Photo-Reactivity and Photo-Transformation of Algal Dissolved Organic Matter Unraveled by Optical Spectroscopy and High-Resolution Mass Spectrometry Analysis

Abstract

The rapid proliferation of planktonic algae induced by eutrophication and climate warming make algae dissolved organic matter (AOM) an important source of dissolved organic matter (DOM) in surface waters, but the understanding of the link between AOM composition and photo-reactivity/photo-transformation of DOM in aquatic systems is limited. Here, intracellular organic matter (IOM) from Microcystis aeruginosa was extracted and subjected to molecular weight (MW) fractionation. Results indicated that IOM had lower aromaticity and higher photosensitive activity compared to Suwannee River fulvic acid (SRFA). The photosensitive activity of IOM relied on both its molecular weight distribution and fluorescence components. The IOM fraction with the highest MW proteins had the lowest quantum yields of reactive intermediates (Φ RIs ), which increased with the decrease of MW, while the fractions with more low-excitation tyrosine-like components had relatively higher Φ RIs . Parallel factor analysis and high-resolution mass spectrometry revealed that light radiation of IOM resulted in the composition transformation from tryptophan-like and tyrosine-like components to humic-like components, forming less aromatic and more saturated recalcitrant dissolved organic carbon. Our findings provide new insights into the photo-reactivity and photo-transformation of algae-derived organic matters and help to predict DOM formation involved in carbon cycling in water environment.

Microplastics Reshape the Fate of Aqueous Carbon by Inducing Dynamic Changes in Biodiversity and Chemodiversity

“…The samples were left undisturbed for one week to allow the microbes in the water to reach a stable state prior to the experiments. A concentration of 5 mg/L AOM with 13 C was added to track the utilization of labile organic matter; the AOM concentration was based on the background organic matter content of the water and a previous study . A gas-permeable poly­(ether sulfone) (PES) membrane was used to cover each bottle to avoid excessive evaporation.…”

“…Algal organic matter (AOM) is a crucial component of natural organic matter (NOM) that is related to eutrophication and net primary productivity (NPP). , As a freshwater phytoplankton belonging to Chlorophyta, Chlorella sp. is widely distributed in aquatic systems. , Chlorella sp.…”

“…A concentration of 5 mg/L AOM with 13 C was added to track the utilization of labile organic matter; the AOM concentration was based on the background organic matter content of the water and a previous study. 20 A gaspermeable poly(ether sulfone) (PES) membrane was used to cover each bottle to avoid excessive evaporation. Four treatments were prepared: 5 mg/L AOM, 5 mg/L AOM + 0.1 mg/L PS, 5 mg/L AOM + 1 mg/L PS and 5 mg/L AOM + 10 mg/L PS.…”

“…AOM plays an important role in regulating DOM chemodiversity in aquatic environments and in controlling the fate of aqueous carbon. ,, However, the effects of MPs on the utilization of the AOM remain unclear. Here, 13 C-labeled Chlorella sp.…”

Deep-Learning-Based Automated Tracking and Counting of Living Plankton in Natural Aquatic Environments

“…As a vital component in the aquatic environment, plankton play a pivotal role in the flow of energy through ecosystem nutrients and carbon cycling − and provide early warning signs of risky environmental changes . Previous studies have revealed the correlations between water quality and plankton, including zooplankton and phytoplankton.…”