Ó Springer 2006
Hydrobiologia (2006) 560:323–334 DOI 10.1007/s10750-005-1280-4
Primary Research Paper
Seasonal variation of virioplankton in a eutrophic shallow lake Yan-Ming Liu, Qi-Ya Zhang*, Xiu-Ping Yuan, Zheng-Qiu Li & Jian-Fang Gui State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences; Graduate school of the Chinese Academy of Sciences, 430072 Wuhan, China (*Author for correspondence: Tel.: +86-27-68780792; Fax: +86-27-68780123; E-mail:
[email protected]) Received 21 March 2005; in revised form 26 October 2005; accepted 23 November 2005
Key words: virioplankton, bacterioplankton, seasonal variation, shallow lake, eutrophication
Abstract Lake Donghu is a typical eutrophic freshwater lake in which high abundance of planktonic viruses was recently revealed. In this study, seasonal variation of planktonic viruses were observed at three different trophic sites, hypertrophic, eutrophic, and mesotrophic regions, and the correlation between their abundances and other aquatic environmental components, such as bacterioplankton, chlorophyll a, burst size, pH, dissolved oxygen, and temperature, was analyzed for the period of an year. Virioplankton abundance detected by transmission electron microscope (TEM) ranged from 5.48 108 to 2.04 109 ml)1 in all the sites throughout the study, and the high abundances and seasonal variations of planktonic viruses were related to the trophic status at the sampled sites in Lake Donghu. Their annual mean abundances were, the highest at the hypertrophic site (1.23109 ml)1), medium at the eutrophic site (1.19109 ml)1), and the lowest at the mesotrophic site (1.02109 ml)1). The VBR (virus-to-bacteria ratio) values were high, ranging from 49 to 56 on average at the three sampled sites. The data suggested that the high viral abundance and high VBR values might be associated with high density of phytoplankton including algae and cyanobacteria in this eutrophic shallow lake, and that planktonic viruses are important members of freshwater ecosystems.
Introduction Virioplankton, the planktonic viruses in natural waters, have been revealed to be the most abundant and dynamic components in aquatic ecosystems (Wommack & Colwell, 2000; Zhang, 2002). As summarized by Wommack & Colwell (2000), the abundance of viruses ranged from 108 ml)1 in the studied aquatic ecosystems. They can regulate biomass production, species diversity, population dynamics and community structure in the aquatic microbial communities, influence carbon and nutrient recycling in food chain and water environment, and even have direct implications on the global climate (Bergh et al., 1989; Bratbak & Heldal, 2000; Bettarel et al., 2004).
Bacterioplankton biomass and virioplankton abundance have been reported to be related to different environmental parameters, such as temporal variation, depth variation and trophic status (Fuhrman, 1999; Wommack & Colwell, 2000). Since the ecological significance of virioplankton in aquatic ecosystems must be realized by their interaction with the hosts (e.g. bacteria, cyanobacteria and algae), enumeration of viruses and their hosts in water samples is an important first step for elucidating the virus–host interaction. In most instances, viral abundance was significantly correlated with bacterioplankton abundance (Wommack & Colwell, 2000), but in a few studies, it showed significant correlation with chlorophyll a concentration (Boehme et al., 1993; Maranger &
324 Bird, 1995). Temporal fluctuations in viral abundance have been studied at time scales ranging from hours (Bettarel et al., 2002) to seasons (Hofer & Sommaruga, 2001; Fischer &Velimirov, 2002; Bettarel et al., 2003). Generally, there is a fall in viral abundance in winter (Weinbauer et al., 1995; Cochran & Paul, 1998), and the greatest abundance is usually reached at the end of autumn (Jiang & Paul, 1994; Wommack & Colwell, 2000). In the past, the studies on virioplankton abundance and temporal changes were mainly performed in marine environments (Wommack & Colwell, 2000). Recently, some interesting studies have been also conducted in freshwater ecosystems. For example, Hofer & Sommaruga (2001) found that viral particles varied seasonally from a low of
