The Effect of Light on Growth and Dry Matter Allocation Patterns of Alternanthera philoxeroides (Mart.) Griseb.

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Abstract
Alligator weed (Amaranthaceae), a species found in habitats varying in the amount of light received, was grown at 4 photosynthetic photon flux densities (PPFD) to determine the effect of PPFD on production and partitioning of biomass. After 56 days of growth, the average dry weight of plants at the highest PPFD (40 mol m-2 day-1) was greater than 9-fold that of plants at the lowest PPFD (8 mol m-2 day-1). The relationship between PPFD treatment and plant dry weight on day 56 was linear. Among PPFD treatments, leaf area per plant was not as dissimilar as dry weight per plant was; as a result, the ratio of leaf area to plant dry weight tended to increase as PPFD treatment decreased. The highest PPFD treatment produced plants with the highest ratio of leaf dry weight to leaf area. Although the rate of leaf emergence was linear for all plants, the rate of leaf emergence was reduced in the 2 lowest PPFD treatments. The efficiency of dry weight production for PPFD received was estimated to increase at the lowest PPFD treatment. The minimum PPFD necessary for growth was estimated to be 5 mol m-2 day-1, and dry matter production per plant could increase to the maximum PPFD received in unshaded habitats of the southeastern USA.