JCSET | Watershed Studies Institute Research Symposium
Do bald cypress knees control belowground nutrient cycling?
Academic Level at Time of Presentation
Graduate
Major
Watershed Science
List all Project Mentors & Advisor(s)
Jessica B. Moon
Presentation Format
Oral Presentation
Abstract/Description
Bald cypress (Taxodium distichum) knees are an integral part of bottomland hardwood forest understory. While little is known about why they evolved, knees have been shown to contribute to wetland methane (CH4) fluxes and models have predicted they might aid in developing soil nutrient “hot spots.” We are investigating whether knees alter belowground environments through soil and pore water chemistry and soil flux measurements near and away from knees. Pore water chemistry (i.e., dissolved organic carbon (DOC), nitrate/nitrite, conductivity, etc.) was measured monthly from May to October 2024 in knee and no knee plots at Dunn Slough in Clarks River National Wildlife Refuge, the edge of Kentucky Lake reservoir, and the edge of a depressional cypress pond at Murphy’s Pond State Nature Preserve. Methane and carbon dioxide (CO2) flux measurements were also measured in Dunn Slough from soils in 1 m2 plots with no knees, low (1 - 3 knees), medium (4 - 6 knees), and high (> 6 knees) knee densities during the fall of severe (2022) and moderate (2023) drought years. We found that pore water DOC in knee plots was significantly higher than plots without knees at the pond edge (p-value < 0.001). DOC differences at Murphy’s Pond may be attributed to hydrologic conditions, as knees are located closer to the pond, and a positive correlation between DOC and distance to the pond was found (p-value < 0.001). There were no other differences in pore water chemistry between knee and no knee plots across the sampling period. Soil CH4 and CO2 fluxes did not differ between knee densities across both years. However, during the severe drought only, soil CO2 fluxes were significantly higher in high knee density plots compared to no knees (p-value = 0.04), and there appeared to be a non-significant trend of greater CH4 uptake in higher knee densities. Our results show that knees may influence belowground nutrient cycling, but ongoing investigation into longer term stores (i.e., soil chemistry) may reveal greater insights.
Spring Scholars Week 2025
Watershed Studies Institute Research Symposium
Do bald cypress knees control belowground nutrient cycling?
Bald cypress (Taxodium distichum) knees are an integral part of bottomland hardwood forest understory. While little is known about why they evolved, knees have been shown to contribute to wetland methane (CH4) fluxes and models have predicted they might aid in developing soil nutrient “hot spots.” We are investigating whether knees alter belowground environments through soil and pore water chemistry and soil flux measurements near and away from knees. Pore water chemistry (i.e., dissolved organic carbon (DOC), nitrate/nitrite, conductivity, etc.) was measured monthly from May to October 2024 in knee and no knee plots at Dunn Slough in Clarks River National Wildlife Refuge, the edge of Kentucky Lake reservoir, and the edge of a depressional cypress pond at Murphy’s Pond State Nature Preserve. Methane and carbon dioxide (CO2) flux measurements were also measured in Dunn Slough from soils in 1 m2 plots with no knees, low (1 - 3 knees), medium (4 - 6 knees), and high (> 6 knees) knee densities during the fall of severe (2022) and moderate (2023) drought years. We found that pore water DOC in knee plots was significantly higher than plots without knees at the pond edge (p-value < 0.001). DOC differences at Murphy’s Pond may be attributed to hydrologic conditions, as knees are located closer to the pond, and a positive correlation between DOC and distance to the pond was found (p-value < 0.001). There were no other differences in pore water chemistry between knee and no knee plots across the sampling period. Soil CH4 and CO2 fluxes did not differ between knee densities across both years. However, during the severe drought only, soil CO2 fluxes were significantly higher in high knee density plots compared to no knees (p-value = 0.04), and there appeared to be a non-significant trend of greater CH4 uptake in higher knee densities. Our results show that knees may influence belowground nutrient cycling, but ongoing investigation into longer term stores (i.e., soil chemistry) may reveal greater insights.
