Contributions of plant breeding to soil carbon storage: Retrospect and prospects.

There is interest in harnessing cropland C storage potential at a large scale to mitigate climate change and improve land productivity. While the effects of soil management practices on C storage have been studied extensively, opportunities to select for C sequestration traits in crop plants remain largely unexplored. This review describes how genetic improvement of major US crops may have altered soil C stocks historically and identifies potential opportunities for plant breeding to increase cropland C stocks. Through quantitative literature review, we find that breeding has led to an increase in aboveground residue C inputs to the soil for corn (Zea mays L.) and soybeans (Glycine max (L.) Merr) and a decrease in aboveground residue C inputs for wheat (Triticum aestivum L. and Triticum turgidum L.). Breeding has largely not altered the root:shoot ratio of these crops. Given that there is limited potential for further major improvements in harvest index, breeding for high grain yields may necessitate increasing aboveground biomass and residue production in the future. Crop root traits and residue quality may influence the stabilization of crop‐derived C in soil, but there is uncertainty regarding historical changes in these traits due to breeding, the magnitude of their effect on soil organic C stocks, and tradeoffs or synergies with breeding for high yield. Nevertheless, root traits such as suberin content, rhizodeposition, mycorrhizal association, and depth emerge as potential targets for more efficient C stabilization. There is also a large opportunity for plant breeding to enhance the performance of cover crops, double crops, perennial grains, and perennial groundcovers, which can increase annual C inputs to the soil by occupying fallow periods. Our review reveals that there are many opportunities for plant genetic improvement to fix more C in cropping systems and enhance its stabilization in the soil to meet the goals of sustainable intensification and cropland C capture. Core Ideas: Plant breeding has increased aboveground residue C inputs to the soil for corn and soybean, but not for wheat.Root:shoot ratio and mycorrhizal colonization have not substantially changed due to plant breeding.There is little evidence that breeding has altered the quality or placement of C inputs.There is opportunity for plant breeding to increase soil C by overcoming barriers to cropping system enhancement. [ABSTRACT FROM AUTHOR]