Effects of nitrogen sources and glucose on the consumption of ethylene and methane by temperate volcanic forest surface soils

Precipitation changes regulate the annual methane uptake in a temperate desert steppe

Desert soils are an important sink of atmospheric methane (CH₄) and regulate the global CH₄ budget. However, it is still unclear how CH₄ fluxes respond to precipitation changes in desert-steppe soils. Therefore, a two-year in situ control experiment was conducted to investigate the effect of precipitation changes on CH₄ uptake in desert steppe of Inner Mongolia in northwest China and its driving mechanism. The result showed that this desert steppe was an important sink of CH₄, with an annual uptake of 2.93 (2.64-3.22) kg C ha^-1. It was found that CH₄ uptake was reduced significantly for decreasing precipitation, especially in spring and summer. In contrast, an increasing trend of CH₄ uptake was observed for increasing precipitation, although it was not statistically significant. Further analyses found that CH₄ uptake was more sensitive to decreasing precipitation than increasing precipitation. This may be mainly due to the fact that only moderate water-filled pore space (WFPS) induced by precipitation promoted CH₄ uptake, while too-high (>32%) or too-low WFPS inhibited its uptake. A structural equation model showed that the copy number of the pmoA functional gene was the most important factor affecting CH₄ uptake. In contrast, soil moisture had a very important indirect effect on CH₄ uptake, mainly through significantly affected soil porosity, the above-ground plant biomass and NO₃^--N content, further affected CH₄ uptake. Overall, CH₄ sinks in desert steppe was still mainly controlled by methane-oxidizing bacteria containing the key functional gene pmoA and WFPS. Therefore, precipitation plays an important role in regulating the intensity of CH₄ sinks in desert steppe, while it is worth noting that too-little precipitation will significantly weaken CH₄ sinks.

Effects of changes in throughfall on soil GHG fluxes under a mature temperate forest, northeastern China

Climate change scenarios predict a change in the rainfall regimes for this current century, which has different impacts on soil greenhouse gas (GHG) fluxes. However, how changes in annual rainfall affect annual GHG fluxes of forest soils remain unknown. A six-year field experiment with -25% and -50% throughfall (TF) and +25% TF manipulation was performed to explore the mechanisms involving GHG fluxes under a mature temperate forest, northeastern China and to work out whether the TF effect sizes on annual soil GHG fluxes vary with dry and wet years. The results showed that both -25% TF and -50% TF treatments depressed annual soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions but increased annual soil methane (CH₄) uptake. A contrary pattern of annual soil GHG fluxes was observed in the +25% TF treatment. When annual TF input was decreased by 100 mm, annual soil N₂O and CO₂ emissions were decreased by 18.1 ± 3.1 mg N m^-2 and by 39.4 ± 6.1 g C m^-2 during the growing season, respectively, and annual soil CH₄ uptake was increased by 11.5 ± 3.4 mg C m^-2. Both -25% TF and -50% TF treatments reduced annual soil dissolved organic C (DOC) leaching by 29.3% and 45.6% and dissolved total N (DN) leaching by 30.8% and 39.6%, respectively. Contrary to annual soil N₂O and CO₂ emissions, annual soil CH₄ uptake during the growing season significantly decreased with an increase in the annual leaching fluxes of soil DOC, inorganic N, and DN. Besides soil moisture and temperature and pH, soil GHG fluxes under manipulating TF condition were regulated by soil labile C and N status. Our findings indicated that the TF effect sizes on both annual GHG fluxes and net annual GHG balance (GWP) of forest soils varied with dry and wet years in northeastern China. The results highlight the importance of altered annual rainfall in regulating annual soil GHG fluxes and the GWP in temperate forests under global climate change.

