Theme 1
Project 1071

Subproject 1, the ecophysiological (actuo) component
Project leader: Prof. dr. J. G. M. Roelofs
Researcher(s): Drs. M. M. L. van Kempen
Starting date: 1-okt-06

The free-floating aquatic fern Azolla is distributed worldwide in mainly fresh water ecosystems. It has a symbiotic association with the nitrogen fixing alga Anabaena azollae. Phosphorus is the most important and often limiting nutrient for Azolla growth, and one of the current questions is how P recycled; the circumstances under which Azolla bloomed in the Eocene Arctic Ocean still remain largely unclear. Surface waters were probably somewhat brackish implying that the Azolla-Anabaena complex should have been able to withstand relatively high salt concentrations. Some extant Azolla species are able to grow in brackish waters, and these can be used for comparative studies. Furthermore, the Arctic Azolla bloom was sustained with strong seasonality and pCO2 up to ten times pre-industrial values. Along the scope of the DARWIN Azolla project, here we will mimic Eocene Arctic environmental conditions allowing an Azolla bloom to be evaluated using extant species. We shall simultaneously vary salinity, pCO2, nutrient concentrations (N and P), photoperiod and temperature, and we shall unravel the anaerobic decomposition of Azolla litter grown under different environmental conditions, and assess consequences for global nutrient cycles.

Speelman, E.N., van Kempen, M.M.L., Barke, J., Brinkhuis, H., Reichart, G.J., Smolders, A.J.P., Roelofs, J.G.M., Sangiorgi, F., de Leeuw, J.W., Lotter, A.F., Sinninghe Damsté, J.S. (2009). The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown . Geobiology7 (2): 155-170.
Darwin Center authors: Barke J., Brinkhuis H., van Kempen M. M. L., Lotter A. F., Reichart G. J., Roelofs J. G. M., Sinninghe Damsté J. S., Speelman E. N.

Judith Barke, Johan van der Burgh, Johanna H.A. van Konijnenburg-van Cittert, Margaret E. Collinson, Martin A. Pearce, Jonathan Bujak, Claus Heilmann-Clausen, Eveline N. Speelman, Monique M.L. van Kempen, Gert-Jan Reichart, André F. Lotter, Henk Brinkhuis (2012). Coeval Eocene blooms of the freshwater fern Azolla in and around Arctic and Nordic seas. Palaeogeography, Palaeoclimatology, Palaeoecology337-338: 108-119.
Darwin Center authors: Barke J., Brinkhuis H., van Kempen M. M. L., Lotter A. F., Reichart G. J., Speelman E. N.

Monique M.L. van Kempena, Alfons J.P. Smolders, Gerard M. Bögemann, Leon L.M. Lamers, Eric J.W. Visser, Jan G.M. Roelofs (2013). Responses of the Azolla filiculoides Stras.–Anabaena azollae Lam. association to elevated sodium chloride concentrations: Amino acids as indicators for salt stress and tipping point. Aquatic Botany106: 20-28.
Darwin Center authors: van Kempen M. M. L., Lamers L. P. M., Roelofs J. G. M.