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Atmospheric reactive nitrogen (Nr) pollution leads to enhanced Nr deposition. There still big gaps in understanding atmospheric nitrogen deposition because of limited monitoring sites in arid land ecosystems of Central Asia. To determine Nr concentrations and deposition in the study area, we have set up 20 monitoring sites to collect gaseous, particulate, and precipitation samples and measure their Nr components since 2009. Nr concentrations in air showed large spatial variations. Based on the Nr concentrations, dry deposition was calculated using the monthly average Nr concentrations by the corresponding deposition velocities modeled, which was varied between 3.15 and 27.92 kg N ha-1 yr-1 across desert, grassland, desert-grassland, forest, farmland, and city/suburb ecosystems. Ammonia N deposition varied between 0.50 asnd 8.66 kg N ha-1 yr-1, and nitrate N deposition c varied between 0.67 and 4.22 kg N ha-1 yr-1, respectively, in precipitation. Annual N deposition is following the order of desert (4.0) < grassland (6.0) < desert-grassland (7.6) < forest (16.1) < farmland (18.4) < city/suburb (35.4) ecosystems. Dry deposition contributed 52.7, 53.8, 100, 68.2, 73.7, and 78.9% of total N deposition in grassland, desert-grassland, desert, forest, farmland and city/suburb ecosystems, respectively. Reduced nitrogen deposition accounted for 62% of total N deposition in the arid area. Dry NH3 deposition made an important contribution (on average 40%) to total N deposition. Therefore, understanding the characteristics of Nr pollution especially NH3 emission is indispensable to atmospheric pollution control in arid region. [ABSTRACT FROM AUTHOR]

Increased nitrogen (N) availability induced by fertilizer use, rapid urbanization, and livestock cultivation has important effects on the biogeochemical cycles of plant N and phosphorus (P). Knowledge of the long-term N enrichment effects on the biogeochemical cycling of N and P via plant ecological stoichiometry and nutrient resorption remains limited. Nutrient resorption plays an important role in the plant nutrient economy and nutrient cycling. A three-year field experiment was performed to test the effects of N addition on leaf nutrient resorption of two dominant grass species (Leymus tiansecalinus and Festuca ovina) from an 11-year grassland experiment involving four N levels (0, 30, 90, and 150 kg N ha−1 year−1) in an alpine grassland of Tianshan Mountains in northwestern China. Nitrogen addition significantly increased aboveground biomass (AGB) and soil N availability. The N concentrations and N:P ratio in mature and senesced leaves consistently increased with increasing N across all three years. The P concentrations in mature and senesced leaves notably decreased with increasing N. The N addition resulted in decreased N resorption efficiency (NRE) and increased P resorption efficiency (PRE). The divergent responses of plant N and P resorption and N:P ratios resulted in the decoupling of the plant internal nutrient cycles for both grass species, attributed to increased soil N availability and nonsignificant effects on soil available P caused by N addition. In addition, the N:P resorption ratios were negatively correlated with increasing N levels, suggesting different sensitivities of plant N and P to N addition. The aboveground production of both grass species was positively correlated with PRE and negatively correlated with NRE. Under the background of the currently high and steadily increasing atmospheric N deposition, the imbalance of plant nutrient cycling will likely alter plant community compositions and subsequent litter decomposition, ultimately affecting ecosystem stability and function. [ABSTRACT FROM AUTHOR]

Arid areas play a significant role in the global nitrogen cycle. Dry and wet deposition of inorganic nitrogen (N) species were monitored at one urban (SDS) and one suburban (TFS) site at Urumqi in a semi-arid region of central Asia. Atmospheric concentrations of NH3, NO2, HNO3, particulate ammonium and nitrate (pNH4+ and pNO3−) concentrations and NH4-N and NO3-N concentrations in precipitation showed large monthly variations and averaged 7.1, 26.6, 2.4, 6.6, 2.7 µg N m−3 and 1.3, 1.0 mg N L−1 at both SDS and TFS. Nitrogen dry deposition fluxes were 40.7 and 36.0 kg N ha−1 yr−1 while wet deposition of N fluxes were 6.0 and 8.8 kg N ha−1 yr−1 at SDS and TFS, respectively. Total N deposition averaged 45.8 kg N ha−1 yr−1at both sites. Our results indicate that N dry deposition has been a major part of total N deposition (83.8% on average) in an arid region of central Asia. Such high N deposition implies heavy environmental pollution and an important nutrient resource in arid regions. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition is considered to be an important source of atmospheric N 2 O emission. Although N deposition simulated experiments have been conducted in grassland, forest and arctic tundra, the effect of long-term N deposition on N 2 O emission is not well understood in alpine grassland. To assess the response, a 9-yr N addition experiment was conducted in an alpine grassland of the Tianshan Mountains of Central Asia, to characterize the relationship between N 2 O emission and N application rate. An N addition rate of 10 kg N ha−1 yr−1 had no significant effect on N 2 O, while increases in N 2 O emission were clearly observed with N deposition of up to 30 kg N ha−1 yr−1 with a low emission factor (EF). The average N 2 O emission factor was 0.19% (range: 0.03%–0.42%), lower than the current IPCC default value of 1%. Nitrogen application significantly increased soil accumulated N 2 O emission throughout the growing season from 2013 to 2017, showing an increasing tendency in N 2 O emission with time. Depending on the amount and duration of N application, the interannual variability was 48.55%, 27.56%, 15.12% and 10.16% at the control (no N addition), 10, 30, 90 kg N ha−1 yr−1 plots, respectively. These would help to refine the accuracy of N 2 O mitigation protocols with insignificant N 2 O promotion under double present N deposition scenarios in alpine grassland. • N 2 O emissions increased quickly with N input ≥30 kg N ha−1 yr−1. • The longer N was added and the larger N addition effects on N 2 O emission appeared. • The current IPCC EF should be re-estimated for non N-saturation alpine grasslands. [ABSTRACT FROM AUTHOR]