Abstract

Increases in temperature are expected to facilitate encroachment of tropical mangrove forests into temperate salt marshes, yet the effects on ecosystem services are understudied. Our work was conducted along a mangrove expansion front in Louisiana (USA), an area where coastal wetlands are in rapid decline due to compounding factors, including reduced sediment supply, rising sea level, and subsidence. Marsh and mangrove ecosystems are each known for their ability to adjust to sea-level rise and support numerous ecosystem services, but there are some differences in the societal benefits they provide. Here, we compare carbon and nitrogen stocks and relate these findings to the expected effects of mangrove encroachment on nitrogen filtration and carbon sequestration in coastal wetlands. We specifically evaluate the implications of black mangrove (Avicennia germinans) encroachment into Spartina alterniflora-dominated salt marsh. Our results indicate that black mangrove encroachment will lead to increased aboveground carbon and nitrogen stocks. However, we found no differences in belowground (that is, root and sediment) nitrogen or carbon stocks between marshes and mangroves. Thus, the shift from marsh to mangrove may provide decadal-scale increases in aboveground nitrogen and carbon sequestration, but belowground nitrogen and carbon sequestration (that is, carbon burial) may not be affected. We measured lower pore water nitrogen content beneath growing mangroves, which we postulate may be due to greater nitrogen uptake and storage in mangrove aboveground compartments compared to marshes. However, further studies are needed to better characterize the implications of mangrove encroachment on nitrogen cycling, storage, and export to the coastal ocean.

中文翻译：

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黑美洲红树（Avicennia Germinans）入侵互花米草盐沼中生态系统氮和碳分配的变化。

摘要

预计温度的升高将促进热带红树林渗入温带盐沼，但对生态系统服务的影响尚未得到研究。我们的工作是在美国路易斯安那州的红树林扩张带进行的，该地区由于复合因素（包括减少的泥沙供应，海平面上升和沉降）而使沿海湿地迅速减少。沼泽和红树林生态系统因适应海平面上升并支持众多生态系统服务而闻名，但它们提供的社会效益却有所不同。在这里，我们比较了碳和氮的储量，并将这些发现与红树林入侵对沿海湿地的氮过滤和碳固存的预期影响联系起来。我们专门评估了黑红树林的含义（Avicennia菌种）侵害互花米草。占主导地位的盐沼。我们的结果表明，黑红树林的入侵将导致地上碳和氮的储量增加。但是，我们发现沼泽和红树林之间地下（即根和沉积物）的氮或碳储量没有差异。因此，从沼泽向红树林的转变可能使地上的氮和碳固存增加数十倍，但地下的氮和碳固存（即碳埋藏）可能不会受到影响。我们测量了生长的红树林下面的孔隙水中氮含量较低，我们推测这可能是由于与沼泽地相比，红树林地上隔间的氮吸收和存储量更大。但是，需要进一步研究以更好地表征红树林入侵对氮循环，存储和向沿海海洋出口的影响。