Human activities have decreased global salt marsh surface area with a subsequent loss in the ecosystem functions they provide. The creation of marshes in terrestrial systems has been used to mitigate this loss in marsh cover. Although these constructed marshes may rapidly recover ecosystem structure, biogeochemical processes may be slow to recover. We compared denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates between a 32‐year‐old excavation‐created salt marsh (CON‐2) and a nearby natural reference salt marsh (NAT) to assess the recovery of ecosystem function. These process rates were measured at 5 cm increments to a depth of 25 cm to assess how plant rooting depth and organic matter accumulation impact N‐cycling. We found that, for both marshes, denitrification and DNRA declined with depth with the highest rates occurring in the top 10 cm. In both systems, N‐retention by DNRA accounted for upwards of 75% of nitrate reduction, but denitrification and DNRA rates were nearly 2× and 3× higher in NAT than CON‐2, respectively. Organic matter was 6× lower in CON‐2, likely due to limited plant belowground biomass production. However, there was no response to glucose additions, suggesting that the microbial functional community, not substrate limitation, limited nitrate reduction recovery. Response ratios showed that denitrification in CON‐2 recovered in surficial sediments where belowground biomass was highest, even though biomass recovery was minimal. This indicates that although recovery of ecosystem function was constrained, it occurred on a faster trajectory than that of ecosystem structure.

中文翻译：

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硝酸盐还原能力受到32岁的盐沼地下植物恢复的限制

人类活动减少了全球盐沼的表面积，并随之丧失了它们提供的生态系统功能。在陆地系统中形成沼泽已被用来减轻沼泽覆盖的这种损失。尽管这些人工沼泽可以迅速恢复生态系统结构，但生物地球化学过程可能恢复缓慢。我们比较了32年发掘产生的盐沼（CON-2）和附近的自然参考盐沼（NAT）之间的反硝化作用和异化硝酸盐还原率（DNRA），以评估生态系统功能的恢复。这些加工速率以5厘米的增量测量到25厘米的深度，以评估植物生根深度和有机物质积累如何影响N循环。我们发现，对于两个沼泽，反硝化作用和DNRA随深度下降，最高速率发生在顶部10厘米。在这两个系统中，DNRA的氮保留量最多可减少硝酸盐减少75％，但NAT中的反硝化和DNRA率分别比CON-2高近2倍和3倍。CON-2中的有机物含量降低了6倍，这可能是由于地下植物的生物量生产受限所致。但是，对添加葡萄糖没有反应，这表明微生物功能群落而不是底物限制了硝酸盐还原的回收率。响应比表明，CON-2的反硝化作用在地下生物量最高的表层沉积物中得以恢复，即使生物量的回收量很小。这表明，尽管生态系统功能的恢复受到限制，但发生的轨迹比生态系统的结构快。