Warming and nutrient enrichment in combination increase stochasticity and beta diversity of bacterioplankton assemblages across freshwater mesocosms

Abstract

The current climate warming and eutrophication are known to interactively threaten freshwater biodiversity; however, the interactive effects on lacustrine bacterioplankton diversity remain to be determined. Here, we analyzed the spring bacterioplankton community composition (BCC) in 24 outdoor, flow-through mesocosms (mimicking shallow lake environments) under 3 temperature scenarios and 2 nutrient regimes. Our results revealed that neither long-term warming (8.5 years) nor nutrient enrichment had significant effects on bacterioplankton alpha diversity, whereas long-term enhanced warming (elevated 50% above the IPCC A2 climate scenario) and nutrient enrichment in combination increased bacterioplankton beta diversity. We also found that BCC shifted significantly under enhanced warming and nutrient-enriched conditions towards decreased relative abundances of Actinobacteria, Bacteroidetes and Betaproteobacteria, whereas the percentages of Cyanobacteria, total rare phyla and unclassified phyla significantly increased. Null-model tests indicated that deterministic processes played a more important role than stochastic processes in determining BCC. However, the relative importance of stochasticity, primarily ecological drift, was enhanced and contributed to the increased beta diversity of BCC under enhanced warming and nutrient-enriched conditions. Overall, our study suggests that the synergetic effects of warming and nutrient enrichment may result in high variability in the composition of bacterioplankton communities in lacustrine water bodies.

Bacterioplankton Metacommunity Processes across Thermal Gradients: Weaker Species Sorting but Stronger Niche Segregation in Summer than in Winter in a Subtropical Bay

“…In summer seawater, we found lower percentages of Actinobacteria at sites with more thermal effluents, which was probably related to the obviously increased relative abundance of Cyanobacteria. This finding is consistent with previous reports showing negative relationships between the relative abundances of Cyanobacteria and Actinobacteria in aquatic ecosystems (19,41). Furthermore, Bacteroidetes have been found to be likely to attach to marine eukaryotic algae or animals (42,43).…”

“…Among all the environmental factors examined, the spatially structured temperature created by thermal effluents played the strongest role in determining bacterioplankton metacommunity structure across thermal gradients in both seasons studied. Differences in traits cause different bacterial populations to have different sensitivities to temperature during their growth processes (44)(45)(46)(47); thus, temperature is one of the most important factors in shaping bacterioplankton community structure (19,35,48). This finding was further confirmed by the positive linear correlations between BCC dissimilarities and temperature differences in any pairwise comparison of sampling sites.…”

“…Exploring the mechanisms of bacterioplankton assembly is one of the major goals of marine microbial ecology (17)(18)(19). Generally, aquatic bacterioplankton community structure is shaped by environmental or dispersal-related processes (see, e.g., references 20 to 22).…”

Factors influencing aquatic and terrestrial bacterial community assembly

“…The underlying mechanisms are unclear, but include the increased likelihood for priority effects at higher productivity because growth of early colonizers is promoted under such conditions (Steiner, 2014;Fukami, 2015). Support for similar processes operating in natural bacterial communities comes from two experimental studies from soil and freshwater bacterial communities (Ren et al, 2017) where fertilization increased the importance of stochastic processes in relation to deterministic processes, in the latter case in particular in combination with warming. On the contrary, Langenheder et al (2012) found in a field survey that species sorting processes were important in bacterioplankton communities at times when productivity in the metacommunity was high.…”

Spatial and temporal dynamics of bacterioplankton community composition in a subtropical dammed karst river of southwestern China

“…Ren et al. () found that spring bacterioplankton community composition shifted significantly under enhanced warming and nutrient‐enriched conditions. Although the above studies provide an exceptional opportunity to gain insight into the controlling factors of bacterioplankton community composition and structure in inland aquatic ecosystems, factors related to bacterioplankton diversity and communities in the city‐river section, reservoir area, and outflow area of dammed karst rivers are still unknown.…”