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Colony formation by the green alga Chlorella vulgaris in response to the competitor Ceratophyllum demersum

Dong, Jing, Gao, Yunni, Chang, Mengyang, Ma, Hanhui, Han, Kun, Tao, Xin, Li, Yan
Hydrobiologia 2018 v.805 no.1 pp. 177-187
Ceratophyllum demersum, Chlorella vulgaris, algae, biomass, carbohydrates, direct contact, energy, freshwater ecosystems, macrophytes, nutrients, photosynthesis, secretion
In shallow freshwater ecosystems, submerged macrophytes and algae usually compete for nutrients, light and space. Previous studies mainly focused on the growth effects (biomass, growth rate, photosynthetic activities) of algae by submerged macrophytes. The present study found that submerged macrophytes could also have morphological influences on green algae. We used the green alga Chlorella vulgaris and the photosynthetic competitor Ceratophyllum demersum in our experiments. Results revealed the following: (1) both direct contact and extracts of macrophytes could promote colony formation by C. vulgaris; (2) high biomass of macrophytes caused the formation of more and larger colonies; (3) evidence was found to support the hypothesis that competitive pressure promotes facultative rather than constitutive colony formation. This temporary defensive strategy might be the result of increased carbohydrate production and secretion induced by macrophyte competition. After removal of macrophytes, colony cells reverted to individual cells and the accumulated carbohydrates in the colony cells could provide sufficient energy for rapid development of the algae. Thus, the response of C. vulgaris morphology to macrophytes might represent an effective co-evolutionary or co-existence strategy.