Chapter 28: Biogeochemical Cycles & Microbes in Climate Change

Biogeochemical Cycles & Microbes in Climate Change cycles are driven by the metabolic versatility of bacteria and archaea, whose activities are heavily influenced by the redox potential of their specific environments, determining which compounds can be used as electron donors or terminal electron acceptors. The carbon cycle highlights microbial roles in carbon fixation (autotrophs) and the decomposition of organic matter through mineralization and immobilization. Crucially, only archaea perform methanogenesis (producing methane, a potent greenhouse gas), which is naturally limited by methanotrophs that oxidize methane aerobically or anaerobically. The complex nitrogen cycle features nitrogen fixation (converting N₂ to ammonia), nitrification (oxidizing ammonium to nitrate), and various forms of reduction, including denitrification (producing N₂ and the greenhouse gas N₂O) and the anaerobic anammox reaction. The chapter also details the sulfur cycle (including dissimilatory sulfate reduction), the cycling of metals like iron and manganese (which interchange between oxidized and reduced states), and the mercury cycle, where microbial methylation leads to dangerous biomagnification. Finally, the chapter connects disruptions in these natural fluxes to global climate change. Since the industrial era, the rate of release of greenhouse gases (CO₂, methane, and nitrogen oxides) from fossil fuel combustion and excessive agricultural fertilizer use has overwhelmed the natural recycling capacity of the biosphere. This imbalance is leading to measurable increases in global surface temperature and altered infectious disease patterns, as warmer climates expand the geographical range of disease vectors like insects and ticks.