DYNAMICS OF CHLOROPHYLL FLUORESCENCE AND ECO-MORPHOLOGICAL PROPERTIES OF Microcystis BLOOM IN MEILIANG BAY OF LAKE TAIHU, CHINA

Abstract

Eutrophication has become a serious concern in many lakes, resulting in cyanobacterial blooms. Some variations of physiological activity and eco-morphological property in Microcystis bloom, especially in field experiment, are currently less studied. This study aimed to describe what changes of physiological activity and eco-morphological property had happened, and identify what is the key factor resulting in the decline of Microcystis bloom. The chlorophyll fluorescence, buoyancy and colony sizes of Microcystis and variation of physico-chemical data in the Meiliang Bay estuary of Lake Taihu, China, was investigated everyday from July 18, 2009 to July 29, 2009. In field investigation, F(v)/F(m) Phi(PSII) and qP can regarded as effective indicators to evaluated physiological activity and the growth state of Microcystis bloom. We found on sunny days, photoinhibition occurred 2 hours later than that on cloudy days, but photodamage indicated by unrecoverable decreasing F(v)/F(m), was observed after exposure to high light for a long time. While on cloudy days, the photoinhibition of Microcystis seemly occurred more easily and recovered quickly at weak light. Controlling experiment showed that nutrient depletion could lead to decreased buoyancy, dis-aggregated colonies and dropping photosynthesis of Microcystis. Based on these results of high light, rich DO, a negative correlation between DO and F(v)/F(m), and a lagged photoinhibition on sunny days, we inferred Mehler's reaction was a protective mechanism of photosystem for a short time, but results in photodamage when exposure is long enough. In all, we conclude the long-term illumination of high light companied with nutrient depletion caused by rapid growth of Microcystis might be the main reasons for the bloom decline