草酸是楊桃果實中最主要的有機酸，當人體内草酸含量過高時，容易罹患高草酸 尿症，增加腎結石的風險。本試驗以五種硝酸態氮與銨態氮比例之養液處理2年生‘馬來西 亞’楊桃盆株，比較營養生長、光合作用速率、葉片與果實礦物元素與有機酸含量等變化， 評估利用肥培管理降低楊桃果實草酸含量之可行性，並期望能找出與果實草酸含量相關性 之指標，以應用於低草酸楊桃品種之選育。處理26週後的植株，平均枝條長度及葉片數以 硝酸態與銨態氮比例為75 : 25之處理組最高；淨光合作用值、總氮及可滴定酸濃度以比例 為100 : 0及75 : 25兩處理組最高。葉片可滴定酸與草酸、蘋果酸及抗壞血酸間皆有顯著 正相關，其中草酸與蘋果酸間也呈顯著正相關趨勢。而果實品質方面，果長、果重、總可 溶性固形物、硬度、可滴定酸及有機酸皆以硝酸態與銨態氮比例為75 : 25之處理組最高； 比例為50 : 50處理果實草酸濃度較低；果實總氮濃度則是以比例為75 : 25及0 : 100兩處 理最高。果實中可滴定酸含量與草酸及總氮濃度間呈顯著正相關。相關性比較顯示果實的 草酸與葉片的草酸並無相關性，無法藉由葉片草酸含量推估果實之草酸含量。

Oxalic acid is a major organic acid in Carambola (Averrhoa cara^bola L.) fruit. When oxalate concentration become high in the human body, it is called hyperoxaluria, which increased the risk of kidney stones. The purpose of this research was by treating different ratio of nitrate (NO3-) and ammonium (NH4+) nutrient solution on pot-planted ‘Malaysia5 carambola, then to investigate the vegetative growth, photosynthesis, the concentration of mineral elements , organic acid variation among leaves and fruits, and so on. To assess the feasibility of decreasing the content of oxalic acid by using the fertilizer control and to search for the index of breeding the lower oxalic acid variety of carambola. Twenty-six weeks after using 75:25 NO3-/NH4+ treatment, the average plant shoot length and leaf numbers were the highest. It was also found that 100:0 and 75:25 NO3-/NH4+ had the highest total nitrogen concentration, titratable acidity and net photosynthesis of carambola leaves. Leaves showed a significantly positive correlation between titratable acidity and oxalic acid, malic acid and ascorbic acids, oxalic acid and malic acid of leaves also showed a significantly positive correlation. On the other hand, the 75:25 NO3-/NH4+ was better than the others regarding to length, weight, total soluble solids, firmness, titratable acidity and organic acid content of fruit. Lower oxalic acid concentration of fruit was found when 50:50 NO37NH4+were applied. When 75:25 and 0:100 N〇3-/NH4+ was used, total nitrogen concentration was higher than the other ratios. A notably positive correlation was found between titratable acidity of fruit, oxalic acid and total nitrogen concentration. The correlation coefficients imply that oxalic acid concentrations between the fruits and leaves are non-significant, using oxalic acid concentration of leaf to predict the oxalic acid concentration of fruit is infeasible.