Effects of soil phosphate level and shade on plant growth and mycorrhizas

Abstract

Seedling growth of 11 forest species was compared in steamed soils containing 11, 14, 25, and 60 ppm Truog available phosphorus. Species with coarse root systems required progressively higher soil-P levels for growth without mycorrhizas. In the soil with 60 ppm Truog P, coarse-rooted plants were still mycorrhizal but fine-rooted plants were not. Fuchsia excorticata with fine roots benefitted from mycorrhizas only at 11 ppm P; at 25 ppm P mycorrhizas decreased its growth. Mycorrhizal seedlings of shade-tolerant species had less infection when grown in heavy shade than in full sun and did not accumulate P, whereas light-demanding species retained high infection levels and accumulated P in heavy shade. Rhizophagus tennis appeared to be a more effective mycorrhizal inoculum than Acaulospora laevis.