A comparison of arbuscular and ectomycorrhizal Eucalyptus coccifera : Growth response, phosphorus uptake efficiency and external hyphal production

Abstract

Eucalyptus coccifera Hook., a plant capable of forming both arbuscular mycorrhizas and ectomycorrhizas, was used to compare the effects of the two mycorrhizal types on phosphorus uptake and C allocation. Seedlings were grown in a P-deficient soil/sand mixture inoculated with peat/vermiculite spawn of Laccaria bicolor (Maire) Orton or Thelephora terrestris (Ehrh.) Fr.; or with 250-μm sievings from leek colonized by Glomus caledonium (Nicol. and Gerd.) Trappe and Gerde., Glomus sp. type E3 or Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe or with autoclaved spawn (non-mycorrhizal control). Before the 89-d harvest, a subset of the harvested plants was labelled with 14C (45-60-min pulse, 202-h chase). Growth promotion and the increase in seedling P content was largest in the two ectomycorrhizal treatments. Production of fluorescein diacetate-stained external hyphae was three to seven times higher by ectomycorrhizal (ECM) fungi compared with arbuscular mycorrhizal (AM) fungi and was highly correlated with P uptake and shoot weight. Phosphorus inflow rates of ECM and AM seedlings were 3.8 times, and 2.0-2.7 times those of non-mycorrhizal seedlings. Phosphorus acquisition efficiencies were similar (11.2 and 10.0 μmol P mmo1-1 C for T. terrestris and Glomus E3 plants, respectively) for the two mycorrhizal types, and appeared to be greater than in uninoculated plants (7.2 μmol P mmol-1 C) grown at the same P level.