Six-year monitoring of pine ectomycorrhizal biomass under a temperate monsoon climate indicates significant annual fluctuations in relation to climatic factors

Ectomycorrhizas (EM) are among the most active components of forest soil biomass because they represent the dominant soil carbon efflux from forests. However, temporal patterns of EM biomass in relation to climatic factors and host tree growth remain unclear. We sampled EM and fine roots of pine each month for 6 years (May 2003 to June 2009) in a 40–50-year-old Pinus densiflora forest in Japan. Tree ring width of host pines in the plot was measured to assess the chronological sequence of annual tree growth. EM biomass was not stable during the 6 years of monitoring and seasonal patterns were indistinct. Multiple correlation analyses revealed that the autumn precipitation in the previous year was the most determinative factor of EM biomass in the current year, with a negative correlation. In contrast, tree ring width generally showed a stable annual growth pattern throughout the monitoring period. Clarification of such a carbon allocation pattern is important in understanding forest carbon dynamics under a temperate monsoon climate.