Effects of plant diversity on primary production and species interactions in brackish water angiosperm, communities

Research on plant biodiversity and ecosystem functioning has mainly focused on terrestrial ecosystems, and our understanding of how plant species diversity and interactions affect processes in marine ecosystems is still limited. To investigate if plant species richness and composition influence plant productivity in brackish water angiosperm communities, a 14 wk field experiment was conducted. Using a replacement design with a standardized initial aboveground biomass, shoots of Zostera marina, Polamogeton filiformis and P. perfoliatus were planted on a shallow, sandy bottom in replicated monocultures and all possible species combinations. Response variables included aboveground and belowground biomass, shoot density, space Occupation and porewater nutrients. To determine whether selection and/or complementarity controlled productivity, additive partitioning and D-i were calculated. Richness effects were species-specific and only increased the biomass production of P. perfoliatus and tuber production of P. filiformis, while species composition generally had a stronger effect on biomass production. Additive partitioning indicated a positive complementarity effect for the aboveground biomass production in bicultures in general, while a positive net effect was found in the P. perfoliatus and P. filiformis biculture. Despite the absence of significant results for other treatments and plant variables, a trend of positive complementarity and negative selection effects were present. Plant diversity had no clear effect on sediment porewater nutrient concentrations, indicating weak richness effects on resource use.