Nitrogen enrichment enhances the dominance of grasses over forbs in a temperate steppe ecosystem

Publication Type

Journal contribution

Authors

Song, L., Bao, M., Liu, X.J., Zhang, Y., Christie, P., Fangmeier, A., Zhang, F.S.

Year of publication

2011

Published in

Biogeosciences Discussions

Band/Volume

8/

ISBN / ISSN / eISSN

doi:10.5194/bgd-8-1-2011

Page (from - to)

5057–5082

Chinese grasslands are extensive natural ecosystems that comprise 40% of the total land area of the country and are sensitive to N deposition. A field experiment with six N rates (0, 30, 60, 120, 240, and 480 kgNha^-1 yr^-1) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperature steppe ecosystem. The dominant plant species in the plots were divided into two categories, grasses and forbs, on the basis of species life forms. Enhanced N deposition, even as little as 30 kgNha^-1 yr^-1 above ambient N deposition (16 kgNha^-1 yr^-1), led to a decline in species richness. The cover of grasses increased with N addition rate but their species richness showed a weak change across N treatments. Both species richness and cover of forbs declined strongly with increasing N deposition as shown by linear regression analysis (p < 0.05). Increasing N deposition elevated aboveground production of grasses but lowered aboveground biomass of forbs. Plant N concentration, plant ¹⁵N and soil mineral N increased with N addition, showing positive relation ships between plant ¹⁵N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kgNha^-1 yr^-1 treatment in 2009 and 2010 led to a slight recovery of the forb species richness relative to total cover and aboveground biomass, coinciding with reduced plant N concentration and soil mineral N. The results show that N deposition induced changes in soil N transformations and plant N assimilation that are key to changes in species composition and biomass accumulation in this temperate steppe ecosystem