Elevational variations in fine root production, turnover, and rhizosphere autotrophic soil respiration in subalpine forests

Although aboveground forest biomass and growth decrease with elevation, elevational variation in belowground production has not been well studied. Information on belowground production is necessary to clarify the production and carbon cycling processes of forests in mountainous regions. This study aimed to clarify the elevational variations in fine root biomass, fine root production rate, and rhizosphere autotrophic soil respiration at four elevations (1600, 2000, 2300, and 2500 m above sea level) in central Japan. The fine root production rate was measured using the ingrowth core method. The lower three elevations were characterized by subalpine coniferous forests, whereas light-demanding dwarf pine Pinus pumila and deciduous hardwood Betula ermanii were characteristic of the highest elevation (i.e., treeline ecotone). The aboveground biomass, fine root biomass and fine root production rates were lower at higher elevations. The fine root biomass and fine root production rate per fine root biomass per day during the growing season were also lower at higher elevations, indicating that the lower fine root production rates at high elevations were associated with shorter growing seasons and lower turnover (i.e., fine root production rates per biomass). The rhizosphere autotrophic soil respiration rate per fine root biomass was positively correlated with soil temperature and was higher at higher elevations at all soil temperatures, indicating higher root activities during the growing season at higher elevations. The results of this study will contribute to the understanding of elevational changes in root dynamics in the temperate zone.