The responses of phytoplankton communities to elevated CO 2 show seasonal variations in the highly eutrophic Lake Taihu

• Published in: Canadian journal of fisheries and aquatic sciences 2016-05, Vol.73 (5), p.727-736
• Main Authors: Shi, Xiaoli, Zhao, Xuhui, Zhang, Min, Yang, Zhou, Xu, Ping, Kong, Fanxiang
• Format: Article
• Language: English
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/cjfas-2015-0151

From April 2012 to January 2013 (over four seasons), in situ microcosm experiments were conducted in Lake Taihu, perturbed over a range of pCO 2 scenarios (270, 380, and 750 μatm; 1 atm = 101.325 kPa). The influence of CO 2 level on microcosms was greatest during the spring because of the high growth rate of phytoplankton. In this season, rising CO 2 levels caused a pH reduction, and the maximum reduction was 0.6 units when CO 2 level was enhanced from the present level to 750 μatm. The doubling of CO 2 level could increase the net primary production (NPP) by 65% during spring when the concentrations of other nutrients were maintained. The rise of NPP could cause a decline of dissolved inorganic carbon (DIC) concentration, and CO 2 enrichment might mitigate the extent of this decline. Meanwhile, higher CO 2 may slow or prevent a loss of diversity of phytoplankton in microcosms in this season. During the other three seasons, Microcystis predominated, and the percentage of cyanobacteria did not alter with the change of CO 2 . We did not observe a significant increase in the abundance of any taxa with the rise of CO 2 during the in situ microcosm experiments.