Environmental Drivers And Ecological Correlations Of Dissolved Organic Matter And Microbial Communities In Lakes

Lakes have low continental coverage but exhibit irreplaceable importance in terms of providing freshwater resources,maintaining regional biodiversity,participating in biogeochemical cycles,and responding of global change.Since entering the Anthropocene,the increasing human activities are leading to global environmental changes and endangering the survival of creatures and human beings on the earth.The response of lakes to environmental changes is related to the ecological stability of the local environment and even the world.However,the nature of the macroscopic response of lakes mainly depends on microscopic microbial activities.Meanwhile,dissolved organic matter(DOM)has undoubted importance,not only as an important link in the biogeochemical cycle of lake water,but also as an important nutrient source for the survival of lake microorganisms.Although many studies attempted to identify environmental drivers of lake microbes or DOM,the existing publications are often single or small-scale and cannot explain the complex relationships of multiple environmental factors at the macro-scale.Therefore,it is necessary and urgency to comprehensively investigate the distribution characteristics,driving factors of DOM and microbial communities,and ecological associations between the ecological functions of the microbial community and DOM in the lake,via combining a macroscopic perspective with microscopic analysis.Accordingly,we collected lake surface water samples from 45 lakes across China,and nearly 50 natural or anthropogenic factors were obtained through field testing and information collection.The composition and diversity of microbial communities in lake water were characterized by amplicon sequencing technology.Furthermore,the internal network relationship of microbial communities was analyzed by co-occurrence network,and the correlations between microbial communities and regional economic levels were further analyzed with a macro perspective.Meanwhile,the anti-interference ability of microorganisms in response to extreme rainfall events was evaluated through co-cultivation in a constructed microcosm.The composition of DOM molecules in lakes was determined by means of ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry.Finally,the ecological correlations between microorganisms,DOM and dissolved greenhouse gas emission were comprehensively analyzed.Results obtained based on above researches were as follow:Lake microbes were associated with regional economic level.Significant differences were observed in the structure and composition of microbial communities in lakes with different economic levels.Microbial community composition responds to regional economic level at the levels of phyla and genus,and its internal network relationship is also significantly correlated with economic level differences.Compared with the middle-level regions,the internal interactions of microorganisms in the lakes with low-or high-economic-level were more closely.The bacterial diversity of the lakes in the high economic level area was significantly lower than that in the low economic level area,while the fungal diversity showed an opposite result.The microbial diversity of lakes was mainly disturbed by anthropogenic activities including atmospheric particulate matter,waste emissions,environmental urbanization and aquaculture.In addition,the appropriate economic level(between 45,000 to 90,000 yuan/person)was helpful to maintain the diversity of lake microorganisms and the anti-interference ability to cope with extreme rainfall events,and macroeconomic measures may also be an effective means to regulate lake ecosystems.A total of 13,952 DOM molecules was identified from 45 lake DOM samples using the Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS),of which 1,959 DOM molecules were ubiquitous in all lakes and 2,242 DOM molecules only exist in a single lake.In the DOM composition in lakes,the abundance of highly unsaturated and phenolic compounds was the highest(> 64%),followed by aliphatic compounds and vascular plant-derived polyphenols(～12.4%).While the component of combustion-derived polyphenols and polycyclic aromatic hydrocarbons were the lowest(< 8.6%).The variation of chemical composition of DOM attributed to the differences of nutrient concentrations and hydrology in lakes.Human activities mainly affect the diversity of DOM in lakes through atmospheric pollution,such as atmospheric particulate matter and ozone.The differences of lake DOM response to natural and anthropogenic factors were determined by the ration of O/C and H/C of DOM molecules.The influence of environmental factors on the chemodiversity of DOM in lakes depending on sulfur-containing compounds.The composition of the DOM was associated with the release of dissolved greenhouse gases from the lake.Specifically,nitrogen-containing compounds were significantly positively correlated with carbon dioxide emissions,while N and S-free compounds were positively correlated with nitrous oxide emissions.Spearman correlation coefficient between the abundance of microbial composition in the lake and the content of DOM components was further calculated.Results indicate that the abundance of bacterial community represented by cyanobacteria in lakes was related to the elemental composition of DOM,especially sulfur compounds.DOM showed significant differences in response to various types of microbial communities at the molecular level.It not only responded to the number of DOM molecules,but also closely related to the characteristic of O/C,H/C and aromaticity in DOM molecules.DOM composition correlated with microbial functions,such as bacterial internal functions and ecological functions.N modification of S-containing compounds may be an effective way to reduce the effect of DOM on bacterial genetic information.Furthermore,fungal community function was far less active than bacterial community function in response to DOM composition.At the macro level,the direct correlation between microbial diversity and chemical diversity was not significant,and a significantly positive correlation was observed between bacterial diversity and the concentration of carbon dioxide.This study comprehensively and deeply investigated the response mechanism of microbial communities and DOM of lakes on environmental factors,and provided more comprehensive theoretical support for formulating relevant strategies to deal with global change.These results facilitate a comprehensive understanding of the interactions between lake DOM,microbial communities and the surrounding environment,thereby providing a reference for the formulation of strategies aimed at the harmonious development of human and natural environments.