Effects of Simulated Nitrogen Deposition on Ectomycorrhizae Community Structure in Hybrid Larch and Its Parents Grown in Volcanic Ash Soil: The Role of Phosphorous

With the rapid industrial development and modern agricultural practices, increasing nitrogen (N) deposition can cause nutrient imbalance in immature volcanic ash soil commonly found in Japan. Larch species, widely distributed in northeast Eurasia, are associated with ectomycorrhizal (ECM) fungi which play a critical role in nutrient acquisition for their hosts. In this study, we investigated species richness and diversity of ECM fungi associated with a hybrid larch (F₁) and its parents, Dahurian larch (Larix gmelinii var. japonica) and Japanese larch (L. kaempferi), under simulated N deposition (0 and 100 kg ha⁻¹ yr⁻¹) with/without phosphorous (P) (0 and 50 kg ha⁻¹ yr⁻¹). Seedlings planted in immature volcanic ash with low nutrient availability were subjected to the N and P treatments for fifteen months. We found that response of ECM community structure to the increased nutrient availability depended on host genotypes. Nutrient addition significantly affected ECM structure in Japanese larch, but no such significant effect was found for Dahurian larch. Effects of the nutrient addition to ECM fungal community in F₁ were intermediate. F₁ was tolerant to high N loading, which was due to consistent, relatively high association with Suillus sp. and Hebeloma sp. F₁ showed heterosis in relative biomass, which was most apparent under high N treatments. This co-variation of ECM fungal community structure and F₁ biomass in response to N loading suggest that ECM community structure might play an important role in host growth. The present findings indicate effects of N deposition on ECM fungal community structure can depend on larch species, thus it is challenging to predict general trends.