Plant Cell Walls Play a Major Role in Carbon Flow through Ecosystems
Most plant cell walls are constructed in a way to resist enzymatic digestion—a defense against pathogen invasion—and so the recycling of the carbon and energy locked in the cell wall is mostly carried out by saprophytic fungi and bacteria armed with a suite of specialized enzymes capable of digesting cell walls. Some animals, such as ruminants and termites, are also able to partake in this fibrous feast, with the aid of gut microbes similarly equipped with cell-wall digesting enzymes. The organic substances that make up humus in the soil and that enhance soil structure and fertility are derived from cell wall residues—one of many legacies of plants to their environment. Finally, as the major source of dietary fiber, the plant cell wall is a significant factor in human health and nutrition.