Dynamics of fine root, fungal rhizomorphs, and soil respiration in a mixed temperate forest: Integrating sensors and observations

Fine roots and rhizomorphs have important implications for the global carbon balance, but the processes underlying these carbon sinks are not well understood. In this study, we coupled continuous minirhizotron observations with an array of solid-state CO(2) sensors. We calculated soil respiration using a gradient flux method. Using a Kaplan-Maier survival analysis, we determined a median longevity of 347 d for fine roots and of 400 d for rhizomorphs. Radiocarbon ((14)C) analysis suggested an age of 7 yr for fine roots < 1 mm and 17 yr for roots of 1 mm in diameter. We found rapid changes in root length (maximum of 38.1 cm m(-2) d(-1)) and rhizomorph length ( maximum of 105.4 cm m(-2) d(-1)) during sampling of four consecutive days. Changes in rhizomorph length were more variable than root length, and rhizomorphs were negatively correlated with daily changes in soil moisture. The variation in root length may be associated to prior environmental conditions. Fine root length was correlated with daily CO(2) production, and variation in daily fine root length could contribute up to 4680 g C ha(-1) d(-1). We observed a clockwise diurnal hysteresis effect in soil respiration with soil temperature that changed in amplitude and shape along the year. Our results show the importance of shorter intervals of minirhizotron measurements to understand rapid fine roots and rhizomorphs variation. Furthermore, continuous minirhizotron measurements should be couple with continuous measurements of multiple sensor arrays to explain biophysical factors that regulate belowground carbon dynamics.