Extensive belowground carbon storage supports roots and mycorrhizae in regenerating scrub oaks

Portions of a regenerating scrub oak ecosystem were enclosed in open-top chambers and exposed to elevated CO₂. The distinct ¹³C signal of the supplemental CO₂ was used to trace the rate of C integration into various ecosystem components. Oak foliage, stems, roots and ectomycorrhizae were sampled over 3 years and were analyzed for ¹³C composition. The aboveground tissue ¹³C equilibrated to the novel ¹³C signal in the first season, while the belowground components displayed extremely slow integration of the new C. Roots taken from ingrowth cores showed that 33% of the C in newly formed roots originated from a source other than recent photosynthesis inside the chamber. In this highly fire-prone system, the oaks re-establish primarily by resprouting from large rhizomes. Remobilization from belowground C stores may support fine roots and mycorrhizae for several years into stand re-establishment and, therefore, may explain why belowground tissues contain less of the new photosynthate than expected. Though it has been shown that long-term cycles of C storage are theoretically advantageous for plants in systems with frequent and severe disturbances, such patterns have not been previously examined in wild systems.