Distribution of arbuscular mycorrhizal fungi in upland field soil of Japan - 1. Relationship between spore density and the soil environmental factor

To quantify the effects of arbuscular mycorrhizal fungi (AM fungi) on the growth of upland field crops cultivated in Japan, we analyzed soil samples from 124 sites in 18 Japanese prefectures for available P content, pH and AM fungal spore density. The AM fungal spore density in the 124 soil samples was 1.7 per g DW on the average, and lower than 1.0 per g dry soil (DW) in about half of the soil samples. The maximum spore density was 20.6 spores per g DW. The density of AM fungal spore did not vary significantly with the sampling site and the kind of cultivated crop in the sampling field. The pH of the soil with a high spore density ranged from 6 to 8, and in the soil samples with a pH lower than 6 and higher than 8, the spore density was lower than 5 spores per g DW. Thus, in the acid or alkaline soil, the sporogenesis of AM fungi is suppressed. Because available P content was consistently low in the soil samples with a high spore density, P content was considered to correlate with the AM fungal spore density. Therefore, crop cultivation with limited P fertilizer application and reduced available P content may be important to increase AM fungal spore density in upland field soil.