ABSTRACT: The rhizophytic seaweed Caulerpa prolifera has been expanding rapidly in the Ria Formosa lagoon, southern Portugal, taking over deeper unvegetated areas and mixing with the native seagrass Cymodocea nodosa in shallower areas. In the Ria Formosa lagoon, belowground ammonium uptake from the sediment represents the main source of nitrogen for the 2 macrophytes, except during the ammonium pulses from the sediment to the water column that are incorporated through aboveground plant parts. We examined the competition for inorganic and organic nitrogen between C. prolifera and C. nodosa through a series of ¹⁵N-ammonium and ¹⁵N-amino acid surge uptake experiments combining single-species and mixed incubations at a range of nutrient concentrations. Our results showed that C. prolifera is generally faster than C. nodosa in the acquisition of ammonium and amino acids by both above- and belowground parts, and that the uptake rates of ammonium and amino acids of one species were not affected by the presence of the other species. The exception was the amino acid uptake through the rhizoids of C. prolifera, which was slightly enhanced in the presence of C. nodosa. In this situation, the aboveground ammonium uptake becomes the main contributor to the nitrogen budget of C. nodosa but not to that of C. prolifera. When ammonium pulses are considered, C. nodosa is more competitive for nitrogen than C. prolifera. In this case, the leaf uptake of ammonium is the largest contributor to the total nitrogen (ammonium plus amino acids) budget of the seagrass. Our results showed that the different nutritional strategies of the 2 macrophytes allow their coexistence in the Ria Formosa lagoon.

中文翻译：

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海藻Caulerpa prolifera和海草Cymodocea nodosa之间的氮竞争

摘要：有根藻的海藻Caulerpa prolifera在葡萄牙南部的Ria Formosa泻湖中迅速扩张，占领了较深的无植被地区，并与较浅的海藻Cymodocea nodosa混合。在Ria Formosa泻湖中，沉积物从地下吸收的铵盐是2种大型植物的主要氮源，但从沉积物到水柱的铵脉冲是通过地上植物部分吸收的。我们通过一系列¹⁵ N铵和¹⁵ N考察了C. prolifera和C. nodosa之间无机和有机氮的竞争N-氨基酸浪涌吸收实验结合了多种营养浓度下的单种和混合培养。我们的研究结果表明，C.苔通常速度比是C.性多动脉炎在采集酸铵和由两个地上和地下部分的氨基酸，并且铵的吸收率和一个物种的氨基酸并没有受到影响的存在其他物种。唯一的例外是通过的假根的氨基酸摄取C.苔，将其略微的存在而增强C.性多动脉炎。在这种情况下，地上铵的吸收成为结节藻氮预算的主要贡献者，而不是促生枝藻的氮预算。。当考虑使用铵脉冲时，结节隐孢子虫对氮的竞争性要比激增梭状芽胞杆菌高。在这种情况下，叶片吸收铵盐是海草总氮（铵加氨基酸）预算的最大贡献者。我们的结果表明，两种大型植物的不同营养策略允许它们在Ria Formosa泻湖中共存。