高臭氧浓度对土壤微量元素生物有效性的影响机制-FACE研究

The average ozone (O3) concentration in the troposphere has dramatically increased during the last century. More recent studies suggested that further globally increase in O3 concentrations is expected, including the parts of China. Influence of elevated tropospheric O3 concentration on ecosystems has become a research hotspot in recent years. Experiments conducted in China have shown that elevated O3 concentrations may lead to wheat and rice losses. The research about soil nutrient cycle under elevated O3 is relatively lacking. Understanding the response of soil nutrient cycle to elevated O3 is the important foundation to assess accurately influence of elevated O3 on the productivity of farmland ecosystem. Based on Ozone Free-air Concentration Enrichment (O3-FACE) system under rice-wheat rotation in Jiangdu County, the objective of this project is to study influence mechanism of elevated atmospheric O3 concentration on the bio-availability of trace elements in farm land soil, combined with two aspects of soil trace element supply and crop absorption. Through the determination of trace elements in the crop, the status of root growth, composition of root exudates, status and distribution of trace elements in soil, soil biological properties including soil microorganisms, soil respiration and soil enzyme activity, and soil chemical properties including soil pH, Eh, dissolved organic C, dissolved CO2 in soil solutions at different stages of plant under rice-wheat rotation, the influence of elevated O3 on forms and bioavailability of trace elements in soil and absorption of rice and wheat will be investigated, and the internal mechanism between bioavailability of trace elements in soil and soil biological properties, soil chemical properties, root exudates, absorption of plant will be explored. The purpose of this project is to reveal the effect of elevated atmospheric O3 concentration on bioavailability of trace elements in soil under rice-wheat rotation from the aspect of soil biogeochemical cycle, to improve the corresponding knowledge of soil and plant nutrition, and to provide the scientific basis for the food developing and security strategies of China.

近地表大气臭氧浓度升高对生态系统的影响近年来已成为研究热点，其中土壤元素循环对臭氧污染的响应是准确评估大气O3浓度升高对农田生态系统生产力影响的重要基础。本项目借助于我国首个建立于典型稻麦轮作生态系统的臭氧FACE试验平台，结合土壤化学、生物学性质和作物吸收、根系分泌物等两个方面，研究臭氧浓度升高对稻麦轮作系统土壤微量元素生物有效性的影响机制。通过测定作物体内微量元素含量、根系生长状况、根系分泌物组成、土壤微量元素生物有效性，土壤呼吸、酶活力和土壤微生物等生物学性质，以及土壤pH、Eh、CO2分压等化学指标，研究大气O3浓度升高对土壤微量元素生物有效性、土壤生物化学性质和对作物吸收微量元素的影响规律，明确其内在关联性机制，从生物地球化学循环的角度揭示土壤微量元素生物有效性对高臭氧浓度的响应特征，从而推进土壤与植物营养学这一领域的理论认识，也为国家制定粮食安全保障策略提供科学依据。

大气臭氧浓度升高作为全球气候变化的重要因素之一，对土壤生态环境和农作物生长发育造成了很大的影响。已有的研究主要集中在臭氧胁迫对作物地上部分的影响，而对地下过程的研究尚少，尤其是土壤生态系统中微量元素生物有效性方面的研究鲜见报道。因此，为明确大气O3浓度升高对土壤微量元素生物有效性的影响机制，本项目利用开顶式熏气室，设置正常大气和臭氧浓度升高（比周围大气高40 nmol·mol-1）处理，结合BCR连续提取法、DTPA提取法和DGT技术评价盆栽稻麦轮作土壤微量元素的生物有效性。研究发现，大气臭氧浓度升高显著降低了稻麦植株的生物量和产量，显著增加了小麦籽粒中Fe、Mn和Cu的含量，降低了Zn的含量。O3浓度升高不同程度地影响了稻麦轮作系统中微量元素的生物有效性，在不同土壤深度、不同作物生育期表现出不同的影响程度。臭氧浓度升高显著提高了麦季根际土壤中DGT-Mn和DGT-Cu 的含量，而显著降低了DGT-Zn的含量。大气臭氧浓度升高提高了稻季土壤中BCR弱酸溶解态和DTPA提取态微量元素Mn和Cu的含量，降低了Fe和Zn的含量。O3浓度升高不同程度地提高了小麦成熟期土壤过氧化氢酶、多酚氧化酶、脱氢酶和转化酶活性，并且显著提高了根际土壤中柠檬酸和苹果酸含量；显著降低了根际土壤pH、电导率、总碳和总氮含量，增加了土壤氧化还原电位（Eh）；显著降低了小麦根系生物量、总根长和根总表面积，而增加了根平均直径。本研究结果表明，O3浓度升高影响了农作物的生长发育, 并通过植物的介导作用影响土壤理化性质的变化，从而影响土壤中微量元素的形态转化及其生物有效性。