Department of Biogeochemistry, Max Planck Institute for Marine Microbiology, Bremen, Germany.
ISME J. 2010 Apr;4(4):585-94. doi: 10.1038/ismej.2009.140. Epub 2009 Dec 24.
Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring (35)S sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.
深入了解反复冻融对沉积物和土壤中微生物过程的影响，对于理解受全球变暖剧烈影响的高纬度地区沉积物碳循环至关重要。本研究使用从季节性冻融条件下暴露的潮间带采集的北极沉积物（斯瓦尔巴特群岛的 Ymerbukta），通过三个互补实验研究了微生物对反复冻融条件的响应。沉积物经历了振荡冻融孵育，温度逐渐从-5°C 升至 4°C，或突然从-20°C 升至 10°C。测量了低分子量羧酸（挥发性脂肪酸）的浓度，并通过测量（35）S 硫酸盐还原率（SRR）来评估硫酸盐还原。逐渐的冻融孵育将冷冻状态下的微生物活性降低到初始水平的 0.25%，但在解冻状态下迅速恢复，达到初始活性的>60%。暴露于连续的大温度变化（-20°C 与 10°C）使 SRR 降低了初始活性的 80%，这表明细菌群落的一部分能够从极端温度波动中迅速恢复。这得到了基于 16S rRNA 基因的变性梯度凝胶电泳图谱的支持，该图谱显示在反复冻融循环下主要微生物类群的持续存在。SRR 的快速恢复表明，解冻的北极沉积物中的碳矿化可以毫不延迟或微生物种群的大量生长而恢复。
