capacity of soils in the Chinese grasslands was significantly lower in the 2010s than
that in the 1980s, with an overall reduction of 14% (Fang et al. 2017). The
proportional reduction of cation exchange capacity in alpine meadow, alpine steppe,
meadow steppe, and typical steppe were 11%, 20%, 27%, and 9%, respectively.
Such significant changes of soil chemical characters might alter plant community
composition and ecosystem functioning and consequently trigger vegetation
changes in the grasslands of China.
Given that grasslands in China generally have relatively short history of N
deposition/addition and receive less accumulative atmospheric N inputs compared
with grasslands in Europe and North America, they are very sensitive to N enrichment and may serve as a wonderful model system to uncover the initial impacts of N
deposition on ecosystem properties, processes, and functioning in grasslands.
10.2.3 Nitrogen Enrichment Experiments in China
Given the background of increasing atmospheric N deposition over the grasslands
distributed in China, many experiments had been set up in different grasslands of
China, including meadow steppe, typical steppe, desert steppe, and alpine grassland
(see Fig. 9.1 in Chap. 9 for more information on the distribution of manipulated N
enrichment experiments), with the aim to understand the role of N deposition in
driving changes in community composition and ecosystem function. Here, we will
introduce some N addition experiments carried out in the grasslands of China, the
scientific findings from which have substantially improve our understanding of the
responses of grassland ecosystems to N enrichment.
To the best of our knowledge, the earliest N addition experiments in China were
established in 1999 in the typical steppe by the Inner Mongolia Grassland Ecosystem
Research Station (IMGERS), which is located in the Xilin River Basin, Inner
Mongolia Autonomous Region of China (116
42
0 E, 43
38
0 N). In this semiarid
region, the mean annual precipitation is 345 mm, with 60–80% of which falling
during the growing season from May to August. They aimed to investigate the role
of N deposition in driving grassland community composition and functions in two
ecosystems with contrasting conditions, one mature site and one previously
degraded by livestock grazing (Bai et al. 2010). In each site, they set 9 replications
for each of 19 treatments, including a control treatment, and 6 different levels of N
addition. Nitrogen was added as NH 4 NO 3 with the rates of 0, 17.5, 52.5, 105, 175,
and 280 kg N ha
À1 year
À1 in three different application times including the early
May (the early growing season) and early July (the middle of growing season) and
50% of N being applied at each time. To assure that N is the single-limiting nutrient
in the experiment, they added phosphorus sulphur and other nutrients (Zn and Mn)
for all treatments except control.
In most of related studies using N addition to simulate increasing atmospheric N
deposition in grasslands, one particular type of N compounds is always added one
time during the growing season or added by splitting the total amount of N
compounds into a few times per year. The case of atmospheric N deposition is
218
X. Lü et al.
that in the 1980s, with an overall reduction of 14% (Fang et al. 2017). The
proportional reduction of cation exchange capacity in alpine meadow, alpine steppe,
meadow steppe, and typical steppe were 11%, 20%, 27%, and 9%, respectively.
Such significant changes of soil chemical characters might alter plant community
composition and ecosystem functioning and consequently trigger vegetation
changes in the grasslands of China.
Given that grasslands in China generally have relatively short history of N
deposition/addition and receive less accumulative atmospheric N inputs compared
with grasslands in Europe and North America, they are very sensitive to N enrichment and may serve as a wonderful model system to uncover the initial impacts of N
deposition on ecosystem properties, processes, and functioning in grasslands.
10.2.3 Nitrogen Enrichment Experiments in China
Given the background of increasing atmospheric N deposition over the grasslands
distributed in China, many experiments had been set up in different grasslands of
China, including meadow steppe, typical steppe, desert steppe, and alpine grassland
(see Fig. 9.1 in Chap. 9 for more information on the distribution of manipulated N
enrichment experiments), with the aim to understand the role of N deposition in
driving changes in community composition and ecosystem function. Here, we will
introduce some N addition experiments carried out in the grasslands of China, the
scientific findings from which have substantially improve our understanding of the
responses of grassland ecosystems to N enrichment.
To the best of our knowledge, the earliest N addition experiments in China were
established in 1999 in the typical steppe by the Inner Mongolia Grassland Ecosystem
Research Station (IMGERS), which is located in the Xilin River Basin, Inner
Mongolia Autonomous Region of China (116
42
0 E, 43
38
0 N). In this semiarid
region, the mean annual precipitation is 345 mm, with 60–80% of which falling
during the growing season from May to August. They aimed to investigate the role
of N deposition in driving grassland community composition and functions in two
ecosystems with contrasting conditions, one mature site and one previously
degraded by livestock grazing (Bai et al. 2010). In each site, they set 9 replications
for each of 19 treatments, including a control treatment, and 6 different levels of N
addition. Nitrogen was added as NH 4 NO 3 with the rates of 0, 17.5, 52.5, 105, 175,
and 280 kg N ha
À1 year
À1 in three different application times including the early
May (the early growing season) and early July (the middle of growing season) and
50% of N being applied at each time. To assure that N is the single-limiting nutrient
in the experiment, they added phosphorus sulphur and other nutrients (Zn and Mn)
for all treatments except control.
In most of related studies using N addition to simulate increasing atmospheric N
deposition in grasslands, one particular type of N compounds is always added one
time during the growing season or added by splitting the total amount of N
compounds into a few times per year. The case of atmospheric N deposition is
218
X. Lü et al.