Photosynthetic characteristics of Myriophyllum spicatum and six submersed aquatic macrophyte species native to Lake George, New York

SUMMARY.1 The macrophyte community of Lake George, New York is diverse, composing of forty‐eight submersed species representing a wide range of habitats, depth ranges and life‐history strategies. The photosynthetic rates of seven representative submersed aquatic macrophytes were determined in laboratory studies using measurements of short‐term changes in oxygen concentration at eight light intensities from 0 to 1000 μmol m −2 s −1 at 20°C. The species examined were: Elodea canadensis, Myriophyllum spicatum, Potamogeton amplifolius, P. gramineus, P. praelongus, P. robbinsii , and Vallisneria americana.2 Comparisons of maximum net photosynthesis, Michaelis–Menten V max and K m for photosynthesis versus irradiance, and dark respiration rates correlated with changes in community composition and species distribution with depth. 3 In particular, Myriophyllum spicatum exhibited a high photosynthetic rate (V max ) and high light requirement (both in compensation point and higher half‐saturation constant ( K m ) indicative of a high light‐adapted species. In contrast, the native species exhibited shade‐tolerant characteristics. 4 Simple daily carbon balance models indicate that M. spicatum has a higher positive carbon balance near the surface than the native species, but carbon balance decreased more rapidly with decreased light. All species showed greatly reduced carbon balances under a simulated M. spicatum canopy, indicating that native species might not survive. Myriopyllum spicatum leaves would experience self‐shading and eventual sloughing.