PHOTOSYNTHETIC PLASTICITY IN POTAMOGETON-PECTINATUS L FROM ARGENTINA - STRATEGIES TO SURVIVE ADVERSE LIGHT CONDITIONS

Argentine Potamogeton pectinatus L. was grown in The Netherlands under laboratory conditions at four light intensities (50, 100, 150 and 200 mu E m(-2) S-1), and photosynthetic performance was evaluated after a bout 1, 2 and 3 months of growth. At these moments, chlorophyll-a and -b and tissue N and P content were also determined. During the growing period, plant lengths and number of secondary shoots were measured. I n the field in Argentina, photosynthetic performance of P. pectinatus was also measured at different light intensities created by artificial shading at various times during the growing season. Field and laborat ory photosynthetic results were in good agreement. P. pectinatus showe d a significant plasticity in its photosynthesis, rather than in morph ology. A fairly constant maximum photosynthetic rate with reduced ligh t enabled the plants to maintain net production rates rather unaffecte d at low light intensities. Still, it can be predicted that increasing turbidity from 1-2 m(-1) at present to 3 m(-1) could lead to a strong ly light-limited growth which should reduce the present weed problem c onsiderably. Such a turbidity increase might be achieved by the introd uction of a fairly dense bottom-feeding fish population like Common ca rp (Cyprinus carpio L.).