田间耕作条件下苹果短枝型品种与普通型品种的硝酸还原酶活性（ＮＲＡ）分析表明：ＮＲ普遍存在于根系与叶片中，但皮层没有检测到，其活性以根系最高；ＮＲＡ的周年变化动态与植株的３次根系活动高峰相一致，说明其与根系旺盛的土壤Ｎ吸收有关。追施硝态氮（ＮＯ３—Ｎ）能显著提高ＮＲＡ，但高剂量的铵态氮（ＮＨ４—Ｎ）并未造成ＮＲＡ的下降；ＮＲＡ在两类品种间存在差异，短枝型品种的ＮＲＡ高于其相应的普通型品种，表明前者的耐肥性较高。 Nitrate reductase activity (NRA) analysis showed that NR was commonly found in roots and leaves but not detected in cortex, and its activity was the highest in root system. The annual variation of NRA It is consistent with the third root activity peak of the plant, indicating that it is related to the N uptake by the root system. Topdressing nitrate nitrogen (NO3-N) significantly increased NRA, but NH4-N did not decrease the NRA. NRA differed between the two types of cultivars, and the NRA of the spur type The corresponding common type, indicating that the former high resistance.