Variation in Root Architecture of Common Bean and Effects on Phosphorus Acquisition
Open Access
- Author:
- Walk, Tom Campbell
- Graduate Program:
- Plant Physiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2004
- Committee Members:
- Jonathan Paul Lynch, Committee Chair/Co-Chair
Kathleen Marie Brown, Committee Member
Simon Gilroy, Committee Member
Wayne Roger Curtis, Committee Member
Virendra Puri, Committee Member - Keywords:
- computer simulation
gravitropism
phosphorus
nutrient acquisition
common bean
root architecture
fractal analysis
adventitious roots
basal roots - Abstract:
- This thesis studies relations between root architecture and acquisition of diffusion limited nutrients. Gravitropism was studied in one day and kinetics observations for Phaseolus vulgaris basal roots, secondary roots that emerge from the root-shoot interface. Variation in gravitropism among genotypes, phosphorus treatments, basal root whorls, or ethylene treatments was tested. Basal root responses to gravistimulation varied among genotypes and whorls. In kinetics observations, there were differences between the two genotypes tested in curvature and timing of graviresponsiveness. Decreased mean and increased variance of curvature responses to gravistimulation were observed with ethylene treatment, and this was not attributable to growth rate differences. Results suggest that graviresponsiveness and ethylene modulation play roles in development of root architecture. The geometric simulation model SimRoot was used to dynamically model root systems for testing how tradeoffs in allocation between adventitious and basal roots, or how variation in root architecture as determined by fractal analysis affect phosphorus acquisition. Empirical data validated simulations. Phosphorus acquisition and efficiency increase with adventitious rooting in soil conditions encountered in nature and agriculture, where more phosphorus is available near the surface than in deeper soil. This benefit of adventitious rooting is limited to plants with similar respiration among basal and adventitious roots. Adventitious roots complement basal roots, so that the most phosphorus is expected to be acquired with 30 or more adventitious roots, shallow basal roots, and seeds planted within the phosphorus rich surface soil stratum. Results will be useful in developing ideotypes for more nutrient efficient crops. Fractal analysis of simulated roots using fractal dimension, fractal abundance and lacunarity reveals higher correlation with soil phosphorus depletion volume or competition for phosphorus when fractal parameters are combined in multiple regression than when used individually in simple regression. Root length is highly correlated with soil phosphorus depletion and competition volumes, but, in practice, it is difficult to measure. Fractal analysis with two dimensional slices indicates correlation of fractal parameters with phosphorus depletion and competition, and this was verified with field trench data. Results suggest that fractal analysis of roots should include fractal abundance, and possibly lacunarity, along with fractal dimension.