Soil bacteria and fungi are key drivers of carbon released from soils to the atmosphere through decomposition of plant-derived organic carbon sources. This process has important consequences for the global climate. While global change factors, such as increased temperature, are known to affect bacterial- and fungal-mediated decomposition rates, the role of trophic interactions in affecting decomposition remains largely unknown. We designed synthetic microbial communities consisting of eight bacterial and eight fungal species and tested the influence of predation by a model protist, Physarum polycephalum, on litter breakdown at 17 and 21 °C. Protists increased CO₂ release and litter mass loss by ~35% at 17 °C lower temperatures, while they only had minor effects on microbial-driven CO₂ release and mass loss at 21 °C. We found species-specific differences in predator–prey interactions, which may affect microbial community composition and functioning and thus underlie the impact of protists on litter breakdown. Our findings suggest that microbial predation by fast-growing protists is of under-appreciated functional importance, as it affects decomposition and, as such, may influence global carbon dynamics. Our results indicate that we need to better understand the role of trophic interactions within the microbiome in controlling decomposition processes and carbon cycling.

土壤细菌和真菌是通过分解植物衍生的有机碳源将碳从土壤释放到大气中的关键驱动因素。这一过程对全球气候具有重要影响。虽然已知全球变化因素（例如温度升高）会影响细菌和真菌介导的分解速率，但营养相互作用在影响分解中的作用仍然很大程度上未知。我们设计了由 8 种细菌和 8 种真菌组成的合成微生物群落，并测试了模型原生生物多头绒泡菌捕食对 17°C 和 21°C 凋落物分解的影响。在 17 °C 较低的温度下，原生生物增加了约 35% 的 CO ₂释放和垃圾质量损失，而它们对微生物驱动的 CO 的影响很小₂在 21 °C 时释放和质量损失。我们发现捕食者 - 猎物相互作用的物种特异性差异，这可能会影响微生物群落组成和功能，从而成为原生生物对垃圾分解影响的基础。我们的研究结果表明，快速生长的原生生物对微生物的捕食具有未被充分认识的功能重要性，因为它会影响分解，因此可能会影响全球碳动态。我们的结果表明，我们需要更好地了解微生物组内营养相互作用在控制分解过程和碳循环中的作用。