摘要：

土壤酸化会降低玉米的产量和氮素积累量,但生理机制尚未明确。在大田设置中性(pH=7,CK)、弱酸(pH=6,T1)、中酸(pH=5,T2)和强酸(pH=4,T3)4种土壤酸度处理,比较各处理下玉米产量、氮素积累量、籽粒蛋白含量、叶片与茎秆中氮代谢相关酶活性、基因表达量以及硝态氮( {{\mathrm{NO}}_3}^{-})、铵态氮( {{\mathrm{NH}}_4}^{+})、可溶性蛋白、游离氨基酸含量的差异。结果表明,相比于CK,T1、T2、T3处理产量分别降低4.2%,30.7%,52.3%;穗粒数分别降低1.8%,28.1%,42.8%;籽粒蛋白质含量呈现下降趋势,其中T3处理显著降低14.5%。在大喇叭口期,随着酸度增加,叶片氮素积累量显示出下降趋势,其中T2和T3处理分别显著降低28.1%和56.2%;茎秆中氮素积累表现出先增加后降低的趋势,T1处理显著增加33.1%,T3显著降低65.4%。大喇叭口期,T3处理下叶片和茎秆中硝酸还原酶、谷氨酸脱氢酶、谷氨酸合成酶活性均显著高于CK,而叶片中谷氨酰胺合成酶活性显著下降;茎秆中氨基酸表现先下降后上升的趋势。转录组分析表明,随着土壤酸度的增加,ZmGln2与ZmFd-GOGAT表达量上调,促进了光呼吸释放 {{\mathrm{NH}}_4}^{+}与 {{\mathrm{NO}}_3}^{-}还原产生 {{\mathrm{NH}}_4}^{+}的同化;ZmGln1.2~ZmGln1.4、叶片中ZmNADH-GOGAT2和茎秆中ZmNADH-GOGAT1表达量下调,降低了蛋白质分解代谢释放产生 {{\mathrm{NH}}_4}^{+}的同化。玉米通过上调或下调相关基因表达,促进氮代谢产生更多的游离氨基酸、可溶性蛋白等渗透调节物质用以抵御酸胁迫,但也因此减少了氮积累量,导致产量、籽粒蛋白质含量降低。

关键词: 玉米, 土壤酸化, 产量, 氮代谢, 转录组

Abstract:

Yield and nitrogen accumulation of maize will decline under soil acidification,but the physiological mechanism is not clear.Field experiment was conducted with four different soil acidity gradients:nautral acid(pH=7,CK),weak acid(pH=6,T1),medium acid(pH=5,T2)and strong acid(pH=4,T3),comparing yield,nitrogen accumulation,grain protein content,nitrogen metabolism-related enzyme activities,gene expression,nitrate nitrogen,ammonium nitrogen,soluble protein,free amino acid content in leaf and stem of maize.The results showed that compared with CK,the yield of T1,T2 and T3 treatments declined by 4.2%,30.7% and 52.3%,respectively.Grain number per spike decreased by 1.8%,28.1% and 42.8%;grain protein content showed a downward trend with T3 treatment significantly reduced by 14.5%.At the big flare stage,with the increase of soil acidity,nitrogen accumulation in leaves showed a downward trend,it was significantly decreased in T2 and T3 treatment by 28.1% and 56.2%,respectively.In stem,the nitrogen accumulation increased firstly and then decreased.Compared with CK,T1 treatment was significantly increased by 33.1%,and T3 treatment significantly decreased by 65.4%.At the big flare stage, the activities of nitrate reductase, glutamate dehydrogenase and glutamate synthase in leaf and stem under T3 treatment were significantly higher than those in CK, while the activities of glutamine synthase in leaf were significantly decreased. The amino acids in stem decreased first and then increased.With the increase of soil acidity,the expressions of ZmGln2 and ZmFd-GOGAT were up-regulated,which promoted the assimilation of {{\mathrm{NH}}_4}^{+} released by photorespiration and {{\mathrm{NH}}_4}^{+} produced by {{\mathrm{NO}}_3}^{-} reduction;the down-regulated expression of ZmGln1.2-ZmGln1.4, ZmNADH-GOGAT2 in leaf and ZmNADH-GOGAT1 in stem decreased the assimilation of {{\mathrm{NH}}_4}^{+} released by catabolism.By up-regulating or down-regulating the expression of relevant genes,maize could promote the production of more free amino acids and soluble proteins during nitrogen metabolism to resist acidification stress,but also reduced the nitrogen accumulation,resulting in lower yield and grain protein content.

Key words: Maize, Soil acidification, Yield, Nitrogen metabolism, Transcriptome