Effects Of Plant Diversity On Primary Productivity And Macrobenthos Community Of Wetland Ecosystem

Along with the rising global extinction rate, studies about the ecological consequences caused by species loss are attracting more and more attention. The relationships between biodiversity and ecosystem functioning (Biodiversity-ecosystem function relationship; BEF) has become an important scientific problem in the field of current ecology. However, many academic disputes exist in this field, such as the different results between field investigation and controlled environment experiment, and whether species identity or species diversity of community has important effects on productivity and other ecosystem functions. In order to cover the shortage of single experiment, we conducted synthetic assemblage experiment as well as field investigation in Chongming Dongtan. I used multiple methods to study the effects of intra and interspecific diversity and species identity on ecosystem function, and the influence of environmental heterogeneity and duration time on BEF. In addition, I also studied the effects of plant community structure and diversity on benthic invertebrate community. Discussion on these issues is not only verification or supplement of theories in this field, but also contributes to biodiversity conservation and restoration of wetland ecosystem. The results of this study showed that:1. In 2012, cutting treatment had significant effects on all growth parameters of plant community except ramet density (all P<0.01). Species richness and species composition had significant effects on all plant growth parameters (P<0.01). The effect of treatment*richness interaction were significant on aboveground biomass, belowground biomass, total biomass and canopy height (all P<0.01). In control treatment, total biomass, aboveground biomass and belowground biomass of plant community all showed the pattern of 3 species> 6 species> 1 species, but in cutting treatment, biomass in 3 species community was lower than those in 1 species and 6 species communities. Biomass was higher in control treatment than in cutting treatment in 3 species and 6 species community. Canopy height showed the pattern of 1 species< 3 species< 6 species in control treatment, but 1 species> 6 species> 3 species in cutting treatment. Ramet density showed the pattern of 1 species> 3 species> 6 species in both treatments.In 2013, community biomass was higher than that in 2012. Species richness had significant effects on aboveground, belowground, total biomass and canopy height (all P< 0.01). Species composition had significant effects on all parameters (all P< 0.01). Cutting treatment and treatment* species richness interaction had significant effects on aboveground biomass only (P< 0.01). Community total biomass, aboveground and belowground biomass showed the pattern of 6 species> 1 species> 3 species in control treatment, but the biomass of 3 species community was lower than that in 1 species and 6 species community in cutting treatment. Biomass in cutting treatment was lower than that in control treatment of 3 species and 6 species communities. Canopy height was higher in 6 species community than in 1 species and 3 species community in both treatments.2. Ecotype number had significant effects on belowground biomass, total biomass and density of Phragmites australis populations (all P<0.05), and ecotype composition had significant effects only on density (P<0.05). Belowground biomass, total biomass and density in two ecotype populations are higher than those in single ecotype populations. Of different Phragmites australis ecotype combinations, density of saline+dryland and saline+brackish population is higher than that of dryland+ brackish population.3. Aboveground, belowground and total biomass of Phragmites-Spartina community were significantly higher than Spartina-Scirpus community, Phragmites-Spartina-Scirpus community and Typha-Phragmites-Carex community. Canopy height was largely determined by dominant species, and ramet density was influenced by the existence of Scirpus mariqueter.Within all plant communities, Gastropoda was dominant family, and three Assiminea species dominate in all plant species. Density of macrobenthos showed the pattern of Spartina-Scirpus> Typha-Phragmites-Carex> Phragmites-Spartina> Spartina-Scirpus. Diversity index did not differed significantly among plant communities. Total biomass of macrobenthos was negatively correlated with plant community biomass and positively correlated with plant diversity index. There was no significant relationship between plant diversity index and macrobenthos diversity index.In conclusion, effects of species diversity and identity on ecosystem function vary with environmental fluctuation and time, which is important to wetland ecosystem restoration. Thus, in restoration practice, we should not only focus on species combination, but also choose proper richness level. In long term restoration project, high initial biodiversity can maintain community structure and promote the development of wetland ecosystem. In Chongming Dongtan, two-ecotype Phragmites australis (e.g., saline+dryland or saline+brackish) may be better choice for restoration. We should also increase the ramet density of Scirpus mariqueter when constructing plant diversity to promote the restoration of macrobenthos.