Spatial patterns in picoplankton communities along a cascade reservoir system (Limay River, Patagonia) in relation to environmental factors

LU, LUNHUI; SÁNCHEZ, MARÍA LAURA; LI, ZHE; BERNAL, M. CAROLINA; VERA, M. SOLANGE; PORCEL, SOL; SABIO Y GARCÍA, CARMEN; SINISTRO, RODRIGO; IRINA, IZAGUIRRE

Ciudad del Cabo

Simposio; ISME 2020; 2020

International Society for Microbial Ecology

Picoplanktonic abundances and diversity were analyzed along a system of three cascade oligo-mesotrophic reservoirs (Alicura, Piedra del Águila and Ramos Mexía) of the Limay River, and an affluent (Collon Cura River-CC). Eleven sampling sites were established encompassing lentic and lotic sections. The main limnological variables were measured at each sampling site. The abundance of autotrophic and heterotrophic picoplankton was obtained using flow cytometry, and bacterioplankton diversity was assessed by Illumina MiSeq. Total picoplankton abundance showed an increasing trend downstream in the overall system, with local decreases at lotic stretches. In all sites heterotrophic bacteria (HB) abundance exceeded autotrophic picoplankton (APP), and these were dominated by phycoerithrin-rich picocyanobacteria (PE-rich Pcy). One picoeukaryote (Peuk) and two PE-rich Pcy cytometric populations were mainly observed, although Ramos Mexía Reservoir displayed an additional Peuk cytometric population. Most sites showed dominance of low nucleic acid-containing bacteria (LNA) over high nucleic acid-containing bacteria (HNA). A total of 1319 OTUs were obtained by Illumina MiSeq, with a total of ?.. reads. Actinobacteria dominated in all sites except in CC, where Bacteroidetes prevailed. OTU richness displayed a spatial pattern, with higher values at lotic sites and lower ones at lentic sites, whereas equitability showed the inverse pattern. Canonical Correspondence Analysis (CCA) and Non Metric Multi-Dimensional Scaling were performed based on bacterial OTU diversity; both revealed a clear spatial pattern, where samples of each reservoir appeared closer to each other. CCA showed that the main variables associated to this pattern were turbidity, DOC, Chlorophyll a and conductivity, all increasing downstream. Despite a slight increase in trophic status at Ramos Mexía Reservoir, overall picoplankton community structure was typical of oligotrophic environments.