Comparison of root system architecture and developmental processes among clones of Cryptomeria japonica D. Don

Breeding for traits that enhance growth, pest resistance, and environmental adaptability is essential for sessile plants, particularly in the context of climate change. The root system architecture (RSA) of trees plays a critical role in slope stabilization. Root traits undergo complex morphological changes to adapt to soil conditions, but due to their inaccessibility, understanding of tree RSA lags behind that of herbaceous species. Consequently, it remains unclear whether tree RSA can be improved through breeding. In the present study, we excavated the entire root systems of three 10-year-old Japanese cedar clones-nine individuals in total—to assess intraspecific variation in root system traits, which is key to breeding improvement. We counted the primary roots emerging from the trunk and measured the cross-sectional area (CSA) of roots at 30 cm, 60 cm, and 90 cm from the trunk to analyze root system structure. Additionally, we estimated root system development using growth ring analysis of root samples. While no clear differences were observed among clones in root development processes, we did find variation in the number of primary roots and root direction. These findings suggest that Japanese cedar breeding, which has been traditionally focused on above-ground traits, can be extended to include below-ground characteristics, aiming to develop forests optimized for both growth and slope stabilization.