Data from: Multiple-stressor effects on leaf litter decomposition and fungal decomposers in agricultural streams contrast between litter species

Agricultural land use commonly exerts multiple stressors on the functioning of stream ecosystems, including leaf litter decomposition and the utilization of this resource in stream food webs. If stressors interact, their cumulative effects on biotic responses cannot be predicted from knowledge of individual stressor effects, posing challenges for management and restoration of these ecosystems. We examined the individual and interactive effects of four common agricultural stressors and the role of litter quality on leaf litter decomposition and fungal decomposers. In 128 outdoor, flow-through mesocosms, we manipulated levels of nutrients, a nitrification inhibitor (dicyandiamide), deposited fine sediment, and flow velocity. Interactions among these stressors can ensue because, for instance, they jointly affect physicochemical conditions around leaf litter such as the availability of dissolved oxygen and nutrients. The two litter species used, deciduous birch and evergreen mahoe, showed contrasting decomposition dynamics and these differences influenced their response to stressors. Fungi were important for birch litter decomposition but played a minor role for mahoe. Overall, flow velocity reduction and deposited fine sediment had the strongest, mainly negative effects on fungi and litter decomposition, probably as a consequence of reductions in dissolved oxygen available to fungi. However, fine sediment substantially increased mahoe litter mass loss, pointing at fungi-independent processes being relevant for its decomposition. Although interactions among stressors were uncommon, they showed effects of the same magnitude as stressor main effects. Potential mechanisms underlying interactions included reductions in dissolved oxygen and changes in microbial community composition. Knowledge of the effects of multiple agricultural stressors and of litter quality on litter decomposition and litter-associated fungi is crucial for management of forested riparian corridors, which have been shown to efficiently mitigate impacts of agricultural stressors on streams. The contrasting responses of the litter species used in our study warrant consideration of species diversity of the riparian vegetation.

农业土地利用通常会对溪流生态系统的多项功能造成多重胁迫，涵盖叶片凋落物分解过程，以及该资源在溪流食物网中的利用途径。若多种胁迫因子发生交互作用，则无法通过单一胁迫因子的效应来预测其对生物响应的累积影响，这为这类生态系统的管理与修复带来了挑战。本研究探究了4种常见农业胁迫因子的单一与交互效应，以及凋落物质量在叶片凋落物分解与真菌分解者群落中的作用。我们在128个室外流水式中型实验生态系统（flow-through mesocosms）中，对养分水平、硝化抑制剂（nitrification inhibitor，双氰胺dicyandiamide）、沉积细泥沙以及流速进行了调控。这类胁迫因子间可能产生交互作用，例如它们会共同影响叶片凋落物周围的物理化学环境，如溶解氧与养分的可利用性。本研究选用的两种凋落物物种——落叶桦木（deciduous birch）与常绿马霍木（mahoe）——表现出截然不同的分解动态，且这种差异会影响它们对胁迫因子的响应模式。真菌在桦木凋落物分解过程中发挥了关键作用，但对马霍木凋落物分解的贡献相对有限。整体而言，流速降低与沉积细泥沙对真菌及凋落物分解产生了最为显著的负面影响，这可能是由于真菌可获取的溶解氧含量下降所致。但沉积细泥沙却显著提升了马霍木凋落物的质量损失率，这表明其分解过程中存在不依赖真菌的相关途径。尽管胁迫因子间的交互作用并不常见，但其效应强度与单一胁迫因子的主效应相当。交互作用背后的潜在机制包括溶解氧含量下降以及微生物群落组成的改变。了解多重农业胁迫因子与凋落物质量对凋落物分解及凋落物关联真菌的影响，对于森林河岸带廊道的管理至关重要——已有研究表明，河岸带廊道可有效缓解农业胁迫因子对溪流生态系统的负面影响。本研究中不同凋落物物种的响应差异，提示我们在管理中需重视河岸带植被的物种多样性。