Plant-assisted microbially driven mitigation of greenhouse gas emissions from landfill cover soils

Abstract:

Landfills are a vital component of our solid-waste management system. Methane (CH4), a major greenhouse gas (GHG), is produced through the decomposition of organic wastes in landfills. Although CH4 emissions from landfills have decreased due to the installation of gas-collection systems, a significant amount of CH4 still escapes primarily via diffusion through the cover soil, putting landfills the third-largest anthropogenic source of CH4. It is well established that a considerable amount of CH4 can be removed in situ by CH4-oxidizing bacteria (methanotrophs) in landfill cover soils. Although nitrogen amendments have been shown to be most effective to stimulate methanotrophic activity, nitrogen can lead to increased nitrous oxide (N2O) production, another potent GHG, by stimulating other microbial groups (i.e., nitrifying microorganisms). Therefore, any amendment strategy should not only attempt to increase methanotrophic activity, but also control the biogenic production of N2O. Recent studies have discovered that certain plant species produce and release biochemicals from roots (also known as biological nitrification inhibitors, or BNIs) to suppress nitrifying microorganisms. If this activity can be harnessed by selecting and planting BNI-producing plants in the landfill cover soils together with nitrogen amendment, the rhizosphere of the cover soil will become an effective biofiltration system minimizing GHG emissions. Here, we performed soil column experiments using Brachiaria, which is known to produce brachialactone, a type of BNI, and demonstrated the total greenhouse gas emission was minimized by this novel strategy. This is a “proof of concept” study.