Soil chemistry of local vegetation gradients in sandy calcareous grasslands

Acidification and N-deposition are continuous processes that alter the composition of plant communities. We investigated vegetation transitions in sandy grasslands and tested two hypotheses: (1) a shift from vegetation dominated by Koeleria glauca to one dominated by Corynephorus canescens is due to acidification and (2) a shift from vegetation dominated by K. glauca to one dominated by Arrhenatherum elatius is due to increased mineral-N. The occurrence of K. glauca and C. canescens followed pH shifts strikingly well. However, the pH varied considerably between sites, and we found that differences in preference for bare sand may be important for the coexistence of these two species at both high and low pH. In 75% of the gradients, the dominance of A. elatius was related to high content of mineral-N. Most species preferred lime-rich soils and we concluded that both N-enrichment and acidification may lead to loss of species in calcareous sandy grasslands.