Nitrogen isotopic relationship between diatom-bound and bulk organic matter of cultured polar diatoms
Nitrogen isotopic relationship between diatom-bound and bulk organic matter of cultured polar diatoms
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培养极地硅藻的硅藻结合物和本体有机质之间的氮同位素关系
DOI：
10.1029/2010pa002080
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
D. Sigman
中科院分区：
文献类型：
--
作者：
M. Horn;R. Robinson;T. Rynearson;D. Sigman
[1]采用批培养的方法，测定了4种极地硅藻（白柱硅藻、kerguelensis、pseudonitzschia seriata和nordenskioeldii）和1种温带硅藻（thalassisira aestivalis）在硝酸盐池逐步消耗过程中硅藻结合有机质的15N/14N（以下简称δ15N），并与总硅藻生物量的δ15N进行了比较。总的来说，海水中溶解硝酸盐的δ15N大于生物量的δ15N，而生物量的δ15N大于硅藻的δ15N。观察到rayleigh型关系，可以估计每种物种的同位素效应，其范围在1.0‰~ 14.0‰之间。在所有培养菌株中，硅藻结合部分（δ15NDB）的δ15N值均低于总硅藻生物量（δ 15n生物量）。生物量与硅藻结合氮之间的同位素偏移量（δ15NDBoffset = δ15Nbiomass - δ15NDB）沿生长曲线相对稳定，但在不同种间变化较大，范围为1.9‰~ 11.2‰。当λ和δ15NDBoffset与细胞大小和表面积体积比进行比较时，确定了弱关系。更显著的是，除伪硝氏菌外，δ15NDBoffset与δ15NDBoffset呈显著正相关。虽然培养数据表明所有硅藻物种的δ15NDBoffset为正，但表面沉积数据表明沉积组合的δ15NDBoffset为负。这表明：(1)我们培养物的生长条件对δ15NDBoffset有一定的影响，或者(2)在早期成岩作用中，我们测量的硅藻断结氮的低δ 15n成分丢失了。考虑到有记录的组合变化，我们对相关物种的培养数据并不表明在冰期南极观测到的较高δ15NDB可以用沉积体-硅藻结合同位素差异的物种相关变化来解释。未来对原位营养条件下培养硅藻中的硅藻结合物质、沉积物陷阱和网拖物质分析以及漏斗溶解实验的研究将更全面地评估这一古代用品。
[1] Using batch cultures, the 15N/14N (hereafter δ15N) of diatom-bound organic matter was measured and compared to the δ15N of total diatom biomass during the progressive consumption of a nitrate pool in four polar diatom species (Fragilariopsis cylindrus, Fragilariopsis kerguelensis, Pseudo-nitzschia seriata, and Thalassiosira nordenskioeldii) and one temperate species (Thalassiosira aestivalis). In general, the δ15N of the dissolved nitrate in seawater was greater than that of the biomass, which was greater than that of the diatom-bound N. Rayleigh-type relationships were observed, allowing for estimation of the isotope effect (ɛ) for each species, with a range from 1.0‰ to 14.0‰ across all species. For all cultured strains, the δ15N values of the diatom-bound (δ15NDB) fraction was lower than those of the total diatom biomass (δ15Nbiomass). The isotopic offset between the biomass and diatom-bound N (δ15NDBoffset = δ15Nbiomass − δ15NDB) was relatively constant along the growth curve for each individual species but varied among species, with a range of 1.9‰–11.2‰. Weak relationships were determined when ɛ and the δ15NDBoffset were compared to cellular size and surface area:volume ratio. More significantly, with the exception of Pseudo-nitzschia seriata, a strong positive relationship was found between ɛ and δ15NDBoffset. While the culture data indicate a positive δ15NDBoffset across all studied diatom species, surface sediment data suggest a negative δ15NDBoffset for sedimentary assemblages. This indicates that either (1) the growth conditions of our cultures had some effect on δ15NDBoffset or (2) a low-δ15N component of the N that we measure as diatom frustule–bound is lost during early diagenesis. Given documented assemblage changes, our culture data for relevant species do not suggest that the higher δ15NDB observed in the Antarctic during ice ages can be explained by species related changes in the sedimentary bulk-to-diatom-bound isotopic difference. Future work on the diatom-bound material in cultured diatoms grown under in situ nutrient conditions, analysis of sediment trap and net tow material, and frustule dissolution experiments will more completely assess this paleoproxy.