Testing the priming effect in the deep ocean: are microbes too starved to consume recalcitrant organic carbon?

The oceans store vast amounts dissolved organic carbon (DOC) that can resist microbial degradation for thousands of years. The mechanisms that underlie the long-term stability of DOC in the ocean are still debated. Microorganisms in this environment exhibit low metabolic activity and are energetically starved. We tested whether the microbial degradation of DOC could be stimulated through the addition of labile compounds. Surprisingly, alleviating energetic constraints did not stimulate the consumption of deep ocean DOC. Additionally, our results suggest that competition among taxa is an important constraint on dissolved organic carbon consumption, with implications for ecosystem processing. Our study indicates that an increase in fresh organic carbon to the deep ocean may enhance carbon sequestration since marine microbes are known to produce recalcitrant compounds. This finding is of consequence for ongoing geoengineering efforts that aim to remove atmospheric carbon by increasing carbon export to the deep sea.

海洋储存着巨量溶解性有机碳（dissolved organic carbon, DOC），这类碳可抵御微生物降解达数千年之久。目前，海洋中溶解性有机碳长期稳定的背后机制仍存在争议。该环境中的微生物代谢活性极低，且处于能量匮乏状态。本研究通过添加易降解化合物，探究是否可借此刺激海洋溶解性有机碳的微生物降解过程。令人意外的是，缓解能量限制并未促进深海溶解性有机碳的消耗。此外，研究结果显示，微生物类群间的竞争是限制溶解性有机碳消耗的重要因素，这一发现对生态系统碳循环过程具有重要启示。本研究表明，由于海洋微生物可生成难降解有机化合物，向深海输入更多新鲜有机碳或可增强碳封存效果。该发现对于当前旨在通过增加碳向深海输出以清除大气中二氧化碳的地球工程研究，具有重要参考价值。