Drought decreases carbon flux but not transport speed of newly fixed carbon from leaves to sinks in a giant bamboo forest

Abstract Carbon (C) allocation among different plant tissues is crucial for maintaining C balance in forest ecosystems, especially under changing climate conditions. The partitioning of newly assimilated C among plant tissues, interconnected ramets and soil in forests dominated by giant clonal plants, such as moso bamboo ( Phyllostachys edulis ), and the influence of drought on this partitioning remain poorly understood. In August 2019, we performed in situ labelling of the entire crown of R0 (ramets that emerged in 2019) of moso bamboo with 13 CO 2 in plots subjected to a 5‐year drought or left untreated (ambient control) in subtropical China. We then traced the 13 C signatures in the leaves, twigs and fine roots of R0, R1 (ramets that emerged in 2018 and are connected with R0) and R2 (ramets that emerged in 2017 and are connected with R1), as well as in soil organic C (SOC) and soil respiration over the course of 1‐year post‐labelling. Drought reduced leaf 13 C assimilation and its allocation to sink tissues but did not alter the velocity of C transport from source to sink compared to controls. The peak 13 C signal was observed on day 15 for SOC and on day 5 for respired CO 2 in both drought and ambient control forests. Labelled 13 C was detected in R1 ramets on day 3 and in R2 on day 7 post‐labelling. This study reveals that new assimilates produced by the ‘younger’ R0 ramets are preferentially retained within their own tissues to meet their own demands rather than being allocated to interconnected neighbouring R1 and R2 ramets. Synthesis . In forests dominated by large clonal plants, such as giant moso bamboo, drought can alter the allocation of newly assimilated C within the tissues of source ramets but may not affect its allocation among interconnected ramets or within plant–soil systems. Our findings highlight the complexity of newly assimilated C partitioning in these forests and suggest that clonal integration may mitigate drought‐induced dieback in older ramets through resource sharing under climate change.