China could be classified into four major types, including meadow steppe, typical
steppe, desert steppe, and alpine steppe (Sun 2005).
Most of the grasslands in China occur in semiarid and arid areas. Meadow steppe
is the one type of grasslands occurring on the moistest and fertile areas, generally in
areas with mean annual precipitation of ~450 mm and soils with high organic matter
content. The meadow steppes are generally dominated by plant species including
Stipa baicalensis Roshev, Cleistogenes mucronate Keng, Filifolium sibiricum (L.)
Kitam, and Leymus chinensis Tzvel. The typical steppes are generally distributed on
plateau with altitude ranging from 1000 m to 1500 m a.s.l. and on sites with semiarid
climate. The mean annual precipitation in the typical steppe area is around 350 mm.
Most of the plant species in the typical steppe are more drought tolerant than those in
the meadow steppe. The typical steppes could be classified into 13 types based on the
dominant species in the plant community, including the Stipa steppes, the Leymus
steppes, the Artemisia steppes, and the Festuca steppes (Sun 2005).
10.2.2 Atmospheric N Deposition in the Grasslands of China
Atmospheric reactive N deposition has substantially increased in China since 1980
largely due to rapid economic development. The total N inputs in China have been
substantially increased, from ~3000 kg km
À2 in the mid of 1980s to more than
5400 kg km
À2 in the mid of 2000s (Ti et al. 2012), with the chemical fertilizer as the
dominant resource of N input. While biological N fixation was the second important
N input pathway before 1990, atmospheric deposition had been the second most
important input source after then and accounted for 24% of the total inputs in 2007
(Ti et al. 2012). The annual bulk of N deposition increased from 13.2 kg N ha
À1 year
À1
in the 1980s to 21.1 kg N ha
À1 year
À1 in 2010 (Liu et al. 2013). It has been estimated
that gaseous N, precipitation N, and particulate N contributed to 48.3%, 39.4%, and
12.3% of the estimated N deposition in NW China, where most of the arid and
semiarid grassland are being located (Xu et al. 2015). In the Tibetan Plateau where
alpine grasslands are being located, precipitation N is the most important component
for the total N deposition, constituting about 50% of the total deposition (Xu et al.
2015). It has been estimated that the rate of atmospheric nitrogen deposition varied
from 5.2 to 18.7 kg N ha
À1 year
À1 in most of the grasslands in China (Lü and Tian
2007), which had been accelerated during the past decade.
The increases of atmospheric N deposition have significant impacts on soil
chemical properties in the grassland ecosystems of China. For instance, soil pH
has declined in both the alpine grasslands on the Tibetan Plateau and in temperate
grasslands on the Inner Mongolian Plateau, with a decrease of 0.63 units during the
two decades from the 1980s to 2000s (Yang et al. 2012). The N:P ratios of grassland
soils in the surface layer had increased from 2.9 during the 1980s to 3.5 during the
2000s, with an average increase of 0.6 unit. The magnitude of such increases was
higher in the temperate grasslands on the Inner Mongolian Plateau and lower in the
alpine grasslands on the Tibetan Plateau (Yang et al. 2014). Cation exchange
10 Impacts of Nitrogen Deposition on China’s Grassland Ecosystems
217
steppe, desert steppe, and alpine steppe (Sun 2005).
Most of the grasslands in China occur in semiarid and arid areas. Meadow steppe
is the one type of grasslands occurring on the moistest and fertile areas, generally in
areas with mean annual precipitation of ~450 mm and soils with high organic matter
content. The meadow steppes are generally dominated by plant species including
Stipa baicalensis Roshev, Cleistogenes mucronate Keng, Filifolium sibiricum (L.)
Kitam, and Leymus chinensis Tzvel. The typical steppes are generally distributed on
plateau with altitude ranging from 1000 m to 1500 m a.s.l. and on sites with semiarid
climate. The mean annual precipitation in the typical steppe area is around 350 mm.
Most of the plant species in the typical steppe are more drought tolerant than those in
the meadow steppe. The typical steppes could be classified into 13 types based on the
dominant species in the plant community, including the Stipa steppes, the Leymus
steppes, the Artemisia steppes, and the Festuca steppes (Sun 2005).
10.2.2 Atmospheric N Deposition in the Grasslands of China
Atmospheric reactive N deposition has substantially increased in China since 1980
largely due to rapid economic development. The total N inputs in China have been
substantially increased, from ~3000 kg km
À2 in the mid of 1980s to more than
5400 kg km
À2 in the mid of 2000s (Ti et al. 2012), with the chemical fertilizer as the
dominant resource of N input. While biological N fixation was the second important
N input pathway before 1990, atmospheric deposition had been the second most
important input source after then and accounted for 24% of the total inputs in 2007
(Ti et al. 2012). The annual bulk of N deposition increased from 13.2 kg N ha
À1 year
À1
in the 1980s to 21.1 kg N ha
À1 year
À1 in 2010 (Liu et al. 2013). It has been estimated
that gaseous N, precipitation N, and particulate N contributed to 48.3%, 39.4%, and
12.3% of the estimated N deposition in NW China, where most of the arid and
semiarid grassland are being located (Xu et al. 2015). In the Tibetan Plateau where
alpine grasslands are being located, precipitation N is the most important component
for the total N deposition, constituting about 50% of the total deposition (Xu et al.
2015). It has been estimated that the rate of atmospheric nitrogen deposition varied
from 5.2 to 18.7 kg N ha
À1 year
À1 in most of the grasslands in China (Lü and Tian
2007), which had been accelerated during the past decade.
The increases of atmospheric N deposition have significant impacts on soil
chemical properties in the grassland ecosystems of China. For instance, soil pH
has declined in both the alpine grasslands on the Tibetan Plateau and in temperate
grasslands on the Inner Mongolian Plateau, with a decrease of 0.63 units during the
two decades from the 1980s to 2000s (Yang et al. 2012). The N:P ratios of grassland
soils in the surface layer had increased from 2.9 during the 1980s to 3.5 during the
2000s, with an average increase of 0.6 unit. The magnitude of such increases was
higher in the temperate grasslands on the Inner Mongolian Plateau and lower in the
alpine grasslands on the Tibetan Plateau (Yang et al. 2014). Cation exchange
10 Impacts of Nitrogen Deposition on China’s Grassland Ecosystems
217