Grass plays an important role in managing atmospheric carbon. This process, known as carbon sequestration, involves capturing carbon dioxide (CO2) from the air and storing it. While forests are often highlighted for carbon storage, grasslands and lawns also act as significant carbon sinks.
The Science of Carbon Absorption
The fundamental process by which grass absorbs carbon is photosynthesis. This biological mechanism allows plants to convert light energy into chemical energy. During photosynthesis, grass blades take in carbon dioxide from the atmosphere through small pores called stomata. Inside the plant cells, particularly within structures called chloroplasts, sunlight provides the energy to combine carbon dioxide with water, producing sugars and releasing oxygen. The carbon atoms from the absorbed CO2 are then incorporated into the plant’s structure, forming various organic compounds, effectively moving carbon from the air into the plant’s biomass.
Quantifying Grass’s Carbon Impact
The amount of carbon grass can absorb varies considerably based on several factors, with studies estimating sequestration rates for lawns can range from 25 to 450 grams of carbon per square meter annually. These figures are influenced by factors such as grass species (native prairie species often have greater capacity due to deep root systems), climate conditions (temperature and moisture affect plant growth and decomposition), and management practices like mowing frequency and fertilization. For example, leaving clippings on the lawn can enhance carbon storage. Soil type is another important determinant, as higher clay content tends to sequester more carbon than sandier soils, and the age of the turfgrass system also matters, as newly established turfgrass might have higher initial sequestration rates that can decline over time. Overall, urban lawns in the United States are estimated to sequester between 200 and 1,800 pounds of carbon per acre per year.
Beyond the Blades: Carbon Storage in Soil
While above-ground grass blades absorb carbon, a substantial portion of this carbon is ultimately stored beneath the surface. Grass plants allocate significant amounts of carbon to their root systems, and as roots grow and decay, they contribute organic matter directly to the soil. Grass roots also release carbon compounds, known as root exudates or through a process called rhizodeposition, into the surrounding soil, and this continuous input of organic material from living and decaying roots, along with other plant residues, builds up the soil’s organic carbon content. Healthy soil ecosystems, rich in microorganisms, are important in retaining this carbon long-term, as they help convert plant matter into stable forms of soil organic carbon. This underground storage makes grasslands a resilient carbon sink, as carbon stored deep in the soil is less susceptible to release from disturbances like fire compared to above-ground biomass.