Effect of Sterilization on Arbuscular Mycorrhizal Fungal Activity and Soil Nutrient Status

Abstract

The purposes of this study are to evaluate the effect of sterilization on arbuscular mycorrhizal fungal activity and soil nutrient status, and to determine the time needed to eliminate the colonization capability of existing AM fungi, minimize changes in soil nutrient status, and save time and energy needed to create sterile soil samples for AM inoculation. The effects of autoclaving (121 °C, 0.1 Mpa) and heating (180 °C) for 0.5, 1, 2, or 4 h on colonization capability, germination, and viability of the AM fungus Rhizophagus irregularis were investigated. The effects of both sterilization methods on pH and on concentrations of ammonium, nitrate, phosphate, potassium, and organic matter in soil samples 0.1 m thick were compared. For sterilization of longer than 1 h, both autoclaving and heating reduced colonization to less than 0.1% and depressed germination rates and the viability of arbuscular mycorrhizal fungi spores, but increased concentrations of soil macronutrients. Autoclaving for 0.5 h was sufficient to eliminate arbuscular mycorrhizal fungal colonization but heating required at least 1 h. Within 1 h, the influence of both autoclaving and heating on soil nutrient status was limited and acceptable. For the most effective investment of time and energy, arbuscular mycorrhizal-free soil 0.1 m thick can be generated with 0.5 to 1 h of autoclaving (121 °C, 0.1 MPa) or 1 h of heating (180 °C).