Aluminum (Al)stress is a major limitation to crop productivity on acidic soils. To help understand the cellular mechanisms underlying the toxicity and resistance of plants to Al, this thesis involved a large-scale, transcriptomic and proteomic analysis of roots of Arabidopsis thaliana and reports on comparative analysis of transcriptome and proteome of Al stress responses. Using a microarray representing ~93% of the predicted genes in Arabidopsis, a relatively small proportion (3%) of transcripts were detected as Al- responsive. More changes in the transcriptome were detected after long-term (48 h; 1,114 genes), than short-term (6 h; 401 genes) with relatively little overlap of transcripts detected for each time point. These results suggest that Al toxicity is progressive over time and poses some unique challenges to plants. Further, using two dimensional differential in gel electrophoresis (DiGE), 12 (6 h) and 17 (48 h) proteins were found differentially abundant after Al exposure. Most of the identified proteins were involved in primary metabolism and oxidative stress. Cytosolic-malate dehydrogenase (cyt-MDH) was one of the novel Al-responsive protein identified in this study. Transcript abundance of cyt-MDH correlated well with protein abundance, suggesting that cyt-MDH is regulated in part at transcriptional level. Furthermore, homozygous mdh-1 and mdh-2 mutants were more resistant to Al as compared to WT suggesting that regulation of cyt-MDH could play a role in Al resistance. In general, comparative analysis of proteomics data and transcriptomics data showed a poor correlation for both 6 h (r2 = 0.155) and 48 h (r2 = 0.083). The potential role of five class III peroxidases (PER2, PER27, PER34, PER42, PER69) in resistance of roots to Al was explored using quantitative reverse transcriptase PCR and a reverse genetics approach. A diverse range of patterns of transcript abundance was detected using QRT-PCR in response to Al. Furthermore, per2, per21, and per69 mutants showed greater increases in root lengths as compared to WT after Al stress suggesting that regulation of PER might play a role in Al resistance. These results contribute to the identification of candidate genes for the generation of Al-resistant transgenic plants. / Plant Biology

The study of fine roots (FR) (roots < 2 mm in diameter) in the boreal forests has become a focus of many forest researchers in the past decade in an effort to better understand belowground processes and improve current carbon (C) models to better predict possible C sinks and sources. The objectives of this study were: 1) to determine the inter-annual variability in FR C production in relation to C cycling and other fluxes for four Saskatchewan boreal sites during a four year period, 2) to determine if minirhizotron (MR) estimates of root biomass were similar to root coring estimates, 3) to determine how root production, mortality, turnover, and longevity vary with root diameter class and soil depth, and 4) to determine if image collection orientation influenced estimates of FR biomass and production. Four Saskatchewan boreal sites including aspen (Populus tremuloides) (OA), black spruce (Picea mariana) (OBS), and two jack pine (Pinus banksiana) (mature OJP, young HJP94) stands were selected and MR were installed in July of 2002. Minirhizotron images were collected monthly from the end of May through September from 2003 to 2006. Total ecosystem C was estimated to be 47.5, 78.1, 163.1, and 450.5 Mg ha-1 for HJP94, OJP, OA, and OBS, respectively. The FR component of the ecosystem carbon storage ranged from 0.7 Mg ha-1 (1%) at HJP94 to 1.2 Mg ha-1 (< 1%) at OBS. Fine roots were found to contribute a very large portion of C production with estimates of 1.0, 0.6, 1.2, and 1.5 Mg ha-1 yr-1 accounting for 47, 27, 25, and 54% of total ecosystem C production at HJP94, OJP, OA, and OBS, respectively. In a one time comparison of MR and soil cores, FR biomass estimates were found to be similar at OJP, OA, and OBS, with MR estimates being significantly greater at HJP94. Approximately 85, 90, 96, and 96% of FR measured in this study were found to be less than 0.5 mm in diameter with median diameters of 0.250 ± 0.237, 0.225 ± 0.208, 0.175 ± 0.149 and 0.150 ± 0.149 (median ± SD) mm at HJP94, OJP, OA, and OBS, respectively. Fine root longevity was found to increase with increasing diameter and soil depth while turnover decreased. In many cases, it was found that even within a diameter interval of < 0.1 mm, differences in biomass, production, turnover, and longevity were detectable. This brings into question the use of the traditional 2 mm diameter class in FR studies. Fine root data, such as presented in this thesis, help to fill in some of the gaps in the knowledge base, enabling researchers to better understand the underground processes of the boreal forest and develop more complex and accurate C models.

Nitrogen (N) contained in roots and rhizodeposits represents a significant input of crop residue-N into soil that is often unaccounted, despite its contribution to the total N budget and its influence on soil nutrient cycling. Utilizing 15N-labeling methodologies under controlled conditions, the goal of this research was to quantify the input of belowground N (BGN), including rhizodeposits and roots, to soil and to investigate the influence of BGN on soil N cycling processes from the major pulse and oilseed crop grown across the Canadian prairies—namely, field pea and canola, respectively. Using continuous 15N2 labeling, the input of fixed-N to rhizosphere soil from pea plants amounted to less than 2% of the total plant N assimilated via fixation. Nodulation and root 15N enrichment were positively related to rhizosphere 15N enrichment, suggesting that the relatively low input of fixed-N to soil was due to low N fixation in this system. Shoot 15N-labeling techniques enabled a higher 15N enrichment in roots; as a result, rhizodeposition was detected in the rhizosphere as well as the surrounding bulk soil. Rhizodeposition accounted for 7.6 and 67% of plant N and BGN, respectively, in mature pea. Temporal changes in the pattern of rhizodeposition were detected as evidenced by differing 15N enrichment in rhizosphere versus bulk soils. In comparison to pea, a higher proportion of BGN contributed to the total residue-derived N from canola. The higher quantity of N rhizodeposition by canola was related to greater root biomass. However, pea rhizodeposition contributed more to soil inorganic N pools; this was sustained over time, as a higher proportion of pea BGN contributed to the growth of a subsequent wheat crop. In addition, wheat uptake of residue-derived N was twice as much from belowground compared to straw residues. Whereas the abundance of denitrifying bacterial communities in the rhizosphere was uncoupled from rhizodeposition and denitrification enzyme activity (DEA), root-derived 15N correlated with DEA in pea and canola. This research highlights the importance of belowground inputs from differing crop species on N budgets and soil N cycling.

