森林是陆地生态系统最为复杂的生态系统。在全球汞的生物地球化学循环中，森林生态系统到底是全球大气汞汇还是源的争议，一直悬而未决。日前，中国科学院地球化学研究所冯新斌团队围绕我国亚热带常绿阔叶林生态系统汞的生物地球化学循环规律开展系统研究，通过与温带/寒带森林生态系统汞的生物地球化学循环特征的对比，取得重要进展，相关成果发布于《地球物理学研究杂志：生物地球科学》。

冯新斌团队主要以云南哀牢山的常绿阔叶林为研究对象，进行了为期7年的土壤汞、3年的大气汞干湿沉降通量及2年的凋落物降解的连续监测，结合中国境内上百个常绿阔叶林的生物量数据及凋落物汞含量的数据，与近20年来100多个温带/寒带的森林站点汞的研究数据进行对比。

他们发现，从区域尺度来说，虽然中国背景区大气汞含量普遍高于欧美地区，但我国常绿阔叶林凋落物的汞含量并没有显著高于欧美的温带/寒带的森林系统的凋落物汞含量，这可能是因为常绿阔叶林叶片的气孔导度与叶的寿命的联合作用抵消了高大气汞含量的影响；常绿阔叶林显著升高的凋落物生物量是其凋落物的汞沉降通量显著高于温带/寒带森林系统的沉降量的主因；来自于凋落物的汞沉降是大气汞进入常绿阔叶林地面的主要方式。此外，他们对凋落物的降解过程跟踪研究发现，外界环境的汞继续被固定到凋落物降解残余物中，热带和亚热带森林土壤汞库显著高于温带/寒带的森林土壤汞库。这些研究结果表明，常绿阔叶林可能是一个显著的大气汞汇。（来源：科学网 彭科峰）

Enhanced accumulation and storage of mercury on subtropical evergreen forest floor: Implications on mercury budget in global forest ecosystems

Abstract  Forest ecosystems play an important role in the global cycling of mercury (Hg). In this study, we characterized the Hg cycling at a remote evergreen broadleaf (EB) forest site in southwest China (Mount Ailao). The annual Hg input via litterfall is estimated to be 75.0 ± 24.2 µg m⁻² yr⁻¹ at Mount Ailao. Such a quantity is up to 1 order of magnitude greater than those observed at remote temperate/boreal (T/B) forest sites. Production of litter biomass is found to be the most influential factor causing the high Hg input to the EB forest. Given their large areal coverage, Hg deposition through litterfall in EB forests is appropriately 9 ± 5 Mg yr⁻¹ in China and 1086 ± 775 Mg yr⁻¹ globally. The observed wet Hg deposition at Mount Ailao is 4.9 ± 4.5 µg m⁻² yr⁻¹, falling in the lower range of those observed at 49 T/B forest sites in North America and Europe. Given the data, the Hg deposition flux through litterfall is approximately 15 times higher than the wet Hg deposition at Mount Ailao. Steady Hg accumulation in decomposing litter biomass and Hg uptake from the environment were observed during 25 months of litter decomposition. The size of the Hg pool in the organic horizon of EB forest floors is estimated to be up to 2–10 times the typical pool size in T/B forests. This study highlights the importance of EB forest ecosystems in global Hg cycling, which requires further assessment when more data become available in tropical forests.

原文链接：http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016JG003446/full