优势种去除对崇明东滩盐沼湿地生态系统的影响

盐沼生态系统环境梯度明显,物种组成较简单,是研究生物多样性与生态系统功能关系的理想对象。本研究以崇明东滩盐沼湿地为研究区域,研究优势种去除对植物群落结构以及底栖动物群落的影响。结果表明:(1)去除处理仅对植物群落分株密度有极显著效应(P0.01)。去除组和对照组物种组成差异随时间增加而减小,处理效应逐渐减弱。(2)去除组底栖动物密度均低于对照组,但差异不显著。(3)盐沼植物群落特征与底栖动物群落有密切关系,植物密度、冠层高度与底栖动物密度相关性极显著。去除优势种后,植物群落分株密度升高,群落内剩余物种占比有所上升,次优势种对群落的补偿效应具有较大贡献;而底栖动物群落密度下降,其生物量和多样性指数的变化趋势与密度并不一致。上述结果表明生物多样性变化影响了盐沼湿地生态系统植物群落和底栖动物群落结构,进而可能影响物质循环和能量流动过程。

Effects of dominant species removal on salt marsh ecosystem in Chongming Dongtan

The salt marsh ecosystem is considered ideal for studying the biodiversity-ecosystem functioning relationship(BEF) because of its steep environmental gradients and relatively few plant species. The salt marsh ecosystem is one of the ecosystems most affected by anthropogenic activities, which has drawn our attention to the need to protect and restore it intensively. The current research studies on BEF are mostly focused on grasslands ecosystems rather than salt marshes. The understanding of how the removal of specific species or functional groups would influence the structure and functioning of salt marsh ecosystems is still lacking. Therefore, this study, which was performed at Chongming Dongtan in the Yangtze estuary, examined the effects of dominant species removal on plant community structure and macrobenthic invertebrate communities. We also analyzed the relationship between plant community attributes and macrobenthic invertebrate communities using linear regression. The aim of the study was to provide a scientific basis for wetland restoration. The major findings of this study are as follows (1) Community type, season and their interaction had significant effects on the ramet density and canopy height of manipulated plant communities(P<0.01), whereas the removal treatment had significant effects on the ramet density only(P<0.01). Ramet density in species removal treatment was higher than that in the control treatment was, but the effect was not significant. The differences in species composition among the different plant communities decreased with time, indicating that the effects of species removal treatment weakened gradually. The probable underlying mechanism was that the system recovered from the initial disturbance and became more similar to the intact communities. There were no significant differences in ramet density, canopy height and belowground biomass of all the different plant communities between the control and species removal treatments. This might be due to the species compensatory effects and the recovery ability of dominant species since only the aboveground parts of the dominant plants were removed. (2) Community type and the season significantly affected the density and Shannon-Weiner diversity index of the macrobenthic invertebrate communities(P<0.01). Community type and interaction between the season and community type had significant effects on the biomass of macrobenthic invertebrates(P<0.01). The density of macrobenthic invertebrates in the species removal treatment was lower than that in control treatment, but the effects were not significant. The highest density, biomass and Shannon-Weiner diversity index of the macrobenthic invertebrates were observed in the Spartina alterniflora-Scirpus mariqueter community. This was mainly caused by differences in environmental factors and plant species attributes of the inhabiting communities. (3) There was a close relationship between salt marsh vegetation and benthic community. The density of macrobenthic invertebrates was positively and negatively correlated with shoot density and canopy height of the inhabiting plant communities, respectively (all P<0.01). After removal of the dominant species, ramet density of the plant communities and proportion of remaining species increased, while the subdominant species contributed greatly to the compensatory effect. The density of macrobenthic invertebrates decreased, but the pattern of biomass and diversity index change differed from that of the density, probably because of the influence of other environment factors. The above results indicated that the biodiversity change could affect the structure of plant and macrobenthic invertebrate communities to different degrees, which may then alter the processes of the biogeochemical cycle and energy flow. During our study, the removal effects were relatively weak in the intertidal zone of Chongming Dongtan, and they diminished with time. Therefore, the simple removal of dominant species may not be sufficient to restore the ecosystem functions of salt marshes, and further management measures should be used to maintain the long-term effects of habitat modification.