Root exudation, the export of low-molecular weight organic carbon (C) from living plant roots to soil, influences microbial activity, nutrient availability, and ecosystem feedbacks to climate change, but the magnitude of this C flux at ecosystem and global scales is largely unknown. Here, we synthesize in situ measurements of root exudation rates and couple those to estimates of fine root biomass to estimate global and biome-level root exudate C fluxes. We estimate a global root exudate flux of 13.4 (10.1–20.2) Pg C y⁻¹, or about 9% (7–14%) of global annual gross primary productivity. We did not find differences in root mass-specific exudation rates among biomes, though total exudate fluxes are estimated to be greatest in grasslands owing to their high density of absorptive root biomass. Our synthesis highlights the global importance of root exudates in the terrestrial C cycle and identifies regions where more in situ measurements are needed to improve future estimates of root exudate C fluxes.

根系分泌物，即低分子量有机碳 (C) 从活植物根部向土壤的输出，会影响微生物活动、养分可用性以及生态系统对气候变化的反馈，但生态系统和全球尺度上这种碳通量的大小很大程度上取决于未知。在这里，我们综合了根系分泌物速率的原位测量结果，并将其与细根生物量的估计值结合起来，以估计全球和生物群落水平的根系分泌物碳通量。我们估计全球根系分泌物通量为 13.4 (10.1–20.2) Pg C y ⁻¹ ，约占全球年总初级生产力的 9% (7–14%)。我们没有发现生物群落之间的根质量特定渗出率存在差异，但由于吸收性根生物量的高密度，估计总渗出液通量在草原中最大。我们的综合强调了根系分泌物在陆地碳循环中的全球重要性，并确定了需要更多原位测量以改进根系分泌物碳通量未来估计的区域。