Specific leaf area, photosynthesis, and respiration in two sympatric nymphaeaceae populations

Sympatric populations of Nuphar variegatum Engelm and Nymphaea tuberosa Paine, sharing the same light regime, developed different patterns of leaf thickness vs. surface area during a growth season. The leaves of Nymphaea surfaced slightly later than those of Nuphar and, within the restricted spaces available, were smaller but thicker, i.e. they had a lower specific leaf area (area per unit weight). Nymphaea leaves exhibited higher rates of photosynthesis per unit are throughout the growing season, and lower rates of respiration for most of the season, than did the thinner leaves of Nuphar. Induction of variations in specific leaf area (SLA) and related metabolic responses by a light intensity gradient, the normally observed causal relationship in plants, was not a factor here. Competition for water surface area is suggested as an alternative mechanism.