Vertical mixing within the epilimnion modulates UVR-induced photoinhibition in tropical phytoplankton from Southern China

VIRGINIA ESTELA VILLAFAÑE; KUNSHAN GAO,; PING LI,; GANG LI,; WALTER HELBLING, E

FRESHWATER BIOLOGY (PRINT)

Año: 2007 vol. 52 p. 1260 - 1270

0046-5070

1. The importance of vertical mixing in modulating the impact of UVR on phytoplanktonphotosynthesis was assessed in a tropical, shallow lake in southern China from late winterto mid-spring of 2005.2. Daily cycles of fluorescence measurements (i.e. photosynthetic quantum yield, Y) wereperformed on both ‘static’ and in situ samples. Static samples were of surface waterincubated at the surface of the lake under three radiation treatments – PAB (PAR + UVR,280–700 nm), PA (PAR + UV-A, 320–700 nm) and P (PAR, 400–700 nm). In situ sampleswere collected every hour at three different depths – 0, 0.5 and 1 m.3. The general daily pattern was of a significant decrease in Y from early morning towardsnoon, with partial recovery in the afternoon. Samples incubated under static conditionsalways had lower Y than those under in situ conditions at the same time of the day.4. Under stratified conditions, no overall impact of UVR impact could be detected in situwhen compared with the static samples. Further rapid vertical mixing not onlycounteracted the impact of UVR but also stimulated photosynthetic efficiency.5. Based on these measurements of fluorescence, the mixing speed of cells moving withinthe epilimnion was estimated to range between 0.53 and 6.5 cm min)1.6. These data show that mixing is very important in modulating the photosyntheticresponse of phytoplankton exposed to natural radiation and, hence, strongly conditionsthe overall impact of UVR on aquatic ecosystems.