short-term experiment of N addition in an alpine meadow (Jiang et al. 2010). Higher
CO 2 emissions were found during the early growing season. In general, the response
of CO 2 emissions to warming was small, and there was no significant change pattern
to nitrogen addition. In alpine grassland ecosystems of the Qinghai-Tibetan Plateau,
N deposition interactive with warming has significantly effect on CO 2 emission
(Zhao et al. 2017). Nitrogen addition had no significant effect on seasonal pattern of
ecosystem respiration in growing season in an alpine swamp meadow of the
Qinghai-Tibet Plateau. However, the interaction between N addition and warming
significantly affected ecosystem respiration in the late growing season (Chen et al.
2017a). Nitrogen addition tended to significantly increase CO 2 emission during the
growing season, and the average CO 2 emissions were about 85 mg m
À2 h
À1 ; slight
CO 2 emissions were found with different nitrogen levels outside the growing season
(Li et al. 2012a). The grassland ecosystems acted as a typical CO 2 sink during the
growing seasons. The impacts of water amendments and nitrogen addition on
character of annual cumulative CO 2 uptake over growing seasons. N addition and
water amendment stimulated CO 2 uptake by 3.3 Æ 1.0 g C m
À2 (g N)
À1 and
0.2 Æ 0.1 g C m
À2 (mm H 2 O)
À1 , respectively. A synergistic effect between nitrogen
and water was found on in semiarid grassland. CO 2 emissions were affected with the
interactive effect of water and nitrogen addition in semiarid grassland.
10.4.2 CH 4
The semiarid grassland soil acted as a sink of CH 4 . Based on data reviewed from
published papers with grazing intensity and N addition treatments in temperate
grassland in China, CH 4 uptake rate averaged 58 μg CH 4 m
À2 h
À1 (Wang et al.
2014). In a 2-year experiment of N addition in an alpine meadow, CH 4 uptake rates
ranged from 1.4 to 71.9 μg m
À2 h
À1 gradually increased from the beginning of the
growing season, reached maximum uptake value, and then gradually declined (Jiang
et al. 2010), and CH 4 uptake was suppressed significantly with low-level nitrogen
addition (Fang et al. 2014). Based on a 5-year experiment in an alpine grassland of
the Tian Shan Mountains in China, we found there were no significant effect of N
addition on CH 4 uptake. Annual average of CH 4 uptake was very highly significant
with average uptake between 52.9 and 106.6 μg C m
À2 h
À1 ; these results show that
change of CH 4 uptake was slight under N addition in a long-term experiment in
alpine grassland (Yue et al. 2016). CH 4 consumption decreased 36%, 31%, and 18%
with sheep urine, fresh dung, and compost, respectively, in a temperate grassland in
Inner Mongolia of China. In general, N deposition could inhibit the methane uptake.
⁄
ä
Fig. 10.4 (continued) (T) and nitrogen addition (N) are also presented. Data are shown as
mean + SE. Within each litter type, different letters above bars indicate significant differences at
P < 0Á05 among N treatments based on a one-way ANOVA. ÃP < 0Á05; ÃÃP < 0Á01; ÃÃÃP < 0Á001.
(This figure was adapted from Li et al. (2017) with permission by John Wiley and Sons)
10 Impacts of Nitrogen Deposition on China’s Grassland Ecosystems
227
CO 2 emissions were found during the early growing season. In general, the response
of CO 2 emissions to warming was small, and there was no significant change pattern
to nitrogen addition. In alpine grassland ecosystems of the Qinghai-Tibetan Plateau,
N deposition interactive with warming has significantly effect on CO 2 emission
(Zhao et al. 2017). Nitrogen addition had no significant effect on seasonal pattern of
ecosystem respiration in growing season in an alpine swamp meadow of the
Qinghai-Tibet Plateau. However, the interaction between N addition and warming
significantly affected ecosystem respiration in the late growing season (Chen et al.
2017a). Nitrogen addition tended to significantly increase CO 2 emission during the
growing season, and the average CO 2 emissions were about 85 mg m
À2 h
À1 ; slight
CO 2 emissions were found with different nitrogen levels outside the growing season
(Li et al. 2012a). The grassland ecosystems acted as a typical CO 2 sink during the
growing seasons. The impacts of water amendments and nitrogen addition on
character of annual cumulative CO 2 uptake over growing seasons. N addition and
water amendment stimulated CO 2 uptake by 3.3 Æ 1.0 g C m
À2 (g N)
À1 and
0.2 Æ 0.1 g C m
À2 (mm H 2 O)
À1 , respectively. A synergistic effect between nitrogen
and water was found on in semiarid grassland. CO 2 emissions were affected with the
interactive effect of water and nitrogen addition in semiarid grassland.
10.4.2 CH 4
The semiarid grassland soil acted as a sink of CH 4 . Based on data reviewed from
published papers with grazing intensity and N addition treatments in temperate
grassland in China, CH 4 uptake rate averaged 58 μg CH 4 m
À2 h
À1 (Wang et al.
2014). In a 2-year experiment of N addition in an alpine meadow, CH 4 uptake rates
ranged from 1.4 to 71.9 μg m
À2 h
À1 gradually increased from the beginning of the
growing season, reached maximum uptake value, and then gradually declined (Jiang
et al. 2010), and CH 4 uptake was suppressed significantly with low-level nitrogen
addition (Fang et al. 2014). Based on a 5-year experiment in an alpine grassland of
the Tian Shan Mountains in China, we found there were no significant effect of N
addition on CH 4 uptake. Annual average of CH 4 uptake was very highly significant
with average uptake between 52.9 and 106.6 μg C m
À2 h
À1 ; these results show that
change of CH 4 uptake was slight under N addition in a long-term experiment in
alpine grassland (Yue et al. 2016). CH 4 consumption decreased 36%, 31%, and 18%
with sheep urine, fresh dung, and compost, respectively, in a temperate grassland in
Inner Mongolia of China. In general, N deposition could inhibit the methane uptake.
⁄
ä
Fig. 10.4 (continued) (T) and nitrogen addition (N) are also presented. Data are shown as
mean + SE. Within each litter type, different letters above bars indicate significant differences at
P < 0Á05 among N treatments based on a one-way ANOVA. ÃP < 0Á05; ÃÃP < 0Á01; ÃÃÃP < 0Á001.
(This figure was adapted from Li et al. (2017) with permission by John Wiley and Sons)
10 Impacts of Nitrogen Deposition on China’s Grassland Ecosystems
227