Rob Moir on Biotic Regulation and Biotic Pump

This is quite the Gordian knot of complexity, facts and suppositions. Many ecology textbooks state that soil gains energy from decomposing detritus, including plant fibers and animal parts—growth balanced by decomposition results in homeostasis. We were told soils took thousands of years to build become fertile. Plants have more agency than we give them credit. To obtain the necessary nutrients from decomposition, the bacteria and archaea that fix nitrogen and prepare minerals require plant energy. These obligate bacteria and fungi are species-specific and are contained in plant seeds. Whenever a plant photosynthesizes, about two-thirds of the carbohydrates go to building plant fibers, and one-third is pushed out as root exudate to feed soil microbes. The ratio of biomass to exudate is fixed. Step on grass or browse it, and it stimulates growth to repair; the amount of exudate increases. Grasses can build an inch of soil in a year. The sticky carbohydrates hold mineral grains so far apart that four inches of soil can hold seven inches of rainwater. Plant fibers are very tough. Grazing animals walk on their toenails to begin the process of breaking fiber. Animals, including springtails, cut plant fibers smaller. Worms pass the mash into gizzards for grinding and then on to a chamber of bacteria that make it more useable by plants. Complex organic molecules, such as cellulose, lignin, and proteins, are broken down. The soil is then ready to undergo a series of chemical reactions to form humus. Humus, the black gold of soil, aggregating and holding together, is very stable and can retain carbon for thousands of years, facilitating long-term carbon sequestration. This process of accumulating carbon results in the world’s soil containing approximately 2,800 billion tons of carbon, while biomass contains only 564 billion tons. Perhaps there is more carbon in the ground, deeper soils, than we know.