Studies of fine root phenology and respiration in forest ecosystems are reviewed. Direct, nondestructive observation methods, such as the minirhizotron imaging systemand the rootwindow, provide simultaneous quantitativemeasurements of root production and mortality. Temporal patterns are discussed, as well as endogenous and exogenous factors (e.g., soil temperature and moisture) controlling fine root dynamics. Both root respiration and microbial respiration release CO2 from the soil to the atmosphere
methods that distinguish them are evaluated. Finally, factors controlling root respiration, such as root age and diameter and soil nitrogen concentration, are reviewed, and approaches for scaling up root respiration to stand level are discussed.