Vol.:(0123456789) 1 3 Journal of Plant Research https://doi.org/10.1007/s10265-019-01162-2 TECHNICAL NOTE Comparative analysis of borate fusion versus sodium carbonate extraction for quantifcation of silicon contents in plants Ryosuke Nakamura 1  · Jean‑Thomas Cornelis 2  · Felix de Tombeur 2  · Michiko Nakagawa 3  · Kaoru Kitajima 1 Received: 28 November 2019 / Accepted: 15 December 2019 © The Botanical Society of Japan and Springer Japan KK, part of Springer Nature 2020 Abstract Studies of plant-silicon (Si) interaction beneft from safe, afordable 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 (Na 2 CO 3 ) extraction, in combination of two detec- tion methods (ICP, molybdenum-blue colorimetry).We compared the results obtained by these methods, using dried leaf samples of fve tropical tree species that difer 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, R 2 = 0.998). However, compared to the extraction with borate fusion, the 1% Na 2 CO 3 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% Na 2 CO 3 , which is the least expensive and safest among commonly used methods for extraction of Si from land plants. Keywords Borate fusion · ICP · Silicon · Sodium carbonate extraction · Tropical tree phytoliths Introduction The role of Si in plant biology is increasingly studied in various disciplines (Katz 2018), including agronomy (Liang et al. 2015; Ma and Takahashi 2002), biogeochemistry (Cor- nelis and Delvaux 2016; Schlesinger and Bernhardt 2013) and ecology (e.g. Cooke and Leishman 2011; Hartley and DeGabriel 2016; Johnson et al. 2019). Much of Si contained in plants exists as opal phytoliths, which are insoluble to even strong acid (Van Keulen and Young 1977). Therefore, researchers have used diferent methods to extract plant Si, some of which require more cost and safety precautions than others. For example, even though hydrofuoric acid can com- pletely dissolve any silica bodies, most labs avoid its use for cost and safety reasons as well as for the loss of Si as gaseous SiF 4 . Ecological and physiological studies of plants involving a large number of samples beneft from a safe, cheap and reliable method of Si extraction and quantifca- tion. It is also important to ensure comparability of meth- ods for a wide range of Si concentrations found among land plants (0.1–10.0% Si in dry weight) (Hodson et al. 2005; Ma and Yamaji 2006). Chemical extraction methods widely-used by published studies include alkaline digestion (using 1% sodium carbon- ate (Na 2 CO 3 ) or sodium hydroxide solutions, sometimes in combination with high temperature) (e.g. Clymans et al. 2016; Faisal et al. 2012), hydrofuoric acid (e.g. Puppe et al. 2017; Saito et al. 2005), extraction following fusion with lithium meta-borate (e.g. Alexandre et al. 1997) and extrac- tion with Tiron (C 6 H 4 Na 2 O 8 S 2 ) (Guntzer et al. 2010). Non- chemical methods include gravimetric determination of acid- insoluble ash (e.g. Geis 1973), electrothermal vaporization (Masson et al. 2007), and portable X-ray fuorescence spec- trometer (Reidinger et al. 2012). These methods come with various pros and cons in terms of cost and safety concerns. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10265-019-01162-2) contains supplementary material, which is available to authorized users. * Ryosuke Nakamura rnakamura3825@gmail.com 1 Graduate School of Agriculture, Kyoto University, Kyoto, Japan 2 TERRA Teaching and Research Centre, Gembloux Agro-Bio Tech, Université de Liège, Gembloux, Belgium 3 Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan