Nitrogen (N) deposition is predicted to impact on the structure and functioning of Mediterranean ecosystems. In this study, we measured plant species composition, production and root phosphatase activity in a field experiment in which N (0, 10, 20 and 50 kg N ha−1 year−1) was added since October 2007 to a semiarid shrubland in central Spain. The characteristically dominant annual forb element responded negatively to N after ~2.5 and ~3.5 years. In contrast, the nitrophilous element (mainly crucifers) increased with N after ~2.5 and ~5.5 years, a response controlled by between-year variations in rainfall and the heterogeneous distribution of P availability. We also described a hierarchy of factors driving the structure and composition of the plant community: soil fertility was the most important driver, whereas calcareousness/acidity of soils and shrub cover played a secondary role; finally, N deposition contributed to explain a smaller fraction of the total variance, and its effects were predominantly negative, which was attributed to ammonium toxicity. Root phosphatase activity of three species was not responsive to N after ~2.5 years but there was a negative relationship with soil P in two of them. We conclude that increased N deposition in semiarid Mediterranean ecosystems of Europe can contribute to cause a shift in plant communities associated with an increase in the nitrophilous element and with a decline in abundance of various forb species adapted to the local conditions.

This research was financially supported by the Spanish Ministerio de Educación y Ciencia (CGL-2009-11015 and REMEDINAL-2 S2009/AMB-1783).

Received: 4 August 2014 /Accepted: 18 December 2014 /Published online: 1 February 2015

Peer reviewed