Variations in fine root dynamics and turnover rates in five forest types in northeastern China

Quantifying fine root (<= 2.0 mm in diameter) distribution and turnover is essential for accurately estimating forest carbon budgets. However, fine root dynamics are poorly understood, possibly because of their inaccessibility. This study quantifies fine root distribution and turnover rates for five representative Chinese temperate forests types. Fine root number, diameter, biomass, necromass, production, mortality, and turnover rates were measured using a minirhizotron over a 12-month period. More than 90% of the fine roots were < 0.5 mm in diameter, with thin fine roots at shallow layers, and thicker ones in deeper soil layers. The fine root dynamics were significantly different among the forest types. Coniferous plantations had fewer fine roots, less biomass, necromass, production and mortality but greater average diameters than fine roots of broadleaved forests. All traits, except for diameter, decreased along the soil profile. Fine root numbers and production exhibited a unimodal seasonal pattern with peaks occurring in summer, whereas biomass, necromass and mortality progressively increased over the growing season. The turnover rates of roots < 0.5 mm varied from 0.4 to 1.0 a(-1) for the five forest types, 0.5-1.0 a(-1) for the soil layers and 0.2-1.1 a(-1) for the seasons, with the largest turnover rate at the 0-10 cm depth in summer. The patterns of fine root numbers, biomass, necromass, production, mortality, and turnover rates varied with forest types, soil depths, growing season and diameter classes. This study highlights the importance of forest types and diameters in quantifying fine root turnover rates.