Improved seed yield and phosphorus accumulation in soybean are associated with the enhanced root exudates in south-west China

Background and aims Shoot traits related to soybean yield improvement are well characterized, but little is known about changes in root traits and their contribution to yield improvements under different P levels.

Methods Field experiments conducted in 2018 and 2019 (two sites each year under 0 (P0) and 35 (P35) kg P ha(-1)) compared root morphology, P and N accumulation and uptake efficiencies, and seed yield of 12 soybean cultivars released from 1995 to 2016. A supplementary pot experiment with the same soybean cultivars compared root exudates and arbuscular mycorrhizal (AM) colonization rates under 0 and 60 mg kg(-1) P supply.

Results The four site x year field combinations revealed significant genetic gain from soybean breeding for seed yield under P35 (2.1-2.3%) and PO (1.8-2.0%), respectively. Soybean breeding significantly increased P and N accumulation, which positively correlated with seed yield under P35 and P0. Root length, specific root length, and carboxylate exudation were associated with P and N accumulation and uptake efficiencies, but only root exudates significantly improved with year of cultivar release. The AM colonization rate increased under low soil availability but did not change with year of release.

Conclusions Our results suggest that indirect selection of root traits, such as root exudates, during soybean breeding could improve P and N accumulation and uptake efficiencies to improve seed yield.