Plant roots are responsible for transporting large quantities of nutrients in forest ecosystems and yet are frequently overlooked in global assessments of Hg cycling budgets. In this study, we systematically determined the distribution of total Hg mass and its stable isotopic signatures in a subtropical evergreen forest to elucidate sources of Hg in plant root tissues and the associated translocation mechanisms. Hg stored in roots and its isotopic signatures show significant correlations to those found in surrounding soil at various soil depths. The odd mass-independent fractionation (MIF) of root Hg at a shallow soil depth displays a −0.10‰ to −0.50‰ negative transition compared to the values in aboveground woody biomass. The evidence suggests that root Hg is predominantly derived from surrounding soil, rather than translocation of atmospheric uptake via aboveground tissues. The cortex has a more negative mass-dependent fractionation (MDF) of −0.10‰ to −1.20‰ compared to the soil samples, indicating a preferential uptake of lighter isotopes by roots. The similar MDF and odd-MIF signals found in root components imply limited Hg transport in roots. This work highlights that Hg stored in plant roots is not a significant sink of atmospheric Hg. The heterogeneous distribution of Hg mass in roots of various sizes represents a significant uncertainty of current estimates of Hg pool size in forest ecosystems.

中文翻译：

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亚热带森林根部的汞吸收、积累和易位：全球汞预算的影响

植物根系负责在森林生态系统中运输大量养分，但在汞循环预算的全球评估中经常被忽视。在这项研究中，我们系统地确定了亚热带常绿森林中总汞质量的分布及其稳定同位素特征，以阐明植物根组织中汞的来源及其相关的易位机制。储存在根部的汞及其同位素特征与在不同土壤深度的周围土壤中发现的汞显着相关。与地上木质生物量的值相比，浅层土壤深度根 Hg 的奇数质量独立分馏 (MIF) 显示出 -0.10‰ 至 -0.50‰ 负转变。证据表明，根系汞主要来自周围的土壤，而不是通过地上组织转移大气吸收。与土壤样品相比，皮层具有更负的质量依赖性分馏 (MDF)，为 -0.10‰ 至 -1.20‰，表明根部优先吸收较轻的同位素。在根成分中发现的类似 MDF 和奇数 MIF 信号意味着根中汞的运输受限。这项工作强调了储存在植物根部的汞并不是大气汞的重要汇。不同大小根系中汞质量的不均匀分布代表了目前对森林生态系统中汞库大小的估计存在很大的不确定性。在根成分中发现的类似 MDF 和奇数 MIF 信号意味着根中汞的运输受限。这项工作强调了储存在植物根部的汞并不是大气汞的重要汇。不同大小根系中汞质量的不均匀分布代表了目前对森林生态系统中汞库大小的估计存在很大的不确定性。在根成分中发现的类似 MDF 和奇数 MIF 信号意味着根中汞的运输受限。这项工作强调了储存在植物根部的汞并不是大气汞的重要汇。不同大小根系中汞质量的不均匀分布代表了目前对森林生态系统中汞库大小的估计存在很大的不确定性。