1College of Resources and Environmental Sciences, Key Laboratory of Plant–Soil Interactions of the Ministry of Education, China Agricultural University, Beijing 100193, China
2State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences (CAS), Urumqi 830011, China
3Agri-Environment Branch, Agri-Food and Biosciences Institute, Belfast BT9 5PX, UK
4Institute of Plant and Landscape Ecology, University of Hohenheim, 70593 Stuttgart, Germany
Received: 30 Apr 2011 – Published in Biogeosciences Discuss.: 25 May 2011
Abstract. 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 kg N ha−1 yr−1) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperate 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 kg N ha−1 yr−1 above ambient N deposition (16 kg N ha−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 δ15N and soil mineral N increased with N addition, showing positive relationships between plant δ15N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kg N ha−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 N deposition-induced changes in soil N transformations and plant N assimilation that are closely related to changes in species composition and biomass accumulation in this temperate steppe ecosystem.
Revised: 12 Aug 2011 – Accepted: 15 Aug 2011 – Published: 26 Aug 2011
Song, L., Bao, X., Liu, X., Zhang, Y., Christie, P., Fangmeier, A., and Zhang, F.: Nitrogen enrichment enhances the dominance of grasses over forbs in a temperate steppe ecosystem, Biogeosciences, 8, 2341-2350, doi:10.5194/bg-8-2341-2011, 2011.