TEMPERATURE MAY BE THE DOMINATING FACTOR ON THE ALTERNANT SUCCESSION OF Aphanizomenon flos-aquae AND Microcystis aeruginosa IN DIANCHI LAKE

This field investigation studied the effects of environmental factors on the seasonal dynamics and alternant succession of two cyanobacterial species, Aphanizomenon flosaquae and Microcystis aeruginosa from November 2008 to May 2009 in Dianchi Lake of China. Temperature, pH, conductance, and transparency were measured in Fubao Bay of Dianchi Lake every week. At the same time, dissolved oxygen and inorganic carbon, total nitrogen and phosphorus, chlorophyll-a and phytoplankton biomass were field-investigated. The results analyzed by CCA (canonical correspondence analysis) indicated that temperature is the most correlative impact factor on A. flos-aquae and M. aeruginosa's seasonal succession. Total nitrogen, total phosphorus and transparency are the second correlation factors. Temperature gradient experimentation in laboratory indicated that A. flos-aquae could grow under all of the 4 temperature conditions: 10, 15, 20 and 25 degrees C, but growth of A. flos-aquae at 10 and 15 degrees C was slower than that at 20 and 25 degrees C. M. aeruginosa could not grow at 10 degrees C and very slowly at 15 degrees C, but faster than A. flos-aquae at 20 and 25 degrees C. The result of the laboratory experimentation is coincident with the field investigation. It suggests that temperature may be the dominating factor on the alternation succession of A. flos-aquae and M. aeruginosa in Dianchi Lake.