Crops should be bred to not only bring higher yields, but store more carbon, according to Chinese researchers — who also set the stall out for how it could be done.
The team, based at Northwest A&F University in Yangling, reviewed research to date on breeding crops to improve crop yield and biomass. They noted that while there is an established correlation between root biomass and soil organic carbon, breeding for below-ground crop traits, crucial for this long-term carbon sequestration in plant material, has been “largely untapped.”
The untapped potential below ground
They pointed to research in cereal crops which has resulted in higher above-ground biomass and yield, with either no change or a decrease in below-ground biomass. At the same time, other work has shown that root biomass is positively related to shoot biomass and yield.
They presented a new framework for next-generation breeding of what they term ‘high-carbon crops.’ This would involve a focus on above-ground traits like the efficiency with which they transform energy from the sun and how that energy is distributed to the tissues of crops, as well as traits critical to what goes on below the soil such as root size and composition.
Rebalancing photosynthesis and carbon allocation
Part of this approach is addressing the role of natural photosynthesis in carbon cycling. The scientists pointed to it only operating at “one third of its maximum potential,” while noting that recent advances have made it possible to address this efficiency problem by fine-tuning key genetic pathways in crops.
A renewed focus on crops’ below-ground traits would involve moving beyond optimising single traits in crops to integrating multiple roots characteristics into breeding efforts. Long-term carbon sequestration has been linked to how carbon is distributed to the subsoil, where decomposition rates are lower, and the team point to several studies showing that deeper roots increase carbon stored in this part of the soil.
Genes already identified
Genes that could be targeted for high-tech breeding approaches producing longer roots have been found in wheat, rice and maize, they said, while plant cultivars have been created which release different levels of compounds which help fix carbon.
“By simultaneously reducing atmospheric CO2 levels and enhancing plant productivity and soil organic carbon formation, this approach aligns ecological goals with agronomic performance,” the researchers explained in the journal Crop and Environment.
“Importantly, carbon-optimized breeding and yield-focused breeding are not mutually exclusive; rather, they can be strategically integrated to develop crop varieties that support both productivity and long-term soil health.”
Trade-offs and practical barriers
There remains some way to go before such dual aims can be realised, however. Analysis of the relative contributions of shoots, roots and the chemicals roots produce to stable soil organic carbon is needed. So is data on the extent of genetic variation in root traits and whether such genetic differences or environmental variation is more important.
The researchers also stressed that trade-offs between fine-tuning that alters root traits and plant growth should be acknowledged and mitigated against, and that plants bred for different root systems should be compatible with agronomic practices used by farmers in different environments.
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