However, a few studies have been reported that N addition could stimulate or have
no effects on CH 4 uptake. Soil CH 4 uptake was also affected by inorganic N, and soil
inorganic N status determined the inhibition or promotion effect to CH 4 uptake.
Moreover, CH 4 uptake was affected by climate warming, water regime, and N
addition in grassland ecosystems (Wang et al. 2014). The variations of activity and
structure of methanotrophic community need to be understood in grassland ecosystems under climate change and N deposition. Quantifying the effect of climate
change and N addition on the CH 4 budget needs to be conducted through processbased models and inverse models. Response of CH 4 uptake to interactive effect of N
addition and climate change needs to be also researched in a long-term spatial and
temporal scale.
10.4.3 N 2 O
The effect of N addition on N 2 O emission have been studied in grassland ecosystems
of China, and N addition increased N 2 O emission. N 2 O fluxes range between À2.05
and 5.65 μg m
À2 h
À1 during growth season in a mountain meadow, and no clear
seasonal pattern was found in a short-term experiment (Jiang et al. 2010). It had
shown a very slight change of N 2 O emission with water and N application across a
3-year experiment in a semiarid grassland, excluding several pulse fluxes of N 2 O
after N and water application. The highest N 2 O flux was 141.2 Æ 36.9 μg m
À2 h
À1
with the interactive effect of N and water addition, while the lowest N 2 O emission
was À26.9 Æ 3.5 μg m
À2 h
À1 with only N treatment (Zhang et al. 2017). In low-level
N addition or interactive effect of N deposition and warming, N 2 O emissions had
small change in growth season in alpine grasslands of the Qinghai-Tibetan Plateau.
N 2 O fluxes ranged between less than zero to above zero, showing that there was no
consistent emission or absorption (Zhao et al. 2017). N 2 O fluxes ranged from
À4.88 Æ 2.03 to 10.43 Æ 2.24 μg m
À2 h
À1 , and it showed a small change of N 2 O
flux in a swamp meadow on the Qinghai-Tibetan Plateau. There was no significant
N 2 O emission in growing season with N addition treatment, and the interaction
between warming and N addition had also not changed its pattern of N 2 O emission
(Chen et al. 2017a). Models have been used to assess the pattern of N 2 O emission
and to verify the potential effects of climate change in grassland ecosystems. Mean
annual N 2 O flux was 2.02 Æ 0.04 kg N ha
À1 over the past 50 years by using the N
and water management model, and nitrification was the predominant driving process
of N 2 O emission (Du et al. 2016). These results have been carried out only during the
growing season, and these experiments also have been short term (Jiang et al. 2010).
N 2 O fluxes are far from negligible on an annual basis during spring thaw and winter
but are missing when measurements have not been made during these parts of the
year. In fact, N 2 O fluxes need to be measured and monitored throughout the year in
grassland ecosystems. A short-lived pulse of N 2 O emission in spring thaw period
dominated the annual N 2 O budget. However, no pulse effect of N 2 O emissions was
found in the spring thaw period with N addition treatments in alpine grassland of the
228
X. Lü et al.
no effects on CH 4 uptake. Soil CH 4 uptake was also affected by inorganic N, and soil
inorganic N status determined the inhibition or promotion effect to CH 4 uptake.
Moreover, CH 4 uptake was affected by climate warming, water regime, and N
addition in grassland ecosystems (Wang et al. 2014). The variations of activity and
structure of methanotrophic community need to be understood in grassland ecosystems under climate change and N deposition. Quantifying the effect of climate
change and N addition on the CH 4 budget needs to be conducted through processbased models and inverse models. Response of CH 4 uptake to interactive effect of N
addition and climate change needs to be also researched in a long-term spatial and
temporal scale.
10.4.3 N 2 O
The effect of N addition on N 2 O emission have been studied in grassland ecosystems
of China, and N addition increased N 2 O emission. N 2 O fluxes range between À2.05
and 5.65 μg m
À2 h
À1 during growth season in a mountain meadow, and no clear
seasonal pattern was found in a short-term experiment (Jiang et al. 2010). It had
shown a very slight change of N 2 O emission with water and N application across a
3-year experiment in a semiarid grassland, excluding several pulse fluxes of N 2 O
after N and water application. The highest N 2 O flux was 141.2 Æ 36.9 μg m
À2 h
À1
with the interactive effect of N and water addition, while the lowest N 2 O emission
was À26.9 Æ 3.5 μg m
À2 h
À1 with only N treatment (Zhang et al. 2017). In low-level
N addition or interactive effect of N deposition and warming, N 2 O emissions had
small change in growth season in alpine grasslands of the Qinghai-Tibetan Plateau.
N 2 O fluxes ranged between less than zero to above zero, showing that there was no
consistent emission or absorption (Zhao et al. 2017). N 2 O fluxes ranged from
À4.88 Æ 2.03 to 10.43 Æ 2.24 μg m
À2 h
À1 , and it showed a small change of N 2 O
flux in a swamp meadow on the Qinghai-Tibetan Plateau. There was no significant
N 2 O emission in growing season with N addition treatment, and the interaction
between warming and N addition had also not changed its pattern of N 2 O emission
(Chen et al. 2017a). Models have been used to assess the pattern of N 2 O emission
and to verify the potential effects of climate change in grassland ecosystems. Mean
annual N 2 O flux was 2.02 Æ 0.04 kg N ha
À1 over the past 50 years by using the N
and water management model, and nitrification was the predominant driving process
of N 2 O emission (Du et al. 2016). These results have been carried out only during the
growing season, and these experiments also have been short term (Jiang et al. 2010).
N 2 O fluxes are far from negligible on an annual basis during spring thaw and winter
but are missing when measurements have not been made during these parts of the
year. In fact, N 2 O fluxes need to be measured and monitored throughout the year in
grassland ecosystems. A short-lived pulse of N 2 O emission in spring thaw period
dominated the annual N 2 O budget. However, no pulse effect of N 2 O emissions was
found in the spring thaw period with N addition treatments in alpine grassland of the
228
X. Lü et al.