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Background and aims In the Mediterranean basin, reduction in cloudiness owing to climate change is expected to enhance solar ultraviolet (UV) levels and to decrease rainfall over the coming years, which would be accompanied by more frequent and intense wildfires. The aim of the present study was to investigate the role of solar UV-A and UV-B radiation in C and N pools of a Mediterranean shrubland and whether drier conditions could alter this role before and after a fire. Methods Over a three-year field experiment, 18 plots of 9 m 2 were subjected to three UV conditions (UV-A + UV-B exclusion, UV-B exclusion or near-ambient UV-A + UV-B exposure) combined with two rainfall regimes (natural or reduced rainfall). Several parameters related to C and N cycles in the soil and in the leaves and litter of two dominant plant species (Arbutus unedo and Phillyrea angustifolia) were measured before and after an experimental fire. Results UV-A exposure increased soil moisture throughout the study period, as well as respiration before the fire. The additional presence of UV-B decreased βglucosidase activity at 5-10 cm depth and soil respiration and pH. UV-B exposure also raised leaf C concentration in P. angustifolia and δ 15 N values in A. unedo. Reduced rainfall often emphasized the opposite effects of UV-A and UV-B on the studied parameters. After the fire, most of the UV and rainfall effects were lost. Conclusion UV-A exposure seems to stimulate soil biological activity and, thus, C and N turnover , while the effect of UV-B would be the opposite. At least in the short term, the Bhomogenizing influence^of fire would

Allozyme electrophoresis was used to measure levels and distribution of genetic diversity in the critically endangered (CR) Silene sennenii (Caryophyllaceae), a narrow endemic plant species found in northeastern Catalonia (Spain). At present, only 5 populations remain, containing no more than 5,000 individuals, which are subjected to several human pressures such as habitat fragmentation and land use changes. Interestingly, the largest population is located in and around a fortress built in the XVIII century, a circumstance which might facilitated its preservation until now. From the 21 satisfactorily interpreted loci, low levels of genetic variation were detected (P = 20.9, A = 1.31 and H e = 0.071), which may be related to small population size, isolation, and fragmentation of extant populations. Moderate to high levels of inbreeding were also found, probably as consequence of the population's genetic structuring. The conservation of the population located in the fortress would allow the preservation of all the alleles detected at species level; nevertheless, conservation of other populations, coupled with the inclusion of S. sennenii in the Spanish Catalogue of Endangered Species, would also be desirable in order to ensure the long-term survival of the species.

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