Better understanding the fate of the atmospheric carbon (C) captured by plant photosynthesis is essential to improve natural C flux modelling. Soils are considered as the major terrestrial bioreactor and repository of plant C, whereas channel networks of floodplain rivers collect and transport, throughout the aquatic continuum, a significant part of plant primary production until its export through outgassing or sequestration in marine sediments. Here, we show that river meandering in forested floodplains is a crucial and widely overlooked Earth surface process promoting C fluxes from the atmosphere to the aquatic continuum, via the floodplain vegetation. Over a recent period of 35 years (1984-2019), we quantified those C fluxes in one of the most active meandering rivers on Earth, the Ucayali River, Peru, South America. We used map time series combined with above-ground forest C data to derive the amount of C that is annually captured by the growing floodplain vegetation within the active meander belt, as well as exported to the aquatic continuum by lateral channel erosion. We found that the annual building and erosion of forested floodplain areas was nearly balanced over time with 19.0±7.7×10³ ha^-1 yr^-1 and 19.8±6.7×10³ ha^-1 yr^-1, respectively. While growing forests within the active meander belt annually captured 0.01±0.05×10⁶ Mg C yr^-1, lateral channel erosion provided the nearly 100-fold amount of C to the river channel and its streamflow, i.e. 0.9±0.4×10⁶ Mg C yr^-1. Our findings revealed that the migration of the Ucayali River channel provided nearly 10-times more lignified C per unit area to the aquatic continuum (44.7±21.4 Mg C ha^-1 yr^-1) than non-meandering central Amazonian floodplains do. Together, these findings point to the importance of quantifying the overall contribution of meandering rivers to natural C fluxes worldwide.

更好地理解植物光合作用捕获的大气碳（C）的命运对于改善自然C通量建模至关重要。土壤被认为是植物C的主要陆地生物反应器和储存库，而漫滩河道网络在整个水生连续体中收集和运输了植物初级生产的重要部分，直到通过除气或隔离在海洋沉积物中将其出口为止。在这里，我们表明，在森林漫滩中蜿蜒的河水是一个至关重要的且被广泛忽视的地球表面过程，可通过漫滩植被促进C从大气到水生连续体的通量通量。在最近的35年（1984-2019年）中，我们量化了地球上最活跃的曲折河流之一，乌卡亚里河，秘鲁，南美的碳通量。我们使用地图时间序列与地上森林碳数据相结合，得出活动曲折带内不断增长的洪泛区植被每年捕获的碳量，并通过横向河道侵蚀将其输出到水生连续体。我们发现，森林泛滥区的年建筑量和侵蚀量随时间推移几乎达到平衡，为19.0±7.7×10³ ha ^-1 yr ^-1和19.8±6.7×10 ³ ha ^-1 yr ^-1。在活动曲折带内生长的森林每年捕获0.01±0.05×10 ⁶ Mg C yr ^-1时，侧向河道侵蚀向河道及其河流提供了几乎100倍的C量，即0.9±0.4×10 ⁶ Mg C yr ^-1。我们的研究结果表明，乌卡亚里河河道的迁移使单位面积木质素碳增加了近10倍（44.7±21.4 Mg C ha ^-1 yr ^-1）比非蜿蜒的中亚亚马逊河平原做得好。总之，这些发现指出了量化蜿蜒河流对全球自然C通量的总体贡献的重要性。