The effect of origin and species on peatmoss growth response to temperature

Sammanfattning

Peatlands are ecosystems engineered by mosses that drive slow decomposition rate and accumulation of dead organic matter. Through time, these layers become peat. Peat-mosses belong to the genus Sphagnum and dominate in European temperate and boreal regions, where most of the old peatlands store globally relevant amounts of carbon. The stability of these ecosystems are uncertain under climate change, as especially at northern latitudes temperatures are expected to rise at higher rates than in the rest of the continent. Previous works on the dominant S. magellanicum showed a positive response to higher temperature, even though contrasting results have been found when considering different proxies for growth (i.e. length increment, net primary production, photosynthetically active radiation). Recent studies uncovered genetic structure in what is the S. magellanicum complex, a complex of cryptic species, where the geographical distribution of the two newly defined S. divinum and S. medium seems to partially overlap in the European continent. Therefore, scientists wonder if this could imply for S. divinum and S. medium to have different temperature and habitat preferences, as no clear evidence has been found yet. From a total number of 234 accessions collected across the European latitudinal gradient, I have analysed data of length increment from an experimental growth chamber setup, with two temperature treatments (average temperature 8°C vs. 15°C). As a result, I found support for conditional neutrality, and premises for locally adapted accessions in S. medium, where samples coming from relatively colder territories showed limited growth rate when placed in warmer experimental conditions. In S. divinum, the response was instead governed by original conditions in terms of either growth season length, or moisture, and sexes displayed an opposite response in the warm treatment. Finally, trajectories of climate might affect species differently, determining possibly shifts in species composition. Particularly, according to the results of the present work, increased temperatures might reduce S. medium competitiveness in colder regions, while S. divinum might respond worse in drier locations. Our work can represent a preliminary and easy to implement method to define niche extents for Sphagnum species. Because of their role as ecosystem builders, further investigations on the two organisms might allow for a better understanding of not just their ecology, but also of the stability of European peatlands, which globally play an important function as a sink of carbon and climate cooler.