Endomycorrhizas ofMetrosideros umbellataandWeinmannia racemosa

Abstract

The seed of Weinmannia racemosa is small (>0.1 mg) and, though it contains a high concentration of phosphorus (0.5 %), unless Endogonaceous mycorrhizas were formed seedlings were difficult to keep alive in soils low in available P. Seedlings resembled those of Coprosma robusta in their degree of dependence on infection for growth, in the minimum % P found in healthy foliage (0.04 %), and in the morphology of the root system, particularly the rare and short (0.07 mm) root hairs. The seed of Metrosideros umbellata is likewise small, but has a low concentration of phosphorus (0.05%). Yet seedlings grew slowly without mycorrhizas, even in low-P soils. They showed a growth increment on infection only in the poorest soil tested (Truog P 4 µg/ml), though P was still limiting growth in more fertile soils. M. umbellata also had a minimum of 0.04 % P in healthy foliage but it was comparable with Leptospermum scoparium in root morphology, including the intermittent production of rather short hairs (0.3 mm). It was, however, less able than L. scoparium to accelerate growth when P uptake increased. Mycorrhizal plants were stimulated by apatite and uninfected plants were not. Forest soils were estimated to contain 4 000–20 000 Endogonaceous spores per litre, and root infection to be 8–24 % in adult trees of W. racemosa and up to 76 % in seedlings. Adult infection in M. umbellata was 1–14 %.