Fine root dynamics in a Japanese cedar (Cryptomeria japonica) plantation throughout the growing season

To elucidate the dynamics of fine roots and root tips, which are key components in water and nutrient uptake by plants, sequential soil coring was conducted in a 28-year-old Japanese cedar (Cryptomeria japonica) plantation in the northern part of the Kanto plain, Japan. Biomass, necromass, and the number of white and brown root tips of fine roots <1 mm in diameter were determined every 6 weeks from early March to mid-November 2004. The production and mortality of fine roots and their tips between sampling periods were also estimated.Fine root mass and the number of root tips were largest in the uppermost soil layer and showed seasonal changes. Fine root biomass increased until late summer (August) and then declined, while necromass was lower in summer than in other seasons. The largest number of white root tips was observed in early summer (June) and in autumn (October) at a soil depth of 0–15 and 15–35 cm, respectively. The number of brown root tips was greater in late summer to autumn (August–October) than during other sampling periods. These results suggest that Japanese cedar has a high potential for water and nutrient uptake in summer, although the potential in autumn may also be considerable.The production of fine root dry matter peaked in summer (June–August), except in the lowest soil layer (25–35 cm deep). The production of white root tips in topsoil also reached a peak in mid-summer (July–August), whereas seasonal variation was unclear in deeper soil. Fine root production in the topsoil ceased during the early summer (June–July), probably due to drought stress or to the predominant allocation of carbon into aboveground organs. The mortality rates of fine roots were low until late summer (March–August), but sharply increased thereafter (August–November). Thus, the production and mortality of fine roots of Japanese cedar show clear seasonal changes. Soil depth, appears to strongly affect seasonal dynamics, suggesting that external conditions, such as soil temperature and moisture, together with the physiological status of the trees, substantially influence the fine-root dynamics of Japanese cedar.