The physiological role of old stolon material in white clover (Trifolium repens L.)

Clonal plants of white clover (Trifolium repens L.), consisting of a single stolon plus roots and either three fully unfolded leaves or one fully unfolded leaf at the stolon apex, were grown in a controlled environment and sampled three times (after 7, 49 and 85 d growth) to examine the effects of increasing respiratory demand imposed by an increasing mass of old stolon material upon carbon allocation patterns and plant morphology. Where the total pool of available carbohydrate remained more-or-less constant over time, greater C allocation to stolon tissue was associated with reduced allocation to new leaf growth between d 7 and d 49. Rapid death of old stolon material began about d 70, perhaps as the result of withdrawal of C previously supplied to stolon tissue by leaves at the apex. Current assimilate no longer needed to maintain this old stolon material was, in part, reallocated to the apex region. Stolon death was greater when stolons were covered rather than fully illuminated, reflecting the elimination of direct CO₂ assimilation by stolon tissue (estimated to be 12-22% as efficient as leaves in assimilating CO₂ , on a surface area basis) and accentuation of the carbohydrate deficit. Respiration accounted for an estimated 32% of C fixed by leaves on d 85 when stolons were covered, compared to 25 % when stolons were fully illuminated. The relevance of these results to the seasonal changes in plant morphology in pastures, and the effects of stolon burial, are discussed.