近地层臭氧浓度升高对麦田土壤氧化亚氮排放的影响机制

The impact of surface ozone (O3) pollution on plant growth is one of the hottest issues in recent years. However, the mechanisms of O3 effect on below-ground processes, particularly on the soil nitrous oxide (N2O, important greenhouse gas) emission are poorly understood. In this study, winter wheat fields will be exposed to different O3 concentrations in a set of open-top chambers. The temporal features of soil N2O emissions under various O3 levels will be evaluated. The responses of different N2O-generating processes to O3 will be analyzed using a 15N incubation test on undistributed soil columns. Two routes by which the O3 influence soil N2O emission will be revealed: (1) O3 –photosynthate partition – root exudate – soil microbial ecology, and (2) O3 – leaf area index/evapotranspiration – soil hydraulic/thermal dynamics. Finally, a process-based model will be established to explain the response of soil N2O emission flux to stomatal phytotoxic O3 dose. The objective of this research is to investigate the influencing mechanisms of O3 on soil N2O emission, systematically and quantificationally. This work could provide (1) an efficient tool for estimating and predicting N2O emission from wheat field, (2) a scientific basis for comprehensive understanding the effect of O3 on ecosystems, and (3) a theoretical basis for objectively evaluating regional and global climate change.

近地层臭氧（O3）污染对植物生长的影响是近年来的研究热点之一，但有关O3对生态系统地下过程，尤其是对土壤氧化亚氮（N2O，重要温室气体）排放的影响机制仍未明晰。本研究拟选择冬小麦田为对象，利用开顶式气室开展田间原位O3熏蒸实验，观察不同O3浓度下土壤N2O的排放特征；结合室内原状土15N培养实验，分析N2O产生的各微生物过程对O3浓度升高的响应；分别从“O3–光合产物分配–根系分泌物–土壤微生态”和“O3–叶面积指数/蒸发蒸腾–土壤水热动态”两方面，阐述O3污染影响麦田土壤N2O排放的途经；建立土壤N2O排放通量对小麦气孔O3毒性吸收剂量的响应机理模型，系统、定量地揭示O3对土壤N2O排放的影响机制；为准确估算和预测O3浓度升高情景下麦田土壤N2O排放量提供有效方法，为全面认识O3对生态系统的影响提供科学依据，为客观评价区域和全球气候变化提供理论基础。

近地层臭氧浓度升高可影响植物根系生长和根系分泌物的组成，进而通过植物介导影响土壤生态系统。本研究分析了近地层臭氧浓度升高如何影响麦田土壤N2O排放。以冬小麦（Triticum aestivum L.）农田为研究对象，采用开顶箱气室开展了连续两个生长季的野外实验研究。采用静态箱-气相色谱法监测土壤CO2和N2O释放量。取根际土，分析了溶解性有机碳（DOC）、铵态氮（NH4+-N）、硝态氮（NO3--N）、微生物生物量碳（MBC）、微生物生物量氮（MBN）含量。测定了硝酸盐还原酶（NR）、亚硝酸盐还原酶（NiR）、羟胺还原酶（HR）的活性。此外，观测了实验期间土壤含水量和植株生物量的动态变化。研究发现，近地层臭氧浓度升高能够显著抑制冬小麦田土壤CO2释放，但促进土壤N2O释放。臭氧浓度升高是的土壤NH4+-N和NO3--N含量增加，NR和NiR酶活性增强，但是DOC、MBC和MBN含量降低，HR酶活性受到一定程度的抑制。在臭氧熏蒸条件下，植物蒸腾速率减弱，土壤含水量较对照下降较慢。根系生物量以及土壤有机碳源量的减少是近地层臭氧浓度升高抑制土壤CO2排放的可能原因。而在臭氧浓度升高条件下，由于矿质氮源含量增加和土壤含水量增大，从而引起反硝化活性增强，进而引起土壤N2O排放速率增加。本研究所获结果可以为准确预测O3浓度升高情景下，植物生长和农田土壤N2O排放特征和规律提供科学依据，为准确计算O3和N2O的大气收支情况提供理论基础，对于客观评价区域和全球气候变化状况具有重要意义。