Submerged macrophytes are known for their positive effects on water clarity, especially in shallow lake
ecosystems.
Eutrophication of these systems, however, has often resulted in a decline of submerged
vegetation
and a dominance of cyanobacteria, producing and releasing allelopathically active substances.
Whether
and how these allelochemicals affect submerged macrophytes is, however, largely unknown. tested
the effect of exudates and extracts of one of the most common cyanobacteria species, Microcystis
aeruginosa,
on seed germination and seedling growth and photosynthesis of the submerged macrophyte
Potamogeton
malaianus, a common species in Chinese shallow lakes. We found that: (1) low and high
exudate
concentrations significantly promoted or inhibited P. malaianus seed germination, respectively,
while
extracts had no effect; (2) low exudate and medium extract concentrations significantly increased,
whereas
high concentrations decreased the biomass of P. malaianus seedlings; (3) chlorophyll content
and
maximum quantum yield of PS II (F
v
/F
) of the seedlings were decreased by all levels of exudates;
(4)
of the various responses tested, seedling leaf F
m
v
/F
showed the greatest sensitivity to M. aeruginosa
allelochemicals;
(5) the allelopathic effects of M. aeruginosa exudates were stronger than those of extracts.
Our
results indicate that cyanobacteria exudates can allelopathically inhibit submerged macrophytes. The
early
growth of seedlings rather than seed germination seems to be a sensitive phase for the impactcyanobacterial
allelochemicals.
m