氮素水平对沙地燕麦叶片非结构性碳氮代谢的影响

为分析追施氮肥对沙地燕麦叶片非结构性碳氮代谢的影响,在内蒙古通辽市科左中旗珠日河牧场的沙化草地,于苗期、分蘖期、拔节期、抽穗期4个生育时期,按照15%、40%、25%、20%比例,对燕麦追施70、140、210、280 kg·hm^-2氮肥(纯N),分别用N₇₀、N₁₄₀、N₂₁₀、N₂₈₀表示,以不施氮肥为对照,用N₀表示;检测孕穗期、抽穗期、灌浆期沙地燕麦不同部位叶片的可溶性糖、淀粉、氨基酸、可溶性蛋白含量及硝酸还原酶活性(nitrate reductase,以下简称NR),检测灌浆期沙地燕麦不同部位叶片的蔗糖含量及蔗糖合成酶活性(sucrose synthase,以下简称SS)。结果表明:追施氮肥极显著(P<0.01)降低沙地燕麦叶片的可溶性糖、淀粉、蔗糖等糖类物质含量,且随着氮肥施用水平的增加,沙地燕麦叶片的蔗糖、可溶性糖、淀粉含量呈逐渐降低趋势;追施氮肥沙地燕麦叶片的游离氨基酸含量均较对照增加,在孕穗期和抽穗期N₂₈₀ 氮素处理的沙地燕麦叶片游离氨基酸含量最高,在灌浆期N₂₁₀氮素处理的游离氨基酸含量最高;可溶性蛋白含量在不同生育时期均极显著高于对照(P<0.01),在孕穗期N₂₁₀ 氮素处理的可溶性蛋白含量最高,在抽穗期则以N₂₈₀ 氮素处理含量最高,在灌浆期上部叶以N₂₁₀ 氮素处理含量最高,中部叶和下部叶以N₂₈₀ 氮素处理含量最高;沙地燕麦叶片在灌浆期上、中、下部叶片的蔗糖合成酶活性(3.61、6.50、13.44 μg·g^-1FW·h^-1)和硝酸还原酶活性(81.6、84.8、76.2 μg·g^-1FW·h^-1)均在N₇₀氮素处理最强,极显著(P<0.01)高于对照和其他氮素水平处理,且随着氮肥施用水平的增加蔗糖合成酶和硝酸还原酶活性降低极显著(P<0.01)或显著(P<0.05);追施氮肥对沙地燕麦叶片的硝态氮含量没有明显的影响;孕穗期对照(N₀)燕麦上、中、下部叶片的C/N均最大,分别是9.00、5.70、1.48,进入抽穗期和灌浆期,则以N₂₁₀氮肥处理的上部叶和N₂₈₀氮肥处理的中部叶及下部叶C/N最大。综合考虑沙地燕麦叶片碳氮含量、碳氮代谢关键酶活性及产量特性,本试验条件下,追施N₂₁₀氮素处理,有利于碳氮代谢的协调进行。

Effects of nitrogen fertilizer level on non-structural carbon and nitrogen metabolite levels in oats grown in sandy desert soil

This study was located at Kezuozhong near Tongliao City,in the Inner Mongolia Autonomous Region of China,and investigated the effects of nitrogen fertilizer application on non-structural carbon and nitrogen metabolite levels in leaves of oats (Avena sativa) grown in a desert environment.Nitrogen fertilizer was applied as urea at 70,140,210 and 280 kg · ha-1 elemental N,and with a no-N treatment as a control (designated N70,N140,N210,N280,and N0,respectively).Separate fertilizer applications comprising 15％,40％,25％,and 20％ of the total,respectively,were made at seedling,tillering,jointing,and heading stages of crop development.Soluble sugar,starch,amino acid,soluble protein (SP) content and nitrate reductase activity (NR)were measured for leaf samples collected from various positions at the booting,heading and grain filling growth stages.Sucrose content and activity of sucrose synthase (SS) were also measured at the grain filling stage.It was found that nitrogen fertilizer significantly (P＜0.01) reduced the carbohydrate content (including soluble sugars,starches and glucose),with the size of the reduction in proportion to the quantity of N applied.Conversely,free amino acid levels in leaves were increased by N fertilizer and were highest in the N280 treatment at booting and heading stages,and were also high in the N210 nitrogen treatment at the watery dough stage of grain fill.Similarly,SP content was significantly higher in N-treated plants than in the control (P＜0.01) and varied across growth stages,with highest values recorded in the N210 treatment at the booting stage,and in the N280 treatment at the heading stage.In terms of variation within the plant,SP concentration in the upper leaves was the highest in the N210 treatment,while in the middle and lower leaves SP was the highest in N280 nitrogen treatment in the watery dough stage.At grain filling stage,in the N70 treatment,SS activities were 3.61,6.50,and 13.44μg · g-1 FW · h-1,respectively,for upper,middle and lower leaves,and corresponding values for NR activities were 81.6,84.8,76.2 μg · g-1 FW · h-1.SS and NR activities were significantly decreased (P＜0.01 and P＜0.05 for SS and NR,respectively) with application of N at higher rates than N70.Topdressing of N fertilizer had no obvious influence on the nitrate-nitrogen content in the oat leaves.The C ∶ N ratios were largest in the N0 treatment at the booting stage,being respectively 9.00,5.70 and 1.48 for upper,middle,and lower leaves.However,the C ∶ N values of the upper leaves of N210and the middle and lower leaves of the N280 treatment nitrogen were maximized at the heading and filling stages.This study provides comprehensive data on developmental changes in carbon and nitrogen contents,on activities of key enzymes in carbon and nitrogen metabolism and on yield characteristics of oats grown in a desert soil,and will assist understanding of the coordination of carbon and nitrogen metabolism.