Data from: Inorganic fungicides as routinely applied in organic and conventional agriculture can increase palatability but reduce microbial decomposition of leaf litter

1. The application of fungicides is considered an indispensable measure to secure crop production. These substances, however, may unintentionally enter surface waters via runoff, potentially affecting the microbial community. To assess such risks adequately, authorities recently called for suitable test designs involving relevant aquatic microorganisms. 2. We assessed the structural and functional responses of leaf-associated microbial communities, which play a key role in the breakdown of allochthonous leaf material in streams, towards the inorganic fungicides copper (Cu) and elemental sulphur (S). These substances are of particular interest as they are authorized for both conventional and organic farming in many countries of the world. We used the food-choice of the amphipod shredder Gammarus fossarum (indicative for microorganism-mediated leaf palatability) as well as microbial leaf decomposition as functional endpoints. Moreover, the leaf-associated microbial communities were characterized by means of bacterial density, fungal biomass and community composition facilitating mechanistic understanding of the observed functional effects. 3. While Gammarus preferred Cu-exposed leaves over unexposed ones, microbial leaf decomposition was reduced by both Cu and S (up to 30%). Furthermore, Cu-exposure decreased bacterial densities (up to 60%), stimulated the growth of leaf-associated fungi (up to 100%) and altered fungal community composition, while S did not affect any of the assessed structural endpoints. 4. Synthesis and applications. We observed both structural and functional changes in leaf-associated microbial communities at inorganic fungicide concentrations realistic for surface water bodies influenced by conventional and organic farming. Our data hence justify a careful re-evaluation of the environmental safety of the agricultural use of these compounds. Moreover, inclusion of an experimental design similar to the one used in the present study in lower-tier environmental risk assessments of antimicrobial compounds may aid to safeguard the integrity of aquatic microbial communities and the functions they provide.

1. 杀菌剂的施用是保障作物生产不可或缺的手段。然而，此类物质可通过地表径流意外进入地表水，进而可能对水生微生物群落（microbial community）造成潜在影响。为充分评估此类风险，相关监管机构近期呼吁采用包含典型水生微生物的适宜试验方案。
2. 本研究针对溪流中在外源叶源物质分解过程中发挥关键作用的叶附生微生物群落（leaf-associated microbial community），评估其对无机杀菌剂铜（Cu）与单质硫（S）的结构与功能响应。这两种药剂在全球多数国家均被批准用于常规农业与有机农业，因此具备重要的研究价值。本研究以碎食性端足类钩虾（Gammarus fossarum）的食物选择行为（用于表征微生物介导的叶片适口性）以及叶片微生物分解速率作为功能终点指标。此外，通过测定细菌密度、真菌生物量及群落组成，对叶附生微生物群落进行表征，以深入解析观测到的功能效应的内在机制。
3. 尽管钩虾相较于未暴露叶片更偏好取食经铜处理的叶片，但铜与单质硫均会抑制叶片微生物分解过程（最大抑制率可达30%）。此外，铜暴露可使细菌密度降低最高达60%、促进叶附生真菌的生长（最大增幅可达100%）并改变真菌群落组成，而单质硫则未对所有评估的结构终点指标产生显著影响。
4. 综合与应用。本研究观测到，在受常规农业与有机农业活动影响的地表水水体中，当无机杀菌剂浓度处于现实环境水平时，叶附生微生物群落会出现结构与功能的改变。因此，本研究数据支持对这类化合物的农业施用进行审慎的环境安全性重新评估。此外，在抗菌化合物的低层级环境风险评估中纳入与本研究相似的试验设计，将有助于维护水生微生物群落及其所提供的生态功能的完整性。