| Summary: | Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats. National Science Foundation (Grant 1114155) National Science Foundation (Grant 1114161) NSF (Award 0628647) US Department of Energy, Office of Science, Office of Biological and Environmental Research (contract DE-SC0012088) US Department of Energy Office of Biological and Environmental Research under the Genomic Science program (Award DE-SC0004632) US Department of Energy Office of Biological and Environmental Research under the Genomic Science program (Award DE-SC0010580) US Department of Energy Office of Biological and Environmental Research under the Genomic Science program (Award DE-SC0016440) NASA Interdisciplinary Studies in Earth Science program (Award NNX17AK10G) US Department of Energy Office of Biological and Environmental Research under the Terrestrial Ecosystem Sciences program (Award DE-SC0012272)
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