Does microwaving or freezing reduce the losses of non-structural carbohydrates during plant sample processing?

Context: Non-structural carbohydrates (NSC) mediate tree survival, but precise determinations of NSC concentrations remain challenging. An unclear aspect is whether carbohydrate losses during sample processing can be reduced by different sample treatments. Aims: We postulated that due to higher metabolic rates, leaves should be more responsive to sample treatments than branch sapwood, and resource-acquisitive species should be more responsive to sample treatment than resource-conservative species. Methods: In leaves and branch sapwood of six tree species, we compared the effects of three sample treatments on the concentrations of NSC, starch, and low-molecular weight sugars: sample microwaving before drying (microwave), sample freezing at -20ºC before drying (freezing), and only drying (stove). Results: We found that across species and tissues, freezing led to significantly higher NSC and sugar concentrations than microwave and stove. This effect was, however, entirely driven by the leaves. Although the effect of sample treatments on NSC, starch, and sugar concentrations differed among species, resource-acquisitive species were not necessarily more affected by sample treatments than resource-conservative species. Conclusion: Results suggest that either freezing or microwaving does not reduce carbohydrate losses in branch sapwood during sample handling and processing; however, freezing reduces leaf sugar and NSC losses when compared to microwave or direct stove-drying.研究背景：非结构性碳水化合物（non-structural carbohydrates, NSC）对树木存活具有介导作用，但精准测定其浓度仍颇具挑战。目前尚不明确的是，不同样品处理方式能否降低样品处理过程中的碳水化合物损失。 研究目的：我们提出如下假设：由于叶片代谢速率更高，其对样品处理的响应程度应高于枝条边材；且资源获取型树种对样品处理的响应程度应高于资源保守型树种。 研究方法：我们以6个树种的叶片和枝条边材为材料，对比了3种样品处理方式对非结构性碳水化合物、淀粉及低分子量糖浓度的影响：干燥前微波处理（微波法）、干燥前-20℃冷冻保存（冷冻法），以及仅进行干燥处理（烘箱法）。 研究结果：我们发现，在所有树种和组织中，冷冻法测得的非结构性碳水化合物和糖浓度均显著高于微波法与烘箱法，但该效应完全由叶片驱动。尽管不同树种间，样品处理对非结构性碳水化合物、淀粉及糖浓度的影响存在差异，但资源获取型树种未必比资源保守型树种受样品处理的影响更大。 研究结论：结果表明，在样品处理与制备过程中，冷冻法或微波法均无法降低枝条边材的碳水化合物损失；但与微波法或直接烘箱干燥法相比，冷冻法可减少叶片中糖与非结构性碳水化合物的损失。