The study of fine roots (FR) (roots < 2 mm in diameter) in the boreal forests has become a focus of many forest researchers in the past decade in an effort to better understand belowground processes and improve current carbon (C) models to better predict possible C sinks and sources. The objectives of this study were: 1) to determine the inter-annual variability in FR C production in relation to C cycling and other fluxes for four Saskatchewan boreal sites during a four year period, 2) to determine if minirhizotron (MR) estimates of root biomass were similar to root coring estimates, 3) to determine how root production, mortality, turnover, and longevity vary with root diameter class and soil depth, and 4) to determine if image collection orientation influenced estimates of FR biomass and production. Four Saskatchewan boreal sites including aspen (Populus tremuloides) (OA), black spruce (Picea mariana) (OBS), and two jack pine (Pinus banksiana) (mature OJP, young HJP94) stands were selected and MR were installed in July of 2002. Minirhizotron images were collected monthly from the end of May through September from 2003 to 2006. Total ecosystem C was estimated to be 47.5, 78.1, 163.1, and 450.5 Mg ha-1 for HJP94, OJP, OA, and OBS, respectively. The FR component of the ecosystem carbon storage ranged from 0.7 Mg ha-1 (1%) at HJP94 to 1.2 Mg ha-1 (< 1%) at OBS. Fine roots were found to contribute a very large portion of C production with estimates of 1.0, 0.6, 1.2, and 1.5 Mg ha-1 yr-1 accounting for 47, 27, 25, and 54% of total ecosystem C production at HJP94, OJP, OA, and OBS, respectively. In a one time comparison of MR and soil cores, FR biomass estimates were found to be similar at OJP, OA, and OBS, with MR estimates being significantly greater at HJP94. Approximately 85, 90, 96, and 96% of FR measured in this study were found to be less than 0.5 mm in diameter with median diameters of 0.250 ± 0.237, 0.225 ± 0.208, 0.175 ± 0.149 and 0.150 ± 0.149 (median ± SD) mm at HJP94, OJP, OA, and OBS, respectively. Fine root longevity was found to increase with increasing diameter and soil depth while turnover decreased. In many cases, it was found that even within a diameter interval of < 0.1 mm, differences in biomass, production, turnover, and longevity were detectable. This brings into question the use of the traditional 2 mm diameter class in FR studies. Fine root data, such as presented in this thesis, help to fill in some of the gaps in the knowledge base, enabling researchers to better understand the underground processes of the boreal forest and develop more complex and accurate C models.

published_or_final_version / Paediatrics and Adolescent Medicine / Master / Master of Philosophy

Plant roots provide important soil reinforcement and improve the stability of slopes. From an engineering view, roots mechanically increase soil shear strength by transforming shear stress from soil into tensile forces of roots themselves via interface friction thus acting like soil nails. However, due to the complex spatial geometries and mechanical heterogeneities of natural root systems, more specific considerations are needed when analyzing the root reinforcement issues. According to a literature review, most studies on slope stability consider root reinforcement as an apparent cohesion by upscaling the behaviour of static individual roots. However, recent studies have shown that better predictions can be made if the progressive failure of roots is considered, thus highlighting the importance of load-displacement relations of soil-root interaction. Therefore, numerical pull-out tests considering the progressive friction interface relationship were carried out in this study to investigate the mechanism and the influences of various factors on plant root pull-out behaviour, which is of great importance to evaluating the stabilization effect of roots. In this study, the classic Coulomb friction model was adopted to simulate the interaction along the root-soil interface with the surface to surface modelling technique available in ABAQUS. The numerical investigations could be mainly divided into three parts: study of single straight root pull-out behaviour, study of the branched root segments with only first-order lateral branches (herringbone system), and study of the root segments with second-order branches (dichotomous system). Conclusions regarding the mechanism of the root pull-out process, the influence of geometry-related factors and the influence of the intrinsic factors related to mechanical properties and root-soil interaction were drawn based on the observations of the numerical pull-out tests. Progressive stick-to-slip behaviours along the root-soil interface were observed in the numerical models. Generally, the pullout resistance of roots increased with the branch depth and branch length. It was also observed that the pullout resistance had strong regression with the weight of the soil potentially lifted by the root system. The most efficient branch angle for providing pull-out resistance for the herringbone system was between 60 and 90 degrees and the most efficient branch angle for the dichotomous root system was shown to be around 45. The central symmetrical branch arrangement pattern was observed to be the most efficient in providing pull-out resistance compared with the plate symmetrical and asymmetrical patterns. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

In the study of mathematics, one of the most useful, relevant topics explored in secondary mathematics remains the zeros of polynomials. This paper will present various ways to explore this topic while preserving the fundamental concept as a whole. In addition, this paper will reveal some distinct relationships between roots and their behavior within the different branches of mathematics. The purpose of this paper is to show how this topic can be inserted at key points in the developmental curriculum to preserve the autonomy of this vital mathematical concept, allowing students to experience the behavior and value of this topic in a variety of contexts. / text

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