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近海养殖区沉积物固氮及氧化亚氮源汇过程对季节性低氧的响应探究
Alternative TitleInvestigation on the Response of Sediment Nitrogen Fixation and Nitrous Oxide Source-Sink Processes to Seasonal Hypoxia in Nearshore Mariculture Zone
尧诚
Subtype硕士
Thesis Advisor张晓黎
2023-05-28
Training institution中国科学院烟台海岸带研究所
Degree Grantor中国科学院大学
Place of Conferral中国科学院烟台海岸带研究所
Degree Name理学硕士
Degree Discipline海洋生物学
Keyword近海养殖区 季节性低氧 固氮 氧化亚氮释放 宏转录组
Abstract近海养殖业对保障国家食品安全、满足居民膳食营养结构多元化需求、稳定和促进沿海地区经济发展有重要作用。海水养殖活动中大量营养物质的输入易引起近海水体发生季节性低氧,破坏生态稳定性,影响生源要素的生物地球化学循环。固氮过程是近海生态系统氮输入的重要途径;氧化亚氮(N2O)是一种具有显著增温效应的温室气体,对全球气候变化具有重要影响,且其释放也是近海生态系统中氮输出的重要途径。然而,人们对近海固氮过程和N2O源汇过程对季节性低氧的响应机制仍知之甚少,低氧区对整个海洋生态系统氮通量的贡献以及沉积物中相关过程微生物类群随季节性低氧发展的动态变化也有待探究。在海洋低氧面积扩大、持续时间增长以及全球气候剧烈变化的大背景下,探究近海生态系统氮循环过程对低氧的响应机制对维持海洋生态环境平衡具有重要的参考意义。 本文以烟台近海养殖区为研究对象,利用氮同位素标记、功能基因定量和组学技术,结合原位测定与微宇宙构建,围绕养殖区沉积物固氮过程、氧化亚氮源汇过程对季节性低氧的响应机制开展研究,以期为缺氧对海岸带生态功能影响的生态学评估提供参考,为温室气体N2O的减排提供科学依据。主要研究结果如下: (1)烟台近海养殖区沉积物固氮速率介于0.013-10.199 μmol kg-1 h-1之间,受季节性低氧影响显著(ANOVA,p < 0.05)。此外,固氮活性还与底层水叶绿素a(Chl-a)浓度、pH值以及沉积物孔隙水铵盐浓度显著相关(p < 0.05)。Geobacteraceae(地杆菌科,63.95%)(铁还原微生物)是近海养殖区沉积物中的优势固氮菌,且当缺氧发生时,铁还原细菌可能联合硫酸盐还原细菌实现最大的固氮效率。另外,固氮微生物的丰度和群落结构受沉积物中总有机碳(TOC)、总氮和铁含量(Fe(III))影响显著。 (2)季节性低氧期间,烟台近海水体N2O处于过饱和状态(最高可达226%)。严重缺氧(8月份)期间,DO最低的S8站位(1.84 mg L-1)具有显著高的N2O净释放速率(2.83 μmol m-2 h-1),且回归分析表明沉积物N2O释放速率与DO显著负相关(p < 0.05)。qPCR结果显示,低氧发生时,沉积物亚硝酸盐还原酶基因nirS和氧化亚氮还原酶基因nosZ丰度显著升高,且nosZ基因表达量高出nosZII一个数量级,古菌氨单加氧酶基因amoA的表达量高于细菌。低氧发生前(6月),表层沉积物中转录本主要来自Bacillariophyta(硅藻门,41.9%),随着低氧的发生逐渐演替为以Proteobacteria(变形菌门,33.85%)和Desulfobacterota(脱硫杆菌门,22.85%)为主。Thermoproteota(泉古菌门)和Desulfobacterota(脱硫杆菌门)分别是养殖区低氧沉积物N2O硝化和反硝化“源”的主要驱动者。来自Proteobacteria的nosZ型微生物则主要驱动N2O的“汇”。 (3)在DO梯度模拟培养过程中,所有DO浓度处理组均在2 h时达到N2O的释放峰值,铵盐和硝酸盐均在前2 h内迅速消耗,表明微宇宙体系在2 h内迅速完成了N2O的积累。外源添加氨氮和硝态氮时,沉积物释放N2O的潜力分别提升了3倍和30倍。qPCR结果显示,N2O累积过程中(0-2 h),nirS基因丰度迅速升高,而在N2O消耗的过程中(2-24h),nosZ和nosZⅡ基因丰度明显升高。宏转录组分析结果表明,所有样品中Proteobacteria(49.99%)和Desulfobacterota(20.44%)占主导;推测氨氧化过程可能由Thermoproteota主导,反硝化过程可能由Proteobacteria主导。
Other AbstractThe nearshore mariculture industry plays a significant role in ensuring national food security, meeting the diversified dietary needs of the population, and stabilizing and promoting economic development in coastal areas. The intensive input of nutrients from mariculture has the potential to cause seasonal hypoxia in coastal waters, which can destroy ecological stability and affect the biogeochemical cycling of biogenic elements. Nitrogen fixation is important processes for N-input in coastal ecosystems. Nitrous oxide (N2O) is a greenhouse gas that has an important impact on global climate change because of its significant warming effect. N2O emission also serves as an important pathway for N-output in coastal ecosystems. However, the mechanisms of nitrogen fixation and the source-sink processes of N2O in response to seasonal hypoxia are still poorly understood. The contribution of the hypoxic area to the nitrogen flux of the entire marine system and the dynamic changes of microbial communities in related sediment processes with the development of seasonal hypoxia remain to be explored. Given the prolonged expansion of marine hypoxia areas and the rapid and drastic changes in global climate, it is of great significance to investigate the response mechanism of N-input and N-removal to hypoxia in coastal ecosystems in order to maintain the balance of the marine ecological environment. In this study, we investigated the response mechanisms of nitrogen fixation and nitrous oxide source-sink processes to seasonal hypoxia in the nearshore mariculture zone of Yantai City using nitrogen isotope labeling, functional gene quantification, and omics techniques, in combination with in-situ sample determination and