Influenza di due livelli di intensità luminosa su alcune caratteristiche fisiologiche e morfologiche di Solanum nigrum L. ed Amaranthus cruentus L.

The influence of two photosynthetic photon flux densities (420 and 210 æmol m-2 s-1) on the growth, physiological and morphological characteristics of two weeds (Solanum nigrum L. and Amaranthus cruentus L., C3 and C4 species respectively) with different photosynthetic cycles, was examined. The plants were grown in a controlled environment at 27/18 °C day/night temperatures and with a photoperiod of 15 h. At both light intensities, S. nigrum consistently produced amounts of dry matter and leaf area exceeding those of A. cruentus. This response may be due to the higher seed weight and earlier and faster leaf area development shown by the C3 species. The A. cruentus appeared to be particularly susceptible to the lower light level. The two species showed different response strategies to the light availability. S. nigrum had a distribution pattern of biomass which was fairly independent of the light conditions (LWR and RSR not varying greatly), concentrating the adaptations on the leaf structure (SLA); while A. cruentus showed a different distribution of dry matter and a different structure and chlorophyll content of the leaves. The height of the two weeds was greatly modified by the light treatment, confirming the higher competitiveness of S. nigrum at low light levels. The analysis of the results shows the fundamental role of the early vegetative stages in determining the competitiveness of two species.