Dynamics of Rare Earth Element Uptake and Partitioning in Two Soybean Cultivars Under Background Soil Conditions

Rare earth elements (REEs) are present in agricultural ecosystems, but their baseline soil-plant transfer dynamics require systematic understanding. This study investigated the 'source-to-sink' biogeochemical distribution of REEs in soybean under background soil conditions.

We characterized REE concentrations and fractionation patterns in the composite surface soil samples and analyzed two soybean cultivars ('Jiyu 201' (JY) and 'Ping'an 16' (PA)). A seven-stage sampling scheme (20-80 days post-sowing) using whole-plant samples was employed to evaluate temporal concentration dynamics, followed by discrete organ-level analysis at maturity.

The composite surface soil samples exhibited a light REE (LREE)-enriched signature with negative cerium (Ce) and europium (Eu) anomalies. While plants consistently mirrored the soil's negative Eu anomaly, an observable shift toward a positive Ce anomaly was detected in plant tissues during the 45-65 days post-sowing window. REE concentrations were markedly higher in roots than in aerial tissues, indicating strong root-associated retention and limited acropetal translocation; however, the root values include both internalized and surface-associated fractions. Acropetal transport was accompanied by preferential LREE enrichment. Final organ-level partitioning was highly genotype-dependent: the indeterminate cultivar PA accumulated higher REEs in beans, whereas the sub-determinate cultivar JY retained them primarily in vegetative stems.

Under background soil conditions, REE uptake and partitioning in soybean exhibit dynamic and genotype-dependent patterns. The observed shift in the Ce anomaly presents a notable biogeochemical phenomenon. Establishing these baseline dynamics is vital for evaluating crop elemental homeostasis and utilizing REEs as biogeochemical tracers.