Aquatic hyphomycete assemblages of Abies sachalinensis leaf litter immersed in a stream in Hokkaido, Japan

Aquatic hyphomycetes are key decomposers of plant-litter in freshwater environments. Previous studies have shown that conifer needles are colonized less frequently by aquatic hyphomycetes than broad-leaf species. Sakhalin fir (Abies sachalinensis) is the most common coniferous tree species planted for timber production in Hokkaido, Japan. Herein, we investigated aquatic hyphomycete assemblages involving Sakhalin fir needle litter and compared them with those of broad-leaf tree species, including Japanese oak (Quercus crispula) and Japanese linden (Tilia japonica), during immersion in a stream. Seventy percent of the total fungal species observed in fir needles were also observed in broad-leaf litter. However, the structure of the aquatic hyphomycete assemblages differed between the fir and two broad-leaf species, especially in the middle to late stages of the immersion period. The increase in species number and conidia number in fir needles was slower than that in oak leaves in the early stages of the immersion period. However, they continued to increase rapidly relative to the broad-leaf tree litter during the middle stages of the immersion period. These results suggest that fir needle litter was not difficult for aquatic hyphomycetes to colonize in the middle to late stages of the immersion period.