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

Publication Type

Journal contribution (peer reviewed)

Authors

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

Year of publication

2011

Published in

Biogeosciences

Band/Volume

8/

Page (from - to)

2341-2350

Conference date

doi:10.5194/bg-8-2341-2011

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 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 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
d15N and soil mineral N increased with N addition, showing
positive relationships between plant d15N 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 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.