Variation Patterns of Fine Root Biomass, Production, and Turnover Rates in Four Subtropical Forests of China

Fine roots (diameter &le: 2 mm) play a critical role in regulating soil organic carbon storage and nutrient cycling in forest ecosystems. However, the variability in fine root biomass, production, and turnover rates across different forest types remains poorly understood. This study investigates fine root dynamics, including biomass, distribution, and turnover, across four major monoculture plantation forests in subtropical China: Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), Masson pine (Pinus massoniana Lamb.), Chinese sweet gum (Liquidambar formosana Hance), and camphor tree (Cinnamomum camphora (L.) J. Presl). Using a sequential coring method, soil samples were collected monthly to monitor live and dead fine root biomass across different soil depths (0&ndash:15 cm, 15&ndash:30 cm, 30&ndash:45 cm, and 45&ndash:60 cm). Fine root production and turnover rates were estimated using three methods: Max&ndash:Min, Integral and Decision Matrix. The results showed that fine root biomass was highest in the camphor tree forest (1.96 t ha&minus:1), followed by Masson pine (1.12 t ha&minus:1), Chinese fir (0.89 t ha&minus:1), and Chinese sweet gum (0.83 t ha&minus:1). Approximately 90% of the total fine root biomass was composed of live roots across all forest types, highlighting their significant role in nutrient uptake. Both live and dead fine roots were predominantly concentrated in the upper 0&ndash:30 cm soil layer, with a notable decline in biomass in deeper layers. Fine root biomass production was highest in the camphor tree forest (2.66&ndash:2.90 t ha&minus:1 a&minus:1), followed by Masson pine (1.16&ndash:1.83 t ha&minus:1 a&minus:1), Chinese fir (0.87&ndash:0.97 t ha&minus:1 a&minus:1), and Chinese sweet gum (0.87&ndash:0.93 t ha&minus:1 a&minus:1). Turnover rates were highest in the camphor tree forest (1.25&ndash:1.36 a&minus:1), followed by Masson pine (0.96&ndash:1.51 a&minus:1), and both Chinese fir and Chinese sweet gum (0.94&ndash:1.05 a&minus:1 and 0.97&ndash:1.04 a&minus:1, respectively). This study identifies significant differences in fine root dynamics among subtropical forest types, providing baseline data critical for optimizing forest management, particularly in urban and peri-urban areas. These insights can enhance reforestation efforts, ecosystem resilience, and sustainable forest productivity.