基于营养盐调控的半叶马尾藻与浒苔的氮竞争机制研究

Reproduction and growth of fouling algae is one of main reasons on death and abscission of Sargassum seedlings in artificial culture. The studies on prevention and cure of fouling alga were focused on physical or chemical processes, but few were on ecological method. It has been reported that an interspecific difference in nutrient demand of macroalgae. Competitive abilities of macroalgae in co-culture were changed with nutrients. Macroalgae those are sensitive to nutrients give way to the insensitive ones. This project will focus on Sargassum hemiphyllum and its fouling algae Ulva prolifera. Uptake rate of two species of macroalgae in co-culture will be determined using stable isotope 15N tracer technique to study the competitive uptake of the single nitrogen species and the preferential uptake of the various nitrogen species by the two macroalgae. Combined with the long-term experiments, nitrogen pools of thalli will be measured to analysis nitrogen transforming rules in thalli and discuss the effect of nutrients on the physiological processes of nitrogen competitive metabolism. Weights and chlorophyll fluorescence parameters will be determined to analysis the growth and photosynthesis of macroalgae and their correlations with nutrients, and illustrate the competitive characteristics of macroalgae for nitrogen requirement in different nutrients. This study will reveal nutrient for selective action in co-culture from nitrogen competition angle. The conclusion will provide the basis for evaluating the feasibility on prevention and cure of fouling alga by regulating nutrients in water.

杂藻繁生是造成马尾藻幼苗死亡、脱落的主要原因之一。防治杂藻的研究多集中在物理和化学方法，而对生态方法的研究较少。已有研究表明，海藻对营养盐的需求存在种间差异，营养盐的变化可改变共培海藻的竞争能力，对营养盐胁迫敏感的种类让位于不敏感的种类。本研究以半叶马尾藻Sargassum hemiphyllum及其杂藻浒苔Ulva prolifera为研究对象，采用共培方法，利用稳定同位素15N示踪技术测定不同营养环境下海藻对N的吸收速率，研究海藻对单一N源的竞争吸收及对多种N源的选择吸收特性；结合长周期实验，测定海藻各氮库含量，分析氮在藻体内的转化规律，探讨营养盐对海藻的N竞争代谢的影响；测定海藻重量和叶绿素荧光参数，研究藻体生长和光合作用与营养盐间的相关性，阐明海藻在不同营养环境下对N需求的竞争特性。旨在从氮竞争角度揭示营养盐在共培海藻中的“选择”作用，为评估营养盐调控方法防治杂藻的可行性提供依据。

本项目拟对海藻间竞争关系进行研究，回答“营养环境在半叶马尾藻和浒苔共同培养过程中扮演何种选择的角色？”这一科学问题。项目申请书和计划任务书拟只针对半叶马尾藻与浒苔的共培养体系开展研究，但本项目在实验实施过程中发现单培半叶马尾藻和单培浒苔是重要的对照组，可用来对比分析共培体系中的两藻是否受到促进或抑制，因此本项目对研究内容进行了扩展，增加了半叶马尾藻单培和浒苔的单培实验。通过室内模拟不同N营养条件研究半叶马尾藻幼苗的生长速率和藻体生理生化指标的变化，阐明营养盐环境可调节海藻Ｎ源积累利用过程，探索适合半叶马尾藻幼苗生长的营养环境；采用单培和共培相结合方法，利用传统生理生态学和稳定同位素15N示踪技术测定不同营养环境下海藻对N的吸收速率，在低浓度≤10 μM NO3-、NH4+环境下，两藻间出现N竞争吸收现象，共培可提高半叶马尾藻对N源亲和力，吸收能力强于浒苔，而在高浓度＞10 μM NO3-环境下，化感作用限制了两藻对NO3-的吸收速率，但是浒苔对NO3-吸收速率仍高于半叶马尾藻；结合长周期实验，通过测定单培和共培体系中半叶马尾藻和浒苔的生长速率和藻体组织Ｎ含量发现，低浓度NO3-、NH4+环境下，浒苔N含量低于其N需求，比半叶马尾藻更易受到N限制，浒苔生长被半叶马尾藻抑制，抑制率在低浓度NO3-下比低浓度NH4+下要高，同时未添加N营养盐的对照组半叶马尾藻的生长速率显著低于5-10 μM NO3-，因此，培养水体NO3-浓度维持在5-10 μM范围内，可有效促进半叶马尾藻对N吸收、N积累和N利用，为室内幼苗顺利度夏培育提供保障。综上，本研究发现不同N源和N浓度对半叶马尾藻和浒苔的N吸收利用具有重要影响，营养条件可改变两藻间的N竞争机制。本项目成果初步揭示了营养盐调控共培体系中半叶马尾藻和浒苔的竞争能力，为防治杂藻繁生提供了新的方法和理论依据。