State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, No. 18 Shuangqing Road, Beijing 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, No. 18 Shuangqing Road, Beijing 100085, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Environ Pollut. 2020 Apr;259:113833. doi: 10.1016/j.envpol.2019.113833. Epub 2019 Dec 17.
The emission of mercury (Hg) from cropland soil greatly affects the global Hg cycle. Combinations of different crop cultivars and planting densities will result in different light transmittance under canopies, which directly affects the solar and heat radiation flux received by the soil surface below crops. In turn, this might lead to differences in the soil-air total gaseous mercury (TGM) exchange under different cropping patterns. However, soil-air TGM exchange fluxes in croplands under differing canopies have been poorly investigated. Here, a one-year observation of TGM exchange flux was conducted for cropland soils covering five different crop cultivars and three planting densities in North China Plain using the dynamic flux chamber method. The results showed that light transmittance under the canopies was the key control on soil-air TGM exchange fluxes. High light transmittance can enhance soil TGM emission rates and increase the magnitude of diurnal variations in soil-air TGM exchange fluxes. Furthermore, we found that there were piecewise-function relationships (Peak function-constant equation) between light transmittance under the different canopies and the numbers of days after crop sowing. The soil-air TGM exchange fluxes showed a parabolic response to changes in light transmittance under the different canopies. A second-order model was established for the response relationship between soil-air TGM exchange flux and soil Hg concentration, total solar radiation above the canopy, and numbers of days after sowing. The estimated annual average soil-air TGM exchange flux was 5.46 ± 21.69 ng m h at corn-wheat rotation cropland with 30 cm row spacing using this second-order model. Our results might a data reference and a promising foundation for future model development of soil-air TGM exchange in croplands under different crop cultivars and planting densities.
农田土壤汞（Hg）的排放极大地影响了全球汞循环。不同作物品种和种植密度的组合会导致冠层下的透光率不同，这直接影响到作物下方土壤表面接收到的太阳和热辐射通量。反过来，这可能导致不同种植模式下土壤-空气总气态汞（TGM）交换的差异。然而，不同冠层下农田土壤-空气 TGM 交换通量的研究甚少。在这里，我们采用动态通量室法，对华北平原五种不同作物品种和三种种植密度的农田土壤进行了为期一年的 TGM 交换通量观测。结果表明，冠层下的透光率是控制土壤-空气 TGM 交换通量的关键因素。高透光率可以增强土壤 TGM 排放速率，并增加土壤-空气 TGM 交换通量的日变化幅度。此外，我们发现，不同冠层下的透光率与播种后天数之间存在分段函数关系（峰值函数-常数方程）。土壤-空气 TGM 交换通量与不同冠层下的透光率呈抛物线关系。建立了土壤-空气 TGM 交换通量与土壤 Hg 浓度、冠层上方总太阳辐射和播种后天数之间的响应关系的二阶模型。利用该二阶模型，估计 30 cm 行距玉米-小麦轮作农田的年平均土壤-空气 TGM 交换通量为 5.46 ± 21.69 ng m h。我们的研究结果可能为未来不同作物品种和种植密度下农田土壤-空气 TGM 交换的模型开发提供数据参考和有前景的基础。
