Despite the economic and ecological importance of key carbon (C) traits (concentration, sequestration, and allocation to different tree components), there have been few studies on their variation among populations of a tree species and the possible adaptive significance of these traits. We investigated differences in C traits among 16 white birch populations grown in two provenance trials in northeastern China in relation to their growth and environmental conditions at the origin of the population. Sample collections were done in August, 2011, on an average of 8 trees per provenance per site. The aboveground part of each tree was separated into stem, bark, leaves and branches; and the belowground part (root) was separated into coarse (>5 mm in diameter), medium (2–5 mm) and fine roots(<2 mm). Our objectivewas to determine if variation in C concentration and content depends on volume growth of the provenances, since genetic selections are typically for superior volume increment. To examine if the C traits are adaptive, we related them to environmental variables unique to provenance origin.
Results/Conclusions
Provenances differed significantly in most C traits. Substantial differences among provenances were found (1) in C concentration of the whole tree as well as in bole wood, bark, and fine roots; (2) in the amount of C sequestered in every tree component and in the whole tree; and (3) in the ratio of C partitioning to bole wood, bole bark, leaves, and fine roots. These responses were also affected by tree density. Variation in C concentrations and partitioning ratios were mostly independent of provenance volume growth, while C content was strongly positively correlated with volume growth. Summer climate at the provenance origin was the best predictor of C concentration and allocation. Carbon sequestration showed a clinal pattern following the mean annual temperature at the provenance origin. This suggests that C traits are adaptive in white birch, and that site conditions and/or tree density act strongly on the expression of these traits. This study has implications for national C accounting, trading C credits, and for genetic selection in relation to climate change.