Top-down and bottom-up control in an eelgrass-epiphyte system
Top-down and bottom-up control in an eelgrass-epiphyte system
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DOI：
10.1111/j.0030-1299.2008.16455.x
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发表时间：
2008-05
期刊：
影响因子：
3.4
通讯作者：
S. Jaschinski;U. Sommer
中科院分区：
文献类型：
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作者：
S. Jaschinski;U. Sommer
营养供应和食草动物的存在可以控制水生生态系统中的初级生产者，但自下而上和自上而下的影响的相对重要性仍然没有定论。我们进行了围隔实验和现场研究，调查的独立和交互作用的影响，营养丰富和放牧的初级生产者在一个鳗草床大叶藻。营养治疗包括环境或丰富的（2倍和4倍环境）浓度的无机氮和磷酸盐。放牧处理包括常见的等足类Idotea baltica的字段密度的存在或不存在。我们发现营养物质和放牧对附生植物的强烈和相互作用的影响。附生植物的生物量和生产力提高营养富集和减少存在的食草动物。在高养分供应下，食草动物消耗的真菌生物量的绝对量增加，因此，在没有放牧的情况下，营养效应更强。食草动物和施肥对真菌组成的影响是拮抗性的：链形成硅藻和丝状藻类受益于营养富集，但它们的比例减少放牧。鳗草生长受到放牧和营养富集在中等营养浓度的积极影响。高养分供应降低了鳗草生产力相比，中度营养条件。每月实测的现场数据显示，在夏季的附生植物和鳗草的氮限制，这可以解释营养富集的初级生产者的积极影响。一般来说，现场数据表明，季节性变化的重要性，自下而上和自上而下的控制，在这个系统的主要生产者的可能性。
Nutrient supply and the presence of grazers can control primary producers in aquatic ecosystems, but the relative importance of bottom-up and top-down effects remains inconclusive. We conducted a mesocosm experiment and a field study to investigate the independent and interactive effects of nutrient enrichment and grazing on primary producers in an eelgrass bed Zostera marina. Nutrient treatments consisted of ambient or enriched (2 x and 4 x ambient) concentrations of inorganic nitrogen and phosphate. Grazer treatments consisted of presence or absence of field densities of the common isopod Idotea baltica. We found strong and interacting effects of nutrients and grazing on epiphytes. Epiphyte biomass and productivity were enhanced by nutrient enrichment and decreased in the presence of grazers. The absolute amount of epiphyte biomass consumed by grazers increased under high nutrient supply, and thus, nutrient effects were stronger in the absence of grazing. The effects of grazers and fertilisation on epiphyte composition were antagonistic: chain-forming diatoms and filamentous algae profited from nutrient enrichment, but their proportions were reduced by grazing. Eelgrass growth was positively affected by grazing and by nutrient enrichment at moderate nutrient concentrations. High nutrient supply reduced eelgrass productivity compared to moderate nutrient conditions. The monthly measured field data showed a nitrogen limitation for epiphytes and eelgrass in summer, which may explain the positive effect of nutrient enrichment on both primary producers. Generally, the field data suggested the possibility of seasonally varying importance of bottom-up and top-down control on primary producers in this eelgrass system.