A new aspect of grassland vegetation dynamics: cyanobacterium colonies affect establishment success of plants

Aims: Cyanobacteria may have considerable effects on community functioning, mostly because they produce various metabolites that adversely affect other organisms. Here we synthesized existing knowledge about the effects of toxic cyanobacteria on the germination and growth of terrestrial plants. We also aimed to test the chemical effects of a Nostoc (Cyanobacteria) extract on the ger- mination and growth of species of alkali habitats to investigate whether cyanobacteria can alter community structure and diversity via affecting the establishment success of plants. Location: Cyanobacterium colonies from the Hortob � agy National Park, east Hungary; indoor experiments at the University of Debrecen, Hungary. Methods: To review the effects of toxic cyanobacteria on terrestrial plants, we conducted a literature search. To test these effects on native plants, field-col- lected Nostoc colonies were used to prepare a cell-free water extract, and treat- ments (watering with Nostoc extract and watering with tap water) were tested on 3 9 100 seeds of nine alkali grassland species. After 5 wk, seedling number, seedling length and fresh and dry weights were measured. Results: We collected data on the effects of cyanobacteria on 27 species, but they were mostly focused on crops irrigated with cyanobacteria-containing water, not on floras native to natural ecosystems. In the germination experi- ment species identity and treatment had a significant effect on almost all vari- ables, but their interaction only affected germination rate and fresh weight. Fresh weight decreased significantly only in the invasive Hordeum jubatum ,but germination rate decreased significantly in five species. Conclusions: Based on our findings, terrestrial cyanobacterium colonies can affect the establishment success of grassland plants, through which they may be important in determining which species can be incorporated into the community. Thus, cyanobacteria might play an important role in shaping diversity, species composition and the structure of natural plant communities