1. 18% of rush and sedge field samples were infected with endomycorrhizal fungi.
2. In pot experiments, rushes and sedges remained nonmycorrhizal in soils of Truog P ≤ 3.6 1 μg /ml, despite inoculation with rush and sedge mycorrhizas from the field and with known endogonaceous symbionts.
3. In poor soils, rushes and sedges made growth comparable with that of mycorrhizal Leptospermum scoparium and outgrew mycorrhizal Poa colensoi and achieved shoot P concentrations comparable to those which decreased mycorrhizal infection in Leptospermum and Poa.
4. Rushes and sedges achieved extensive root absorbing surface through a combination of high root productivity, large root length/root weight ratio, and long and persistent root hairs.
5. It is suggested that failure to form mycorrhizas is due to rapid P uptake by the extensive root absorbing surface resulting in high plant P concentrations early in seedling growth, inhibitory to mycorrhizal fungi.
