Litter decomposition plays an important role in biogeochemical cycling in boreal peatlands, where mosses, especially Sphagnum species, are a determinant. In recent decades, these peatlands have experienced a decline in moss cover due to abrupt climate warming and atmospheric nitrogen (N) deposition. To reveal the effect of the reduction in moss cover on litter decomposition, we adopted a field living moss removal experiment (with the senesced tissues remaining) in a Sphagnum-dominated boreal peatland, and investigated litter mass loss and net N loss of three deciduous woody species decomposing in monocultures and mixtures over 3 years. Based on the observed and predicted mass loss and net N loss of litter mixtures, we divided litter mixing effects into additive (no significant difference), synergistic (observed value greater than predicted value), and antagonistic (observed value lower than predicted value) effects. Across 3 years of decomposition, moss removal increased litter mass loss and net N loss, irrespective of single- or mixed-species compositions. Moss removal generally changed litter mixing effects on mass loss from antagonistic to additive effects in the initial 2 years, but from synergistic to additive effects after 3 years of decomposition. Regarding net N loss of litter mixtures, moss removal often resulted in a shift from additive to synergistic effects or from antagonistic to additive effects after 2 and 3 years of decomposition. Our observations suggest that the declines in living moss cover can accelerate litter decomposition and nutrient release, and highlight that living moss loss makes litter mixture decomposition predictable by reducing non-additive effects in boreal peatlands. Given the widespread occurrence of reduced moss cover in boreal peatlands, the mechanisms explaining living moss controls on litter decomposition and N cycling should receive significant attention in further studies.

凋落物分解在北方泥炭地的生物地球化学循环中发挥着重要作用，其中苔藓，特别是泥炭藓物种，是一个决定因素。近几十年来，由于气候突然变暖和大气中氮（N）沉降，这些泥炭地的苔藓覆盖率下降。为了揭示苔藓覆盖减少对凋落物分解的影响，我们在以泥炭藓为主的北方泥炭地中进行了现场活苔藓去除实验（保留衰老组织），并研究了三种落叶木本植物的凋落物质量损失和净氮损失。单一栽培和混合栽培的物种在 3 年内会分解。根据观测和预测的凋落物混合物的质量损失和净氮损失，我们将凋落物混合效应分为加性效应（无显着差异）、协同效应（观测值大于预测值）和拮抗效应（观测值低于预测值） 。经过 3 年的分解，苔藓去除增加了凋落物质量损失和净氮损失，无论单一或混合物种的组成如何。苔藓去除通常会在最初的 2 年内改变垃圾混合对质量损失的影响，从拮抗效应变为相加效应，但在分解 3 年后从协同效应变为相加效应。关于凋落物混合物的净氮损失，在分解 2 和 3 年之后，苔藓去除通常会导致从相加效应转变为协同效应，或从拮抗效应转变为相加效应。我们的观察表明，活苔藓覆盖的减少可以加速凋落物分解和养分释放，并强调，活苔藓的损失通过减少北方泥炭地的非加性效应，使凋落物混合物的分解变得可预测。鉴于北方泥炭地苔藓覆盖减少的普遍现象，解释活苔藓控制凋落物分解和氮循环的机制应该在进一步的研究中受到高度重视。