Role of the rhizosphere of a flooding-tolerant herb in promoting mercury methylation in water-level fluctuation zones


Yongmin Wang , Juan Wang , Yuping Xiang , Xiaosong Tian , Cheng Zhang , Guiqing Gong , Jinping Xue , Tao Jiang , Dingyong Wang , Yong Cai , Xinbin Feng , Shuxiao Wang , Huan Zhong , Ping Li , Yongguang Yin

DOI:10.1016/j.jes.2022.05.008

Received February 24, 2022,Revised , Accepted May 06, 2022, Available online May 20, 2022

Volume 34,2022,Pages 139-151

The water-level fluctuation zone (WLFZ) has been considered as a hotspot for mercury (Hg) methylation. Flooding-tolerant herbs are gradually acclimated to this water-land ecotone, tending to form substantial root systems for improving erosion resistance. Accompanying rhizosphere microzone plays crucial but unclear roles in methylmercury (MeHg) formation in the WLFZ. Thus, we conducted this study in the WLFZ of the Three Gorges Reservoir, to explore effects of the rhizosphere of a dominant flooding-tolerant herb (bermudagrass) on MeHg production. The elevated Hg and MeHg in rhizosphere soils suggest that the rhizosphere environment provides favorable conditions for Hg accumulation and methylation. The increased bioavailable Hg and microbial activity in the rhizosphere probably serve as important factors driving MeHg formation in the presence of bermudagrass. Simultaneously, the rhizosphere environments changed the richness, diversity, and distribution of hgcA-containing microorganisms. Here, a typical iron-reducing bacterium (Geobacteraceae) has been screened, however, the majority of hgcA genes detected in rhizosphere, near-, and non-rhizosphere soils of the WLFZ were unclassified. Collectively, these results provide new insights into the elevated MeHg production as related to microbial processes in the rhizosphere of perennial herbs in the WLFZ, with general implications for Hg cycling in other ecosystems with water-level fluctuations.

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