Five-year study of the effects of simulated nitrogen deposition levels and forms on soil nitrous oxide emissions from a temperate forest in northern China

Abstract

Few studies have quantified the effects of different levels and forms of nitrogen (N) deposition on soil nitrous oxide (N2O) emissions from temperate forest soils. A 5-year field experiment was conducted to investigate the effects of multiple forms and levels of N additions on soil N2O emissions, by using the static closed chamber method at Xi Mountain Experimental Forest Station in northern China. The experiment included a control (no N added), and additions of NH4NO3, NaNO3, and (NH4)2SO4 that each had two levels: 50 kg N ha−1 yr−1 and 150 kg N ha−1 yr−1. All plots were treated to simulate increased N deposition on a monthly schedule during the annual growing season (March to October) and soil N2O emissions were measured monthly from March 2011 to February 2016. Simultaneously, the temperature, moisture, and inorganic N contents of soil were also measured to explore how the main factors may have affected soil N2O emission. The results showed that the types and levels of N addition significantly increased soil inorganic N contents, and the accumulation of soil NO3–-N was significantly higher than that of soil NH4+–N due to N addition. The three N forms significantly increased the average N2O emissions (P < 0.05) in the order of NH4NO3 > (NH4)2SO4 > NaNO3 by 355.95%, 266.35%, and 187.71%, respectively, compared with control. The promotion of N2O emission via the NH4+–N addition was significantly more than that via the NO3––N addition, while N addition at a high level exerted a stronger effect than at the low-level. N addition exerted significantly stronger effects on cumulative N2O emissions in the initial years, especially the third year when the increased cumulative N2O emission reached their maximum. In the later years, the increases persisted but were weakened. Increasing inorganic N concentration could change soil from being N-limited to N-rich, and then N-saturated, and so the promotion on soil available N effect increased and then decreased. Moreover, the soil NH4+–N, NO3–-N, temperature, and water-filled pore space were all positively correlated with soil N2O emissions. These findings suggest that atmospheric N deposition can significantly promote soil N2O emission, and that exogenous NH4+–N and NO3–-N inputs into temperate forests can have synergic effects on soil N2O emission. In future research, both aspects should be better distinguished in the N cycle and balance of terrestrial ecosystems by using 15N tracer methods.

Responses of Soil N2O Emission and CH4 Uptake to N Input in Chinese Forests across Climatic Zones: A Meta-Study

“…Lastly, in soils with varying pH values, the responses of N2O emissio N inputs varied greatly; at soil pH lower than 5, N2O fluxes were increased by a 120.7%, while stimulation effect was significantly smaller at soil pH between 5 a (55.8%). When soil pH is above 7, which was only reported by one study [61], the size had a much larger mean (251.9%), despite varying widely. As shown in Figure 3 relationship between soil pH and response ratios of N2O fluxes are opposite between tropical (negative) and temperate (positive) forests.…”

How do natural soil NH4+, NO3− and N2O interact in response to nitrogen input in different climatic zones? A global meta‐analysis

“…Therefore, the form of soil inorganic N following N deposition may influence N 2 O production pathway and emissions. It has been reported that NH 4 + ‐induced N 2 O emissions were either higher (Xu, Wang, & Yang, 2017) or lower (Delaune, Lindau, Sulaeman, & Jugsujinda, 1998) than NO 3 − ‐induced N 2 O emissions. NH 4 + is often adsorbed to organo‐mineral complexes and diffuses moderately in the soil environment.…”

Contrasting effects of nitrogen and phosphorus additions on soil nitrous oxide fluxes and enzyme activities in an alpine wetland of the Tibetan Plateau

“…In our study, both above- and underground biomass was highly responsive (average 40% and 53% increase, respectively) to N additions, showing that N was the principal limiting nutrient in our study area. Therefore, N addition increased the substrate (NH 4 + -N and NO 3 − -N) for nitrification and denitrification processes and relieved the limitation of N in plants and microbes, increased enzyme activities (NAG activity) related to soil N recycling and increased N 2 O flux [7, 31, 37, 38].…”

“…Soil N 2 O flux (μg N m −2 h −1 ) was calculated from 2014 to 2016 as follows [31]: where F is soil N 2 O flux (μg N m −2 h −1 ); dc/dt is the rate of change between time and N 2 O concentration (10 −6 min −1 ); D refers to molar density of air (mol m −3 ); ; M is the molar mass of N 2 O-N (g mol −1 ); R is gas constant (J mol −1 K −1 ); P and T is air pressure (Pa) and air temperature (K) inside the chamber, respectively, and H is the height of the sampling box (m).…”

“…Soil cumulative N 2 O flux (kg N ha −1 yr −1 ) was calculated spanning the growing season following the method described by Xu et al [31]. where F is the N 2 O flux (μg N m −2 h −1 ); i is the sampling number; i.e., samples collected on the 7 th in May as 1 and those collected next on the 28 th in September as 20; t is the sampling interval time based on the Julian day (day).…”