崇明东滩大型底栖动物食源的稳定同位素示踪

Food Sources of Macrofaunal in East Chongming Salt Marsh as Traced by Stable Isotopes

利用稳定同位素示踪技术,对崇明东滩盐沼湿地夏季不同生境大型底栖动物的食物来源和营养结构进行了初步研究。结果显示,表层沉积有机质稳定碳、氮同位素组成分别在-21.3‰^-24.2‰、4.6‰~5.6‰,不同生境下存在一定差异。植物体各组织的同位素值存在差异,在判别食物来源时需要注意,不能简单地以植物叶片值来代替整个植株。大型底栖动物的1δ3C值为-14.7‰^-23.6‰,表现出食物来源的差异。总体上说,湿地优势植物的活植物体不是大型底栖动物的主要食物来源,沉积有机质是大部分底栖消费者的食物基础。底栖动物的氮同位素能较好地反映其食性和营养级,计算出崇明东滩大型底栖动物营养级在2.0~3.7,为一级消费者和二级消费者。

East Chongming salt marsh,located in the east of Changjiang Estuary, is a large wetland, which exhibits a variety of macrobenthos. Understanding the food sources and trophic level of macrofauna is a foundation to study the material and energy flux in the ecosystem. In this paper, stable carbon and nitrogen isotope ratios of organic matter sources and consumers were inves- tigated in the summer of 2005 in the differents living environments of East Chongming salt marsh. It is found that the δ^13C and δ^15N values of surface sediments vary in different tidal levels, with δ^13C from -21.3‰ to -24.2‰ and δ^15N from 4.6‰ to 5.6‰. These stable isotope values suggest that sediments not only contain the extraneous materials but also are influenced by the autochthonous organic matter. Our data displays that the dominant macrophytes Scirpus mariqueter and Phragraites australis are the main allochthonous sources of sedimentary organic matter and the extraneous source is suspended particulate organic matter. The dominant macrophytes Scirpus mar/queter and Phragmites australis are C3 plants, and Spartina isotopes are variable among different tissues of plants, especially of Phragmites australis, which suggests that care must be taken and the isotope value of leaves may not be used as that of the whole plant when estimating the food sources. The macrofauna shows a wide range of δ^13C, with overall δ^13C values between -23.6‰ and -14.7‰, which suggests significant difference of food sources. As a whole, sedimentary organic matter seems to be food base for macrofauna, while the dominant macrophytes of salt marsh appears to play a negligible trophic role. The nitrogen isotope can reflect the trophic level of macrobenthos. It is calculated that trophic level of macrofauna in East Chongming salt marsh is between 2.0 and 3.7, and thus the invertebrates are primary and secondary consumers.