Benthic microeukaryotes beta diversity, but not alpha diversity, modulates carbon dioxide fluxes in a subtropical unvegetated tidal flat

Unvegetated flats are receiving increasing attention due to their widespread distribution in “non-classical” blue carbon ecosystems. However, the relationship between CO2 flux and benthic microeukaryotes in unvegetated mudflats remains uncertain. This study focused on a subtropical tidal flat in Southeast China, integrating seasonal measurements, co-occurrence network construction, and partial least squares structural equation modeling (PLS-SEM) to elucidate the mechanisms by which microeukaryotes drive carbon sink functionality under seasonal dynamics. Our results showed that the annual CO2 flux showed net absorption, compared to net greenhouse gas source. Pennate diatoms determined seasonal change from CO2 sources to sinks. α-Diversity peaked in winter, while β-diversity showed strong seasonal turnover, directly suppressing CO2 emissions by optimizing species composition. PLS-SEM further confirmed that environmental factors influenced carbon sink functionality through both direct regulation and biodiversity-mediated indirect pathways. Our study provides a critical theoretical foundation for “non-classical” blue carbon ecosystems restoration and carbon neutrality pathway optimization.无植被滩涂因广泛分布于"非典型"蓝碳生态系统（blue carbon ecosystems）中而受到学界日益广泛的关注。然而，无植被潮滩（unvegetated mudflats）中二氧化碳通量与底栖微真核生物（benthic microeukaryotes）之间的相互关系仍未明确。本研究以中国东南部亚热带潮滩为研究对象，整合季节性原位监测、共现网络构建及偏最小二乘结构方程模型（PLS-SEM），阐明了季节动态下微真核生物驱动碳汇功能的内在机制。研究结果显示，年度二氧化碳通量整体呈现净吸收状态，而非温室气体净排放源。羽纹硅藻（Pennate diatoms）主导了二氧化碳源汇格局的季节转变。α多样性（α-Diversity）在冬季达到峰值，而β多样性（β-diversity）则呈现显著的季节周转特征，可通过优化物种组成直接抑制二氧化碳排放。偏最小二乘结构方程模型进一步证实，环境因子可通过直接调控及生物多样性介导的间接路径共同影响碳汇功能。本研究为"非典型"蓝碳生态系统修复及碳中和路径优化提供了关键理论基础。