Mangroves store large amounts of organic carbon (C) in their soils and are important in the global C cycle. These C stocks have been attributed to the below-ground productivity of mangroves, yet there is limited knowledge about the environmental factors that influence mangrove root growth. Thus, this study aimed to assess the role of variation in soil bulk density (BD) on the early development of mangroves. Seedlings of four mangrove species were grown in a pot-experiment in soils with a BD ranging from 0.2 to 1.2 g cm⁻³. Nine functional above- and below-ground plant traits were measured. Above- and below-ground traits of mangrove seedlings were influenced by variation in soil BD, but the effect was species specific. The reaction norms for most plant traits of Bruguiera gymnorrhiza and Rhizophora stylosa suggested a growth optimum at a specific soil BD (0.6 and 0.4 g cm⁻³, respectively), whilst the reaction norm of Avicennia marina was highly variable among traits, and Ceriops australis showed a very limited response. Moreover, A. marina was the most plastic species above-ground, while R. stylosa was the most plastic species below-ground. Ceriops australis was the least plastic species. Hence, soil BD is an environmental factor that influences mangrove root traits and seedling establishment, and may therefore affect mangrove species distributions and ecosystem C stocks.

中文翻译：

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响应于土壤容重变化的红树林地上和地下发育的可塑性

红树林在其土壤中存储大量有机碳（C），在全球碳循环中很重要。这些碳储量归因于红树林的地下生产力，但对影响红树林根系生长的环境因素的知识知之甚少。因此，本研究旨在评估土壤容重（BD）变化对红树林早期发育的作用。在盆栽实验中，在BD范围为0.2至1.2 g cm ^-3的土壤中种植了四种红树林物种的幼苗。测量了九种功能性地上和地下植物性状。红壤幼苗的地上和地下特征受土壤BD变化的影响，但其影响是物种特异性的。裸子藻大多数植物性状的反应规范和Stylosa和Rhizophora stylosa建议在特定的土壤BD（分别为0.6和0.4 g cm ^-3）上生长最佳，而Avicennia marina的反应规范在性状之间变化很大，而Ceriops australis显示的响应非常有限。此外，滨海假单胞菌是地上最多的可塑物种，而圆针金枪鱼是地下最多的可塑物种。南方雪松是最少的可塑性物种。因此，土壤BD是影响红树林根性状和幼苗生长的环境因素，因此可能影响红树林物种分布和生态系统碳库。