Interactions of nitrogen and phosphorus on mycorrhizal development and shoot growth of Eucalyptus globulus (Labill.) seedlings inoculated with two different ectomycorrhizal fungi.

摘要

A number of investigations have demonstrated that balanced fertilizer applications can improve shoot growth of E. globulus plantations. Similar information on the impact of balanced N+P fertilizers on mycorrhizal development is lacking. This study was thus undertaken to determine the combinations of N and P which promote greatest mycorrhizal development and growth of seedlings of E. globulus. The overall objective was to generate information which might be translated into protocols for improved nursery and plantation management. Factorial combinations of 2 ectomycorrhizal fungi (Hydnangium carneum and Laccaria fraterna) and 8 fertilizer regimes containing different combinations of nitrogen (N) and phosphorus (P) were applied to Eucalyptus globulusseedlings. The 4 concentrations of nitrogen in the solutions ranged from 62.5 up to 250 mg litre-1 while those of phosphorus were 10 and 25 mg litre-1. Plants were harvested 12 weeks after inoculation. When given the lower P regime (10 mg P litre-1), increasing amounts of applied N resulted in increasing percentages of infected roots, irrespective of fungal inoculant. Maximum colonization, including frequency of mycorrhizal branching, was observed at 250 mg N litre-1/10 mg P litre-1, with no indicationthat mycorrhizal infection had peaked. For seedlings given the higher P (25 mg litre-1) concentration, increasing amounts of nitrogen tended to decrease percentage root infection. Seedlings given 25 mg P litre-1 grew larger (leaf, stem and shoot dry weight) with increasing concentrations of nitrogen. Those that were given the lower P concentration responded less to N. With the exception of leaf number, a strong positive relationship was found between seedling growth variables and percentage mycorrhizalinfection at 10 mg P litre-1. No such relationship was found at 25 mg P litre-1. The implications of these findings for the development of a balanced N:P fertilizer regime in eucalypt nurseries and plantations are discussed.