摘要
摘要:植物根系分泌物的根际代谢组学分析有助于更好地理解土壤根际微域内植物根系与土壤和土壤生物之间化学信号交流的根际过程。本文采用核磁共振氢谱（¹H nuclear magnetic resonance，¹H NMR）技术，对基于不同施氮处理下[常规施氮（180 kg·hm^-2）、80%常规氮量和55%常规氮量]土壤培养收集的玉米幼苗的根系土壤沥出液（soil leachate，SL）、根鞘土浸提液（rhizosheath soil，RS）和根系水培液（distilled water cultivation，DWC）内的根系分泌物进行检测，并结合多维统计分析对比了不同收集方法以及不同施氮量下玉米幼苗根系分泌物的不同。结果表明：3种不同方法收集的玉米幼苗根系分泌物的核磁共振氢谱谱图轮廓及主要标志物明显不同。其中SL法的谱图峰信号及检测到的根系分泌物数目少，而RS和DWC法的谱图峰信号较多且可检测到玉米幼苗根系分泌物中的糖、有机酸和氨基酸等组分。与常规施氮量比较，在85%施氮量下，玉米幼苗根系分泌物中的α-葡萄糖、苹果酸、亮氨酸、缬氨酸水平显著增加；而当施氮量减少到55%时，玉米幼苗根系分泌物水平不再显著增加并呈现下降趋势。上述根系分泌物的变化可能和玉米根系对土壤氮营养供应水平的适应性调节有关。采用¹H NMR技术，结合RS和DWC收集方法进行根际代谢组学分析，可为根际生态及根际氮素营养研究提供重要理论依据。
关键词:氮肥减施/
玉米/
根系分泌物/
根际代谢组学/
核磁共振氢谱(¹H NMR)
Abstract:As one of the most critical environmental factors driving plant growth, soil N availability significantly influences the composition and quantity of root exudates. Concerning the environmental benefits, the inputs reduction of N fertilizer can be an attractive option for crop production in a more sustainable agriculture system. However, the pattern of root exudates in response to the reduced N levels remains poorly understood, especially for maize (Zea mays L.) plants. Metabolomics of root exudates can potentially help us to better understand the chemical communication between roots, soils and organisms in the rhizosphere. In this study, to characterize root exudation pattern of maize plants grown under conditions with reduced N fertilizer at metabolomics level, three methods were developed for collecting root exudates from maize seedling planted in soils through soil leachate (SL), rhizosheath soil extraction (RS) and distilled water cultivation (DWC), respectively. The metabolomics of root exudates collected by different methods under nitrogen fertilizer reduction conditions were investigated based on ¹H NMR spectroscopy. Partial least squares projection to latent structures-discriminant analysis was performed to quantify the difference of metabolomics among samples and conditions. The results showed that the whole profilings of ¹H NMR were distinctly different among root exudates obtained by three methods, and the major compounds contributing to the discrimination also varied. The most important exudates that differentiated the samples between SL and RS methods were glucose and alanine while more exudates such as acetate, lactate, succinate, sucrose, alanine, leucine, isoleucine and valine accounted for the discrimination between SL and DWC methods. In addition, the most important exudates that differentiated the samples between RS and DWC methods were acetate, lactate, succinate and isoleucine. The peak signals of ¹H NMR and number of assigned metabolites in root exudates detected by method of SL were less while that were rather more in the methods of RS and DWC; and sugars, organic acids and amino acids in root exudates of maize seedlings were detected by the latter two methods. In contrast to the control of 100%-N level (corresponding to the conventional application rate of 180 kg·hm^-2), the levels of α-glucose, malate, leucine and valine increased significantly in root exudates of maize seedlings in treatment with 85%-N level. However, the level of exudates decreased with reducing fertilizer N application rate and its difference between control and 55%-N treatment was not significant. The changes of root exudates may influence soil organic matter turnover and lead to an increase in plant-available N. Our results indicated that maize seedlings might adapt to the variation of nitrogen nutrient situation in soil by regulation of exudation. Metabolomics analysis of root exudates based on ¹H NMR spectroscopy combined with sample collecting methods of rhizosheath soil extraction and distilled water cultivation could provide important theoretical basis for the study on the rhizosphere ecology and nitrogen nutrition. The possible ecological roles of root exudates in response to N reduction should be fully elucidated in the future. A combined approach involving different metabolomic tools will facilitate the understanding of belowground chemical communications and rhizosphere interactions under conditions of N reduction.
Key words:Nitrogen fertilizer reduction/
Maize/
Root exudates/
Rhizosphere metabolomics/
¹H NMR



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