A method for predicting bioavailability of rare earth elements in soils to maize

Area of Science:

• Environmental Chemistry
• Soil Science
• Plant Biology

Background:

• Light rare earth elements (LREEs) are crucial micronutrients for plants.
• Understanding LREE bioavailability in soil is essential for plant uptake and potential toxicity.
• Existing extraction methods may not accurately reflect plant-available LREEs.

Purpose of the Study:

• To compare the effectiveness of a low-molecular-weight organic acids (LMWOAs) extraction method with the European Community Bureau of Reference (BCR) method for assessing LREE bioavailability.
• To determine the correlation between soil-extracted LREE fractions and LREEs bound within plant roots (apoplastic and symplastic fractions).

Main Methods:

• Extraction of LREEs (La, Ce, Pr, Nd) from wet rhizosphere soil using LMWOAs and BCR methods.
• Fractionation of soil extracts into colloidal and truly dissolved components using membrane filtration.
• Distinguishing apoplastic and symplastic LREEs in maize roots via ultrasound-assisted desorption.
• Correlation analysis between soil LREE fractions and root-bound LREEs.

Main Results:

• The LMWOAs extraction method showed a strong correlation between soil colloidal/truly dissolved LREEs and apoplastic/symplastic root LREEs.
• A poor correlation was observed between BCR method fractions (B1, B2) and root-bound LREEs.
• Apoplastic and symplastic LREEs in roots are indicative of bioavailability.

Conclusions:

• The LMWOAs extraction method is recommended for accurately measuring LREE bioavailability in soils.
• The BCR method fractions (B1, B2) are not reliable indicators of LREE bioavailability for plants.
• LMWOAs effectively extract bioavailable LREEs, reflecting plant uptake.