Soil Depth Can Modify the Contribution of Root Structure to Root Decomposition

Abstract Aims Changes in root structure and soil depth affect root decomposition. However, due to soil opacity, many variables of root structure have not been well studied and even measured. Methods To investigate the effects of soil depth and the characteristics of root structure on root decomposition, soil samples (In-situ soil core of 10cm diameter and 60cm length drilled by soil auger in October 2020) were collected in Cunninghamia lanceolata and Pinus taeda plantations (40 years), at six soil depths (0-60cm, every 10cm). The root structure in the in-situ soil cores was analyzed using CT scans and specialized analysis software. Results Root volume, shape, and connectivity were significantly higher in the 0–10 cm soil depth than in the 10-60cm soil depths, but root length and tortuosity were significantly lower than in the 50-60cm soil depth (p༜0.05). The SEM shows that different stand types influenced root biomass and thus root decomposition directly or indirectly through the characteristics of stand types. Root structure variables affected root biomass and thus root decomposition indirectly. Root biomass contributed the most to root decomposition in Cunninghamia lanceolata (20.19%) and Pinus taeda (32.26%) plantations. The contribution of root structure variables to root decomposition exceeded 50% in the 20–30 cm and 40–50 cm soil depths. Conclusions Our findings suggested that the contribution and influence of root structure variables on root decomposition rate varies with soil depth. It deserves more consideration in our future studies.