Roots dominate over extraradical hyphae in driving soil organic carbon accumulation during tropical forest succession

A research team from the Restoration Ecology Group of the South China Botanical Garden, Chinese Academy of Sciences, in collaboration with scientists from the United States, Australia, and Spain, has made a breakthrough in understanding soil carbon sequestration in tropical forests. For the first time, the study systematically demonstrates that plant roots are the primary drivers of soil organic carbon (SOC) accumulation, contributing nearly four times more than extraradical mycorrhizal hyphae. The findings were published in the leading international journal Global Change Biology and offer new insights for managing tropical forest carbon sinks.

The research team selected three representative forest types along a successional gradient in the tropics—Pinus massoniana forest, pine-broadleaf mixed forest, and monsoon evergreen broadleaf forest—and conducted a two-year in situ field incubation experiment. By combining isotope tracing with ingrowth-core bags of different mesh sizes, they were able to precisely quantify the relative contributions of roots and fungal hyphae to soil carbon inputs.

Results showed that roots contributed an average of 1.2 mg C g⁻¹ soil annually, nearly four times higher than extraradical hyphae (0.32 mg C g⁻¹ soil). Roots not only significantly enhanced the incorporation of new carbon but also suppressed the decomposition of existing organic carbon, leading to a net gain in soil carbon. Most of this carbon was stored as particulate organic carbon (POC).

The study also revealed distinct carbon input strategies across forest successional stages. Early-successional forests, dominated by arbuscular mycorrhizal (AM) plants, relied on fast-turnover roots to deliver large amounts of carbon. Mid-successional forests, dominated by ectomycorrhizal (ECM) fungi, showed more stable carbon inputs due to longer-lived hyphae. In late-successional forests, a functionally complementary carbon sequestration mechanism emerged, combining both root and fungal pathways.

This research clarifies the relative roles of roots and hyphae in tropical forest soil carbon sequestration and highlights the central importance of root traits in carbon storage. The authors recommend that tropical forest restoration and management prioritize tree species with high-efficiency carbon input traits, while also integrating mycorrhizal symbiosis strategies to enhance soil carbon sink capacity. The study deepens our understanding of carbon cycling mechanisms in tropical forests and provides a scientific basis for ecological restoration across global tropical regions. Paper Link: https://doi.org/10.1111/gcb.70499

Figure. Conceptual diagram showing how roots and extraradical hyphae influence soil organic carbon dynamics and net change. It illustrates the formation of new SOC, the priming effect on native SOC, and relationships with SOC components such as lignin, dissolved organic carbon (DOC), and microbial-derived carbon. Green arrows indicate positive effects; gray arrows indicate negative effects. Change rates refer to relative differences in concentrations between treatments with and without roots or hyphae.POC: Particulate Organic Carbon; MAOC: Mineral-Associated Organic Carbon. (image by CHEN et al)