Interdisciplinary Research Center for Agriculture Green Development in Yangtze River Basin, College of Resources and Environment, Southwest University, Chongqing 400715, China.
Laboratory of Environmental Nanotechnology & Health Effect, Chinese Academy of Sciences, Research Center for Eco-Environmental Sciences, Beijing 100085, China.
J Environ Sci (China). 2022 Sep;119:139-151. doi: 10.1016/j.jes.2022.05.008. Epub 2022 May 20.
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.
水位波动带（WLFZ）被认为是汞（Hg）甲基化的热点区域。耐淹草本植物逐渐适应了这种水陆交错带，往往会形成大量的根系以提高抗侵蚀能力。伴随的根际微区在 WLFZ 中甲基汞（MeHg）的形成中起着至关重要但尚不清楚的作用。因此，我们在三峡水库的 WLFZ 进行了这项研究，以探讨优势耐淹草本植物（百慕大草）根际对 MeHg 产生的影响。根际土壤中升高的 Hg 和 MeHg 表明，根际环境为 Hg 积累和甲基化提供了有利条件。根际中增加的生物可利用 Hg 和微生物活性可能是百慕大草存在时形成 MeHg 的重要因素。同时，根际环境改变了含 hgcA 微生物的丰富度、多样性和分布。在这里，筛选出了一种典型的铁还原菌（Geobacteraceae），然而，在 WLFZ 的根际、近根际和非根际土壤中检测到的大多数 hgcA 基因尚未分类。总之，这些结果为与 WLFZ 多年生草本植物根际微生物过程相关的 MeHg 产量升高提供了新的见解，对其他具有水位波动的生态系统中的 Hg 循环具有普遍意义。
