氮素形态对油茶苗木生长及生理指标的影响

【目的】探究不同氮素形态对油茶苗木生长及生理指标的影响,以期找到促进油茶个体生长和有利于油茶氮代谢的氮素形态及配比。【方法】以‘湘林1号’(XL1)油茶实生苗为供试材料,采用液体浇灌的方法,观察不同形态氮素配比(m(NO^-₃-N):m(NH⁺₄-N)=10:0、7:3、5:5、3:7、0:10)]对油茶幼苗生长特性及生理指标的影响。【结果】苗高增量、地径增量均随着培养液中铵态氮比例的增加呈先增加后降低的趋势,在m(NH⁺₄-N):m(NO^-₃-N)为5:5时达最大值; m(NH⁺₄-N): m(NO^-₃-N)为7:3和5:5时,干物质量累积最大; 叶片叶绿素含量、硝酸还原酶(NR)活性以及谷氨酰胺合成酶(GS)活性均在m(NH⁺₄-N): m(NO^-₃-N)为5:5时达到最大值; 谷氨酸合酶(GOGAT)活性在m(NH⁺₄-N):m(NO^-₃-N)为10:0时达最大值; 外源氮添加均增加了油茶叶片的全氮含量,m(NH⁺₄-N):m(NO^-₃-N)为3:7时,全氮含量最高。相关性分析结果表明,苗木生长、总干物质量及叶片全氮含量均与总叶绿素含量、NR活性、GS活性呈显著或极显著正相关,地径增量与GOGAT活性呈极显著正相关,总干物质量与GOGAT活性呈显著正相关。【结论】施用混合态氮素比单一形态氮素更有利于油茶苗木的生长,当m(NH⁺₄-N):m(NO^-₃-N)为5:5时,最利于油茶幼苗生长。关键词:油茶; 氮素形态; 氮素配比; 营养生长; 叶片生理指标

Effects of different proportion of nitrogen forms on the growth and physiological characteristics of Camellia oleifera seedlings

【Objective】Camellia oleifera is a unique woody edible oil tree in China, which has great value for exportation and broad market prospects. In the rapidly developing oil tea industry, improved seedlings are vigorously demanded. The quality of seedlings directly affects the development of this industry, and fertilizers play a significant role in the growth and quality of seedlings. Therefore, it is of great importance to study the effects of nitrogen forms on the growth and physiological indexes of Camellia oleifera seedlings, which can guide management of nitrogen fertilizer for Camellia oleifera seedlings. 【Method】 The effects of different nitrogen forms m(NO^-₃-N):m(NH⁺₄-N)=10:0, 7:3, 5:5, 3:7, 0:10] on growth(growth, biomass)and physiological indexes(chlorophyll content, related enzyme activity and leaf total nitrogen content)of Camellia oleifera seedlings were studied by liquid irrigation with XL1 seedlings. The nutrient solution used was the Hoagland nutrient solution, and 7 μmol/L nitrification inhibitor C₂H₄N₄ was added to all nutrient solutions to inhibit nitrification. The experiment was conducted in a completely randomized block with 3 replicates per treatment, 30 plants per replicate, and 10 times a week; 300 mL nutrient solution was used for each seedling. Total nitrogen was determined by the Kjeldahl method, and chlorophyll content was determined by the acetone-ethanol mixture method. Nitrate reductase, glutamate synthase(GOGAT)and glutamine synthase(GS)activities were determined by spectrophotometry. Data were analyzed by Excel 2003 and the SPSS 19.0 software. 【Result】 Increase in seedling height and ground diameter exhibited a volcanic trend with the increases in the ammonium nitrogen ratio of the culture solution, and reached amaximum of 9.700 cm and 1.957 mm when m(NH⁺₄-N):m(NO^-₃-N)was 5:5. Results indicated that the mixed nitrogen forms were more beneficial for growth of Camellia oleifera seedlings when compared with the single nitrogen forms. The greatest dry weight was achieved when m(NH⁺₄-N):m(NO^-₃-N)were 7:3 and 5:5, which were higher than those of pure nitrate or pure ammonium treatments. In addition, chlorophyll a, chlorophyll b, and total chlorophyll content in leaves reached a maximum of 1.190, 0.377, and 1.567 mg/g, respectively, at a m(NH⁺₄-N):m(NO^-₃-N)ratio of 5:5. The largest NR activity observed was 42.883 μg/(g·h),at a m(NH⁺₄-N):m(NO^-₃-N)ratio of 5:5. NR activity of ammonium treatment was lower when compared with that of nitrate treatment, which indicated that NO^-₃-N promoted NR activity. In addition, GS activity reached a maximum of 62.118 μmol/(g·h)when m(NH⁺₄-N):m(NO^-₃-N)was 5:5.GOGAT activity was increased with increased ammonium nitrogen ratio, and the highest value was 26.983 μmol/(g·h)at a m(NH⁺₄-N):m(NO^-₃-N)ratio of 10:0. Addition of exogenous nitrogen increased the total nitrogen content of leaves; total nitrogen content was the highest at 11.600 g/kg when the m(NH⁺₄-N):m(NO^-₃-N)ratio was 3:7. Total nitrogen content under mixed fertilization was higher when compared with that under pure nitrate and ammonium treatments, and showed a trend of initial increasing and then decreasing with increased ammonium nitrogen ratio. In the single nitrogen form T1 m(NH⁺₄-N):m(NO^-₃-N)= 0:10] > T5 m(NH⁺₄-N):m(NO^-₃-N)= 10:0], which indicated that the nitrate nitrogen promoted accumulation of total nitrogen in leaves in the single nitrogen form. Correlation analysis showed that growth of seedlings, total dry weight and total nitrogen content of leaves were significantly or significantly positively correlated with total chlorophyll content, NR activity and GS activity; increase in ground diameter was significantly and positively correlated with GOGAT activity; total dry weight was positively correlated with GOGAT activity.【Conclusion】 The application of nitrogen in different forms was more beneficial to the growth of Camellia oleifera seedlings, and the best m(NH⁺₄-N):m(NO^-₃-N)ratio for growth was 5:5.