Contrasting Community versus Population-Based Estimates of Grazing and Virus-Induced Mortality of Phytoplankton
- 364 Downloads
In this study, grazing and virus-induced mortality of phytoplankton was investigated in a freshwater pond at the University of Toronto Mississauga, Canada, during September 2009. The modified dilution assay, which partitions phytoplankton mortality into virus and grazing-induced fractions, was used along with newly designed, taxon-specific quantitative polymerase chain reaction (qPCR) assays that target psbA gene fragments to estimate growth and mortality rates for both the entire phytoplankton community and four distinct phytoplankton populations. Community mortality was estimated via fluorometric determination of chlorophyll a (Chl a) concentrations, whereas the relative mortality of individual phytoplankton populations was estimated via qPCR. The sources and amounts of mortality for individual phytoplankton populations differed from those of the whole community, as well as from each other. Grazing was found to be the only significant source of mortality for the community (0.32 day−1), and the Prymnesiales (1.65 day−1) and Chroococcales (2.79 day−1) populations studied. On the other hand, the Chlamydomonadales population examined experienced both significant grazing (1.01 day−1) and viral lysis (0.96 day−1), while the Chlorellales population only experienced significant mortality as a result of viral lysis (1.38 day−1). Our results demonstrate that the combination of qPCR and the modified dilution method can be used to estimate both viral lysis and grazing pressure on several individual phytoplankton populations within a community simultaneously. Further, previously noted limitations of the modified dilution method associated with the dilution of specific phytoplankton populations at low abundances can be overcome with the qPCR-based approach. Most importantly, this study demonstrates that when used alone, whole community-based methods of assessing mortality can overlook valuable information about carbon flow in aquatic microbial food webs.
KeywordsPhytoplankton Phytoplankton Population psbA Gene qPCR Primer Viral Lysis
This research was supported in part by the Canadian Foundation for Innovation Leaders Opportunity Fund, and NSERC Discovery grants awarded to S.M.S.
- 1.Falkowski P, Scholes RJ, Boyle E, Canadell J, Canfield D, Elser J, Gruber N, Hibbard K, Hogberg P, Linder S, Mackenzie FT, Moore B, Pedersen T, Rosenthal Y, Seitzinger S, Smetacek V, Steffen W (2000) The global carbon cycle: a test of our knowledge of earth as a system. Science 290:291–296PubMedCrossRefGoogle Scholar
- 7.Wetzel RG (2001) Limnology: lake and river ecosystems. Academic Press, San DiegoGoogle Scholar
- 15.Landry MR (1993) Estimating rates of growth and grazing mortality of phytoplankton by the dilution method. In: Kemp PF, Sherr BF, Sherr EB, Cole JJ (eds) Handbook of methods in aquatic microbial ecology. Lewis Publishers, Boca RatonGoogle Scholar
- 27.Hall TA (1999) BioEdit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucl Acids Symp Ser 41:95–98Google Scholar
- 37.Dorak MT (ed) (2006) Real-time PCR. Taylor & Francis Group, New YorkGoogle Scholar
- 47.Zar JH (1999) Biostatistical analysis. Prentice-Hall, Inc., Upper Saddle RiverGoogle Scholar