Impact Of Species Richness On Biomass And Stability Of The Phytoplankton Assemblage

Concerns over the unprecedented loss of biodiversity have motivated ecologists to conduct considerable researches, to describe the relationship between biodiversity and ecosystem function, and detect the underlying mechanisms. I used experimental aquatic phytoplankton assemblage to explore the relationships between species richness and biomass production, or stability (resistance, resilience and temporal variability). The main results and conclusions are listed as follows:Both algae composition and species richness have effect on biomass. Differences in algae composition explained more of the variation in biomass than did the algae richness. There was no obvious linear relativity between algae richness and biomass. Maximum of biomass did not appeared in assemblage with the largest species richness. The species-rich assemblage reached larger specific growth rate than the species-poor ones. In the experiment, nutrition concentration has significant effect on biomass and no obvious effect on specific growth rate (exponential growth phase).In the experiment, biomass increased with species richness, but its growth pattern was not sole. It revealed obvious monotonous rise relationship between algae richness and biomass when specie richness lower than 5; when specie richness is higher than 5, it continued to maintain the monotonous rise, or the drop, or presents the saturated rise.I applied the methods transgressive overyielding analysis, RYT index,"subset approach", and"additive partitioning"to the experimental data. I examined the mixtures performance relative to the most productive monoculture of the component species, finding transgressively overyielding effect in 2- or 3- species combinations at a relative low frequency, but it enhanced by species richness. RYT was greater than one at every point of time, revealed approximate"hump-shaped"relationship with species richness. In the"subset approach"analysis, for N=2, percentage of plus signs(Fplus) close to 0.5, When N>2, the Fplus always higher than 0.5. The results indicated that the increase in species richness led to increase of complementarity effect at 2-species and higher diversity levels. The selection effect calculated by"additive partitioning"as a whole below zero, the net, complementarity effects as a whole above zero.The resistance of assemblage, measured as relative change in biomass(dB/Bdt, day-1) from day16,18,20(preceding perturbation) to day14(under perturbation). Resilience was measured as the deviation of post-perturbation(day22,24)biomass from pre-perturbation(day14), calculated as ln(biomss22,24/biomass14). For the test of whether perturbation modulated the mechanisms by which species richness influences ecosystem biomass, I used relative yield total(RYT) analysis and additive partitioning method for a quantitive description on the mechanism underlying the diversity-biomass relationship. A manipulated hot perturbation led to greater biomass addition in diverse assemblage than in species-poor systems. Both resistance and resilience increased with species richness during perturbation. The overyielding effect, measured as Relative yield total(RYT), increased with species richness either before or after perturbation, and this effect become stronger through perturbation. Selection effect was below zero either before or during the perturbation, complementarity and net biodiversity effect were above zero.