Estimation of fungal biomass in the decaying cones of Pinus densiflora

Fungal biomass in the decaying cones of Pinus densiflora was investigated. Leaching, immobilization and mobilization phases were recognized in the decomposition process of cones. Fungal biomass was estimated by the agar-film technique, using a conversion factor of 0.62 mg dry wt. mm–3 of hyphal volume to biomass and a factor of 2.5 for inefficiency of homogenization. The fungal biomass was 4.9 ± 2.1 (mean ± S.D.) mg dry wt. g-1 dry matter in the cones on the tree, 11 ± 6 mg g–1 in the leaching phase, 19 ± 7 mg g–1 in the immobilization phase and 30 ± 15 mg g–1 in the mobilization phase. It significantly increased after cones had lain on the forest floor, and also in the immobilization phase. The latter result suggests that the fungal biomass contributed to the immobilization of nitrogen in the decomposition process. The ratio of ergosterol content to fungal biomass in the cones was 2.9-8.8μg mg–1 dry wt., lying in the range of 2-16/μg mg–1 reported for mycelia. This suggested that the estimate of fungal biomass was reasonable. Reduction in this ratio with the dry weight loss in the cones suggested that the proportion of relatively active fungal biomass decreased with the progress of decomposition.