Using hierarchical stable isotope to reveal microbial food web structure and trophic transfer efficiency differences during lake melt season

Abstract

The microbial food web (MFW) is a material and energy source in lake water ecosystems. Although it is crucial to determine its structure and function for water ecological health, MFW changes during lake melt period have not been well studied. In this study, the MFW was divided into three categories by analyzing its structure and trophic transfer efficiency using hierarchical C/N stable isotopes and eDNA sequencing techniques, including the detrital food web (DFC, 15 %), classical grazing food web (CFC, 60 %), and mixed trophic food web (MFC, 25 %). The trophic structure and type of MFW in ice-melting lakes are always in the process of succession and adaptation, which is in a relatively low trophic transfer efficiency stage under stable conditions (i.e. CFC), whereas the input of exogenous debris and organic pollutants may lead to an increase in MFW trophic transfer efficiency (i.e. MFC, DFC). The trophic transfer efficiency from the previous trophic level to protozoa and micrometazoa was 16.32 % and 20.77 % in DFC and 10.20 % and 29.43 % in MFC, respectively. Both are obviously higher than those of the CFC (11.69 % and 9.45 %, respectively). In terms of trophic structure, the community interaction and trophic cascade effect of DFC and MFC were enhanced but easily changed with environmental factors. In contrast, the core species and cascading effects of the CFC were clearer, and the MFW structure was relatively stable. Overall, this study reveals that the explosive increase in MFW trophic transfer efficiency induced by exogenous input during the lake melt period may subsequently lead to the destabilization of the microbial community structure and cause potential ecological risks. These are manifested in the absence of ecological trophic processes, the decrease in trophic structure complexity and stability, and the weakening of microecology self-adaptive regulation ability.