Estimation of the most suitable nitrogen concentration for sporocarp formation in Laccaria japonica colonizing Pinus densiflora seedlings through in vitro mycelial culture.

Abstract

Many ectomycorrhizal (ECM) fungi produce commercially valuable edible sporocarps. However, the effects of nitrogen (N) application on ECM fungal sporocarp formation remain poorly understood. In this study, we investigated the effect of application of various N concentrations (0, 5, 25, 50, 100, and 200mg/L) on the growth of Laccaria japonica mycelia in vitro for 1month. The results showed that L. japonica mycelial biomass was highest in the 50mg/L treatment and was significantly inhibited at N concentrations higher than 200mg/L. Next, we investigated the effects of N application on mycorrhizal colonization and sporocarp formation in L. japonica colonizing Pinus densiflora seedlings in pots. The seedlings were watered with nutrient solutions containing 0, 5, 25, 50, or 100mgN/L. The biomass, photosynthetic rate, and mycorrhizal colonization rates of the seedlings were measured at 45days (first appearance of primordia), 65days (sporocarp appearance on the substrate surface), and 4months after seedlings were transplanted. The numbers of primordia and sporocarps were recorded during the experimental period. Total carbon (C) and N content were determined in seedlings at 4months after transplantation, and in L. japonica sporocarps. Both mycelial growth and sporocarp production reached their maximum at an N application concentration of 50mg/L, suggesting that the most suitable N concentration for ECM fungal sporocarp formation can easily be estimated in vitro during mycelial growth. This finding may help determine the most suitable N conditions for increasing edible ECM fungus sporocarp production in natural forests.