Comparative analysis of borate fusion versus sodium carbonate extraction for quantification of silicon contents in plants

Studies of plant-silicon (Si) interaction benefit from safe, affordable and accurate methods to measure acid-insoluble silica (phytoliths) for a large number of plant samples. This study aimed to evaluate the comparability between two chemical methods to dissolve leaf silica, borate fusion and 1% sodium carbonate (Na₂CO₃) extraction, in combination of two detection methods (ICP, molybdenum-blue colorimetry).We compared the results obtained by these methods, using dried leaf samples of five tropical tree species that differ widely in Si concentrations (4 to 100 mg g DW^-1). Leaf Si concentration values determined after the two extraction methods were highly correlated (y = 0.79x, R² = 0.998). However, compared to the extraction with borate fusion, the 1% Na₂CO₃ method resulted in lower Si concentration per unit dry mass by 16% to 32% (mean of 24.2%). We also found that molybdenum-blue colorimetry method may interfere with certain extraction methods. A simple equation can be used to correct for systematic underestimation of Si contents determined after extraction with 1% Na₂CO₃, which is the least expensive and safest among commonly used methods for extraction of Si from land plants.