Edwards Bethanie R, Bidle Kay D, Van Mooy Benjamin A S
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA 02139; and.
Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901.
Proc Natl Acad Sci U S A. 2015 May 12;112(19):5909-14. doi: 10.1073/pnas.1422664112. Epub 2015 Apr 27.
Diatoms and other phytoplankton play a crucial role in the global carbon cycle, fixing CO2 into organic carbon, which may then be exported to depth via sinking particles. The molecular diversity of this organic carbon is vast and many highly bioactive molecules have been identified. Polyunsaturated aldehydes (PUAs) are bioactive on various levels of the marine food web, and yet the potential for these molecules to affect the fate of organic carbon produced by diatoms remains an open question. In this study, the effects of PUAs on the natural microbial assemblages associated with sinking particles were investigated. Sinking particles were collected from 150 m in the water column and exposed to varying concentrations of PUAs in dark incubations over 24 h. PUA doses ranging from 1 to 10 µM stimulated respiration, organic matter hydrolysis, and cell growth by bacteria associated with sinking particles. PUA dosages near 100 µM appeared to be toxic, resulting in decreased bacterial cell abundance and metabolism, as well as pronounced shifts in bacterial community composition. Sinking particles were hot spots for PUA production that contained concentrations within the stimulatory micromolar range in contrast to previously reported picomolar concentrations of these compounds in bulk seawater. This suggests PUAs produced in situ stimulate the remineralization of phytoplankton-derived sinking organic matter, decreasing carbon export efficiency, and shoaling the average depths of nutrient regeneration. Our results are consistent with a "bioactivity hypothesis" for explaining variations in carbon export efficiency in the oceans.
硅藻和其他浮游植物在全球碳循环中发挥着关键作用，将二氧化碳固定为有机碳，然后这些有机碳可能会通过沉降颗粒被输送到深海。这种有机碳的分子多样性极为丰富，并且已经鉴定出许多具有高度生物活性的分子。多不饱和醛（PUAs）在海洋食物网的各个层面都具有生物活性，然而这些分子对硅藻产生的有机碳命运的影响仍是一个悬而未决的问题。在本研究中，我们调查了PUAs对与沉降颗粒相关的天然微生物群落的影响。从水柱150米深处收集沉降颗粒，并在黑暗中培养24小时，使其暴露于不同浓度的PUAs中。1至10微摩尔的PUA剂量刺激了与沉降颗粒相关细菌的呼吸作用、有机物水解和细胞生长。接近100微摩尔的PUA剂量似乎具有毒性，导致细菌细胞丰度和代谢下降，以及细菌群落组成发生显著变化。沉降颗粒是PUA产生的热点区域，其浓度处于刺激微摩尔范围内，这与之前报道的这些化合物在表层海水中的皮摩尔浓度形成对比。这表明原位产生的PUAs刺激了浮游植物衍生的沉降有机物质的再矿化，降低了碳输出效率，并使营养物质再生的平均深度变浅。我们的结果与一个用于解释海洋中碳输出效率变化的“生物活性假说”相一致。
