The effects of climate extremes on greenhouse gas emissions from Bald cypress “knees”

Project Abstract

Climate change is leading to shifts in the duration and frequency of extremes such as droughts and floods. Because wetland and adjacent stream functions are tightly linked to their hydrologic regimes, they may act as good models for studying the effects of these extreme events on carbon cycling. The objective of this study is to investigate the effect of climate extremes on greenhouse gas (GHG) fluxes from the “knees'' of Bald cypress (Taxodium distichum) trees within a bottomland hardwood wetland of Western Kentucky. Knees are aboveground woody root structures, which can emit or take up methane (CH4) and carbon dioxide (CO2), contributing to GHG emissions. We measured CH4 and CO2 fluxes from knees and soils within a slough in Clarks River National Wildlife Refuge. During a moderate to extreme drought in the Fall of 2022, soils took up CH4, while knees emitted CH4. Overall, both soils and knees (with a few exceptions of uptake) emitted quantifiable CO2. CH4 and CO2 emissions from knees increased with soil temperatures. Interestingly, soil CO2 emissions increased in areas with higher knee density, potentially due to increased root respiration. In the Spring and Summer of 2023, moderate levels of rain (~ 3.2 cm, averaged across a May and July event) during continued drought conditions did not have a discernible effect on CH4 emissions from knees when comparing before and after precipitation. However, a historic rain event, which dropped 17.7 cm of rain in 24 hours, resulted in significantly higher CH4 emissions after flooding. These increases were presumably due to increased methanogenesis in soils with more CH4 available for transport through knees. The results from this study can be used to more accurately quantify how GHG fluxes from exposed woody root structures are impacted by extreme climatic conditions.


Conference Name: American Geophysical Union Fall Meeting 2023

Dates: December 11th - December 15th, 2023

Sponsoring Body: American Geophysical Union

Conference Website:

Funding Type

Travel Grant

Academic College

Jesse D. Jones College of Science, Engineering and Technology


Environmental Science


Master of Science




Jessica B. Moon, PhD

Academic College

Jesse D. Jones College of Science, Engineering and Technology

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