Dying aquatic plants present a double-edged sword for lakes: fueling pollution while locking away carbon

A new study published in Carbon Research has uncovered the complex and contradictory role that dying aquatic plants play in the health of shallow lakes. Using controlled mesocosm experiments, a team of scientists tracked the full life cycle of the floating-leaved macrophyte Trapa bispinosa, revealing that its decline simultaneously poses a risk of eutrophication while enhancing the lake’s ability to sequester carbon through a process known as the microbial carbon pump (MCP).

The research demonstrates that as these plants decay, they release substantial amounts of nitrogen and phosphorus into the water. This nutrient pulse can fuel algal blooms and create hypoxic (low-oxygen) "dead zones," posing a significant threat to water quality. However, this decay process also releases a flood of dissolved organic matter (DOM), the primary food source for aquatic microbes. The study found this isn't just a release of waste; it’s a fundamental shift in the lake’s carbon chemistry.

A Chemical Transformation

By combining advanced spectrometry with ecological network analysis, the researchers observed a dramatic transformation in the nature of the DOM as the plants transitioned from health to decay. Initially, the DOM consisted of simple, labile compounds like proteins and lipids that are easily consumed by bacteria. But as the decay progressed, the DOM became increasingly complex, aromatic, and recalcitrant—meaning it was much harder for microbes to break down. This build-up of tough, carbon-rich molecules like tannins and lignin-like compounds forms a more stable and persistent carbon pool in the lake.

"For the first time, we've tracked the entire health-to-decay cycle of these plants in a controlled setting, linking water chemistry, DOM molecules, and microbial communities," says Dr. Songhe Zhang, the study's corresponding author. "Our results show this transition is a critical, overlooked event in lake ecosystems. It’s not just a process of decay; it's a profound transformation of the lake's chemistry and biology, creating a high-risk, high-reward scenario for carbon and nutrient cycling."

The Microbial Carbon Pump at Work

This chemical shift in DOM fundamentally reshaped the lake's bacterial community. The study found that as oxygen levels dropped and complex DOM accumulated, bacterial diversity declined, and specialized microbes capable of thriving in these harsh conditions, such as Campylobacterota and Desulfobacterota, became enriched. More importantly, the analysis suggests that certain bacteria, including Polynucleobacter and Rhodobacterales, act as key players in the microbial carbon pump. They actively process the simple, plant-derived organic matter and transform it into more resilient, complex carbon forms.

"We discovered a fascinating partnership between the decaying plants and specific microbial communities," explains Jin Lei, the first author of the study. "These bacteria aren't just eating the released organic matter; they are actively re-engineering it into more resilient carbon structures. This process effectively locks carbon away, preventing it from immediately returning to the atmosphere as CO₂ and contributing to the lake’s long-term carbon sink."

The findings present a crucial trade-off for lake managers. In nutrient-polluted lakes, allowing floating plants to fully decay could worsen eutrophication. In these cases, pre-senescence harvesting might be necessary to protect water quality. However, in ecosystems where enhancing carbon sequestration is a priority, managing macrophyte life cycles to promote this microbial transformation could be a valuable nature-based climate solution.

This research provides a new lens through which to view the role of aquatic plants in global carbon cycles. By identifying the decline of floating-leaved macrophytes as a powerful biogeochemical driver, the study offers critical insights for balancing water-quality protection with the enhancement of natural carbon sinks in freshwater ecosystems worldwide.

Corresponding Author: Songhe Zhang

Original Source: https://doi.org/10.1007/s44246-026-00262-8

Contributions: All authors contributed to the study conception and design. Data curation, formal analysis, methodology development, and drafting of the original manuscript were performed by Jin Lei. Funding acquisition, and review and editing of the manuscript were performed by Songhe Zhang. Investigation and methodological support were performed by Hezhou Chen. Visualization and review and editing of the manuscript were performed by Yuyu Li and Wenjie Yuan. Review and editing of the manuscript were performed by Aiyu Qu. All authors read and approved the final manuscript.