| Popis: |
In cold biomes, N2-fixation by filamentous heterocystous cyanobacteria in symbiosis with mosses represents one of the main biological inputs of new nitrogen (N), and greatly support the surrounding ecosystem productivity. In these ecosystems, climate change is expected to result in 2-9°C increase in temperature and two times greater carbon dioxide (CO2) over the next century, yet little is known about the effects of these factors on the community composition of cyanobacteria in symbiosis with mosses. In particular, it is unknown how changes in the cyanobacterial community will affect N2-fixation activity and the resulting impact on the moss growth rate (MGR). Here, we reconstructed the symbiosis between the common feathermoss Pleurozium schreberi and cyanobacteria isolated from feathermosses. P. schreberi gametophytes were inoculated with 1, 5 or 20 genetically distinct strains of cyanobacteria and exposed to different temperature (11°C and 19°C) and CO2 (500 ppm and 1000 ppm) conditions. Changes in MGR, N2-fixation rate, and cyanobacterial community structure and composition were measured at distinct time points: 5, 10, 20, and 30 weeks of exposure. Our results indicate that both elevated temperature and CO2 levels can individually and combined have positive effects on the N2-fixation activities, and consequently on MGR. The underlying biotic mechanisms for increased N2-fixation and MGR were changes in the cyanobacterial community diversity and composition. In general, we observed a reduction in cyanobacterial diversity and an increase in cyanobacterial strain abundance that have adapted and dominated under the elevated temperature and CO2 levels. |
