Trait shift history: Do grazing induced trait shifts in phytoplankton determine the sensitivity to nutrients and sinking? (Acronym: TraitHist)

• Applicant: Professor Dr. Ulrich Sommer
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257184792

It shall be tested whether shifts in phytoplankton size structure caused by zooplankton grazing determines the responsiveness of phytoplankton to nutrient depletion, nutrient enrichment and sinking. Phytoplankton from the Baltic Sea will be subject to zooplankton grazing in mesocosms. The effect of two types of zooplankton will be contrasted. Copepods which are expected to shift phytoplankton size distribution towards a dominance of smaller cell and the rotifer Brachionus plicatilis which is expected to shift the size distribution towards dominance of larger cells. After conditioning by grazing, phytoplankton communities from the copepod mesocosms, the Brachionus mesocosm and the control mesocosms will be subject to nutrient starvation and nutrient enrichment. Sinking rates will be measured at the end of the conditioning phase and in response to the nutrient treatments. The working hypotheses are:1) Copepod grazing will shift protist size distributions to a dominance of small cells.2) Brachionus grazing will shift protist size distributions to a dominance of large cells.3) Copepod-conditioned protist plankton willa) respond with faster growth to nutrient additions.b) better cope with prolonged nutrient shortage.c) be less vulnerable to sinking losses.4) Brachionus-conditioned protist plankton willa) sustain growth after nutrient addition for a longer period.b) initially maintain growth longer after the transition to nutrient shortage.c) be more vulnerable to sinking losses. 5) Sinking rates will also be influenced by nutritional state, as expressed by the C : limiting nutrient ratio in biomass.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1704: Flexibility Matters: Interplay Between Trait Diversity and Ecological Dynamics Using Aquatic Communities as Model Systems (DynaTrait)