油菜秸秆翻埋还田后有机酸释放对水稻秧苗毒害的酶学机制

Incorporation of oilseed rape straw into paddy soil is an important pattern of straw management in Sichuan oilseed rape-rice double cropping region, which can avoid air pollution by straw burning and facilitate mechanical operation. However, oilseed rape straw addition to paddies could induce toxicity on rice seedlings, which has become the bottleneck for the extension of this straw-return technique. Previous study has identified that the accumulation of various organic acids in soil after straw incorporation might be the principal factor which leads to plant toxicity. However, current literature has not well documented the releasing rules of organic acids after straw incorporation and the mechanism of organic acid toxicity on rice seedlings is unclear. By conducting both laboratory and field experiments, this study aims to firstly quantify the accumulation of small molecular organic acids and phenolic acids in the paddy soil after oilseed rape straw incorporation, and secondly explore the relationship between the activity of the key enzymes for vital physiological/biochemical process (such as antioxidative defense, root activity, nitrogen metabolism and photosynthesis) and agronomic traits of rice seedlings. The study is supposed to illustrate the enzymatic mechanism of organic acid toxicity on rice seedling and the conclusions can provide theoretical basis for crop straw management and safety rice cultivation for the Sichuan oilseed rape-rice double cropping region.

油菜秸秆翻埋还田是四川油-稻两熟区减少大气污染、便于机械操作的秸秆利用重要方式。但是，油菜秸秆翻埋还田容易引起后茬水稻僵苗的问题成为该技术推广的瓶颈。前期研究表明秸秆腐解释放的有机酸可能是秧苗受毒害进而发生僵苗的重要因素，然而目前关于油菜秸秆翻埋还田后有机酸的释放规律及其对秧苗的毒害机理尚缺乏深入研究。本项目将通过室内试验与大田试验相互验证，定量研究油菜秸秆翻埋还田后小分子有机酸与酚酸类物质的释放规律，解析有机酸胁迫下水稻秧苗抗氧化保护、根系活力、氮素同化及光合作用等重要生理生化过程关键酶的活性变化及其与农艺性状变化的关系。研究以期阐明油菜秸秆翻埋还田后有机酸毒害水稻秧苗的酶学机制，为四川油-稻两熟区油菜秸秆科学还田以及制定合理的水稻栽培措施提供理论依据。

油菜秸秆翻埋还田是四川“油-稻”两熟区减少大气污染、便于机械操作的秸秆利用重要方式。前期研究表明油菜秸秆腐解释放的有机酸可能是水稻秧苗受毒害进而发生僵苗的重要因素，然而目前关于油菜秸秆翻埋还田后有机酸释与秧苗受毒害的关系尚缺乏深入研究。本研究探究了油菜秸秆翻埋还田条件下土壤水溶液中小分子有机酸的消长规律，并分析了有机酸消长与水稻秧苗重要生理生化过程关键酶的活性及农艺性状变化的关系。主要要点如下：1）量化了油菜秸秆翻埋还田后土壤水溶液中小分子有机酸消长规律；2）摸清了秸秆翻埋还田后水稻重要生理生化过程关键酶活性与农艺性状的变化；3）掌握了小分子有机酸对水稻秧苗毒害的临界浓度值；4）分析了油菜秸秆翻埋还田后有机酸消长与水稻秧苗受毒害的关系。结果表明：油菜秸秆翻埋还田显著增加了稻田土壤小分子有机酸含量，抑制了水稻根系生长、诱导提高了叶片SOD、POD、NR和GS酶的活性；各小分子有机酸均表现出低浓度促进而高浓度抑制水稻生长的现象，然而，大田试验所测小分子酸浓度普遍低于临界值，只有当秸秆不均匀还田时，秸秆量较高的地块才会出现有机酸毒害秧苗的情况。因此，在四川盆地“油-稻”两熟区，油菜秸秆翻埋应避免还田不均造成有机酸毒害的现象。