Evidence of grazer control on nitrogen fixation by eelgrass epiphytes in a temperate coastal bay
Evidence of grazer control on nitrogen fixation by eelgrass epiphytes in a temperate coastal bay
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温带沿海海湾放牧者控制鳗草附生植物固氮的证据
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
R. Howarth
中科院分区：
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作者：
Laura K. Reynolds;Roxanne Marino;M. Muth;Natalie A. McLenaghan;M. Hayn;A. C. Tyler;K. McGlathery;R. Howarth
在本研究中，我们提供的数据支持这样的假设，即食草动物对附生植物的去除是温带海草草甸夏季固氮的重要控制因素。之前在美国马萨诸塞州西法尔茅斯港的研究发现，在氮负荷最大、磷酸盐浓度最低的部分港口（Snug Harbor）附生固氮率最高，这一结果有些矛盾，表明生物地球化学控制不是调节这种固氮的主要因素。在固氮率最高的Snug Harbor，无脊椎食草动物对附生藻类（主要是Bittiolum alternatum）的密度最小。反向移栽试验表明，从外源氮负荷较低但食草动物密度高4倍的外源港（Outer Harbor）移栽到Snug Harbor的海草芽，经过12 d的培养，附生固氮量增加了5倍以上。从Snug Harbor移栽到Outer Harbor的芽在6 d后，附生植物固氮率迅速下降，这可能是由于附生植物的消耗。我们的研究结果表明，营养控制是温带海草草甸附生固氮速率的潜在重要决定因素。
: In this study, we present data to support the hypothesis that removal of epiphytes by grazers is an important control of nitrogen fixation in temperate seagrass meadows during the summer. Previous work in West Falmouth Harbor, Massachusetts, USA, found highest rates of epiphytic nitrogen fixation in the part of the harbor (Snug Harbor) with the greatest nitrogen load and the lowest phosphate concentrations, a somewhat paradoxical result suggesting that biogeochemical controls are not the major factor regulating this nitrogen fixation. Here we report that the density of invertebrate grazers on epiphytic algae (predominantly Bittiolum alternatum) was least in Snug Harbor, where nitrogen fixation rates were greatest. Reciprocal transplant experiments showed that seagrass shoots transplanted into Snug Harbor from the part of the harbor (Outer Harbor) where external nitrogen loading was lower but grazer densities were 4-fold higher, had a more than 5-fold increase in epiphytic nitrogen fixation after a 12 d incubation period. Shoots transplanted from Snug Harbor to Outer Harbor showed a large, rapid reduction in epiphytic nitrogen fixation rates after only 6 d, likely due to consumption of epiphytes. Our results suggest that trophic control is a potentially important determinant of epiphytic nitrogen fixation rates in temperate seagrass meadows.