Cross-Tissue and Spatial Pattern of Carbon Fraction in 41 Fagaceae Species from China

Fagaceae trees dominate in the temperate and subtropical forests in East Asia. Understanding the spatial patterns of their carbon contents and the influencing factors can support high-precision forest carbon accounting. A comprehensive understanding of the changes in carbon in multiple organs of trees such as Fagaceae trees is still lacking at a large scale. This study investigated the inter-tissue variation, spatial patterns, and climatic drivers of carbon fraction across nine tissues (leaves, branches, bark, sapwood, heartwood, stump, coarse roots, medium roots, and fine roots) in 41 Fagaceae species (5 genera) from 12 sites across China’s major forest biomes. The sampling sites ranged from northern temperate to northern-tropical and covered an elevation range of 1200 m. The carbon fraction was measured with dry combustion after dried at 60 °C. Variance decomposition revealed that geographical location was the dominant source of variation (16%–55%), outweighing differences at the species and genus levels. Significant disparities in carbon fraction were observed among tissues, following a general pattern of leaves (517 mg g−1) ≈ fine roots (516 mg g−1) > heartwood (510 mg g−1) > sapwood (504 mg g−1) > branches (501 mg g−1) ≈ medium roots (500 mg g−1) > bark (495 mg g−1) > coarse roots (488 mg g−1) ≈ stump (487 mg g−1). This indicated a “high-at-both-ends” arcuate pattern from leaves to fine roots. Spatially, carbon fractions in most tissues exhibited significant declining trends with increasing latitude and eastward longitude. Generalized additive models identified mean annual temperature and precipitation as the most influential factors for most above-ground tissues, while fine roots were primarily regulated by temperature seasonality. These findings help us understand the differences in tree carbon fraction from an organ perspective, highlighting the critical importance of multi-tissue sampling protocol. We recommend integrating the spatial and climatic drivers for refining forest carbon accounting. More species should be included to separate the species and climatic effects in the future.