Potential importance of physiologically diverse benthic foraminifera in sedimentary nitrate storage and respiration
Potential importance of physiologically diverse benthic foraminifera in sedimentary nitrate storage and respiration
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DOI：
10.1029/2012jg001949
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发表时间：
2012-07-03
影响因子：
3.7
通讯作者：
Edgcomb, Virginia P.
中科院分区：
文献类型：
--
作者：
Bernhard, Joan M.;Casciotti, Karen L.;Edgcomb, Virginia P.
直到最近，反硝化过程（硝酸盐或亚硝酸盐转化为气态产物）还被认为仅由原核生物和真菌进行。有孔虫进行完全反硝化的发现可能会影响我们对沉积物中硝酸盐去除的理解以及我们对真核呼吸的理解，尤其是在真核呼吸广泛存在的情况下。然而，这一过程的细节以及这些反应在有孔虫中的亚细胞位置仍不确定。例如，原核内生生物，而不是有孔虫本身，可以进行反硝化，正如最近在同种异体有孔虫中所显示的那样。在这里，测量了细胞内硝酸盐浓度和同位素比率（δ N-15（NO3）和δ O-18（NO3）），以评估从加利福尼亚州圣巴巴拉盆地回收的四种底栖有孔虫物种（Bolivina argentea、Buliminella tenuata、Fursenkoina cornuta、Nonionella stella）的硝酸盐动态，这些有孔虫具有不同的细胞结构以及与微生物内生物的关联。每个物种的细胞硝酸盐浓度都很高 (12-217 mM)，并且细胞内硝酸盐通常具有升高的 delta N-15(NO3) 和 delta O-18(NO3) 值。包括 B. argentea 的低氧和缺氧培养在内的实验表明，随着时间的推移，细胞内硝酸盐浓度下降，而 delta N-15(NO3) 和 delta O-18(NO3) 增加，表明有孔虫内存在硝酸盐呼吸和/或反硝化作用。结果表明，硝酸盐还原发生在一系列有孔虫物种中，包括一些拥有内生生物（包括叶绿体隔离物种）和其他缺乏内生生物的物种，这意味着微生物伙伴可能不仅仅负责有孔虫中的这一过程。此外，我们还表明，底栖有孔虫可能是沉积物中硝酸盐储存的重要储存库，也是硝酸盐去除的媒介。
Until recently, the process of denitrification (conversion of nitrate or nitrite to gaseous products) was thought to be performed exclusively by prokaryotes and fungi. The finding that foraminifera perform complete denitrification could impact our understanding of nitrate removal in sediments as well as our understanding of eukaryotic respiration, especially if it is widespread. However, details of this process and the subcellular location of these reactions in foraminifera remain uncertain. For example, prokaryotic endobionts, rather than the foraminifer proper, could perform denitrification, as has been shown recently in an allogromiid foraminifer. Here, intracellular nitrate concentrations and isotope ratios (delta N-15(NO3) and delta O-18(NO3)) were measured to assess the nitrate dynamics in four benthic foraminiferal species (Bolivina argentea, Buliminella tenuata, Fursenkoina cornuta, Nonionella stella) with differing cellular architecture and associations with microbial endobionts, recovered from Santa Barbara Basin, California. Cellular nitrate concentrations were high (12-217 mM) in each species, and intracellular nitrate often had elevated delta N-15(NO3) and delta O-18(NO3) values. Experiments including suboxic and anoxic incubations of B. argentea revealed a decrease in intracellular nitrate concentration and an increase in delta N-15(NO3) and delta O-18(NO3) over time, indicating nitrate respiration and/or denitrification within the foraminifera. Results illustrate that nitrate reduction occurs in a range of foraminiferal species, including some possessing endobionts (including a chloroplast-sequestering species) and others lacking endobionts, implying that microbial associates may not solely be responsible for this process in foraminifera. Furthermore, we show that benthic foraminifera may represent important reservoirs of nitrate storage in sediments, as well as mediators of its removal.