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Freshwater reservoirs are an important source of the greenhouse gas methane (CH(4)) to the atmosphere, but global emission estimates are poorly constrained (13.3–52.5 Tg C yr(−1)), partially due to extreme spatial variability in emission rates within and among reservoirs. Spatial heterogeneity in the availability of organic matter (OM) for biological CH(4) production by methanogenic archaea may be an important contributor to this variation. To investigate this, we measured sediment CH(4) potential production rates, OM source and quantity, and methanogen community composition at 15 sites within a eutrophic reservoir in Ohio, USA. CH(4) production rates were highest in the shallow riverine inlet zone of the reservoir, even when rates were normalized to OM quantity, indicating that OM was more readily utilized by methanogens in the riverine zone than in the transitional or lacustrine zones. Sediment stable isotopes and C:N indicated a greater proportion of terrestrial OM in the particulate sediment of this zone. Methanogens were present at all sites, but the riverine zone contained a higher relative abundance of methanogens capable of acetoclastic and methylotrophic methanogenesis, likely reflecting differences in decomposition processes or OM quality. While we found that methane potential production rates were negatively correlated with autochthonous carbon in particulate sediment OM, rates were positively correlated with indicators of autochthonous carbon in the porewater dissolved OM. It is likely that both dissolved and particulate sediment OM affect CH(4) production rates, and that both terrestrial and aquatic OM sources are important in the riverine methane production hot spot.

Tropical forests represent 50% of the planet's species and play a disproportionately large role in determining climate due to the vast amounts of carbon they store and exchange with the atmosphere. Currently, disturbance patterns in tropical ecosystems are changing due to factors such as increased land use pressure and altered patterns in hurricanes. At the same time, these regions are expected to experience unprecedented warming before 2100. Despite the importance of these ecosystems for forecasting the global consequences of multiple stressors, our understanding of how projected changes in climate and disturbance will affect the biogeochemical cycling of tropical forests remains in its infancy. Until now, no studies to our knowledge have evaluated forest recovery following hurricane disturbance within the context of concurrent climatic change. Here, we present soil biogeochemical results from a tropical forest field warming experiment in Puerto Rico where, a year after experimental warming began, Hurricanes Irma and Maria greatly altered the forest, allowing a unique opportunity to explore the interacting effects of hurricane disturbance and warming. We tracked post-hurricane forest recovery for a year without warming to assess legacy effects of prior warming on the disturbance response, and then reinitiated warming treatments to further evaluate interactions between forest recovery and warmer temperatures. The data showed that warming affected multiple aspects of soil biogeochemical cycling even in the first year of treatment, with particularly large positive effects on soil microbial biomass pools (e.g., increases of 54%, 33%, and 38% relative to the control plots were observed for microbial biomass carbon, nitrogen, and phosphorus, respectively after 6 months of warming). We also observed significant effects of the hurricanes on soil biogeochemical cycling, as well as interactive controls of warming and disturbance. Taken together, our results showed dynamic soil responses that suggest the future of biogeochemical cycling in this tropical wet forest will be strongly shaped by the directional effects of warming and the episodic effects of hurricanes.