Tissue-specific carbon concentration, carbon stock, and distribution in Cunninghamia lanceolata (Lamb.) Hook plantations at various developmental stages in subtropical China

Abstract

Carbon (C) concentrations in Cunninghamia lanceolata (Lamb.) Hook plantations differed significantly among tissue types and were greater for aboveground than belowground tissues. Plantation C stock increased with a developmental stage from young to mature to overmature, but at all stages, the majority occurred as soil organic carbon (SOC) and was more influenced by belowground fine roots than by aboveground litterfall. Failing to account for tissue-specific variation in the C concentration can result in inaccurate forest C stock estimates. We aimed to quantify the relative magnitudes of C stock for Chinese fir plantations at different developmental stages. Specifically, we focused on assessing tissue-specific C concentrations and C dynamics return of above- and belowground litterfall. Carbon traits (C concentration, C flux, C stock, and distribution at tree and ecosystem scales) were quantified in a chronosequence of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) monoculture plantation stands at young (10), mature (22), and overmature (34 years old) developmental stages. Carbon concentrations differed significantly among tissue types, with mean values of 48.5 ± 0.1% and 42.5 ± 0.2% for above- and belowground biomass, respectively. The aboveground tissue C concentration, tree- and plantation-scale C stock, and SOC stock depended on developmental stage. Carbon return in litterfall, tree C stock, and SOC increased from the young to the overmature stage. SOC stock accounted for the majority of plantation C stock at all developmental stages (78.3, 59.6, and 55.7% in the young, mature, and overmature stages, respectively) and was more highly influenced by belowground fine roots than aboveground litterfall. Carbon stocks in Chinese fir plantations were 86, 129, and 153 t ha−2 at the young, mature, and overmature stages. Prolonging Chinese fir rotation increases C sequestration potential and should be the focus of forest management strategies. The tissue-specific C concentrations provide detailed information for more accurate biomass C stock estimates for Chinese fir plantations and other subtropical coniferous forests. They indicate that current guidelines result in an overestimation of belowground biomass C stocks. Using the standard 0.47 biomass to C conversion factor, the belowground C stock would have been overestimated by 7.6–13.0% for the Chinese fir developmental stages investigated, while tree C stock would be underestimated by 0.08–3.24%. Therefore, developing species- and tissue-specific conversion factors are required for supporting C plantation and forest C accounting strategies.