Plants do the hard work of splitting the oxygen from the carbon. Native grasslands with large roaming herds of herbivores will act as a massive carbon pump into the ground. Grasslands have higher density carbon per acre than forests - because 80% of grass is in the roots, and the roots go 40-50 feet deep. When they are grazed, they abandon proportional roots and this becomes carbon in the soil.
Biochar stabilizes some of the carbon in the plants, so that it will not return to the air - and acts as a carbon sink.
Biochar is a way to get a lot of energy, and preserve some of the carbon - which vastly multiplies the fertility of the soil. Carbon bonds with
everything and soil biology "loves" to live in it, and it cleans water, too. Compost instead of lasting 6-10 years - can last up to 1,000 years, when there is enough carbon in the soil.
A 1% increase in carbon in the top 6" of soil on earth is equivalent to ~40PPM of Carbon dioxide in the atmosphere. Terra preta is about 20% carbon - and it is fabulously fertile. Plants grow robustly, and they rarely need "help" fighting off pests and fungi.