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Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Peatlands account for 15 to 30% of the world's soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10-20 cm layer, were 440 ± 85.1 g kg-1 and 13.9 ± 7.4 g kg-1, with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446-532 g kg-1) and lowest in intermediate and extremely rich fens (375-414 g kg-1). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks., Competing Interests: There are no competing interests, (Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.)

Tropical peatlands in Indonesia have attracted international and domestic attention and concern in recent decades. Indonesian peatlands provide globally significant climate regulation and biodiversity provisioning ecosystem services and are central to the lives of local communities, yet they have undergone significant degradation via drainage and fire. There is a growing call for scientific knowledge of the social, environmental and practice dimensions of peatland restoration in Indonesia. This Special Volume of Mires and Peat is a collaborative effort by an Indonesian and Australian team of biophysical and social scientists to showcase primary research and systematic reviews that engage with the complexity of tropical peatland fire, conservation and restoration in Indonesia. We explore lives above ground (people and plants) and below ground (microbes, plants and the dynamic peat itself) and identify the following four themes that cut across the individual articles: 1) Livelihoods and land use; 2) Community engagement; 3) Bringing together multiple knowledges; and 4) Carbon; and draw out globally applicable lessons. We suggest that these themes highlight future directions for research which engage with the complexity of tropical peatland restoration in Indonesia, while centring the voices of local communities to support equity and sustainability in the transition to rewet peatlands. [ABSTRACT FROM AUTHOR]