Radiocarbon-derived ages of carbon in live, dead, and newly emerged fine roots in a cool-temperate Japanese beech forest

Koarashi, Jun   ; Atarashi-Andoh, Mariko  ; Ishizuka, Shigehiro*; Noguchi, Kyotaro*; Kadono, Atsunobu*; Nakayama, Masataka*

Maintaining and enhancing the forest carbon (C) sinks are key to mitigating climate change; however, the forest C dynamics related to the production and turnover of fine roots (2 mm in diameter) have not been well captured. In this study, we examined ages of C in fine roots in a cool-temperate Japanese beech forest by measuring the natural abundance of radiocarbon (C). Root samples were collected and categorized by diameter size class and live/dead status. Newly emerged roots were also obtained using the ingrowth mesh bag method. The mean ages of fine root C were estimated to be 5-23 years for live roots and 1-34 years for dead roots, respectively. In contrast, the C signatures of newly emerged roots indicated the use of current-year photosynthetic products for new root production. Given the negligible time lag between photosynthetic C fixation and the use of the fixed C for new root production, the observed ages for live fine root C suggest that plants use current-year photosynthetic products to produce new roots but utilize older (C-enriched) internally stored C to support subsequent root growth, and/or that some fine roots live for many years. Our results provide a piece of knowledge to comprehensively understand belowground C allocation processes in plants.