1. Microplastics in soils have become an important threat for terrestrial systems as they may potentially alter the geochemical/biophysical soil environment and can interact with drought. As microplastics may affect soil water content, this could exacerbate the well‐known negative effects of drought on ecosystem functionality. Thus, functions including litter decomposition, soil aggregation or those related with nutrient cycling can be altered. Despite this potential interaction, we know relatively little about how microplastics, under different soil water conditions, affect ecosystem functions and multifunctionality.
2. To address this gap, we performed an experiment using grassland plant communities growing in microcosms. Microplastic fibres (absent, present) and soil water conditions (well‐watered, drought) were applied in a fully factorial design. At harvest, we measured soil ecosystem functions related to nutrient cycling (β‐glucosaminidase, β‐D‐cellobiosidase, phosphatase, β‐glucosidase enzymes), respiration, nutrient retention, pH, litter decomposition and soil aggregation (water stable aggregates). As terrestrial systems provide these functions simultaneously, we also assessed ecosystem multifunctionality, an index that encompasses the array of ecosystem functions measured here.
3. We found that the interaction between microplastic fibres and drought affected ecosystem functions and multifunctionality. Drought had negatively affected nutrient cycling by decreasing enzymatic activities by up to ~39%, while microplastics increased soil aggregation by ~18%, soil pH by ~4% and nutrient retention by up to ~70% by diminishing nutrient leaching. Microplastic fibres also impacted soil enzymes, respiration and ecosystem multifunctionality, but importantly, the direction of these effects depended on soil water status. That is, under well‐watered conditions, these functions decreased with microplastic fibres by up to ~34% while under drought they had similar values irrespective of the microplastic presence, or tended to increase with microplastics. Litter decomposition had a contrary pattern increasing with microplastics by ~6% under well‐watered conditions while decreasing to a similar percentage under drought.
4. Synthesis and applications. Single ecosystem functions can be positively or negatively affected by microplastics fibres depending on soil water status. However, our results suggest that microplastic fibres may cause negative effects on ecosystem soil multifunctionality of a similar magnitude as drought. Thus, strategies to counteract this new global change factor are necessary.

中文翻译：

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微塑料和干旱对土壤生态系统功能和多功能性的影响

1. 土壤中的微塑料已成为陆地系统的重要威胁，因为它们可能会改变地球化学/生物物理土壤环境，并可能与干旱相互作用。由于微塑料可能会影响土壤水分，因此可能加剧干旱对生态系统功能的众所周知的负面影响。因此，可以改变包括凋落物分解，土壤聚集或与养分循环有关的功能。尽管存在这种潜在的相互作用，但我们对在不同土壤水分条件下的微塑料如何影响生态系统功能和多功能性的了解相对较少。
2. 为了解决这一差距，我们使用缩微生长的草原植物群落进行了一项实验。在全因子设计中应用了微塑性纤维（不存在，存在）和土壤水分状况（浇水充足，干旱）。在收获时，我们测量了与养分循环相关的土壤生态系统功能（β-氨基葡萄糖苷酶，β-D-纤维二糖苷酶，磷酸酶，β-葡萄糖苷酶），呼吸作用，养分保留，pH，凋落物分解和土壤聚集（水稳定聚集体）。由于地面系统同时提供这些功能，因此我们还评估了生态系统的多功能性，该指数涵盖了此处测量的生态系统功能的阵列。
3. 我们发现，微塑料纤维与干旱之间的相互作用影响了生态系统的功能和多功能性。干旱通过减少多达39％的酶活性而对养分循环产生不利影响，而微塑料通过减少养分浸出而使土壤聚集增加了〜18％，pH值增加了约4％，养分保持率增加了约70％。超细塑料纤维还影响土壤酶，呼吸作用和生态系统的多功能性，但重要的是，这些作用的方向取决于土壤的水分状况。也就是说，在充水的条件下，这些功能随着微塑性纤维的作用而降低了约34％，而在干旱条件下，无论微塑性存在与否，它们的功能值都相似，或者随着微塑性的增加而趋于增强。
4. 综合与应用。取决于土壤水分状况，微生态纤维可以对单个生态系统功能产生正面或负面影响。但是，我们的结果表明，微塑性纤维可能会对生态系统的土壤多功能性产生负面影响，其程度与干旱相似。因此，有必要采取应对措施来应对这一新的全球变化因素。