Extended Data Fig. 7: The effect of fresh and aged biochar on CH4 mitigation.
This schematic figure illustrates the adverse effects of biochar aging on CH₄ emission reduction, highlighting the degradation of its physical structure, loss of nutrient retention, decline in root oxygen exudation capacity, and the resulting increase in soil ammonium levels. As biochar ages, its pore structure breaks down, gradually diminishing its ability to supplement nutrients. Compared to fresh biochar, aged biochar in HS is less effective at supporting root growth than in AL, leading to weakened root systems with reduced oxygen exudation capacity. This decline in root activity is directly linked to decreased aerobic methanotrophic activity. In HS, repeated agricultural practices further accelerate the breakdown of biochar’s pores, exposing more surface area and speeding up its oxidation. This process increases the concentration of oxygen-containing functional groups, such as carboxyl groups, which in turn raises soil ammonium ion levels. The elevated ammonium concentration is detrimental to methanotrophs unless they can mitigate ammonium toxicity, leading to decreased methanotroph diversity. In the long term, this inhibition may not only reduce CH₄ mitigation but could potentially promote CH₄ emissions.
