Mycorrhizal colonization is compatible with exponential fertilization to improve tree seedling quality

This study tested the ability of exponential fertilization to minimize the tradeoff of increased seedling size and nutrient concentration with good root colonization by mycorrhizae. Two native Hawaiian tree species were tested. Four rates of nitrogen (N) (0–3 g per seedling) were delivered by the method of exponential fertilization to seedlings with and without inoculation with a native strain of arbuscular mycorrhizal fungus. For both species, the highest growth and nutrient concentrations occurred with mycorrhizal colonization at 1–2 g N per seedling. Growth of inoculated seedlings was significantly lower at 3.0 g N per seedling, likely due to a large reduction in mycorrhizal colonization. Our results demonstrate that mycorrhizal colonization is not only compatible with exponential fertilization, combined they produce larger seedlings with higher nutrient content. This should improve outplanting success in degraded or challenging sites.