For one-third of Earth’s land surface, precipitation passes through tree canopies (as throughfall or stemflow) before entering watersheds. Over a century of research has described fluxes of water and solutes along these “hydrologic highways”, yet little is known about their “traffic” – that is, the organisms and nonliving particulates frequently discarded from water samples after filtration in the lab. A comprehensive understanding of the composition of sub-canopy precipitation is necessary to estimate the total nutrient and pollutant inputs to watersheds for redistribution downstream, as well as to systematically investigate precipitation effects on organismal exchanges along the atmosphere–plant–soil continuum. Here, we review current concepts and research showing that the hydrologic highways from tree canopies to soil carry ecologically relevant quantities of biologic (viruses, microbes, microfauna, and meiofauna) and abiotic particulates. Their fate may have important consequences for the biogeochemistry and biodiversity of terrestrial systems.

中文翻译：

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贯穿和茎流是通过树冠的微粒交通的主要水文高速公路

对于地球陆地表面的三分之一，降水在进入流域之前通过树冠（如直通或茎流）。一个多世纪的研究已经描述了这些“水文高速公路”上的水和溶质的流量，但对其“流量”知之甚少——即实验室过滤后经常从水样中丢弃的有机体和无生命颗粒。全面了解次冠层降水的组成对于估计流域的总养分和污染物输入以重新分配下游，以及系统地研究降水对大气-植物-土壤连续体中生物交换的影响是必要的。这里，我们回顾了当前的概念和研究，表明从树冠到土壤的水文高速公路携带生态相关数量的生物（病毒、微生物、微型动物和小型动物）和非生物颗粒。它们的命运可能对陆地系统的生物地球化学和生物多样性产生重要影响。