Reconciling biological and geochemical perspectives on the production of oxygen on early Earth

大氧化事件（GOE）是指地球大气中游离氧的水平从零上升到今天的10-5倍以上的时期。然而，在太古时期的浅水环境和陆地地壳中发现了早期局部氧合的证据，即所谓的“嗅”。考虑到最近的基因组系统发育研究表明，蓝藻是唯一能够进行氧化光合作用的细菌，至少在2.7 Ga出现，而水的氧化分解进化得更早，问题就出现了，为什么地球大气的氧化作用又花了0.3 Ga。一种假设是，限制生物必需营养素，如硝酸盐、磷酸盐和微量金属，意味着蓝藻无法茁壮成长。另一种假说认为，海底地壳矿物的局部氧化吸附了蓝藻释放的氧气。本项目通过利用海洋和淡水固氮蓝藻的液体培养来解决这些假设，以确定在CO2升高的还原性厌氧太古宙大气下的光合作用和生物固氮速率。据此进行了评估太古宙期间营养限制对蓝藻初级生产影响的试验。通过在地面岩石的固体基质上生成假卫星，我们将能够确定矿物：微生物界面上发生的关于O2浓度、pH值和氧化还原变化的确切相互作用。结合来自个体的数据，同步液体培养与从假藻中获得的数据，将提供对古代蓝藻的现代后代在个体有机体水平上的生长和生理反应以及生态群落在垫中的反应的见解。实验获得的数据将与海洋和非海洋环境中保存的微生物垫层和叠层石的富有机层中测定的总氮和微量元素含量进行比较。这是第一个研究太古宙晚期蓝藻的潜在营养限制，以及它们通过矿物基质的风化获取必需微量元素的能力，从而导致GOE的研究。

The Great Oxygenation Event (GOE) is the period during which the level of free O2 in the Earth’s atmosphere rose from zero to above ~ 10-5 times that of today. However, evidence of early pockets of localised oxygenation, the so called "whiffs", are being found in Archeal shallow water environments and subaerial crust. When considered together with recent genomic phylogenetic investigations indicating that cyanobacteria, the only bacteria able to conduct oxidative photosynthesis, arose at least 2.7 Ga, and that the oxidative splitting of water evolved even earlier, the question arises as to why it took another 0.3 Ga for the oxygenation of the Earth’s atmosphere. One hypothesis is that limitation of bioessential nutrients such as nitrates, phosphates and trace metals, meant that the cyanobacteria were unable to thrive. Another hypothesis suggests that localised oxidation of subaerial crustal minerals adsorbed O2 released by cyanobacteria. This project addresses these hypotheses by utilising liquid cultures of both marine and freshwater nitrogen fixing cyanobacteria to determine the rates of photosynthesis and biological nitrogen fixation under a reducing, anaerobic Archean atmosphere with elevated CO2. Pursuant to this are trials to assess the effects of nutrient limitation on cyanobacterial primary production during the Archean. By generating pseudomats on a solid matrix of ground rocks, we will be able to determine the exact interactions occurring at the mineral: microbe interface with respect to O2 concentrations as well as pH and Redox changes. Combining data from the individual, synchronised liquid cultures with that obtained from pseudomats, will provide insight into the growth and physiological responses of modern-day descendants of ancient cyanobacteria at the level of the individual organism AND the ecological community response in mats. The experimentally obtained data will be compared to the total N and trace element content determined for organic rich layers of preserved microbial mats and stromatolites from marine and non-marine settings. This is the first study to investigate the potential nutrient limitations on cyanobacteria during the late Archean, and their ability to source essential trace elements via weathering of their mineral substrates, leading up to the GOE.