源地沙尘对南海东北部海域异养细菌生物量及群落结构的影响

Effect of dust on heterotrophic bacterial biomass and community structure in northeastern South China Sea

沙尘沉降是海洋营养元素的重要来源之一,对海洋异养细菌的意义十分重大。为研究沙尘沉降对于海洋异养细菌的作用过程,于2013年3月对A1、A2两个站位的海水进行了源地沙尘添加培养,探讨大、小两种粒径沙尘对南海东北部海域异养浮游细菌生物量及群落结构的影响过程和机制。结果表明,南海东北部海域海水营养物质的浓度和异养细菌生物量水平较低;而两种沙尘的添加在短期内都可以溶出DOC和DIN,在一定程度上能够缓解一部分营养限制;其中小粒径沙尘在短期内溶出的营养物质较多,平均使系统中DOC和DIN浓度增加了0.65倍和0.36倍。添加沙尘后,两个站位的培养系统中异养细菌生物量出现不同程度增长,沙尘的单独添加在短期和长期内都可以促进异养细菌生物量的增长;其短期内,小粒径沙尘的添加使得异养细菌生物量的增加比原位沙尘更明显;而在添加氮和磷的情况下,两种沙尘的添加并不能明显促进异养细菌生物量的增长,在长期内甚至起抑制作用。通过对A1在添加两种沙尘7 d前后的细菌群落结构的分析发现,培养后细菌群落的生物多样性降低并且群落结构趋于简化,其中小粒径沙尘的作用最为明显;而两种不同沙尘添加后细菌群落结构的更替情况基本一致,能够利用外源营养的α-变形菌纲(Alphaproteobacteria)和γ-变形菌纲(Gammaproteobacteria)成为培养结束后的优势菌群,而叶绿体(chloroplast)等自养菌在培养结束后的优势度消失,细菌群落偏向于异养。研究发现源地沙尘能够促进海洋异养细菌生长,改变了细菌群落结构,提高了其在海洋生态系统中的生态功能。

Dust deposition, one of the sources of marine nutrients, played a critical role in community dynamics of marine heterotrophic bacteria. Enrichment experiments were carried out in March 2013 at stations A1 and A2 in northeastern South China Sea to evaluate the process and mechanism of the dust originated from a dust storm outbreak affecting the biomass and community structure of heterotrophic bacteria. The results indicated that the heterotrophic bacterial biomass was low in the northeastern South China Sea and the dust could relieve nutrient limitation through inputs of DOC and DIN. Particularly, the dust with small grain size increased the DOC and DIN concentration in seawater by a factor of 0.65 and 0.36, respectively. The addition of dust triggered an increase in heterotrophic bacterial biomass in both stations. Dust addition alone facilitated heterotrophic bacterial biomass both in the long-term and short-term experiments, whereas the small grain size dust showed more significant effect in the long-term experiments than those in the short-term. With the simultaneous addition of nitrogen and phosphorus, the dust couldn’t enhance bacterial significantly, or even decreased bacterial biomass in the long-term experiments. Comparing the bacteria community with the dust addition before and after an incubation period of 7 days at station A1, we found that the bacterial biodiversity were decreased and bacteria community simplified after incubation, especially for the small grain size dust. The bacteria community structure responded similarly to the two types of dust, with Alphaproteobacteria and Gammaproteobacteria turning into dominant species after incubation whereas Chloroplast losing its dominance, and consequently the bacteria community becoming more heterothrophic. In conclusion, the dust originated from dust storms could obviously promote heterotrophic bacterial growth, significantly change its community structure, and enhance its function in marine ecosystem.