Non-structural carbohydrates (NSC) in plant tissue are frequently quantified to make inferences about plant responses to environmental conditions. Laboratories publishing estimates of NSC of woody plants use many different methods to evaluate NSC. We asked whether NSC estimates in the recent literature could be quantitatively compared among studies. We also asked whether any differences among laboratories were related to the extraction and quantification methods used to determine starch and sugar concentrations. These questions were addressed by sending sub-samples collected from five woody plant tissues, which varied in NSC content and chemical composition, to 29 laboratories. Each laboratory analyzed the samples with their laboratory-specific protocols, based on recent publications, to determine concentrations of soluble sugars, starch and their sum, total NSC. Laboratory estimates differed substantially for all samples. For example, estimates for Eucalyptus globulus leaves (EGL) varied from 23 to 116 (mean = 56) mg g(-1) for soluble sugars, 6-533 (mean = 94) mg g(-1) for starch and 53-649 (mean = 153) mg g(-1) for total NSC. Mixed model analysis of variance showed that much of the variability among laboratories was unrelated to the categories we used for extraction and quantification methods (method category R(2) = 0.05-0.12 for soluble sugars, 0.10-0.33 for starch and 0.01-0.09 for total NSC). For EGL, the difference between the highest and lowest least squares means for categories in the mixed model analysis was 33 mg g(-1) for total NSC, compared with the range of laboratory estimates of 596 mg g(-1). Laboratories were reasonably consistent in their ranks of estimates among tissues for starch (r = 0.41-0.91), but less so for total NSC (r = 0.45-0.84) and soluble sugars (r = 0.11-0.83). Our results show that NSC estimates for woody plant tissues cannot be compared among laboratories. The relative changes in NSC between treatments measured within a laboratory may be comparable within and between laboratories, especially for starch. To obtain comparable NSC estimates, we suggest that users can either adopt the reference method given in this publication, or report estimates for a portion of samples using the reference method, and report estimates for a standard reference material. Researchers interested in NSC estimates should work to identify and adopt standard methods.

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Abstract:The current understanding of the influences of climate and viticultural practices on fruit quality at harvest and on sparkling wine quality is reviewed. Factors such as variety, clone, planting density, pruning method, local climate and soils, and current and future climate warming are discussed in the context of achieving a desired harvest quality. A common observation was the relatively less intensive viticultural management applied to grapes destined for sparkling wines compared to table wines throughout the world. Few studies have focused on management of fruit specifically for sparkling wine production. Given that it is accepted that a lower pH, higher titratable acidity, and lower soluble sugars than table wine are considered desirable for sparkling wine production, the literature from viticultural studies for table wines which influence these desired fruit quality parameters has been reported. Specific findings on canopy management, leaf removal, and yield manipulation for the production of table wines indicate potential for application and development to optimize fruit for the production of sparkling wines. Fruit quality targets are remarkably uniform across international growing regions but distinct combinations of variety, clone, and management are currently used to arrive at those targets. Further, studies of viticultural management, particularly those that alter cluster temperature and exposure to incident light, yield manipulation, and fruit quality are likely to best inform production techniques that result in fruit quality ideal for the production of premium sparkling wines. New challenges include the need for increasing mechanization to maintain cost-effective production and climate warming, which affects the production of fruit for premium sparkling production in terms of flavor development and high acidity. Current trends include the diversification of growing regions to cooler regions that enable the production of high acid fruit and increased exploration of alternative varieties and clones that are better suited to a warmer climate.

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