The double-edged environmental effect of dissolved organic matter in global climate change

Dissolved organic matter (DOM) constitutes a core vector connecting organic carbon cycles in terrestrial and aquatic ecosystems, playing significant roles in various biogeochemical processes. Commencing from DOM quality variations, this review analyzes transformations in its structural properties (e.g., aromatic/aliphatic components, oxygen-containing functional groups, reactivity and stability) and biogeochemical processes (e.g., microbial and photochemical reactions and interaction with aquatic organisms) under global climate change with an emphasis on global warming. This study analyzes and synthesizes the current knowledge on climate-induced modifications to transport-transformation behaviors and bioavailability of environmental pollutants (heavy metals, organic pollutants, microplastics) governed by DOM, while assessing impacts of climate-driven DOM alterations on modulating functions in biological growth and metabolic processes, toxicological ramifications, and xenobiotic toxicity. Furthermore, DOM possesses a bidirectional climate feedback mechanism; its positive/negative feedback is dissected through carbon source-sink switching under climate change. The structural complexity of the DOM, together with the non-equilibrium state and multi-effect superposition characteristic of global climate change, collectively pose significant challenges to the accurate assessment of the climate feedback of DOM. Bidirectional environmental effects of DOM are critical for ecosystem functioning and human survival/development. Global climate change is altering the environmental effects of DOM by modifying its biogeochemical cycling; yet, current understanding remains constrained by system complexity. Systematic comprehension demands interdisciplinary collaboration to generate the necessary data for society to proactively mitigate climate change.