Biological soil crusts increase the resistance of soil nitrogen dynamics to changes in temperatures in a semi-arid ecosystem
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Biological soil crusts (BSCs), composed of mosses, lichens, liverworts and cyanobacteria, are a key component of arid and semi-arid ecosystems worldwide, and play key roles modulating several aspects of the nitrogen (N) cycle, such as N fixation and mineralization. While the performance of its constituent organisms largely depends on moisture and rainfall conditions, the influence of these environmental factors on N transformations under BSC soils has not been evaluated before.
The study was done using soils collected from areas devoid of vascular plants with and without lichen-dominated BSCs from a semi-arid Stipa tenacissima grassland. Soil samples were incubated under different temperature (T) and soil water content (SWC) conditions, and changes in microbial biomass-N, dissolved organic nitrogen (DON), amino acids, ammonium, nitrate and both inorganic N were monitored. To evaluate how BSCs modulate the resistance of the soil to changes in T and SWC, we estimated the Orwin and Wardle Resistance index.
The different variables studied were more affected by changes in T than by variations in SWC at both BSC-dominated and bare ground soils. However, under BSCs, a change in the dominance of N processes from a net nitrification to a net ammonification was observed at the highest SWC, regardless of T.
Our results suggest that the N cycle is more resistant to changes in T in BSC-dominated than in bare ground areas. They also indicate that BSCs could play a key role in minimizing the likely impacts of climate change on the dynamics of N in semi-arid environments, given the prevalence and cover of these organisms worldwide.
KeywordsSemiarid ecosystem N depolymerization rate N mineralization rate DON
We thank the Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario (IMIDRA) for allowing us to work in the Aranjuez Experimental Station (Finca de Sotomayor), J. Durán, A. Rodríguez and two reviewers for their helpful comments and suggestions on previous versions of this manuscript. This research is supported by the European Research Council (ERC) under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement n° 242658 (BIOCOM) and by the Ministry of Science and Innovation of the Spanish Government, Grant nº CGL2010-21381. FTM acknowledges support from the Spanish Ministerio de Educación (“Salvador de Madariaga program”, PR2010-0230) during the writing of the manuscript.
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