Habitat fragmentation has transformed many once contiguous habitats into smaller patches varying in size, especially in forest ecosystems. However, while the consequences of habitat fragmentation for biodiversity and ecosystem functioning (e.g., productivity) have been widely documented, we know much less about how habitat fragmentation affects litter decomposition, a key component of biogeochemical cycling. Here we investigated the effect of forest fragment size on leaf litter decomposition by conducting a litterbag experiment on a group of land-bridge islands in the Thousand Island Lake in subtropical China. We also explored the mechanisms underlying litter decomposition-island area relationship by assessing the bottom-up (via soil nutrients) and top-down (via soil fauna) effects on litter decomposition. We found that the leaf litter of six common plant species with different litter quality, including Castanopsis sclerophylla, Dalbergia hupeana, Liquidambar formosana, Pinus massoniana, Quercus fabri, and Schima superba, consistently decomposed faster on larger islands, where greater soil fertility facilitated decomposition. Soil faunal diversity also enhanced litter decomposition, but its effect was mainly associated with litter quality and unaffected by island size. Our study demonstrates the deleterious effect of habitat fragmentation on litter decomposition, as well as the importance of bottom-up regulation by soil fertility in modulating habitat fragmentation effect on biogeochemical processes.

栖息地的碎片化已经将许多曾经毗邻的栖息地变成了大小不等的小片斑块，尤其是在森林生态系统中。然而，尽管栖息地破碎化对生物多样性和生态系统功能（例如生产力）的后果已得到广泛的记录，但我们对栖息地破碎化如何影响凋落物分解（生物地球化学循环的关键组成部分）的了解却少得多。在这里，我们通过对亚热带千岛湖的一组陆桥岛进行垃圾袋试验，研究了森林碎片大小对叶片凋落物分解的影响。我们还通过评估自下而上（通过土壤养分）和自上而下（通过土壤动物）对凋落物分解的影响，探索了凋落物分解与岛屿面积关系的潜在机制。苦槠，黄檀，枫香，马尾松，白栎，和木荷，一直分解上较大的岛屿，其中较大的土壤肥力促进分解得更快。土壤动物多样性也促进了凋落物分解，但其影响主要与凋落物质量有关，不受岛屿大小的影响。我们的研究表明，生境破碎化对凋落物分解的有害影响，以及土壤肥力自下而上调节对调节生化破碎化对生物地球化学过程的影响的重要性。