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| 浒苔降解过程中颗粒有机碳、氮释放及相关微生物种群丰度变化研究 |
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赵苗苗1,2, 毕蓉1,2, 李鸿妹3, 宋欣荣1, 黄圣荣3,4, 冯秀婷3, 张海龙1,5, 李莉1,2, 赵美训1,5
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1.中国海洋大学 深海圈层与地球系统前沿科学中心 海洋化学理论与工程技术教育部重点实验室
山东 青岛 266100;2.青岛海洋科技中心海洋生态与环境科学功能实验室 山东 青岛 266237;3.中国科学院青岛生物能源与过程研究所 中国科学院生物燃料重点实验室
山东省能源生物遗传资源重点实验室 山东 青岛 266101;4.中国海洋大学化学化工学院 海洋化学理论与工程技术教育部重点实验室 山东 青岛 266100;5.崂山实验室 山东 青岛 266237
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| 摘要: |
| 我国黄海海域已连续18年暴发浒苔(Ulva prolifera)绿潮，数百万吨浒苔在绿潮消亡阶段沉降入海并向海水中释放大量有机质。目前，对于量化浒苔降解过程中颗粒有机碳(particulate organic carbon, POC)、颗粒有机氮(particulate organic nitrogen, PON)的释放及其微生物调控机制的相关研究亟待开展。本研究选择浒苔为对象，设置2种降解密度(1 g/L、5 g/L)，研究90 d降解过程中的POC和PON浓度、POC︰PON及微生物丰度的变化特征，并探究微生物丰度与POC、PON浓度及其比值的相关关系。结果显示，90 d降解过程中POC浓度[1 g/L与5 g/L处理组峰值分别为(90.17±24.77)和(219.99±45.11) μmol/L]、PON浓度[1 g/L与5 g/L处理组峰值分别为(16.15±0.71)和(23.20±7.16) μmol/L]变化显著。POC、PON浓度随时间变化规律不同：前60 d，POC和PON浓度均先上升后下降；第60~90天，POC浓度持续下降约49%，而PON浓度上升约430%。浒苔降解初期POC︰PON升高，表明此时氮的释放滞后于碳；随后，POC︰PON下降，与微生物对氮的固定以及呼吸作用消耗碳有关。微生物丰度与POC、PON浓度显著相关，表明微生物对浒苔降解过程中POC、PON释放具有重要作用。降解密度对POC、PON浓度有显著影响，5 g/L处理组POC、PON浓度约为1 g/L处理组的2~3倍，且5 g/L处理组达到峰值所需时间较长。本研究厘清了浒苔降解过程中POC、PON的释放特征，明确了微生物丰度变化与POC、PON含量及二者比值变化的关系，为深入探究浒苔降解过程中微生物对POC、PON释放的调控机制以及POC、PON降解机制提供了研究基础。 |
| 关键词: 浒苔降解 降解密度 微生物丰度 颗粒有机碳 颗粒有机氮 |
| DOI：10.19663/j.issn2095-9869.20231117002 |
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| 基金项目:崂山实验室科技创新项目(LSKJ202204005)资助 |
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| Release dynamics of particulate organic carbon and nitrogen and the related microbial abundance variation during degradation of Ulva prolifera |
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ZHAO Miaomiao1,2, BI Rong1,2, LI Hongmei3, SONG Xinrong1, HUANG Shengrong3,4, FENG Xiuting3, ZHANG Hailong1,5, LI Li1,2, ZHAO Meixun1,5
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1.Frontiers Science Center for Deep Ocean Multispheres and Earth System, Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China;2.Laboratory for Marine Ecology and Environmental Science, Qingdao Marine Science and Technology Center, Qingdao 266237, China;3.Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics,
Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China;4.Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and
Chemical Engineering, Ocean University of China, Qingdao 266100, China;5.Laoshan Laboratory, Qingdao 266237, China
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| Abstract: |
| Green tides, dominated by Ulva prolifera, have occurred each summer in the Yellow Sea of China from 2007 to 2023 and are characterized by a huge biomass, long duration, and extensive influence areas. During the post-bloom period, millions of tons of U. prolifera settle to the sea floor and release carbon, nitrogen, and phosphorus into the surrounding waters, notably impacting coastal environments. Organic matter released from macroalgae are important contributors to biogeochemical cycles in marine ecosystems. Particulate organic carbon (POC) is an important fraction of the marine organic carbon pool and is crucial in the marine carbon cycle by regulating dissolved organic carbon (DOC); sediment organic carbon; and inorganic carbon via deposition, degradation, and mineralization. Additionally, the ratio of POC and particulate organic nitrogen (PON) affects the sea-air CO2 flux and the efficiency of carbon sequestration. Till date, POC and PON released during the degradation of U. prolifera remain poorly quantified and microbial regulations of POC and PON release remain unclear. We investigated the changes in POC and PON concentrations and their molar ratios, and microbial abundance under different degradation densities (1 g/L and 5 g/L) during a 90-d laboratory degradation of U. prolifera. Under dark conditions, 50 g and 250 g (fresh weight) of U. prolifera were added to polyethylene carboys