Calcite Biomineralization as a Complex Adaptive System.

Many natural and human systems are complex adaptive systems, which by definition have four criteria: (1) the system consists of diverse agents, (2) the agents are connected, (3) the agents are interdependent, and (4) the system adapts to change.  Calcite biomineralization in desert soils was investigated at multiple scales to determine if this process can be thought of as a complex adaptive system to better understand pedogenic carbonate and its role in the global carbon cycle. At the microscopic scale, agents include Ca²⁺, CO₂, HCO₃^-, CO₃^2-, H⁺, H₂O, microorganisms, root hairs, and clay-size CaCO₃. At the soil profile scale, agents include framework grain mineralogy, roots, vegetation type, calcic and petrocalcic horizons, dust, and mean annual soil temperature and rainfall.  Manipulative experiments were conducted to determine if and how these agents are connected and interdependent within and across scales. The experiments included inserting calcareous ceramic tiles and microscope slides into Aridisols and Ultisols and measuring the formation or dissolution of carbonate. The results of these experiments and electron microscopy indicate these agents are connected and are interdependent, thus calcite biomineralization is an adaptive complex system, one that is ultimately linked to continental scale biomes and global climate.