Effects of increased N availability on biodiversity ofMediterranean-type ecosystems: a case study in aNatura 2000 site in Portugal.

• Although Mediterranean-type ecosystems are biodiversity hotspots, very little is known about the effects of increased N availability in these systems; • This paper describes an integrated field study on the effects of increased N availability in a Mediterranean-type ecosystem in a Natura 2000 site in Portugal; • The ecosystem was highly N responsive: visible changes were seen within one year; N additions created new and distinct seasonal patterns of soil N availability; plant and soil bacterial diversity together with plant cover were increased; • The effects of increased N availability appeared to depend on N form - plant evenness; N dose - plant species richness; and on both N form and dose - species cover and soil bacterial richness.