Vertical distribution and seasonal pattern of fine-root dynamics in a cool-temperate forest in northern Japan:: implication of the understory vegetation, Sasa dwarf bamboo

We measured the vertical distribution and seasonal patterns of fine-root production and mortality using minirhizotrons in a cool-temperate forest in northern Japan mainly dominated by Mongolian oak (Quercus crispula) and covered with a dense understory of dwarf bamboo (Sasa senanensis). We also investigated the vertical distribution of the fine-root biomass using soil coring. We also measured environmental factors such as air and soil temperature, soil moisture and leaf area indices (LAI) of trees and the understory Sasa canopy for comparison with the fine-root dynamics. Fine-root biomass to a depth of 60 cm in September 2003 totaled 774 g m(-2), of which 71% was accounted for by Sasa and 60% was concentrated in the surface soil layer (0-15 cm), indicating that understory Sasa was an important component of the fine-root biomass in this ecosystem. Fine-root production increased in late summer (August) when soil temperatures were high, suggesting that temperature partially controls the seasonality of fine-root production. In addition, monthly fine-root production was significantly related to Sasa LAI (P < 0.001), suggesting that fine-root production was also affected by the specific phenology of Sasa. Fine-root mortality was relatively constant throughout the year. Fine-root production, mortality, and turnover rates were highest in the surface soil (0-15 cm) and decreased with increasing soil depth. Turnover rates of production and mortality in the surface soil were 1.7 year(-1) and 1.1 year(-1), respectively.