Reproductive allocation in plants of Scrophularia nodosa grown at various levels of irradiance and soil fertility

The reproductive allocation of dry matter and mineral nutrients to flowers, capsules and seed was studied in plants of Scrophularia nodosa grown in a factorial, three (irradiation) x three (soil fertility), scheme in an experimental garden and in an irradiation gradient (on a natural soil) in a glasshouse. In the irradiation gradient a marked trade-off between sexual reproduction and vegetative propagation was shown: more flowering and seed production at higher irradiation, exclusively rhizome production at the low irradiation. There was no convergence between carbon allocation and nutrient allocation. At decreasing irradiation, biomass production decreased and concentrations of K, N, Na and P increased in all plant parts. In the factorial experiment a reduction of the irradiation from full daylight to 8% of daylight decreased the biomass production and the shoot:root ratio, once more enhanced by decreasing soil fertility, and increased the leaf area ratio. The specific leaf weight was only affected by the irradiation level, except at high soil fertility. The dry weight of the rhizome showed an irradiation and soil fertility interaction.