Arbuscular mycorrhizal propagule densities respond rapidly to ponderosa pine restoration treatments

1. Mycorrhizae form a critical link between above-ground plants and the soil system by influencing plant nutrition, nutrient cycling and soil structure. Understanding how mycorrhizae respond to disturbances may lead to important advances in interpreting above-ground plant recovery. 2. The inoculum potential for arbuscular mycorrhizae (AM) and ectomycorrhizal (EM) fungi was investigated in thinned-only, thinned and prescribed burned (both restoration treatments) and unthinned and unburned control stands in northern Arizona ponderosa pine forests. The relationships between mycorrhizal fungal propagule densities and plant community and soil properties were quantified. 3. The relative amount of infective propagules of AM fungi was significantly higher in samples collected from both restoration treatments than their paired controls (unthinned and unburned stands). In contrast, the same restoration treatments had no significant effect on the relative amount of infective propagules of EM fungi. 4. The relative amount of infective propagules of AM fungi was significantly positively correlated with graminoid cover and herbaceous understorey species richness and negatively correlated with overstorey tree canopy cover and litter cover. 5. Synthesis and applications. These results indicate that population densities of AM fungi can rapidly increase following restoration treatments in northern Arizona ponderosa pine forests. This has important implications for restoring the herbaceous understorey of these forests because most understorey plants depend on AM associations for normal growth. These results also can be applied to other ecosystems that are in a state of restoration or where the role of fire is just beginning to be understood.