Defoliation frequency and the response by white clover to increasing phosphorus supply .2. Non-structural carbohydrate concentrations in plant parts

The concentrations of total non-structural carbohydrate (%TNC) and its various forms (soluble sugars and starch) were measured in white clover plants that were grown in a glasshouse with different levels of P supply (0, 30, 90, and 180 mg/pot) and subjected to 3 defoliation frequencies (1, 2, and 4 defoliations over 36 days). Frequent defoliation reduced %TNC. Increasing P supply to the clover plants had the opposite effect, but to a lesser extent, and tended to reverse the decline in %TNC resulting from frequent defoliation. Stolons were the plant parts where most of the non-structural carbohydrate reserves were stored, with concentrations varying from <2 to >11% TNC on a dry weight basis, according to the treatment received. Minimal changes occurred in the %TNC for the leaves or roots as a result of treatments. The fluctuations in non-structural carbohydrate concentration in the stolons were mainly due to changes in the starch concentration, since the stolen sugar concentration was relatively constant between various treatments. A logistic curve closely defined the relationship (r(2)=0.98) between the starch concentration in the stolons and dry matter yield of leaves, suggesting that stolen starch reserves are a function of the size of the leaf canopy. Canopy size, in turn, was dependent on the duration of the regrowth period and, to a lesser extent, on the P supply. The maximum starch concentration in the stolons was around 8% under the conditions of this experiment.