Long term patterns of picocyanobacteria from a hypertrophic shallow lake inferred through flow cytometry

QUIROGA, M. V.; HUBER, M. P.; OSPINA-SERNA, JULIANA; DIOVISALVI, N.; ODRIOZOLA, MARIANA; CUETO, G.R.; LAGOMARSINO, L.; BUSTINGORRY, J. F.; ESCARAY, R.; ZAGARESE, H.; UNREIN, F.

Congreso; International Society for Microbial Ecology - Latin America (ISME-LA); 2019

Picophytoplankton from eutrophic shallow lakes are generally underrepresented in global models. Here we analyzed picocyanobacteria (Pcy) dynamics along ten years (2007-2017) in the turbid hypertrophic shallow lake Chascomús (Pampa Plain, Argentina). We used flow cytometry to detect changes in Pcy organism abundance (either single-cell and colonial), chlorophyll-a content (FL3) and relative organism size/granularity (SSC), as well as cytometric diversity indexes (flowDiv package for R), and their relation to environmental conditions. Intra- and interannual changes (seasonality and trend) in the former Pcy features were evaluated through generalized additive models (GAM). A second GAM was tested for each response variable with environmental factors as predictors. Contrarily to other freshwater systems, Chascomús lake showed a Pcy seasonality with higher abundances during winter, while the interannual pattern resembled a dilution effect during wet periods. The winter Pcy community was less diverse and even, suggesting that this peak was due to the proliferation of few Pcy taxa. Pcy abundance, FL3, SSC, Shannon-Weaver and Pielou indexes were partially explained by lake depth, turbidity, expected incident radiation and the rate of change of irradiance, unrevealing the importance of underwater light climate in this light limited turbid system. Cladocerans abundance was negatively associated with Pcy abundance and positively related with FL3 and SSC. The cladocerans effect was further asses through in vitro experiments. The cytometric fingerprint (Bray-Curtis beta diversity) detected differences in Pcy community structure strongly related with differences in cladoceran abundance among samples. These results suggest a possible induced shift from unicellular Pcy to microaggregates/colonial forms during periods of high cladoceran abundance.