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

Abstract

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 À2 , 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 À1 and 1.1 year À1 , respectively.

Spatial and seasonal variations of CO2flux and photosynthetic and respiratory parameters of larch forests in East Asia

“…This site was covered with dense Sasa dwarf bamboo, and the contribution of larch to ecosystem leaf area was minor. Thus, the GPP seems to be strongly affected by the seasonal variation of Sasa, which developed new leaves from July to August, and the LAI increased 1-3 months after that of the trees (Fukuzawa et al 2007). On the other hand, RE was maximized from late July to early August at all study sites, owing to the seasonal maximum temperature during that period.…”

Considerations in the study of tree fine-root turnover with minirhizotrons

“…Root-length-based fine-root production data collected by the minirhizotron method is sometimes converted into dry-weight-based production data per unit soil volume directly, without the calculation of turnover value (Noguchi et al, 2004;. In another approach, dry-weight-based fine-root production per unit soil volume is estimated by the combination of two methods under the assumption that the product of the fine-root standing biomass and its turnover per year gives the annual fine-root production (e.g., Gill et al, 2002;Satomura, 2003;Fukuzawa et al, 2007); in this approach, fine-root standing biomass (dry-weight basis) per unit soil volume is derived by soil core sampling, and fine-root turnover is calculated from minirhizotron data on a fine-root length basis. The sum of the dry-weight-based fine-root production per unit soil volume at all soil depths gives the stand-level fine-root production (i.e., the dry-weight-based fine-root production per unit ground surface).…”

“…Hendrick and Pregitzer, 1993;Noguchi et al, 2005;Satomura et al, 2006;Fukuzawa et al, 2007). If we put these data into the equations to calculate the turnover in processes i and ii (or iv and v), production turnover was higher than mortality turnover (or disappearance turnover) in each study.…”

“…Median fine-root life span (year) and turnover time (year) are used in the equations (13) and (14), respectively. # Data taken at soil surface (0-15 cm in depth from ground surface) in a cool-temperate, deciduous forest in the Teshio Experimental Forest in northern Japan (some of the data are shown in Fukuzawa 2007 andFukuzawa et al 2007, and the others are unpublished). Turnover values based on median life span differ among roots produced in May (a), June (b), July (c), and August (d) 2002.…”

“…Soil temperature, water and nutrient availabilities and microbial biomass frequently decrease with depth (Ajwa et al, 1998;Uchida et al, 1998;Fierer et al, 2003;Fujimaki et al, 2004), leading to lower fine-root production and mortality rates (or disappearance rates) in deeper soil (e.g. Aerts et al, 1989;Milchunas et al, 2005;Fukuzawa et al, 2007). In contrast, severely arid soil conditions can reduce root production and mortality rates in shallower depths, according to root biomass distribution patterns, due to the restriction of water and nutrient availabilities at the surface (Rundel and Nobel, 1991).…”