• 作者： 譚?中；莊作權；鄒箎生
• 作者服務機構： 國立中興大學土壤學研究所; 亞洲蔬菜研究發展中心
• 中文摘要： 在整個大豆生長期中，葉片硝酸鹽還原酵素活性與土壤中硝酸態氮素之含量，皆呈現Michaelis-Menten之關係，其 可被誘導之最大活性(Vmax)隨植體年齡之增長而降低，初期生長時km?較小，此些數?也許可被用來檢定大豆對土壤中硝酸態氮素含量之反應的品種間差異。施用大量氮肥對大豆根瘤固氮酵素之活性極?不利。施用較少量的氮肥雖然在初期 生長時減低固氮酵素之活性，?可增加後期生長時之固氮酵素活性。 由相關係數之計算，盆栽試驗之結果顯示，土壤中影響上述兩種酵素活性之無機態氮素，主要是硝酸態氮素。硝酸態氮素增多，硝酸鹽還原酵素活性增加，而根瘤固氮酵素活性?被降低，因此在發芽後四週時此二酵素活性呈直線負相關。 然而，除此直接之影響外，土壤中硝酸態氮素亦可以一種間接的方式影響根瘤固氮酵素活性，因?高度之硝酸根離子濃度 可以誘導?生更高的硝酸鹽還原酵素活性，加速大豆植株早期生長，而使根瘤發育時，能有更多的光合?物供其所需，增 加根瘤固氮酵素之活性。由於受這些直接與間接的因子所影響，此二酵素活性在發芽後六週與十週時，呈現?物線之相關。
• 英文摘要： The nitrate reductase activity of soybean leaf responded to soil NO3-N content with a Michaelis-Menten relationship throughout all growth stages. Maximum nitrate reductase activity decreased as the plant aged. A smaller 'Km' value was observed at earlier growth stages. The results obtained in greenhouse experiments indicate that a certain level of no3-N in the soil is necessary in order to obtain an optimum level of nitrogenase activity at later growth stages. Correlation studies showed that NO3 in the soil is the major form of inorganic nitrogen which affects the leaf nitrate reductase activity and nodule nitrogenase activity. A negative linear relationship between these two enzymatic activities was observed at 4 weeks after germination, while a parabolic relationship was observed at 6 and 10 weeks after germination.
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