| 其他摘要 | Since the industrial revolution, human activities have produced a large amount of CO2, leading to intensified global climate change and a series of environmental and social problems. To this end, countries around the world are adopting carbon neutral strategies based on "reducing carbon emissions and enhancing carbon absorption". The country's carbon peaking and carbon neutral targets were set for 2020. To achieve this goal, it is necessary not only to save energy and reduce emissions, but also to play the carbon sink function of the ecosystem. The ocean is the world's largest carbon sink and plays an important role in regulating the climate. Since the industrial revolution, about 48% of the CO2 released by human activities has been absorbed by the ocean, and the ocean carbon pool is 50 times the atmospheric carbon pool and 20 times the terrestrial carbon pool. About 55% of the biological carbon capture on earth is done by marine organisms, including macroalgae, seagrass, salt marsh plants, mangroves, etc. Macroalgae are one of the main contributors to offshore primary productivity. The global macroalgae net primary productivity (NPP) is about 1521 Tg C yr-1, of which 22% of the NPP (355 Tg C yr-1) was exported as dissolved organic carbon (DOC). Of the exported DOC, 33% of the carbon (117 Tg C yr-1) was formed as recalcitrant dissolved organic carbon (RDOC) by the microbial carbon pump (MCP) for long-term storage in the ocean, accounting for 68% of the carbon stored in macroalgae (173 Tg C yr-1). Therefore, the DOC output of macroalgae is one of the important sources of carbon sink of seaweed beds. As a potential member of "blue carbon", macroalgae have not yet formed a unified standard for the assessment of their carbon sink capacity; The current measurement methods of photosynthetic carbon fixation and DOC release also have some disadvantages, such as not considering the effect of flow rate, narrow measurement system and the influence of incomplete algae. In this study, Sargassum thunbergii was used as the research material. The main reasons are as follows: 1. S. thunbergii is widely distributed in the intertidal zone from south to north in my country, and is a typical intertidal macroalgae; 2. To provide a scientifically and feasible method for the accurate assessment of the carbon sink capacity of intertidal seaweed beds. Scientific problems to be solved: 1. To explore the effect of seawater flow rate on DOC release rate of S. thunbergii in the the measurement system of circulating algal carbon fixation capacity; 2. To explore the influence law and mechanism of desiccation on the DOC release of S. thunbergii; 3. To explore the influence law and mechanism of the transient change of temperature, light and salinity on the release of DOC, as well as the influence law and mechanism of the coupling with desiccation on the release of DOC from S. thunbergii. Research contents: 1. The measurement system of circulating algal carbon fixation capacity was improved, and the effects of three flow rates on photosynthetic carbon fixation and DOC release of S. thunbergii were explored; 2. The process of 4 h desiccation and 1 h rehydration of S. thunbergii was simulated, and the effect of desiccation and rehydration on the DOC release of S. thunbergii was explored; 3. The effect of instantaneous change of temperature, light and salinity on DOC release of S. thunbergii was investigated after culture for 20 min under different temperature, light and salinity conditions. In addition, S. thunbergii was dried out for 4 h, and then rehydrated for 20 min under different temperature, light and salinity conditions to explore the effect of the coupling of dry-out with temperature, light and salinity transient changes on the DOC release of S. thunbergii. The main conclusions were as follows: 1. The net photosynthetic rate, NPP and DOC release rates and N and P uptake rates of S. thunbergii increased with the increase of flow rates; The release rate of DOC increased with the increase of net photosynthetic rate and NPP, which was consistent with the photosynthetic product diffusion hypothesis. 2. Drying out for 4 h decreased the effective photochemical yield (Y(II)) and maximum photochemical yield (Fv/Fm) of S. thunbergii, but enhanced non-photochemical quenching (NPQ), which gradually recovered after rehydration; At the beginning of rehydration, the release rate of DOC was the highest, reaching 28.56 mg C g (FW)-1 h-1, and then gradually decreased to 2.87 mg C g (FW)-1 h-1; In the rehydration process, DOC release was a passive release, which might be related to the increase of osmotic pressure, cell membrane damage and carbon accumulation caused by drying out. 3. The DOC release rate of S. thunbergii was influenced by the photosynthetic carbon fixation rate (light intensity), which was consistent with the photosynthetic product diffusion hypothesis and was an active release; Changes in salinity could significantly affect the DOC release rate by affecting osmotic pressure, which was a passive release; The change of temperature had no significant effect on the release rate of DOC; After rehydration after drying out, the DOC release rate was not significantly affected by the light intensity and temperature, but significantly affected by the salinity of seawater, indicating that the DOC release after rehydration after drying out was a passive release. In this study, it was found that the changes of flow rate, desiccation, salinity and light intensity had significant effects on DOC release rate, while temperature had no significant effect on DOC release. We analyzed that the difference in osmotic pressure inside and outside the cell may be the driving force for DOC release, because both the increase in intracellular organic matter concentration (active release) due to increased photosynthesis (higher flow rate and change in light intensity), cell dehydration due to the dry-out process (passive release), and the decrease in extracellular salt concentration (passive release) lead to an increase in the difference in osmotic pressure inside and outside the cell, promoting an increase in the rate of DOC release. The improved measurement system of circulating algal carbon fixation capacity provides a reference for the study of DOC release mechanism of intertidal macroalgae and the carbon fixation capacity of macroalgae, which has certain scientific value and significance. |
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