Résumé
Background and Aims Fine roots play a major role in the global carbon cycle through respiration, exudation and decomposition processes, but their dynamics are poorly understood. Current estimates of root dynamics have principally been observed in shallow soil horizons (< 1 m), and mainly in forest systems. We studied walnut (Juglans regia x nigra L.) fine root dynamics in an agroforestry system in a Mediterranean climate, with a focus on deep soils (down to 5 m), and root dynamics throughout the year. Methods Sixteen minirhizotron tubes were installed in a soil pit, at depths of 0.0-0.7, 1.0-1.7, 2.5-3.2 and 4.0-4.7 m and at two distances from the nearest trees (2 and 5 m). Fine root (diameter 2.5 m. Conclusions The unexpected growth of very deep fine roots during the winter months, which is unusual for a deciduous tree species, suggests that deep and shallow roots share different physiological strategies and that current estimates based on the shortest root growth periods (i.e., during spring and summer) may be underestimating root production. Although high fine root turnover rates might partially result from the minirhizotron approach used, our results help gain insight into some of the factors driving soil organic carbon content.