Seagrass meadows rank among the most significant organic carbon (C_org) sinks on earth. We examined the variability in seagrass soil C_org stocks and composition across Australia and identified the main drivers of variability, applying a spatially hierarchical approach that incorporates bioregions and geomorphic settings. Top 30 cm soil C_org stocks were similar across bioregions and geomorphic settings (min-max: 20–26 Mg C_org ha⁻¹), but meadows formed by large species (i.e., Amphibolis spp. and Posidonia spp.) showed higher stocks (24–29 Mg C_org ha⁻¹) than those formed by smaller species (e.g., Halodule, Halophila, Ruppia, Zostera, Cymodocea, and Syringodium; 12–21 Mg C_org ha⁻¹). In temperate coastal meadows dominated by large species, soil C_org stocks mainly derived from seagrass C_org (72 ± 2%), while allochthonous C_org dominated soil C_org stocks in meadows formed by small species in temperate and tropical estuarine meadows (64 ± 5%). In temperate coastal meadows, soil C_org stocks were enhanced by low hydrodynamic exposure associated with high mud and seagrass C_org contents. In temperate estuarine meadows, soil C_org stocks were enhanced by high contributions of seagrass C_org, low to moderate solar radiation, and low human pressure. In tropical estuarine meadows formed by small species, large soil C_org stocks were mainly associated with low hydrodynamic energy, low rainfall, and high solar radiation. These results showcase that bioregion and geomorphic setting are not necessarily good predictors of soil C_org stocks and that site-specific estimates based on local environmental factors are needed for Blue Carbon projects and greenhouse gases accounting purposes.

中文翻译：

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决定跨生物区和地貌海草蓝碳的因素

海草草地是地球上最重要的有机碳 (C _org ) 汇之一。我们研究了整个澳大利亚海草土壤碳_组织库和组成的变异性，并确定了变异性的主要驱动因素，采用了结合生物区域和地貌环境的空间分层方法。生物区和地貌环境中前 30 厘米土壤 C_组织储量相似（最小值-最大值：20–26 Mg C _org ha ^-1），但由大型物种（即Amphibolis spp. 和Posidonia spp.）形成的草甸显示出更高的储量(24–29 Mg C _org ha ^-1 ) 比由较小物种形成的那些（例如，Halodule、Halophila、Ruppia、Zostera、Cymodocea和Syringodium；12–21 Mg C _org ha ^-1 )。在由大物质为主温带沿海草地，土壤碳_有机股主要从海草Ç衍生_的有机（72±2％），而异地Ç_有机支配的土壤碳_有机通过在温带和热带河口草地小种（64形成草地股± 5%）。在温带沿海草甸，与高泥浆和海草 C _org含量相关的低水动力暴露增强了土壤 C _org储量。在温带河口草甸，土壤 C _org海草 C _org的高贡献、低到中等的太阳辐射和低人类压力增加了种群。在由小型物种形成的热带河口草甸中，大型土壤碳_组织储量主要与低水动力能、低降雨量和高太阳辐射有关。这些结果表明，生物区域和地貌环境不一定是土壤 C_组织储量的良好预测指标，蓝碳项目和温室气体核算需要基于当地环境因素的特定地点估计。