The effect of nodal rooting on resource integration in Trifolium repens L.

Abstract

The sharing of resources within clonal plants, known as physiological integration, has been well documented. Physiological integration has been interpreted as a means by which clonal plants buffer heterogeneous environments. Resource distribution studies on the clonal perennial herb Trifolium repens (L.) have tended to focus on plants with very sparse nodal rooting, showing the species to be highly physiologically integrated. The impact of nodal rooting on resource distribution patterns and morphology is not a widely studied area in clonal plants. As a result, a series of investigations were carried out to study the effect of nodal rooting on resource integration, primarily in T. repens due to its importance as a forage crop.
The first investigation considered the morphological response characteristics of well rooted clones of T. repens as well as Agrostis stolonifera (L.) to spatial variation in nitrate availability. Two species were used in this study to highlight how species differences in growth strategy and morphological plasticity affect resource allocation and growth. T. repens appeared highly integrated in terms of nitrate due to a lack of intraclonal morphological differences between patches of contrasting quality; A. stolonifera displayed a mostly independent nitrate economy - local proliferations in primary and secondary tillers were restricted to nitrate supplied patches.
The aim of the next experiment was to determine the effect of nodal rooting frequency and distribution on branch establishment in T. repens within a uniformly nutrient supplied environment. Extensive nodal rooting along both the main stolon and branches resulted in significantly greater yield and greater autonomy of branches, revealed on severing the main stolon connections, giving indication of branch establishment with nodal rooting.
The results of this investigation would suggest a local utilization of nutrients by a well rooted branch in a nutrient patchy environment.
A further experiment was carried out to elucidate the resource distribution patterns of extensively rooted plants of T. repens within a nutrient patchy environment. A widespread distribution of nodal roots was initiated along branches, with or without main stolon nodal rooting. Highly localised responses in shoot biomass, root and branch stolon nodal rooting. Highly localised responses in shoot biomass, root and branch proliferations were evident at points of direct nutrient supply, pointing to an independent nutrient economy of well rooted plants of T repens. No significant differences were found in terms of morphology regarding the presence or absence of main stolon nodal roots.
The last experiment investigated carbon (C)-distribution patterns, using clones of T. repens of varying main stolon nodal rooting frequency in both steady-state and disturbed conditions. Significant basipetal movement of recently assimilated C from an apical source to a single basal nodal root was revealed in sparsely rooted plants. In more well rooted clones, i.e. plants with five consecutive main stolon nodal roots, C-distribution patterns were found to be considerably more restricted. On defoliation C was reallocated to most shoot apices in well rooted plants; negligible acropetal transport of C to shoot apices was found in sparsely rooted plants, with the basal nodal root constituting a significant sink for current photosynthate.
Extensive nodal rooting induces resource autonomy; the potential for reintegration was revealed in the defoliation experiment. The results emphasize the need to consider nodal rooting in clonal plant resource integration studies.

Date of Award	Sept 1998
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	Sir William Roberts Scholarship
Supervisor	Chris Marshall (Supervisor)