Long-term warming manipulations reveal complex decomposition responses across different tundra vegetation types

In a rapidly warming tundra, ecosystems will undergo major environmental changes that are predicted to significantly alter belowground processes such as decomposition of plant litter. Making use of International Tundra Experiment sites (ITEX), which were established approximately two decades ago, we examined the long-term impacts of warming on decomposition. We used the Tea Bag Index (TBI) methodology to measure the annual mass loss (%) of two tea types as a proxy for potential decomposition rates, across five tundra vegetation types. Direct effects of warming were assessed by comparing mass loss within and outside warming manipulations. Indirect effects of warming, such as those caused by warming-induced changes in plant community composition, were assessed through the relationship between mass loss of tea and local biotic and abiotic conditions. We found positive effects of warming on decomposition, although the responses varied between vegetation and tea types. Interestingly, we found support for the indirect influence of long-term warming on decomposition through warming-induced changes in the composition of plant communities. Our findings demonstrate the complexity in decomposition responses to warming across different vegetation types and highlight the importance of long-term legacies of warming in decomposition responses across the Arctic.