Effects of UV radiation and rainfall reduction on carbon and nitrogen levels in a Mediterranean shrub community before and after a controlled fire

This study assesses the role of UV radiation on C and N cycles of a Mediterranean shrubland before and after a fire, and whether this role can be altered by water availability. In a field experiment, naturally growing vegetation was subjected to UV-A+UV-B exclusion, UV-B exclusion or near-ambient UV-A+UV-B exposure in combination with two precipitation regimes (natural or reduced rainfall), along with an experimental fire around the middle of the three years of the study. Different parameters related with C and N levels were measured at soil (0-5 and 5-10 cm), litter and plant level throughout the experiment. UV-A exposure increased soil moisture whereas UV-A+UV-B stimulated soil respiration under reduced rainfall. At 5-10 cm depth, but only before the fire, UV-A exposure increased soil ?-glucosidase activity, while UV-A+UV-B reduced it. Mainly under reduced rainfall, plant exposition to UV-B increased foliar C content before the fire and ?15N in Arbutus unedo after the fire. These findings suggest contrasting UV-A and UV-B effects on C and N cycles, often mediated by precipitation levels, together with a homogenizing effect of the perturbation. We are grateful to: UdG (ASING2011/3), Spanish Government (CGL2010-22283 and CGL2010-18546) and Gavarres Consortium (Girona, Spain)