Data from: Sediments and flow have mainly independent effects on multitrophic stream communities and ecosystem functions

Stream ecosystems are affected by multiple abiotic stressors, and species responses to simultaneous stressors may differ from those predicted based on single-stressor responses. Using 12 semi-natural stream channels, we examined the individual and interactive effects of flow level (low or high flow) and addition of fine sediments (grain size < 2mm) on key ecosystem processes (leaf breakdown, algal biomass accrual) and benthic macroinvertebrate and fungal communities. Both stressors had mostly independent effects on biological responses, with sand addition being the more influential of the two. Sand addition decreased algal biomass and microbe-mediated leaf breakdown significantly, whereas invertebrate shredder-mediated breakdown only responded to flow level. Macroinvertebrate community composition responded significantly to both stressors. Fungal biomass decreased and shredder abundance increased when sand was added; thus, organisms at different trophic levels can exhibit highly variable responses to the same stressor. Terrestrial endophytic fungi were abundant in low-flow flumes where leaf mass loss was also highest, indicating that terrestrial endophytes may contribute importantly to leaf decomposition in the aquatic environment. Leaf breakdown rates depended on the identity and abundance of the dominant decomposer species, suggesting that the effects of anthropogenic activities on ecosystem processes may be driven by changes in the abundance of a few key species. The few observed interactive effects were all antagonistic (i.e., less than the sum of the individual effects); for example, increased flow stimulated algal biomass accumulation but this effect was largely cancelled by sand. While our finding that sand and stream flow did not have strong synergistic effects can be considered reassuring for management, future experiments should manipulate these and other human stressors in experiments that run for much longer periods, thus focusing on the long-term impacts of multiple simultaneously operating stressors.河流生态系统受多种非生物胁迫因子（abiotic stressors）的影响，物种对多重胁迫因子的响应可能与基于单一胁迫因子预测的响应存在差异。本研究依托12个半天然溪流槽（semi-natural stream channels），探究了水流水平（低流量或高流量）与细颗粒物沉积物（fine sediments，粒径<2mm）添加这两个因子的单独效应与交互效应对核心生态系统过程（叶片分解（leaf breakdown）、藻类生物量累积（algal biomass accrual））以及底栖大型无脊椎动物（benthic macroinvertebrate）与真菌群落的影响。两种胁迫因子对生物响应大多表现为独立效应，其中细颗粒物添加的影响更为显著。细颗粒物添加会显著降低藻类生物量与微生物介导（microbe-mediated）的叶片分解速率，而无脊椎动物撕食者（invertebrate shredder）介导的叶片分解仅对水流水平产生响应。底栖大型无脊椎动物群落组成对两种胁迫因子均表现出显著响应。添加细颗粒物会导致真菌生物量下降，同时撕食者丰度上升；由此可见，处于不同营养级（trophic level）的生物对同一胁迫因子的响应可能存在显著差异。低流量溪流槽中陆生内生真菌（terrestrial endophytic fungi）的丰度较高，同时该环境下的叶片质量损失率也最高，这表明陆生内生真菌可能在水生环境的叶片分解过程中发挥重要作用。叶片分解速率取决于优势分解物种的种类与丰度，这提示人为活动（anthropogenic activities）对生态系统过程的影响可能由少数关键物种的丰度变化所驱动。本研究中观测到的交互效应均为拮抗效应（antagonistic，即效应强度低于两个因子单独效应的总和）；例如，高流量会促进藻类生物量累积，但这一效应会因细颗粒物添加而被大幅抵消。尽管本研究发现细颗粒物与水流未表现出显著的协同效应（synergistic effects），这一结果对于生态管理而言可视为一个积极信号，但未来的实验应设置更长的试验周期，对该类胁迫因子及其他人为胁迫因子进行操控研究，从而聚焦于多重胁迫因子同时存在时的长期生态影响。