根溫對檬果根生長、開花及葉片中無機要素與碳水化合物含量之影響

Effect of Root Temperature on Flowering, Root Growth and Leaf Mineral Nutrients and Carbohydrate Content of Mango (Mangifera indica L.)

檬果根之生長以長度論，在24℃根溫下最長，其後依次為31℃、17℃、10℃，而10℃下生長極少。但以根直徑而言，則溫度愈低新生根愈粗，此外根溫愈高分枝愈早。10℃根溫下之根有壞死現象，17℃下之根在處理20日之後根尖亦轉黃，顯示檬果根部耐寒性並不高。葉片中硝酸根還原酵素活性隨根溫上長而提高。根部則相反，但後期因低溫下根受損甚至於死亡，故試驗終了時兩者均以24℃下之活性較高。根溫對碳水化合物蓄積之影響較氣溫小，但影響葉片氮、磷、鉀、鈣、鎂之含量。17℃根溫下開花的檬果植株之小花，完全花及雄花數均最多，但完全花比例以24℃下最高，10℃之下不但小花數最少且完全花比例最低。24℃根溫下之著果率最高，31℃次之，17℃在彈珠期有近40%之著果率，但後期落果嚴重，著果率以花序計算時僅餘23.1%，同時使每個花序的平均果數僅達0.3個，10℃下不但初期結實率低，且落果嚴重，每個花序的結果數僅有0.11個，10℃下不但初期結實率低，且落果嚴重，每個花序的結果數僅有0.11個，顯示檬果在低根溫下，不但完全花比例偏低，且其著果及結果率亦較低。

Two years old potted ”Irwin” mango trees were treated with root temperatures at 31℃, 24℃, 17℃ and 10℃ under a plastic rain-off shelter.The effect of root temperture on root growth can be observed in the length and the diameter (radius) of roots. The longest roots appeared at 24℃ and followed by 31℃, 17℃ and 10℃. The roots growth ceased at 10℃. But the diameter (radius) of the roots seems to hold a different attitudes toward the effect of temperatures. Lower temperature enhanced the growth of new-born roots with thicker diameter, while higher temperature forced the earlier branching of roots. Below 10℃, dying of roots occurred. After 20 days of 17℃ treatment, root tips turning yellow. These phenomenons pointed out that the mango roots would not tolerate a too low temperature.In accordance with the increasing root temperature, the nitrate reductase activity increased in the leaves and decreased in the roots. In the experiments, because the roots were damaged by low temperature during the later experiment stage, the NR activity showed its peak at 24℃ both in leaves and roots in the final results.Treatment of root temperature has only little effect on the carbohydrates content in leaves, while it affects the contents of nitrogen, phosphorus, potassium, calcium, magnesium in leaves. Trees treated with high root temperature contain more mineral nutrients and less carbohydrates in leaves than those treated with lower root temperatures.Mango trees flowering at 17℃ root temperature beared the largest quantity of small flowers. The number of small flowers decreased at 31℃, 24℃ and 10℃. The trees treated with 24℃ root temperature had the highest hermaphrodite flower ratio, which gradually decreased at 31℃, 17℃ and 10℃. Trees grown at 10℃ root temperature beared the least amount of small flowers as well as the lowest hermaphrodite flower ratio. The fruit set of the tree grown at 24℃ root temperature had the highest percentage at 'marble' and 'half-size' stages, and it is about the same as those at 31℃.Trees treated with 17℃ had high fruit set at 'marble' stage, but very low at 'half-size' stage. The tree had the lowest fruit set at the stages of both 'marble' and 'half-size' at 10℃ root temperature, which dipicts that a possible embryo abortion might occur when the roots exposed to a temperature lower than 17℃.