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

Carbon (C) allocation among different plant tissues is crucial for
maintaining the 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 remains poorly
understood. In August 2019, we performed in situ
labeling of the entire crown of R0 (ramets that emerged in 2019) of moso
bamboo with 13CO2 in plots subjected to a 5–year drought or left untreated
(ambient control) in subtropical China. We then traced the 13C 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 one year post–labeling. Drought
reduced leaf 13C 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 13C signal was observed on day 15 for SOC and on day
5 for respired CO2 in both drought and ambient control forests. Labeled
13C was detected in R1 ramets on day 3 and in R2 on day 7 post–labeling.
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 neighboring R1 and R2 ramets. 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.