branches (Cui et al. 2017). Different forms of desert plants also differed in nitrogen
retention under various rates of nitrogen deposition (Cui et al. 2018b).
11.3.2 Soil Enzyme Activity
Microbial enzymes are closely related to carbon, N, and P transformation and
changed rapidly and intensively under increasing N deposition (Enrique et al.
2008; Waldrop and Zak 2006; Zeglin et al. 2007). Nitrogen addition pronouncedly
inhibited soil enzyme activities (urease, sucrase, catalase, dehydrogenase), and
effects varied with N addition levels, soil depths, and years in a desert steppe,
south of the Tengger Desert (Su et al. 2014a). In addition, the responses to N
addition were divergent for different types of soil enzyme. For example, the oxidative enzyme activities were stable in desert soil and were only reduced in high N
added rates (Zhou et al. 2012), although the activities in soil fluctuated with the
seasons (Zhou and Zhang 2014c). Higher hydrolytic enzyme activities were found at
upper desert soil depths, and the sensitivity of activities to N addition was higher
than the lower depths. Activities of some hydrolytic enzymes, such as invertase and
alkaline phosphatase, increased with low levels of N addition rates (<30 kg N ha
À1
year
À1 ) and then decreased at higher levels. The activities of N related enzyme
(urease) decreased with rates of inorganic N enhancements in desert soils (Zhou and
Zhang 2014a; Zhou et al. 2011b).
11.3.3 Soil Microbial Biomass and Community Structure
Nitrogen fertilization on the desert soil increased microbial and fungi biomass by
14.0% and by 30.0% in winter, respectively, and the microbial community composition in winter and spring was changed by decreasing Actinobacteria phylum
abundance and increasing Ascomycota phylum abundance (Huang et al. 2018).
Nitrogen addition significantly increased soil bacterial PLFAs but did not affect
soil fungal PLFAs (Su et al. 2016). However, the ratio of fungal and bacterial PLFAs
was similar to ratio of gram-negative and gram-positive bacterial PLFAs (Huang
et al. 2015a). When the desert soil was analyzed in the Biolog system, the microbial
community level physiological profile was not affected by N increase (Zhou et al.
2012), which means that the soil microbial functional diversity was not altered under
increased N. The responses of microbial biomass carbon (MBC) to N addition
depended on the existence of shrubs in desert ecosystems. Nitrogen addition
increased MBC in soil between shrubs (Haloxylon ammodendron) and decreased
them beneath the shrubs (Huang et al. 2015a). Microbial biomass nitrogen (MBN)
was consistently increased by N addition at both microsites of interplant soil and
beneath shrubs, but only the ratio of MBC and MBN beneath shrubs was decreased
(Huang et al. 2015b; Zhou et al. 2012).
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
249
retention under various rates of nitrogen deposition (Cui et al. 2018b).
11.3.2 Soil Enzyme Activity
Microbial enzymes are closely related to carbon, N, and P transformation and
changed rapidly and intensively under increasing N deposition (Enrique et al.
2008; Waldrop and Zak 2006; Zeglin et al. 2007). Nitrogen addition pronouncedly
inhibited soil enzyme activities (urease, sucrase, catalase, dehydrogenase), and
effects varied with N addition levels, soil depths, and years in a desert steppe,
south of the Tengger Desert (Su et al. 2014a). In addition, the responses to N
addition were divergent for different types of soil enzyme. For example, the oxidative enzyme activities were stable in desert soil and were only reduced in high N
added rates (Zhou et al. 2012), although the activities in soil fluctuated with the
seasons (Zhou and Zhang 2014c). Higher hydrolytic enzyme activities were found at
upper desert soil depths, and the sensitivity of activities to N addition was higher
than the lower depths. Activities of some hydrolytic enzymes, such as invertase and
alkaline phosphatase, increased with low levels of N addition rates (<30 kg N ha
À1
year
À1 ) and then decreased at higher levels. The activities of N related enzyme
(urease) decreased with rates of inorganic N enhancements in desert soils (Zhou and
Zhang 2014a; Zhou et al. 2011b).
11.3.3 Soil Microbial Biomass and Community Structure
Nitrogen fertilization on the desert soil increased microbial and fungi biomass by
14.0% and by 30.0% in winter, respectively, and the microbial community composition in winter and spring was changed by decreasing Actinobacteria phylum
abundance and increasing Ascomycota phylum abundance (Huang et al. 2018).
Nitrogen addition significantly increased soil bacterial PLFAs but did not affect
soil fungal PLFAs (Su et al. 2016). However, the ratio of fungal and bacterial PLFAs
was similar to ratio of gram-negative and gram-positive bacterial PLFAs (Huang
et al. 2015a). When the desert soil was analyzed in the Biolog system, the microbial
community level physiological profile was not affected by N increase (Zhou et al.
2012), which means that the soil microbial functional diversity was not altered under
increased N. The responses of microbial biomass carbon (MBC) to N addition
depended on the existence of shrubs in desert ecosystems. Nitrogen addition
increased MBC in soil between shrubs (Haloxylon ammodendron) and decreased
them beneath the shrubs (Huang et al. 2015a). Microbial biomass nitrogen (MBN)
was consistently increased by N addition at both microsites of interplant soil and
beneath shrubs, but only the ratio of MBC and MBN beneath shrubs was decreased
(Huang et al. 2015b; Zhou et al. 2012).
11 Impacts of Nitrogen Deposition on China’s Desert Ecosystems
249