Effects of submersed macrophytes on ecosystem processes

A mechanism to account for macrophyte decline in progressively eutrophicated freshwaters

Under controlled experimental conditions, the influences of light and temperature on the growth and metabolism of Egeria densa Planch, Hydrilla verticillata Royle, and Myriophyllum spicatum L. were comparatively examined. Light was controlled at six levels ranging between 5 and 75% of full sunlight at solar noon. Water temperature was controlled at five levels ranging between 16? and 32?C. Growth considerations included morphology, biomass, and nutrition. Photosynthesis, respiration, and CO2 compensation points were determined to evaluate physiological differences in plant growth as affected by the experimental ranges of temperature and light. External morphology in these species was significantly affected by the different experimental light and temperature conditions. Both low light and high temperature promoted extensive shoot elongation and associated canopy formation. Biomass production and carbon metabolism in all species were influenced more by temperature than by light. Each of the species demonstrated metabolic acclimation to light over a broad range. Conversely, the macrophyte species considered here were not strictly capable of acclimating to temperature. Growth rate and the seasonal progression of senescence were interrelated in these species. Higher temperatures stimulated growth and promoted a compression of the growth cycle. The relationship between photosynthesis and respiration (P:R) was appreciably reduced by senescence, but the CO2 compensation point did not reflect this condition. In the species examined, CO2 compensation points decreased with increasing temperature, suggesting adaptations to low free CO2 levels in the environ- ment. Latitudinal differences in integral seasonal temperature, in relation to species-specific ranges of thermal tolerance, appear to be important in influencing the geographical distribution of the species considered here. Light may be the primary determinant of their depth distribution, but its importance in this regard could be somewhat diminished by their significant abilities to extend to the water surface under low light conditions.

Comparative Influences of Light and Temperature on the Growth and Metabolism of Selected Submersed Freshwater Macrophytes

Laboratory culture of submersed freshwater macrophytes on natural sediments

Release and ecological impact of algicidal hydrolysable polyphenols in Myriophyllum spicatum

The Eurasian watermilfoil (Myriophyllum spicatum L.) has partially replaced wild celery (Vallisneria americana Michx.) as a community dominant in the littoral zones of lakes of Madison, Wisconsin. The two species have very different growth forms, with that of M. spicatum corresponding more closely to the optimal growth form simulated by the macrophyte production model WEED. The objective of this research was to investigate the mechanisms by which Vallisneria could compensate for its nonoptimal growth form and coexist with Myriophyllum.A quantification of midsummer growth form for the two species at a rooting depth of 80-90 cm showed that M. spicatum had 68% of its shoot biomass within 30 cm of the surface, whereas V. americana had 62% of its leaf biomass within 30 cm of the bottom. Vallisneria had a light extinction coefficient ranging from 0.013 to 0.019 m2·g-1, much higher than the value (ca. 0.006 m2·g-1) for M. spicatum. This indicates less effective penetration of light to lower leaves of V. americana. Half-saturation constants describing the light-dependence of carbon uptake in "shade" and "sun" tissues ranged from 60-197 microeinsteins·m-2·s-1 for V. americana, and 164-365 μeinsteins·m-2·s-1 for M. spicatum. The optimum temperature for photosynthesis was 33.6°C for M. spicatum and 32.6°C for V. americana, but Myriophyllum was nearly twice as effective at carbon uptake at 10°C. Integration of all of the above features with WEED showed that, for midsummer conditions, V. americana more than compensated for apparently disadvantageous morphological features by its greater physiological adaptability to low light regimes. Coupled with the temperature-dependence of photosynthesis, it appears that V. americana is favored by midsummer conditions, whereas M. spicatum is at an advantage at other times.

Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx.

Photosynthetic rates and productivity of Myriophyllum spicatum L. were examined in the littoral by incubating shoot sections at three rooting depths using a 14C technique. At a rooting depth of 240 cm, the interrelation of biomass and photosynthetic rates resulted in the production of 56% of the total photosynthetic productivity within 100 cm of the water surface in May. In August, 57% of the total productivity occurred within only 20 cm of the surface. Variations in the depth distribution of biomass, due to differing growth and sloughing patterns, resulted in different depth relations of photosynthesis at the other rooting depths. Light extinction and light adaptation of photosynthetic tissues were other factors determining the depth relations of photosynthesis.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1974.19.3.0377

John E. Titus

Papers

Coexistence and the comparative light relations of the submersed macrophytes Myriophyllum spicatum L. and Vallisneria americana Michx.

Depth distribution of photosynthetic activity in a Myriophyllum, spicatum community in Lake Wingra1