Interacting effects of atmospheric CO2 enrichment and solar radiation on growth of the aquatic fern Azolla filiculoides

Abstract

Summary Azolla spp. rank among the fastest growing plants in the world. Increased atmospheric CO2 concentrations can be expected to have a strong impact on the biomass production of this fast growing floating fern, especially at northern latitudes. We investigated the growth of the northernmost occurring species, A. filiculoides, under past (Eocene), present and predicted future CO2 levels. To study the interacting effects of temperature and solar radiation, we performed the atmospheric CO2 fertilisation experiments in spring, summer and autumn. Azolla filiculoides grown at 1600 ppm CO2 produced twice as much biomass as when grown at 400 ppm CO2 in spring and autumn. However, high summer temperature and solar radiation seemed to significantly lower its maximum growth potential, presumably as a result of a metabolic shift as indicated by water loss. Nutrient availability became more important at higher atmospheric CO2 concentration. In addition, high temperature and solar radiation affected the nitrogen concentrations in A. filiculoides, most likely by inducing photorespiration and photoinhibition. Our results indicate that temperate Azolla may become more productive in temperate regions as a result of rising atmospheric carbon dioxide concentrations. In addition, our results can help to explain the reported massive Azolla event in the Eocene.