RESEARCH PAPER Extracellular phosphatases produced by phytoplankton and other sources in shallow eutrophic lakes (Wuhan, China): taxon-specific versus bulk activity Xiuyun Cao Æ Chunlei Song Æ Yiyong Zhou Æ Alena S ˇ trojsova ´ Æ Petr Znachor Æ Elis ˇka Zapome ˇlova ´ Æ Jaroslav Vrba Received: 30 April 2008 / Accepted: 14 February 2009 / Published online: 24 March 2009 Ó The Japanese Society of Limnology 2009 Abstract Extracellular phosphatases are an important part of the phosphorus cycle in aquatic environments. Phospha- tase activity (PA) in plankton was studied in seven subtropical shallow lakes of different exploitation manage- ment and trophic status in the urban area of Wuhan City. Bulk PA was rather high (range 1.1–11 lmol l -1 h -1 ), although concentrations of soluble reactive phosphorus (SRP) were also high (range 27 lgPl -1 to *1.5 mg P l -1 ) in all lakes. Cell-associated extracellular PA in phyto- plankton was detected using the fluorescence-labelled enzyme activity technique. Phytoplankton species partly contributed to the bulk PA. We found explicit differences in the presence of cell-associated phosphatase within the main phytoplankton groups; species belonging to Chlorophyta and Dinophyta were regularly phosphatase-positive, while Cyanophyta and Bacillariophyceae were phosphatase- negative in all but one case. Furthermore, there is a certain potential of extracellular phosphatases produced by hetero- trophic nanoflagellates in most of the lakes. This new finding compromises the ‘traditional’ interpretation of bulk phos- phatase data as being due to overall phytoplankton or bacterial P regeneration. Keywords ELF97 phosphate Á Phosphorus regeneration Á Polymictic lakes Á Algae Á Heterotrophic flagellates Á Protozoa Introduction Increasing numbers of urban and suburban lakes in China are under severe nutrient loading; especially high concen- trations of phosphorus (P) cause vast problems with phytoplankton blooms and water quality. Therefore, studies on P fluxes are of high importance in urban lakes usually used for irrigation or aquacultures. Bioavailable P (orthophosphate) can be liberated from various dissolved organic phosphorus (DOP) compounds by phosphatase-catalysed hydrolysis (Wetzel 2001; Chro ´st and Siuda 2002). Phytoplankton and bacteria are able to produce their own phosphatases (e.g., Pettersson 1980, 1985; Chro ´st and Overbeck 1987; Feuillade et al. 1990; Istva ´novics et al. 1993; Vrba et al. 1993a; Nedoma et al. 2003a, 2006). Phosphatase activity (PA) is usually high in environments where ambient P is scarce (e.g. Healey and Hendzel 1980; Pettersson 1980; Gage and Gorham 1985). Interestingly, high PA was frequently found even at ample P concentrations in the hypereutrophic urban lake Donghu (Zhou and Zhou 1997; Zhou et al. 2000; Cao et al. 2005). Bulk PA values can be indicative of P demand in a lake, although, it is more important to know the main sources of this activity, i.e. particular populations of planktonic microorganisms. Fluorescently labelled enzyme activity (FLEA—in earlier papers wrongly called ELF technique, as well) was first used by Gonza ´les-Gil et al. (1998) for cultures of marine phytoplankton; this technique allows for the detection of phosphatases in plankton on the species level. Some freshwater FLEA studies consistently showed X. Cao Á C. Song Á Y. Zhou Institute of Hydrobiology, Chinese Academy of Sciences, 430072 Wuhan, People’s Republic of China A. S ˇ trojsova ´ Á P. Znachor Á E. Zapome ˇlova ´ Á J. Vrba (&) Faculty of Science, University of South Bohemia and Biology Centre AS CR, Institute of Hydrobiology, Na Sa ´dka ´ch 7, 37005 C ˇ eske ´ Bude ˇjovice, Czech Republic e-mail: vrba@hbu.cas.cz 123 Limnology (2009) 10:95–104 DOI 10.1007/s10201-009-0265-9