Impacts of Nitrogen Deposition on China’s Desert Ecosystems

In desert ecosystems, nitrogen (N) deposition can alter the soil N pools (soil available N or total N) or plant N uptake while rarely changing other nutrient contents. In this chapter, we reviewed the effects of N deposition on China’s desert ecosystems based on experimental results. Acidification of the soil and toxic effects on the microbes often occur under high N addition. Soil enzyme activities in response to N additions depended on the N applied rates and the specific enzyme types, with oxidative enzymes more stable than hydrolytic enzymes. Soil microbial biomass N was usually increased by N addition, while the responses of microbial biomass carbon depended on shrub existence. The soil microbial community structure was generally not affected by N addition, although increased soil bacterial phospholipid fatty acid (PLFA) and non-changes in soil fungal PLFAs were observed. For the greenhouse gas emission, N addition cannot shift the soil respiration except under high moisture condition. Positive effects of N input on nitrous oxide emission with no or negative methane uptake were found. The growth and biomass allocation of vascular plants under N addition depended on life-forms/species in desert ecosystems. The increased individual growth under N addition was not always observed in productivity because of changes in the community structure. With the increase in N added rates, abundance, richness, and density usually decreased, and the effects were affected by the years exposed to N addition. More water supply can expand the N effects on plant growth and diversity in desert ecosystems. Lower levels of N addition also stimulated growth of nonvascular plants (biocrusts), while higher levels exhibited negative effects.