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Abstract:
Non-structural carbohydrates (NSCs), the stored products of photosynthesis, building blocks for growth and fuel for respiration, are
central to plant metabolism, but their measurement is challenging. Differences in methods and procedures among laboratories can
cause results to vary widely, limiting our ability to integrate and generalize patterns in plant carbon balance among studies. A recent
assessment found that NSC concentrations measured for a common set of samples can vary by an order of magnitude, but sources
for this variability were unclear. We measured a common set of nine plant material types, and two synthetic samples with known
NSC concentrations, using a common protocol for sugar extraction and starch digestion, and three different sugar quantification
methods (ion chromatography, enzyme, acid) in six laboratories. We also tested how sample handling, extraction solvent and centralizing
parts of the procedure in one laboratory affected results. Non-structural carbohydrate concentrations measured for synthetic
samples were within about 11.5%of known values for all three methods. However, differences among quantification methods
were the largest source of variation in NSC measurements for natural plant samples because the three methods quantify different
NSCs. The enzyme method quantified only glucose, fructose and sucrose, with ion chromatography we additionally quantified galactose,
while the acid method quantified a large range of mono- and oligosaccharides. For some natural samples, sugars quantified
with the acid method were two to five times higher than with other methods, demonstrating that trees allocate carbon to a range of
sugar molecules. Sample handling had little effect on measurements, while ethanol sugar extraction improved accuracy over water
extraction. Our results demonstrate that reasonable accuracy of NSC measurements can be achieved when different methods are
used, as long as protocols are robust and standardized. Thus, we provide detailed protocols for the extraction, digestion and quantification
of NSCs in plant samples, which should improve the comparability of NSC measurements among laboratories.