microcosms construction. The aim of this study is to provide references for the ecological assessment of the impact of hypoxia on the ecological function of the coastal zone and a scientific basis for the reduction of greenhouse gas N2O emissions. The main research findings are presented as follows: (1) In the nearshore mariculture zone of Yantai City, the benthic nitrogen fixation rate ranged from 0.013 to 10.199 μmol kg-1 h-1 and was significantly affected by seasonal hypoxia (ANOVA, p < 0.05). Besides, nitrogen-fixing activity was also significantly correlated with pH, the concentration of Chl-a in the bottom water, and the concentration of NH4+ in the sediment pore water (p < 0.05). Geobacteraceae (63.95%, iron-reducing bacteria) was the most dominant nitrogen-fixing bacteria in nearshore mariculture zone sediments. When hypoxia occurs, the iron-reducing bacteria might collaborate with sulfate-reducing bacteria to achieve the maximum nitrogen-fixing efficiency. Additionally, the abundance and community structure of nitrogen-fixing microorganisms were significantly affected by the total organic carbon (TOC), total nitrogen (TN), and iron contents (Fe (III)) of sediments. (2) During seasonal hypoxia, N2O was found to be in a supersaturated state in the offshore water column of Yantai City (up to 226%). Under severe hypoxia (August), Station S8 (with a lowest DO, 1.84 mg L-1) had a significantly high net N2O emission potential (2.83 μmol m-2 h-1), and regression analysis indicated that the N2O emission rate from sediments was significantly and negatively correlated with DO (p < 0.05). The qPCR results indicated a significant increase of nirS (nitrite reductase gene) and nosZ (nitrous oxide reductase gene) gene abundance in sediment under hypoxic condition, and nosZ transcription abundance being one order of magnitude higher than that of nosZII gene. The archaea amoA (ammonia monooxygenase gene) transcription abundance was also higher than that from bacteria. Before hypoxia (June), the majority of transcripts in surface sediments were derived from Bacillariophyta (41.9%), and it gradually evolved into a community dominated by Proteobacteria (33.85%) and Desulfobacterota (22.85%) with the occurrence of hypoxia. Thermoproteota and Desulfobacterota are the primary drivers of N2O production and reduction, respectively, in the hypoxic sediments of nearshore mariculture zone. Meanwhile, microorganisms harboring the nosZ gene from Proteobacteria primarily act as the sinks for N2O. (3) During the DO gradient microcosms simulation incubation, the peak value of N2O emission was reached at 2 h in all treatment groups with DO concentration. The rapid consumption of ammonium and nitrate in the first 2 h indicated that the micro-cosmic system completed the accumulation of N2O rapidly in 2 h. The addition of exogenous ammonium and nitrate increased the potential of sediment to release N2O by 3 and 30 times, respectively. Based on the qPCR results, it was observed that during the process of N2O accumulation (0-2 h), there was a significant increase in nirS gene abundance, whereas during N2O consumption (2-24 h), a notable increase in nosZ and nosZⅡ gene abundance was observed. The metatranscriptomic analysis revealed that Proteobacteria (49.99%) and Desulfobacterota (20.44%) were dominant in all samples. It was speculated that the ammonia oxidation might be dominated by Thermoproteota, and the denitrification might be dominated by Proteobacteria.
Pages101
Language中文
Document Type学位论文
Identifierhttp://ir.yic.ac.cn/handle/133337/32031
Collection中国科学院烟台海岸带研究所知识产出_学位论文
Recommended Citation
GB/T 7714
尧诚. 近海养殖区沉积物固氮及氧化亚氮源汇过程对季节性低氧的响应探究[D]. 中国科学院烟台海岸带研究所. 中国科学院大学,2023.
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