The carbon release from litter decomposition is related to soil respiration. In a
temperate desert, N addition and water did not significantly affect root mass loss and
the content of the N and phosphorus in litter residue (Zhao et al. 2015). In a semiarid
dune grassland, N addition, either alone or plus with water, significantly decreased N
release, and dry mass loss in the plant leaves and roots, with little effect of water, was
observed (Li et al. 2016).
11.4.2 Greenhouse Gas Emission
Carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ) are the three most
important greenhouse gases. The N addition significantly increased the net ecosystem carbon exchange of the desert steppe (Wang 2012), which was more beneficial
for carbon sequestration in deserts and for reduction of CO 2 emission of the
ecosystems. In a temperate desert, CO 2 emissions were not changed by N additions
in the 1st year, while in spring and summer of the 2nd year, CO 2 emissions were
significantly reduced by high N (Zhou et al. 2017). The between-year differences in
CO 2 emission were driven by ephemeral plants (the plant life-form which often
rapidly grows and ends life cycle within 1 or 2 months in spring), such as their root
respiration (Yue et al. 2018; Zhou et al. 2018). Nitrogen addition had gradual effects
on net CO 2 exchange, which indicate the differences between gross ecosystem
productivity and ecosystem respiration (Zhou et al. 2019). The temperate desert
was found to be a small source of N 2 O (0.13 kg N ha
À1 year
À1 ) (Yue et al. 2019).
Nitrogen addition generally increases the N 2 O emission, with the effects varying in
specific seasons and years. N treatments can explain most variation in N 2 O emission
rates (33.44%), followed by interaction between month and N treatments (25.67%)
(Zhou et al. 2017, 2019). The soil in temperate desert was also a small sink for CH 4
(À0.92 kg C ha
À1 year
À1 ), and the CH 4 uptake rates varied among seasons but not
significantly affected by N addition (Yue et al. 2019; Zhou et al. 2017). Interactive
effects of precipitation and N addition on CH 4 uptake were observed, but they
(+16.0–20.3%) were lower than alone effect of N or water (+50.1–79.1%) (Yue
et al. 2019). Across three types of steppe under simulated N deposition in Inner
Mongolia, CH 4 uptake magnitude significantly decreased with the increasing rates of
N deposition (Li et al. 2018). Overall, greenhouse gas fluxes from the temperate
desert soils are sensitive to elevated N deposition.
11.5 Impacts on Plant Growth and Allocation
11.5.1 Plant Growth and Productivity
Effects on N addition on vascular plants depend on life-forms/species in desert
ecosystems. Nitrogen addition stimulated the growth of the four common species
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
251
temperate desert, N addition and water did not significantly affect root mass loss and
the content of the N and phosphorus in litter residue (Zhao et al. 2015). In a semiarid
dune grassland, N addition, either alone or plus with water, significantly decreased N
release, and dry mass loss in the plant leaves and roots, with little effect of water, was
observed (Li et al. 2016).
11.4.2 Greenhouse Gas Emission
Carbon dioxide (CO 2 ), nitrous oxide (N 2 O), and methane (CH 4 ) are the three most
important greenhouse gases. The N addition significantly increased the net ecosystem carbon exchange of the desert steppe (Wang 2012), which was more beneficial
for carbon sequestration in deserts and for reduction of CO 2 emission of the
ecosystems. In a temperate desert, CO 2 emissions were not changed by N additions
in the 1st year, while in spring and summer of the 2nd year, CO 2 emissions were
significantly reduced by high N (Zhou et al. 2017). The between-year differences in
CO 2 emission were driven by ephemeral plants (the plant life-form which often
rapidly grows and ends life cycle within 1 or 2 months in spring), such as their root
respiration (Yue et al. 2018; Zhou et al. 2018). Nitrogen addition had gradual effects
on net CO 2 exchange, which indicate the differences between gross ecosystem
productivity and ecosystem respiration (Zhou et al. 2019). The temperate desert
was found to be a small source of N 2 O (0.13 kg N ha
À1 year
À1 ) (Yue et al. 2019).
Nitrogen addition generally increases the N 2 O emission, with the effects varying in
specific seasons and years. N treatments can explain most variation in N 2 O emission
rates (33.44%), followed by interaction between month and N treatments (25.67%)
(Zhou et al. 2017, 2019). The soil in temperate desert was also a small sink for CH 4
(À0.92 kg C ha
À1 year
À1 ), and the CH 4 uptake rates varied among seasons but not
significantly affected by N addition (Yue et al. 2019; Zhou et al. 2017). Interactive
effects of precipitation and N addition on CH 4 uptake were observed, but they
(+16.0–20.3%) were lower than alone effect of N or water (+50.1–79.1%) (Yue
et al. 2019). Across three types of steppe under simulated N deposition in Inner
Mongolia, CH 4 uptake magnitude significantly decreased with the increasing rates of
N deposition (Li et al. 2018). Overall, greenhouse gas fluxes from the temperate
desert soils are sensitive to elevated N deposition.
11.5 Impacts on Plant Growth and Allocation
11.5.1 Plant Growth and Productivity
Effects on N addition on vascular plants depend on life-forms/species in desert
ecosystems. Nitrogen addition stimulated the growth of the four common species
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
251