Highly predictable photosynthetic production in natural macroalgal communities from incoming and absorbed light.

Photosynthesis-irradiance relationships of macroalgal communities and thalli of dominant species in shallow coastal Danish waters were measured over a full year to test how well community production can be predicted from environmental (incident irradiance and temperature) and community variables (canopy absorptance, species number and thallus metabolism). Detached thalli of dominant species performed optimally at different times of the year, but showed no general seasonal changes in photosynthetic features. Production capacity of communities at high light varied only 1.

Contrasting oxygen dynamics in the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina.

Background: and Aims Submerged plants possess well-developed aerenchyma facilitating intra-plant gas-phase diffusion of O2 to below-ground tissues, which are usually buried in anoxic sediments. However, aquatic habitats differ in terms of O2 fluctuations in the water column and in O2 consumption of the sediment, and aquatic plants differ in aerenchymal volume and resistance to O2 diffusion through the plant and across leaf and root surfaces. The hypothesis that the freshwater isoetid Lobelia dortmanna and the marine seagrass Zostera marina should display pronounced contrasts in intra-plant O2 dynamics because of differences in morphology/anatomy, physiology and growth habitat was tested.