高效氮肥和生物炭施用对稻田反硝化与厌氧氨氧化脱氮速率的影响及其机制

Nitrogen fertilizer efficiency of paddy field is very low in our country. Most of activate nitrogen are lost from denitrification and anammox processes. Previous researches have shown that applications of enhanced-efficiency nitrogen fertilizer (such as urease and nitrification inhibitors) and biochar could decrease volatilization and (or) leaching loss, but not necessarily decrease total fertilizer nitrogen loss and enhance the nitrogen use efficiency. The possible reason is that enhanced-efficiency nitrogen fertilizer and biochar increase denitrification or (and) anammox rate(s) more greatly than they decrease volatilization and leaching loss. However, due to the difficulty in denitrification and anammox rate measurements, we could not test this hypothesis. Membrane inlet mass spectrometer method (MIMS), which was imported from the U.S.A., was proved to be precisely measure N2 emission rate from flooded paddy soil by our previous work. Based on this method, we will measure anammox and denitrification rate with 15N-labeled ammonium and nitrate under application of enhanced-efficiency nitrogen fertilizer and biochar in paddy soil. With coupled measurement of volatilization, we could describe the trade-off between the quantities of volatilization and the denitrification loss, consequently evaluate comprehensively whether it could decrease the total loss of fertilizer nitrogen or not under these applications. This study will directly measure the end production of denitrifiation and anammox for the first time, contribute to more insights of the mechanism of fertilizer nitrogen loss and strategies in decreasing nitrogen loss from paddy soil.

我国稻田氮肥利用率依然低下，反硝化和厌氧氨氧化是稻田活化氮损失的主要途径。前期研究表明，高效氮肥（添加了脲酶抑制剂、硝化抑制剂等的氮肥）和生物炭措施能够减少氨挥发和/或淋溶损失，但并不一定能减少氮肥总损失与提高氮肥利用率，可能原因是这些措施在减少以上损失的同时增加了反硝化或（和）厌氧氨氧化脱氮速率。由于方法的限制这一猜想尚未得到验证。我们引进高精度的膜进样质谱法，预实验表明该法可以准确地测定稻田反硝化产物N2的产生速率。本项目以该方法为基础，结合同位素配对技术，研究高效氮肥与生物炭施用对稻田反硝化和厌氧氨氧化速率的影响及机制，同时测定氨挥发速率，验证反硝化、厌氧氨氧化与氨挥发是否存在消长关系，全面评价其是否能稳定减少稻田氮肥的总损失。这一研究将1）有望首次获得高效氮肥与生物炭施用对稻田反硝化和厌氧氨氧化速率影响的直接测定结果；2）有助于加深对稻田脱氮机制的理解与制定合理减少氮肥损失的措施。

反硝化是稻田系统活化氮损失的主要途径。前期研究表明，高效氮肥（脲酶抑制剂、硝化抑制剂等）和生物炭能够减少氨挥发和/或淋溶损失，但并一定能减少氮肥总损失与提高氮肥利用率，可能原因是这些措施在减少以上损失的同时增加了反硝化损失。由于方法的限制这一猜想尚未得到验证。我们引进美国新开发的高精度膜进样质谱法，对乙炔抑制方法测定的结果进行校准，为全面研究稻田淹水和非淹水土壤反硝化提供了方法基础。田间和室内验证结果表明，高效氮肥措施（脲酶抑制剂和硝化抑制剂）都能显著减少稻田土壤反硝化速率，但是各添加量的影响特点不一样。结果发现10%DCD添加量的抑制反硝化和N2O的效率最高，1.5% 和1.0%的NBPT对反硝化和N2O的抑制效果相当。N2/N2O随着DCD添加量的增加而增加，但当NBPT大于1.0%时无显著效果。进一步研究发现，DCD减少了AOA丰度，而NBPT减少了AOB的丰度。通过培养实验和结构方程模型，明确了稻田系统田面水-自然生物膜-沉积物“三相”界面对反硝化的贡献，沉积物对反硝化的贡献远大于上覆水贡献，自然生物膜对反硝化的贡献居于沉积物与上覆水之间。自然生物膜对反硝化不仅有直接影响，而且通过影响上覆水和沉积物的理化性质间接影响反硝化。进一步研究了生物炭和土壤改良剂施用在水稻不同生育期（分蘖期、拔节期、抽穗乳熟期、成熟期）对稻田反硝化速率、氨挥发速率的影响及其作用机制。比较了高效氮肥和生物炭的农业与环境效益。与当地传统施肥相比，生物炭有利于提高和稳定粮食产量。虽然生物炭措施能减少N2O排放，但同时增加了CH4 排放，因而生物炭添加会导致较高的环境成本。然而，硝化抑制剂有利于增加谷物产量和肥料利用率，降低温室气体排放，对农学与环境有双重利好效应。这一研究首次获得了高效氮肥与生物炭措施对稻田反硝化和厌氧氨氧化速率影响的直接测定结果；有助于深入研究稻田脱氮的机制与减少氮肥损失的对策。

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