Year: 2017
Type: dissertation
Abstract: A large range of labile organic compounds are secreted by roots into the soil, which inevitably leads to changes in nutrient availability and C cycling. Little is known about root exudation variability among species, or at the individual root level, hampering estimates of total C deposition. Environmental controls are believed to influence root exudation at the single root scale, yet are rarely accounted for. Quantifying exudation heterogeneities within the root system permits more accurate upscaling to the whole plant and landscape level, provided the sites of exudation and belowground biomass are well quantified. Root exudate composition was characterized in two model organisms - Eriophorum vaginatum and Rhododendron groenlandicum utilizing localized sampling of root segments. E. vaginatum roots were distinguished into three classes by age, and R. groenlandicum into four classes by fine root abundance and root diameter. Considerable variations in the total efflux, as well as the composition of exudates, was documented at both the species and root class level, confirming that exudation is not homogenous within the root system. Existing root biomass data has little correlation with the vertical gradients of exudation. Whole plant root systems were excavated and digitally mapped at sufficient detail to explicitly distinguish the depth distribution of the roots associated with exudation. Measurements of the normalized root length fraction per depth interval were tested against a variety of density distribution models to infer a suitable function to represent roots for upscaling a single root to the landscape scale. The abundance of key species such E. vaginatum that deposit C directly into the anoxic zone are poorly mapped in peatlands. A new detection methodology, based on phenological timing and the spectral contrast of decomposing litter, was investigated utilizing an expanded version of PROSAIL. Close range imagery indicated the calibrated model was capable of quantifying decaying monocot litter as a unique class, which bodes well for detection at the landscape scale. The studies presented in this thesis document root exudation rates and root distribution data necessary to conduct a simple upscaling from the single root to the landscape level. Collectively, they permit the C flow via the exudation pathway to be estimated, with consideration for vertical gradients that partition exudation into the oxic and anoxic zone.
Source: TSpace (University of Toronto)
Author: Cameron Proctor
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
SDG: Life on land
Open Access status: green
Funder: University of Toronto
OpenAlex ID: W2883716163