Soil microbe contributions in the regulation of the global carbon cycle

Soil microbes play essential roles in agricultural and natural ecosystems by participating in organic matter mineralization that supports plant growth and consequently contributes to the global plant production and cycling of chemical elements such as carbon. Rising levels of greenhouse gases change carbon flows and alter cycles of matter and energy, including processes occurring in the soil. However, the effects of global climate change above ground are still poorly understood below it. Soil is an important global carbon reservoir that mainly depends on plants to fix atmospheric carbon and soil organisms to transform that carbon into the soil. Thus carbon transfer between reservoirs is essentially processed by soil microbes that are directly or indirectly affected by environmental factors such as climate, topography, parent material, organisms, and physicochemical properties of the soil. These environmental factors can accelerate or inhibit the microbial activity that controls carbon inflows and outflows from the soil and consequently affect carbon storage. Soil microbes can stimulate carbon sequestration and storage through beneficial interactions with plants. Some soil bacteria and fungi can also stimulate plant growth through phytohormone production and regulation, and nutrient solubilization that, in turn, increases plant biomass and consequent carbon retention in biomass. Additionally, soil microorganisms help form aggregates that physically protect soil organic carbon from decomposition. On the other hand, these microbes also participate in the decomposition and mineralization of the soil organic matter, emitting greenhouse gases into the atmosphere. As such, soil microorganisms play essential roles in regulating the global carbon cycle.