Influenza di due livelli di intensità luminosa sull'accrescimento di Sorghum halepense (L.) Pers. e Panicum miliaceum L.

The influence of two photosynthetic photon flux densities (100 and 400 µmol m-2s-1) on growth, physiological and morphological characteristics of two weeds (Sorghum halepense L. Pers and Panicum miliaceum L., both Graminaceae with C4 photosynthetic cicle), was examined. The plants were cultivated in controlled environment from 0 to 42 days from the emergence. The two species showed similar adaptatives mechanisms, with great response to the light availability in terms of growth and assimilation rate and also as adaptatives changes of leaf morphology and biomass partitioning. Specific Leaf Area (SLA) of plant grown at low PPFD was stable along the studied period, showing values 2 to 4 times the SLA of plant grown at high PPFD. Very high RGR and NAR was measured from 0 to 14 days from emergence in plant grown under high PPFD, and the consequent advantage in dry matter accumulation was not recovered by low PPFD plants during following period of the trial. At both light intensities, S. halepense consistently produced amounts of dry matter and leaf area exceeding those of P. miliaceum. S. halepense behaviour seems to be ascribed to a competitive strategies (sensu Grime), P. miliaceum can be defined as ruderal.