Effect of Carbohydrate Demand on the Remobilization of Starch in Stolons and Roots of White Clover (Trifolium repens L.) after Defoliation

White clover plants were grown from stolon tips in growth cabinets and then defoliated. Thereafter, changes in the contents of non-structural carbohydrates such as starch, sucrose, glucose, fructose, maltose, and pinitol in stolons and roots were monitored. Initial contents of carbohydrate reserves, photosynthetic supply of new carbohydrates and carbohydrate demand after defoliation were varied by growing the plants at various CO2 partial pressures, by varying the extent of defoliation and by removing either roots or stolon tips at the time of defoliation. Remobilization of carbohydrate reserves in stolons increased proportionally to their initial contents and was greater when plants had been severely defoliated, suggesting that carbohydrates were remobilized according to availability and demand. Starch was the predominant reserve carbohydrate. Starch degradation was associated with decreased contents of sucrose, glucose and fructose in young stolon parts and roots but not in old stolon parts suggesting that starch degradation was not strictly controlled by the contents of these sugars. A decrease in the demand for carbohydrates by removal of roots did not decrease starch degradation but increased the contents of sucrose, glucose, and fructose. Removal of stolon tips decreased starch degradation and contents of sucrose, glucose, and fructose. The results suggest that starch degradation was controlled by a factor other than sucrose, glucose, and fructose which was exported from stolon tips, e.g. gibberelli

Burial Depth and Stolon Internode Length Independently Affect Survival of Small Clonal Fragments

Disturbance can fragment plant clones into different sizes and unstabilize soils to different degrees, so that clonal fragments of different sizes can be buried in soils at different depths. As a short-term storage organ, solon internode may help fragmented clones of stoloniferous plants to withstand deeper burial in soils. We address (1) whether burial in soils decreases survival and growth of small clonal fragments, and (2) whether increasing internode length increases survival and growth of small fragments under burial. We conducted an experiment with the stoloniferous, invasive herb Alternanthera philoxeroides, in which single-node fragments with stolon internode of 0, 2, 4 and 8 cm were buried in soils at 0, 2, 4 and 8 cm depth, respectively. Increasing burial depth significantly reduced survival of the A. philoxeroides plants and increased root to shoot ratio and total stolon length, but did not change growth measures. Increasing internode length significantly increased survival and growth measures, but there was no interaction effect with burial depth on any traits measured. These results indicate that reserves stored in stolon internodes can contribute to the fitness of the A. philoxeroides plants subject to disturbance. Although burial reduced the regeneration capacity of the A. philoxeroides plants, the species may maintain the fitness by changing biomass allocation and stolon length once it survived the burial. Such responses may play an important role for A. philoxeroides in establishment and invasiveness in frequently disturbed habitats