containing 50 L filtered seawater to conduct 1 g/L and 5 g/L degradation experiments. Triplicate replicates were performed for each treatment. Samples for analyzing POC, PON, and microbial abundance were collected on days 0, 4, 6, 8, 14, 21, 28, 60, and 90. The results showed that the degradation period of U. prolifera was divided into the leaching stage (0–14 d), during which soluble materials were lost, and the microbial degradation stage (14–90 d), during which the debris was digested by bacterial or fungal extracellular enzymes. The POC, the maximal values: (90.17±24.77) μmol/L and (219.99±45.11) μmol/L under 1 g/L and 5 g/L, respectively, and PON, the maximal values: (16.15±0.71) μmol/L and (23.20±7.16) μmol/L under 1 g/L and 5 g/L, respectively, concentrations changed significantly during degradation, however, showed different trends. Specifically, the POC and PON concentrations first increased and then decreased during days 0–60; however, POC continued to decrease (approximately 49%) and PON increased (approximately 430%) during days 60–90. The decrease in POC concentrations can be explained by the conversion of POC to DOC by macroalgae-associated microbes and subsequently, DOC was mineralized into dissolved inorganic carbon. The enrichment of nitrogen due to bacterial colonization of particle surfaces may largely explain the increase in PON concentrations. POC:PON first increased and then decreased, indicating that PON showed a lagged release compared to POC when U. prolifera began to degrade, and the subsequent decline of POC:PON can be attributed to nitrogen fixation by microbial and carbon consumption via respiration. Microbial abundance increased during days 0–28, the maximal values: (9.81±3.81)×105 and (26.24±6.98)×105 cells/mL under 1 g/L and 5 g/L, respectively, indicating that the released organic matter was utilized and transformed into microbial biomass. The microbial abundance then decreased during days 28–90. This change may be explained by the decrease in organic matter contents and bioavailability, and the contents of organic matter were deficient for microbial growth, leading to the decrease in microbial abundance. Microbial abundance showed significant correlations with the POC and PON concentrations, indicating the critical roles of microbes in the release of POC and PON during the degradation of U. prolifera. No significant correlations were observed between the microbial abundance and POC:PON. Microbial regulations of POC and PON release during the degradation of U. prolifera are complex and further studies on microbial community structure may help to explore the role of microbes in the release of POC and PON. Degradation density significantly impacted POC and PON concentrations. At the high degradation-density treatment, we observed slow changes in POC and PON concentrations and 2–3 times higher maximal concentrations of the two compared to those at lower degradation-density conditions. We observed that the higher the degradation density, the longer the leaching phase of organic matter. However, POC and PON concentrations did not change proportionally with degradation density. This result may be attributed to the changes in other factors such as pH, dissolved oxygen, and initial nutrient concentrations. The changes in POC and PON concentrations at the end of degradation suggested that more extensive studies are necessary to elucidate the long-term relationship between U. prolifera degradation and microbial communities. Our study provides an important basis for clarifying the changes in POC and PON and their correlations with microbial abundance during the degradation of U. prolifera. This helps to generate a better understanding of the regulation and mechanisms of microbes on U. prolifera degradation. |
| Key words: Ulva prolifera degradation Degradation density Microbial abundance Particulate organic carbon Particulate organic nitrogen |
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