Root system traits and root longevities in two contrasting cultivars of Trifolium repens (White clover)
This study uses sequential digital imaging of rhizotron grown root systems of white clover (Trifolium repens) to evaluate the developmental differences in the architecture of two cultivars with contrasting above-ground characteristics. Root lengths and leaf areas were correlated in both cultivars, with large leaved Alice producing greater leaf area and greater root length than the small leaved S184. The key architectural difference between the two cultivars was that Alice produced a higher ratio of terminal lateral length to axial length than S184. Lateral roots had lower survival times compared with axial roots in both cultivars. Amongst lateral roots, survival was positively influenced by diameter. A 0.1 mm increase in diameter was calculated to result in between 23% and 42% reduction in the risk of lateral root mortality. Destructive investigations of the root systems were made at intervals during the experiment and roots of known age and order were excised and evaluated for C and N content and tissue density. Axial roots were found to have higher tissue density and higher C and N content than laterals, and, these traits increased with increasing axial root age. The hypothesis that axial roots are invested with additional high C compounds to increase their persistence in the soil was supported by microscopic analysis which shown a build up of lignin in axial roots as they aged. A population dynamics model was constructed showing the estimated flux of C and N from plant to soil due to root mortality. The most dynamic C and N pool was in the lateral roots. Breeding and selection of white clover cultivars should aim to maximise the ephemeral lateral root system component to enhance N flux from plant to soil.