Drought increases root and rhizodeposition carbon inputs into soils

Summary

Aims
Increasing droughts affect crop yield and health. Plants can respond to drought by adapting their root biomass, root morphology, and quality and quantity of rhizodeposition to improve water and nutrient uptake. Besides droughts, agricultural management influences roots and rhizodeposition; however, it is not well studied how agricultural management can affect the response of roots and rhizodeposition to drought.
Methods
A semi-continuous 13CO2 isotope labelling experiment was performed in a long-term field experiment comparing biodynamic, mixed conventional, and mineral conventional cropping systems. Rainout shelters were installed to induce drought. Root, net rhizodeposition, and the rhizosphere microbiome were determined at ripening of wheat.
Results
Drought enhanced the total root carbon mainly through the increase of fine roots. Fine root carbon under drought was primarily enhanced in the mixed conventional and biodynamic cropping system, both receiving farmyard manure, whereas no increase was measured in the mineral fertilized conventional system. Net rhizodeposition carbon was enhanced in all cropping systems under drought, particularly in the first 0.25 m. While some plant-growth-promoting genera such as Streptomyces and Rhizophagus showed relative increases under drought, other plant growth-promoting genera often involved in nitrogen fixation such as Rhodoferax and Mesorhizobium were decreased.
Conclusion
This field trial suggests that drought increases total belowground carbon input via fine root and net rhizodeposition carbon inputs. Since fine root carbon increased under drought in cropping systems with farmyard manure, adding manure under future drought periods could be advantageous to increase soil carbon inputs and improve nutrient foraging.