Castillo Monroy, Andrea del Pilar2011-10-172011-10-172010-11-16http://hdl.handle.net/10115/5670Tesis Doctoral leída en la Universidad Rey Juan Carlos en noviembre de 2010. Director de la Tesis: Fernando T. Maestre GilBiological soil crusts (BSCs) greatly influence the N cycle of semi-arid ecosystems, as some organisms forming them are able to fix atmospheric N. However, BSCs are not always taken into account when studying biotic controls on N cycling and transformations. Our main objective was to understand how BSCs modulate the availability of N in a semiarid Mediterranean ecosystem dominated by the tussock grass Stipa tenacissima. We selected the six most frequent soil cover types in the study area: S. tenacissima tussocks (ST), Retama sphaerocarpa shrubs (RS), and open areas with very low (BS), low (LC) medium (MC) and high (HC) cover of well developed and lichen-dominated BSCs. The temporal dynamics of available N dynamics followed changes in soil moisture. Available NH4 +-N did not differ between microsites, while available NO3 --N was substantially higher in the RS than in any other microsite. No significant differences in the amount of available NO3 --N were found between ST and BS microsites, but these microsites had more NO3 --N than those dominated by BSCs (LC, MC and HC). Our results suggest that BSCs may be inhibiting nitrification, and highlight the importance of this biotic community as a modulator of the availability of N in semi-arid ecosystems.enAtribución-NoComercial-SinDerivadas 3.0 Españahttp://creativecommons.org/licenses/by-nc-nd/3.0/es/GeologíaBiologíainfo:eu-repo/semantics/doctoralThesisinfo:eu-repo/semantics/openAccess2511.02 Biología de Suelos