enzyme activities were more stable under the increasing N deposition than hydrolytic enzymes. Nitrogen addition increased the microbial biomass N, while the
effects of microbial biomass carbon were regulated by shrubs. The microbial
community was rarely affected by the N addition.
On an individual and community level, the N addition can increase the growth of
annual plants in desert ecosystems. The patterns of biomass allocation between
aboveground and belowground parts depended on the life-forms or species. Community productivity first increased and then decreased with the years exposed to high
levels of N addition. The changes in community structure contributed to the shift in
productivity, because plant species richness, abundance, and density usually
decreased under chronic N addition.
On the ecosystem scale, greenhouse gas emission responses to N addition showed
gas-specific effects. Stimulated effects on nitrous oxide emission were found under
N addition, with no or negative effects on methane uptake. The N addition on carbon
efflux depends on the rates of N addition and the exposed years to N addition. For the
nonvascular plant biocrusts, moderate N addition can be beneficial for their growth
and biological activity. However, the positive effects might stop at level of 5 kg N
ha
À1 year
À1 , and decreased effects occur with the increase in rates of added N. The
biocrusts were more sensitive to N addition than vascular plants in the desert
ecosystems.
In desert ecosystem, water was undoubtedly the driving factors for the ecological
process. The effects of N on soil microbial activity, greenhouse gas emission, plant
growth, and community species diversity are regulated by the precipitation of the
year or soil moisture in sample obtaining time. Generally, a certain water supply
often expands the N effects on the indices of the ecological process in desert
ecosystems.
In the future, how multifactors affect the N effects on ecological processes in
desert ecosystems deserves to be studied in a long-term scale. We would better focus
on how changes in precipitation patterns (including amount, frequency, extreme
event) interacted with N deposition influence the community structure and function
in these areas. In addition, because of the huge distribution of N-fixed species in the
deserts, such as biocrusts and leguminous plants, the effects of N deposition on these
communities are also crucial for evaluation of the ecological effects under global
changes. Trade-offs between potential N fixation and N deposition need to be
studied for the N balance in desert ecosystems.
References
Adams MB (2003) Ecological issues related to N deposition to natural ecosystems: research needs.
Environ Int 29:189–199
Baez S, Fargione J, Moore DI et al (2007) Atmospheric nitrogen deposition in the northern
Chihuahuan desert: temporal trends and potential consequences. J Arid Environ 68:640–651
Bai C, Alata, Chen H et al (2013) Effects of addition of nitrogen and water on plant community
characteristics of Stipa breviflora desert steppe. Chin J Grassl 35:69–75
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
257
effects of microbial biomass carbon were regulated by shrubs. The microbial
community was rarely affected by the N addition.
On an individual and community level, the N addition can increase the growth of
annual plants in desert ecosystems. The patterns of biomass allocation between
aboveground and belowground parts depended on the life-forms or species. Community productivity first increased and then decreased with the years exposed to high
levels of N addition. The changes in community structure contributed to the shift in
productivity, because plant species richness, abundance, and density usually
decreased under chronic N addition.
On the ecosystem scale, greenhouse gas emission responses to N addition showed
gas-specific effects. Stimulated effects on nitrous oxide emission were found under
N addition, with no or negative effects on methane uptake. The N addition on carbon
efflux depends on the rates of N addition and the exposed years to N addition. For the
nonvascular plant biocrusts, moderate N addition can be beneficial for their growth
and biological activity. However, the positive effects might stop at level of 5 kg N
ha
À1 year
À1 , and decreased effects occur with the increase in rates of added N. The
biocrusts were more sensitive to N addition than vascular plants in the desert
ecosystems.
In desert ecosystem, water was undoubtedly the driving factors for the ecological
process. The effects of N on soil microbial activity, greenhouse gas emission, plant
growth, and community species diversity are regulated by the precipitation of the
year or soil moisture in sample obtaining time. Generally, a certain water supply
often expands the N effects on the indices of the ecological process in desert
ecosystems.
In the future, how multifactors affect the N effects on ecological processes in
desert ecosystems deserves to be studied in a long-term scale. We would better focus
on how changes in precipitation patterns (including amount, frequency, extreme
event) interacted with N deposition influence the community structure and function
in these areas. In addition, because of the huge distribution of N-fixed species in the
deserts, such as biocrusts and leguminous plants, the effects of N deposition on these
communities are also crucial for evaluation of the ecological effects under global
changes. Trade-offs between potential N fixation and N deposition need to be
studied for the N balance in desert ecosystems.
References
Adams MB (2003) Ecological issues related to N deposition to natural ecosystems: research needs.
Environ Int 29:189–199
Baez S, Fargione J, Moore DI et al (2007) Atmospheric nitrogen deposition in the northern
Chihuahuan desert: temporal trends and potential consequences. J Arid Environ 68:640–651
Bai C, Alata, Chen H et al (2013) Effects of addition of nitrogen and water on plant community
characteristics of Stipa breviflora desert steppe. Chin J Grassl 35:69–75
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
257