Silver birch (Betula pendula) is known to contain ice-nucleating macromolecules (INMs) to survive in harsh environments. However, little is known about the release and transport of INMs from birch trees into the atmosphere. In this study, we conducted in situ and in vivo investigations on INMs from nine birches growing in an alpine valley (Ötztal, Austria). A detailed analysis of drill cores showed that INM concentration increases towards outer layers, reaching its maximum near the surface. Aqueous extracts from the surfaces of leaves, bark, primary wood and secondary wood contained INMs (34∕36) with concentrations ranging from 9.9×10⁵ to 1.8×10⁹ INMs cm⁻². In a field study, we analysed the effect of precipitation on the release of these INMs attached to the surface of the trees. These experiments showed that INMs are splashed and aerosolized into the environment during rainfall events, at concentrations and freezing temperatures similar to in vivo samples. Our work sheds new light on the release and transport of INMs from birch surfaces into the troposphere. Birches growing in boreal and alpine forests should be considered an important terrestrial source of INMs.

中文翻译：

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白桦（Betula pendula）的表面是生物冰核的来源：体内和原位研究

已知桦树（Betula pendula）含有冰核大分子（INM），它们可以在恶劣的环境中生存。但是，人们对从桦树向大气中释放和运输INM知之甚少。在这项研究中，我们对来自高海拔山谷（奥地利厄茨塔尔）的九个桦树的INM进行了原位和体内研究。对钻芯的详细分析表明，INM浓度朝着外层增加，在地表附近达到最大值。树叶，树皮，原生木材和次生木材表面的水提物含有INMs（34∕36），浓度范围为9.9×10 ⁵至 1.8×10 ⁹  INMs cm ^-2。在现场研究中，我们分析了降水对附着在树木表面的这些INM释放的影响。这些实验表明，在降雨事件期间，INM会以类似于体内样品的浓度和冻结温度溅入并雾化到环境中。我们的工作为INM从桦树表面到对流层的释放和运输提供了新的思路。在北方和高山森林中生长的桦树应该被认为是国际非典的重要陆地来源。