Table_3_Maize metabolomics in relation to cropping system and growing year.docx

Maize is important to global food security, being one of the predominant cereals in human and domesticated livestock diets worldwide. Due to the increasing human population, it will be important to not only design cropping systems to increase maize yield and sustainability but also to improve the nutritional quality of maize edible tissues. To determine cropping system impacts on maize grain nutritional content, we sampled grain from conventional and organic maize varieties grown for three growing seasons using five cropping systems. We analyzed the grain using metabolic fingerprinting of methanol extracts with ultra-high performance liquid chromatography (UHPLC) coupled with mass spectrometry (MS), adopting both non-targeted and targeted approaches. The cropping systems are part of a long-term study at the Beltsville Agricultural Research Center in Beltsville, Maryland, and were a three-year conventional no-till rotation (NT), a three-year conventional chisel-till rotation (CT), a two-year organic rotation (Org2), a three-year organic rotation (Org3), and a six-year organic rotation (Org6). Each cropping system had been in place for at least 10 years, allowing specific cropping-system-induced alterations of soil edaphic and microbial properties. Non-targeted metabolic fingerprinting detected a total of 90 compounds, the majority of which were phenolics. Metabolic profiling was further targeted toward 15 phenolics, 1 phytohormone, 7 carbohydrates and 7 organic acids, which were quantified in the maize grain originating from the five cropping systems. Statistical analysis of this subset of quantitative data determined that cropping system can significantly influence levels of certain maize grain metabolites. However, natural impacts (growing year) were substantially greater than cropping system impacts, likely masking or over-riding some cropping system impacts. Additionally, maize cultivar genetics had greater impact than cropping system on the maize grain metabolome and was the greatest “managed” impact on the metabolite profiles. Results indicate that until natural environmental impacts on maize grain metabolite levels are understood and managed, the best approach to reliably increase maize grain nutritional quality is through development of maize cultivars with enhanced nutritional content that are robust to natural environmental influence.

玉米作为全球人类与畜禽饲粮中的主要谷物之一，对全球粮食安全至关重要。随着全球人口持续增长，不仅需要优化种植系统以提升玉米产量与可持续性，还需改善玉米可食用组织的营养品质，这两点均至关重要。为明确种植系统对玉米籽粒营养成分的影响，本研究针对五种种植系统下种植的常规与有机玉米品种采集籽粒样本，实验周期覆盖三个生长季。研究采用超高效液相色谱法（Ultra High Performance Liquid Chromatography, UHPLC）与质谱法（Mass Spectrometry, MS）联用技术对甲醇提取物进行代谢指纹图谱分析，同时运用非靶向与靶向两种分析策略。本实验的种植系统均设立于马里兰州贝尔茨维尔市贝尔茨维尔农业研究中心的长期定位试验中，具体包括三年常规免耕轮作（NT）、三年常规凿式耕作轮作（CT）、两年有机轮作（Org2）、三年有机轮作（Org3）以及六年有机轮作（Org6）。各种植系统均已运行至少十年，足以使土壤理化与微生物特性发生由种植系统诱导的特异性改变。非靶向代谢指纹图谱分析共检测到90种化合物，其中绝大多数为酚类物质。靶向代谢分析则聚焦于15种酚类物质、1种植物激素、7种碳水化合物与7种有机酸，并对五种种植系统来源的玉米籽粒中的上述物质完成定量检测。对该定量数据集的统计学分析表明，种植系统可显著影响部分玉米籽粒代谢物的含量水平。但自然环境因素（如生长年份）对代谢物水平的影响显著强于种植系统，或掩盖、甚至抵消了部分种植系统的调控效应。此外，玉米品种的遗传特性对籽粒代谢组的影响亦大于种植系统，是代谢谱特征中影响最大的人为可控因素。本研究结果表明，在尚未明确并管控自然环境对玉米籽粒代谢物水平的影响之前，可靠提升玉米籽粒营养品质的最优途径，是培育营养成分富集且对自然环境胁迫具有较强耐受性的玉米品种。