOOT GROWTH OF SOME PASTURE SPECIES

Differences between plant species in the benefit derived from arbuscul ar mycorrhizal colonization have often been attributed to differences in physical properties of their roots, especially in root hair develop ment. To test this hypothesis, the growth response to phosphate of fiv e pasture species which differed markedly in the length of their root hairs was measured. Plants in the mycorrhizal treatments were inoculat ed with a Glomus sp. (isolate WUM 10(1)) while non-mycorrhizal plants received control inoculum. Benefit was described as the relative effec tiveness of phosphorus (P) for the mycorrhizal plants compared with no n-mycorrhizal plants. The beneficial effect of Glomus sp. was inversel y related to root hair length of the host plant but it was not well re lated to root diameter, root length per plant or root/shoot ratio. It is suggested that root hairs and external hyphae of Glomus sp. act as alternative, similar ways of shortening the distance for the diffusion of phosphate in soils.