水稻根系泌氧与根际土壤氧环境互作及其对氮素吸收的影响

How to effectively improve crop's own nitrogen uptake ability and nitrogen use efficiency by some practices while maintaining the appropriate nitrogen fertilizer application? It's one of the effective solutions to alleviate hazard of agricultural non-point source pollution. Our previous study found that high-yield rice variety showed greater root oxygen loss than low-yield one, which increased the content of oxygen dissolved in the rhizosphere soil significantly. This result led to more production of nitrate transformed from ammonium via nitrification in the rhizosphere soil. A new mechanism of "nitrate coexisting with ammonium and nitrate promoting ammonium" in the rhizosphere was proposed. Rice growth and nitrogen use efficiency might be improved due to more nitrate uptake. The feedback effect of rhizosphere oxygen condition on rice root radial oxygen loss and the effect of their interaction on rice nitrogen uptake were neglected in our previous study. Two paddy soils of different oxygen content will be selected to study the interaction of rice root radial oxygen loss and rhizosphere oxygen condition in this project. Meanwhile the influence of aeration through "oxygen fertilizer" application to rice root radial oxygen loss and rhizosphere oxygen condition and the effect of their advantageous interaction on rice nitrogen uptake will also be illuminated. The advanced methods of quick freezing and slicing, oxygen microelectrode and Non-invasive Micro-test are to be used to provide data "in situ", which will directly reflect rice root radial oxygen loss and rhizosphere oxygen condition and their contributions to rice ammonium and nitrate uptake. The research field for this study keeps to the point of "process and regulation of interaction between crop and soil". It also provides new insight into reasonable regulation of redox status in paddy field and promotion of rice nitrogen use efficiency via "improving of nitrogen uptake by aeration".

在适量施用氮肥的前提下，如何挖掘作物本身高效吸收氮素能力或通过一些措施提高氮素利用率是减轻面源污染危害的有效手段之一。我们以往研究发现高产水稻品种根系泌氧量较大，可有效提高根际土壤氧含量，促进根际铵态氮向硝态氮转化，进而形成根际"硝铵共存，以硝促铵"的新机制，最终促进水稻生长及氮素利用率提高。以上研究并未考虑土壤氧环境对泌氧的反馈作用及二者互作对水稻氮素吸收的影响。本项目选择氧气含量差异较大的两种水稻土，研究水稻泌氧与根际氧环境之间互作；同时通过外源增施氧肥研究增氧对水稻泌氧以及根际氧环境的影响，并最终阐明二者互作对水稻吸氮的影响机理。采用土壤速冻切片、氧电极及非损伤微测等先进方法，提供原位数据直观反映水稻泌氧及土壤氧状况，及二者对水稻吸收铵、硝的贡献。本项目研究领域紧扣作物-土壤互作过程与调控主题，为今后合理调控稻田土壤氧化还原状况，以及通过"以氧带氮"来提高氮素利用率提供新的思路。

尽管稻田土壤由于长期淹水导致土壤处于缺氧环境，我们以往的研究发现，水稻根系泌氧可有效提高根际土壤氧含量，促进根际硝化作用，水稻在“增硝”营养下可有效促进生长及氮素吸收利用。然而土壤氧环境也能显著影响水稻根系泌氧，二者互作对水稻氮素吸收的影响是未知的。本项目选择具有不同氧气含量（低氧：高肥力；高氧：低肥力）背景的水稻土，研究根际土壤氧环境对水稻根系泌氧的影响；同时通过外源增施过氧化尿素研究土壤增氧对水稻泌氧的影响，并最终阐明水稻根系泌氧与土壤氧环境互作对水稻氮素营养的影响机理。研究结果表明，尽管高肥力土壤由于有机质含量较高导致土壤氧气含量较低，但水稻种植于高肥力水稻土后，根系径向泌氧屏障发育更加完善从而保证水稻根系内部有更充足的氧气满足水稻生长需求，同时由于根系外部形态及内部通气组织更加发达使得整株水稻径向泌氧能力更强，从而显著提高淹水层及根际土壤氧含量，并导致根际硝化作用更强，促进水稻生长及提高氮素利用率。外源添加过氧化尿素可有效提高土壤及淹水层氧气含量，显著提高根际土壤硝化强度，同时通过刺激侧根发育提高氮素吸收积累，并促进水稻生长。通过“以氧促氮”挖掘作物自身高效吸收氮素能力，可从源头有效控制稻田氮肥投入，增加氮肥利用率。