小小地质微生物演绎跨圈层的相互作用

Earth sphere interaction reflected in microbial fingerprints through Earth’s history—a critical review

地球系统科学特别关注跨圈层的相互作用,包括深部系统与表层系统的相互作用、表层系统海-陆-气之间的相互作用。这种庞大时空尺度的地质作用过程可以被小小的地质微生物记录下来,足见地质微生物的以小见大、见微知著特征。在二叠纪-三叠纪之交和晚奥陶世这两个完全不同场景的显生宙火山活动过程中,爆发的初期都出现了包括蓝细菌在内的海洋固氮微生物繁盛,紧接着出现了包括藻类、放射虫、有孔虫等真核微生物的繁盛,显示了火山活动引发了从原核微生物向真核微生物群落的转变过程。不仅如此,人们还发现地质微生物可以通过条带状铁建造等生物成因岩石引发了前寒武纪的火山活动,而且还可能启动了最早的板块运动。地质微生物不仅对火山活动这一与碳循环有关的跨圈层地质作用具有很灵敏的响应和反馈能力,而且还能示踪表层系统复杂的海-陆-气相互作用及其物质传输过程。利用地质微生物的诸多干湿古气候代用指标,发现了中国东部地区不同时间尺度干湿状况的三极模态空间变化格局,而且还识别出了西北地区与西太平洋海洋上层热量有关的极端干旱事件。地质微生物记录的这些干湿状况是高纬与低纬的海-陆-气相互作用在水循环方面的体现。地质微生物演绎的与碳循环和水循环有关的这些跨圈层过程仅是地球系统的冰山一角,随着地球生物学的发展和技术方法的创新,越来越多的宜居地球形成之谜会被地质微生物所破解,包括地质微生物与深部过程的互馈效应、地质微生物与地球重大环境转型的关系以及地质微生物对地球生态系统演化的影响。

Interactions between Earth’s spheres,particularly between deep Earth and surface processes or within the surface system between sea,land and the atmosphere,are a critical issue in Earth system science.Such a large-scale geological process could be recorded by tiny microbes preserved in the fossil record.Triggered by volcanic activities during the Permian-Triassic transition and in the Late Ordovician,the bloom of nitrogen-fixation bacteria including cyanobacteria and the subsequent expansion of eukaryotes including algae,radiolarians and foraminifers clearly reflected a volcanism-induced shift from prokaryotes to eukaryotes.Furthermore,it has been shown that microbial activity could lead to banded iron formations to trigger Pre-Cambrian volcanic activity and even initiate plate movement in the early Earth.These data demonstrated the critical interaction between volcanic activity and the microbial community impacting carbon cycling.Microbes could also trace the complex interaction between sea,land,and the atmosphere and its associated long-range material transport process.Using microbial proxies for hydroclimate we identified the tri-pole mode of spatial variability of dry/wet status in eastern China on different time scales,as well as the extreme drought events in northwestern China triggered by the upper-ocean thermal condition in the tropical western Pacific Oceans.The spatiotemporal variations in dry/wet status reflected in the microbial records are due to variations in sea-land-atmosphere interactions between high-and low-latitude environments.The carbon-and water cycle-associated cross-sphere processes reflected in microbial fingerprints only represent a small portion of Earth sphere interactions.The great contribution of the microbial community in shaping the habitable Earth has yet to be fully deciphered.With research advancement and technical/methodological innovation in geobiology more questions can be addressed,including the interaction between geomicrobiological and deep Earth processes,microbial contribution to the major paleoclimatic shifts and paleoenvironmental changes,and impact of the microbial community on ecological evolution.