Rooting depth and root depth distribution of Trifolium repens × T. uniflorum interspecific hybrids.

Root characteristics control the interaction of plants with the soil environment, and may reflect the conditions to which the plants are adapted. Rooting depth, root mass distribution and some root morphological traits were examined in T. repens × T. uniflorum backcross 1 (BC1) hybrids in order to determine whether root characteristics of white clover could be improved through interspecific hybridisation. In well-established plants of T. uniflorum and BC1 hybrids, grown in 1 m deep tubes of sand culture, differences in root shape compared with that of white clover occurred mainly in the upper part of the profile. The roots of the BC1 hybrids, and in particular those of T. uniflorum, also penetrated more rapidly to depth than those of the white clover parents. The root distribution and rooting depth of the BC1 hybrids are likely to have been inherited from the T. uniflorum parent, and may reflect adaptations to limiting soil moisture in its natural environment. Compared with the other clover entries, T. uniflorum had thicker roots at 50-100 mm deep and more of its fine root mass at 400-500 mm. In contrast the hybrids and white clover had more of their fine root mass higher in the profile. These differences were reflected by a higher root length density (RLD) at 400-500 mm for T. uniflorum than for the other clover entries, as well as an increase in RLD with depth, while the RLD of white clover and the hybrids decreased with depth. How these differences in root morphological traits may influence nutrient interception is discussed. These results demonstrate that rooting characteristics of white clover can be altered by hybridisation with T. uniflorum, with potential impacts on nutrient interception and access to water.