Dormant and green-up season mowing maximizes productivity-derived vegetation carbon input potential in coastal wetlands

Managing coastal Phragmites australis wetlands through seasonal mowing can alter belowground C input potential and soil CO 2 and CH 4 fluxes. However, how mowing timing affects vegetation structure and belowground C input potential across phenological stages remains poorly resolved. To address this management gap, we conducted a long-term randomized-block experiment in the Yellow River Delta, comparing an unmown control (CK) with annual mowing at green-up (March, 3M), peak growth (July, 7M), and dormancy (December, 12M). We quantified vegetation structure and production, estimated belowground net primary productivity (BNPP) using ingrowth cores, operationally estimated heterotrophic respiration ( R h ) using root exclusion and derived autotrophic respiration ( R a ) as the difference between total soil respiration and R h , measured soil CH 4 flux, and conducted scenario-based regional scaling of BNPP-derived belowground C input potential using the remotely mapped P. australis area. BNPP-derived belowground C input potential was greatest under December mowing, intermediate under March mowing, and lowest under July mowing. Targeted regressions showed positive associations of shallow coarse-root biomass with R a and shallow fine-root biomass with R h , whereas plant height was negatively associated with soil CH 4 flux. Under the full-coverage scenario, additional regional BNPP-derived belowground C input potential reached 0.170 ± 0.018, 0.100 ± 0.036, and 0.043 ± 0.017 Tg C yr −1 under 12M, 3M, and 7M, respectively. December mowing therefore produced the largest BNPP-derived belowground C input potential among the tested timings, whereas March mowing showed an intermediate response. Scenario-scaled C input potential should not be interpreted as realized ecosystem C sequestration or net climate benefit.