Format: ORAL

Yunyao Ma1, Maaike Y. Bader2, and Philipp Porada1

1 Universität Hamburg, Hamburg, Germany 2 University of Marburg, Marburg, Germany

Environmental filtering is a fundamental process that shapes plant community assembly. Understanding the impact of this process on composition of non-vascular vegetation, such as mosses and lichens, is important since the organisms provide essential ecosystem functions in many regions around the world. Responses of individual non-vascular vegetation to different environmental factors have been explored in a range of field and laboratory experiments. These observational data, however, have rarely been assembled into a comprehensive, consistent framework that allows quantitative exploration of the roles of multiple environmental factors for the performance of non-vascular vegetation, in particular across climatic regions. Here, we applied a data-driven mechanistic model that is driven by microclimate (air temperature, relative humidity, short- and longwave radiation etc.) at six study sites along a climate gradient from dryland, temperate to alpine regions to simulate the annual carbon (C) balance of lichen- and moss-dominated biocrusts, a key measure of their growth and survival. Furthermore, we performed several sensitivity analyses to investigate the relative importance of the driving factors. We found substantial effects of air temperature and CO2 concentration on biocrust C balance, which differed, however, in their patterns across regions: ambient CO2 concentration was the most important factor for biocrusts from drylands, while air temperature had the strongest impact at alpine and temperate sites. Further, we estimated a small annual carbon gain of biocrusts in drylands (e.g., 1.9 gm2 yr1 by moss-dominated biocrust), while the biocrusts lost substantial carbon at some temperate sites (e.g. 92.1 gm2 yr1 for lichen-dominated biocrust), which contradicts the observed survival of the organisms at the sites. We thusconclude that the uncertainties in air temperature, CO2 concentration may be a relevant source of errorand should be taken into account in future approaches that estimate the long-term C balance.