Climate change will exacerbate the degree of abiotic stress experienced by semi-arid Mediterranean ecosystems, as predictions point out to an increase in temperature close to 3ºC annually and a reduction of rainfall close to 20% over current values. While these changes in environmental conditions are predicted to affect attributes of biotic communities such as species composition, diversity and facilitative/competitive interactions, the potential role of these attributes as modulators of ecosystem responses to climate change is largely unknown. We hypothesize that such attributes drive variations in ecosystem functioning, and thus have the potential to drive ecosystem responses to climate change. To test this hypothesis we used biological soil crusts (BSC) dominated by lichens and mosses as a model system, and an ongoing field experiment that is being carried out in different sites of Spain, where we are experimentally manipulating temperature and rainfall as predicted by climate change models. We evaluated the role of biotic community attributes (cover, species richness, species evenness and biotic interactions) as modulators of soil CO₂ flux, nitrogen availability and soil moisture responses to modifications in climatic conditions.

Results/Conclusions

Despite preliminary, the results obtained from this study so far provide evidence of strong short-term effects of climate change on soil respiration, a response that was controlled by the total cover of BSC (i.e. areas of low BSC cover did not shown any response to the warming treatment), but not by species richness, evenness or biotic interactions. These responses were, however, site specific. If warming increases soil respiration, particularly in areas of high BSC cover, BSC-forming organisms such as lichens and mosses may be at risk of C deficits, particularly when air temperatures are high and moisture is limited. This situation may be exacerbated by other ongoing climatic alterations, such as increases in UV radiation, which has been shown to negatively affect the physiological functioning of BSC-forming organisms. Our results indicate that BSC will likely experience added stress under the forecasted future climatic conditions, which may in turn had negative feedbacks on many ecosystem functions modulated by these organisms.