Standing crops and nutrient attributes of litchi (Litchi chinensis) floral nectar in response to the removal of inflorescences

Litchi inflorescences bear hundreds of small flowers, but most flowers need to be removed to reduce the consumption of carbohydrates and increase fruit setting. The production and secretion of nectar are largely affected by the availability and metabolism of carbohydrates. However, the secretion pattern and constituents of litchi nectar in response to the removal of inflorescences are unclear. Here, we showed that the litchi nectar secretion amount ranged from 4 to 10 mg per flower with the cultivar ‘Nuomici’ having the strongest secretion ability. The concentration of total soluble solids in litchi nectar was approximately 30%. Fructose was present in the highest concentration in nectar, followed by glucose and sucrose. Cultivar, flower sex and inflorescence-removal treatment had no significant main effect on soluble sugars but had two-way interaction effects on sucrose. Twenty-seven amino acids were detected, including seven essential amino acids. The concentration of amino acids was significantly affected by cultivar and flower sex, with nectar from the cultivar ‘Guiwei’ and male flowers having a significantly higher concentration. Removal of inflorescences did not show the main effect on the nectar amount, total soluble solids, or protein contents, but had interactive effects on the concentration of sucrose and amino acids.荔枝花序（inflorescences）可着生数百朵小花，但生产中通常需疏除大部分花朵以减少碳水化合物消耗、提升坐果率（fruit setting）。花蜜的产生与分泌在很大程度上受碳水化合物的有效性与代谢水平调控。然而，花序疏除处理后荔枝花蜜的分泌模式与组分特征目前仍不明确。本研究结果显示，单花泌蜜量介于4~10 mg之间，其中‘糯米糍’品种的泌蜜能力最强。荔枝花蜜的总可溶性固形物（total soluble solids）浓度约为30%。花蜜中果糖（fructose）含量最高，其次为葡萄糖（glucose）与蔗糖（sucrose）。品种（cultivar）、花性别以及花序疏除处理对可溶性糖含量无显著主效应，但三者对蔗糖含量存在双向交互作用。本研究共检测到27种氨基酸，其中包含7种必需氨基酸（essential amino acids）。氨基酸浓度显著受品种与花性别影响：‘桂味’品种以及雄花所产花蜜的氨基酸浓度显著更高。花序疏除处理对单花泌蜜量、总可溶性固形物含量以及蛋白质含量无显著主效应，但对蔗糖与氨基酸浓度存在交互调控效应。