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

Abstract

Research on plant biodiversity and ecosystem functioning has mainly focused on terres- trial ecosystems, and our understanding of how plant species diversity and interactions affect pro- cesses 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, Potamogeton 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 partition- ing and Di 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 complemen- tarity 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.