Quality matters: Response of bacteria and ciliates to different allochthonous dissolved organic matter sources as a pulsed disturbance in shallow lakes

Date

2024-03-15

Author

Yalçın, Gülce
Yıldız, Dilvin
Calderó-Pascual, Maria
Yetim, Sinem
Şahin, Yiğit
Parakatselaki, Maria-Eleni
Avcı, Feride
Karakaya, Nusret
Ladoukakis, Emmanuel D.
Berger, Stella A.
Ger, Kemal Ali
Jeppesen, Erik
Beklioğlu, Meryem

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Shallow lake ecosystems are particularly prone to disturbances such as pulsed dissolved organic matter (allochthonous-DOM; hereafter allo-DOM) loadings from catchments. However, the effects of allo-DOM with contrasting quality (in addition to quantity) on the planktonic communities of microbial loop are poorly understood. To determine the impact of different qualities of pulsed allo-DOM disturbance on the coupling between bacteria and ciliates, we conducted a mesocosm experiment with two different allo-DOM sources added to mesocosms in a single-pulse disturbance event: Alder tree leaf extract, a more labile (L) source and HuminFeed® (HF), a more recalcitrant source. Allo-DOM sources were used as separate treatments and in combination (HFL) relative to the control without allo-DOM additions (C). Our results indicate that the quality of allo-DOM was a major regulator of planktonic microbial community biomass and/or composition through which both bottom-up and top-down forces were involved. Bacteria biomass showed significant nonlinear responses in L and HFL with initial increases followed by decreases to pre-pulse conditions. Ciliate biomass was significantly higher in L compared to all other treatments. In terms of composition, bacterivore ciliate abundance was significantly higher in both L and HFL treatments, mainly driven by the bacterial biomass increase in the same treatments. GAMM models showed negative interaction between metazoan zooplankton biomass and ciliates, but only in the L treatment, indicating top-down control on ciliates. Ecosystem stability analyses revealed overperformance, high resilience and full recovery of bacteria in the HFL and L treatments, while ciliates showed significant shift in compositional stability in HFL and L with incomplete taxonomic recovery. Our study highlights the importance of allo-DOM quality shaping the response within the microbial loop not only through triggering different scenarios in biomass, but also the community composition, stability, and species interactions (top-down and bottom-up) in bacteria and plankton.

Subject Keywords

Bottom-up control, Brownification, Mesocosm experiment, Nutrients, Top-down control

URI

https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85184835530&origin=inward
https://hdl.handle.net/11511/108592

Collections

Graduate School of Marine Sciences, Article