A Large Amazonian Peatland Carbon Sink Was Eliminated by Photoinhibition of Photosynthesis and Amplified Ecosystem Respiration

• Published in: Geophysical research letters Vol. 52; no. 13
• Main Authors: Wood, Jeffrey D., Roman, D. Tyler, Griffis, Timothy J., Cadillo‐Quiroz, Hinsby, Castillo, Dennis, Fachin, Lizardo, Lilleskov, Erik, Kolka, Randall K., Rengifo, Jhon, Wayson, Craig
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.07.2025; Wiley
• Subjects: Anthropogenic factors; Canopies; Canopy; canopy photoinhibition; Carbon budget; Carbon cycle; Carbon sinks; Ecosystem disturbance; eddy covariance; Environmental changes; Groundwater table; Interannual variability; Irradiance; palm swamp; Peat; Peatlands; Photoinhibition; Photosynthesis; Plant cover; Respiration; Solar irradiance; Solar radiation; Swamps; Water table
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2025GL114642

The fate of tropical peatland carbon cycling under environmental change is highly uncertain. We found that a palm swamp peatland in the Peruvian Amazon that was a strong annual sink for 2 years switched to carbon neutral in the absence of a major anthropogenic disturbance. We attributed the change in carbon sink strength to (a) photoinhibition of canopy photosynthesis when skies were clearer and thus solar irradiance higher and (b) increased ecosystem respiration when the water table position was below the peat surface, and heterotrophic respiration was amplified. These mechanisms were not, however, synchronous in time. The importance of photoinhibition as a driver of changes in peatland carbon budgets is a novel finding, and an understudied mechanism of canopy photosynthetic impairment. Shifts in climate that increase periods with sustained high solar irradiance and/or low water table are thus likely to amplify interannual variability in the carbon sink strength. Plain Language Summary Peatlands store about one third of global soil carbon despite occupying less than 5% of the land area. Recent estimates show that tropical peatlands store much more carbon than previously thought. There are considerable gaps in knowledge regarding the interannual variability of carbon budgets in tropical peatlands and the way that changing environmental conditions influence the carbon cycling in these ecosystems. We show that a palm swamp peatland in the Peruvian Amazon is sensitive to changes in environmental conditions and can flip from a large carbon sink to carbon neutral when there are prolonged periods with (a) clear skies and higher light intensities that impair canopy photosynthesis and (b) a lower water table that increases peat decomposition. These findings show that the carbon budgets of these ecosystems are highly sensitive to environmental variability. Key Points Clear skies and low water tables caused an Amazonian peatland to switch from a large carbon sink to being carbon neutral Canopy photosynthesis was subject to photoinhibition when there were prolonged periods with clear skies and higher solar irradiance When the water table dropped below the surface, ecosystem respiration increased