Phytoplankton assemblage shifts with dissolved organic matter properties: A functional perspective for sentinel lakes

Abstract

1. Climate change is altering both dissolved organic matter (DOM) properties and phytoplankton dynamics in lakes. High-altitude lakes are good sentinels of global change. However, their value as sentinels depends on how well we understand their functioning. This study analysed physical, chemical and biological data during three pre-defined periods running from complete ice-cover right to the end of the ice-free season, in a high-altitude oligotrophic lake. A functional approach was used to assess how relationships between DOM and the planktonic community vary over time. 2. Phytoplankton functional change was found to occur with shifts in DOM. During the ice-influenced period, from February to the end of the thaw, the phytoplankton community was dominated by small autotrophs and mixotrophic flagellates and DOM from sediment and terrestrial origin dominated the DOM pool of the lake. Phytoplankton diversity and richness increased during the post-snowmelt overturn period, when terrestrial DOM dominated the DOM pool. Finally, large siliceous autotrophs, competitive under low nitrogen concentrations and high temperature, dominated almost exclusively during the late summer period (LSP).Increased phytoplankton biomass meant that phytoplankton-derived DOM was dominant during the LSP.3. These phenological changes in the phytoplankton community resulted in functional shifts at the base of the food web. Based on the relationships between the variables in the study, it can be deduced that the nature of the relationship between phytoplankton and bacteria progressively shifted from strong top-down control exerted by phytoplankton over bacteria towards predominantly bottomup control at the end of the ice-free season. 4. Synthesis. Using a field survey starting from complete ice-cover and lasting right to the end of the ice-free season in a sentinel lake, we show seasonal shifts in the link between DOM properties and plankton community traits. Differences in environmental conditions and DOM origin explained variation in phytoplankton community structure and function, pointing to seasonal shifts in microbial food K E Y W O R D S functional traits, global change, microbial interactions, mountain lakes, trophic interactions | 47

Algal‐ and soil‐derived dissolved organic matter shapes bacteria‐phytoplankton interactions in a high‐altitude lake

“…This last result is not surprising, as the microbial community was sampled in June, just after the snowmelt. During this period, allochthonous DOM has been showed to dominate the DOM pool in high‐altitude lakes (Dory et al., 2022; Sadro et al., 2011). In addition, this rapid response of Hbact production led to a greater lag between the peaks of Hbact and predators, such as ciliates or mixotrophs, that have slower growth rates.…”

Ecological Adaptations and Conservation Challenges of Schizothoracids in High Altitude Environments: A Mini Review

“…To understand their trophic interactions and food web dynamics in high-altitude environments, it is essential to consider the intricate relationships between these fishes and other organisms within their ecosystems. The studies on convergent evolution of rumen microbiomes in high-altitude mammals, mercury levels in wild fish from high-altitude aquatic ecosystems in the Tibetan Plateau, and shifts in phytoplankton assemblages in sentinel lakes gives a comprehensive understanding of their trophic interactions and food web dynamics (Zhang et al, 2016;Zhang et al, 2014;and Dory et al, 2022). This includes understanding the bioaccumulation of mercury in the aquatic food web, the primary productivity and energy flow within high-altitude aquatic ecosystems, and the interactions between phytoplankton and food web components.…”