Quantitative and qualitative differences of ectomycorrhiza formed by evergreen oak species in litter deposition

Evergreen oaks are widely used as landscaping trees in Japan. Litter removal has been carried out as a part of traditional tree management, and its negative effect on tree growth and vitality has been examined. Although oak roots are associated with mycorrhizal fungi to form ectomycorrhiza (ECM), which plays an important role in tree growth, the effect of litter removal on the environment of the trees has been scarcely studied. In this study, we investigated the effect of litter removal on the number of root tips and mycorrhizal formation rate associated with four ectomycorrhizal exploration types of two evergreen tree species. Results revealed that the abundance of root and ECM tips was lower in the litter removal plots of C. sieboldii and Q. glauca. The ectomycorrhizal exploration types of C. sieboldii and Q. glauca mostly comprised contact and short-distance types, whereas other exploration types were rarely observed with or without management. The absence of long- and medium-distance ECM implied that nutrients and water could only be obtained from nearly around the fine roots in the soil, which the litter, the source of nutrients, removed. These results indicate that litter removal management negatively affects the ECM root systems and partially explain the decline of oak trees owing to litter removal treatment.