Lewandowska AM, Breithaupt P, Hillebrand H, Hoppe GH, Jurgens K, Sommer U
Productivity, Diversity, climate change, mesocosm, 1.4 m3, Kiel, Germany
In order to examine the effects of warming and diversity changes on primary productivity, we conducted ameta-analysis on six independent indoor mesocosm experiments with a natural plankton community fromthe Baltic Sea. Temperature effects on primary productivity changed with light intensity and zooplanktondensity and analysed pathways between temperature, diversity and productivity, elucidating direct and indirecteffects of warming on primary productivity during the spring phytoplankton bloom. Our findings indicatethat warming directly increased carbon specific primary productivity, which was more pronouncedunder low grazing pressure. On the other hand, primary productivity per unit water volume did not respondto increased temperature, because of a negative temperature effect on phytoplankton biomass. Moreover,primary productivity response to temperature changes depended on light limitation. Using path analysis,we tested whether temperature effects were direct or mediated by warming effects on phytoplankton diversity.Although phytoplankton species richness had a positive impact on both net primary productivity andcarbon specific primary productivity – and evenness had a negative effect on net primary productivity –both richness and evenness were not affected by temperature. Thus, we suggest that diversity effects onprimary productivity depended mainly on other factors than temperature like grazing, sinking or nutrientlimitation, which themselves are temperature dependent.