‘The view that nutrient acquisition by most plants growing in natural ecosystems is mediated by mycorrhiza-forming symbiotic fungi is now largely accepted’ (Read, 2000). Is this bold claim really true for the whole suite of mineral nutrients that plants require? The case is strongest for nutrients that are not very mobile in soil, especially when present in growth-limiting amounts, and phosphate (P) is the classic example. Arbuscular mycorrhizas are by far the most widespread mycorrhizal symbioses, and the ability of arbuscular mycorrhizal (AM) fungi to take up soil nutrients such as P and transfer them to the host plant is an area of intense research. However, there is great variation in the extent to which AM plants benefit in measurable terms from the symbiosis under a given set of environmental conditions, and a paper in this issue, by Koide et al., addresses this problem (Koide et al., pp. 163–168). The variability is especially apparent in the field, thus obscuring the possible roles of mycorrhizas in community structure and succession (Fitter, 1985; McGonigle, 1988).