Date of Award

Fall 2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Committee Director

Frank P. Day

Committee Member

Eric L. Waters

Committee Member

G. Richard Whittecar

Abstract

The effectiveness of ground penetrating radar (GPR) to identify and quantify coarse roots was tested in a mixed-oak forest in Southeastern Virginia using experimental pits and locally excavated root segments. GPR was found to be highly dependent on low soil moisture levels as it is unable to differentiate root structures if they possess similar moisture content as their surrounding soil. Likewise, GPR was unable to identify simulated dead roots. This does not alter the effectiveness of GPR to measure living coarse root biomass, but does present the potential for underestimation of carbon storage in coarse root structures, as a dead roots continue to store carbon. GPR was able to recognize and quantify increasing root density suggesting an ability to quantify change in root mass over time, but it was not able to reliably represent changes in root diameter.

Coarse root biomass estimation using GPR was conducted using a grid scanning technique applied to sample plots located within multiple systems. GPR effectively measured coarse root biomass across multiple systems, showing no significant difference between estimated and observed coarse root biomass in a Virginia mixed-oak forest ecosystem, a Florida scrub-oak ecosystem, or a Florida longleaf pine flatwoods ecosystem. GPR appears to have difficulty with root structures near the surface, as it is not able to reliably separate these structures from the soil-air interface.

Post-experimental disturbance effects were examined in a Florida scrub-oak ecosystem, following an 11-year open-top chamber elevated CO2 experiment that concluded in 2006 and had been abandoned for seven years. Aboveground harvest showed a significantly higher regrowth two years post fire in previously elevated CO2 plots when compared with plots that were kept at ambient CO2 levels throughout the duration of the original experiment. No significant difference was found in coarse root biomass between the two treatments; however, a non-significant trend of 12% higher biomass in the previously elevated CO2 plots was found that coincided with a similar trend observed during the original experiment. Long-lasting effects of elevated CO2 appear to exist within this system, indicating an ability for plants to store additional carbon and to regrow more rapidly following fire disturbance.

Carbon storage within coarse roots was examined in a Florida longleaf pine flatwoods ecosystem as part of a larger, ongoing effort to quantify total carbon storage and flux within multiple systems relative to longleaf pine restoration. Coarse root carbon storage was estimated at 3.5 – 3.7 kg C/m2, suggesting large carbon storage potential associated with longleaf pine restoration.

GPR is an effective, non-destructive tool for quantifying coarse root biomass and an effective but limited tool for determining root architecture. Both applications of GPR are highly dependent on user-determined settings during data collection and post-collection processing, thus effective GPR application is highly dependent on the level of familiarity possessed by the operator.

ISBN

9781369537222

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