Impact of 13-years of nitrogen addition on nitrous oxide and methane fluxes and ecosystem respiration in a temperate grassland

Nitrogen (N) fertilizer application and atmospheric N deposition will profoundly affect greenhouse gas (GHGs) emissions, especially nitrous oxide (N₂O) and methane (CH₄) fluxes and ecosystem respiration (R_e, i.e. CO₂ emissions). However, the impacts of long-term N inputs and the often associated N-induced soil acidification on GHG fluxes in arid and semi-arid ecosystems, especially temperate grasslands, are still uncertain. An in situ experiment was conducted to investigate the effect of long-term (13-years) N addition on N₂O and CH₄ fluxes and R_e from a temperate grassland in Inner Mongolia, northeast China, from April 2017 to October 2018. Soil pH values in the 0-5 cm layer receiving 120 (N₁₂₀) and 240 (N₂₄₀) kg N ha^-1 decreased from 7.12 to 4.37 and 4.18, respectively, after 13 years of N inputs. Soil CH₄ uptake was significantly reduced, but N₂O emission was enhanced significantly by N addition. However, N addition had no impact on R_e. Structural Equation Modeling indicated that soil NH₄⁺-N content was the dominant control of N₂O emissions, but with less effect of the decreasing pH. In contrast, CH₄ uptake was generally controlled by soil pH and NO₃^--N content, and R_e by forb biomass. The measured changes in N₂O and CH₄ fluxes and R_e from temperate grassland will have a profoundly impact on climate change.

Response of soil methane uptake to simulated nitrogen deposition and grazing management across three types of steppe in Inner Mongolia, China

The response of soil methane (CH₄) uptake to increased nitrogen (N) deposition and grazing management was studied in three types of steppe (i.e., meadow steppe, typical steppe, and desert steppe) in Inner Mongolia, China. The experiment was designed with four simulated N deposition rates such as 0, 50, 100, and 200kgNha^-1, respectively, under grazed and fenced management treatments. Results showed that the investigated steppes were significant sinks for CH₄, with an uptake flux of 1.12-3.36kgha^-1 over the grass growing season and that the magnitude of CH₄ uptake significantly (P<0.05) decreased with increasing N deposition rates. The soil CH₄ uptake rates were highest in the desert steppe, moderate in the typical steppe, and lowest in the meadow steppe. Compared with grazed plots, fencing increased the CH₄ uptake by 4.7-40.2% with a mean value of 20.2% across the three different steppe types. The responses of soil CH₄ uptake to N deposition in the continental steppe varied depending on the N deposition rate, steppe type, and grazing management. A significantly positive correlation between CH₄ uptake and soil temperature was found in this study, whereas no significant relationship between soil moisture and CH₄ uptake occurred. Our results may contribute to the improvement of model parameterization for simulating biosphere-atmosphere CH₄ exchange processes and for evaluating the climate change feedback on CH₄ soil uptake.

Synergistic effects of dissolved organic carbon and inorganic nitrogen on methane uptake in forest soils without and with freezing treatment

There is limited knowledge about how the interaction of dissolved organic carbon (DOC) and inorganic nitrogen (N) released into the soil just after freezing can affect methane (CH₄) uptake in forest soils. Here, we present how freezing treatment and glucose, as a DOC source, can affect the roles of NH₄⁺-N and NO₃⁻-N in inhibiting soil CH₄ uptake, by using soil-core incubation experiments. A long-term freezing at low temperature reduced cumulative CH₄ uptake in the soils sampled from two temperate forest stands without carbon (C) and N addition. The inhibition effects of N addition as NH₄Cl and KNO₃ on the soil CH₄ uptake were much larger than C addition. Freezing treatment eliminated the inhibition effect of NH₄Cl and KNO₃ addition on CH₄ uptake, and this response was affected by glucose addition and forest types. The addition of glucose eliminated the inhibition effect of NO₃⁻-N on CH₄ uptake in the forest soils without and with freezing treatment, while the addition of NH₄⁺-N and glucose inhibited synergistically the soil CH₄ uptake. The results highlight the importance of synergistic effects of DOC and N inputs on the soil CH₄ uptake under forest stands during soil wetting and thawing periods.

A five-year study of the impact of nitrogen addition on methane uptake in alpine grassland

It remains unclear how nitrogen (N) deposition affects soil methane (CH₄) uptake in semiarid and arid zones. An in situ field experiment was conducted from 2010 to 2014 to systematically study the effect of various N application rates (0, 10, 30, and 90 kg N ha⁻¹ yr⁻¹) on CH₄ flux in alpine grassland in the Tianshan Mountains. No significant influence of N addition on CH₄ uptake was found. Initially the CH₄ uptake rate increased with increasing N application rate by up to 11.5% in 2011 and then there was gradual inhibition by 2014. However, the between-year variability in CH₄ uptake was very highly significant with average uptake ranging from 52.9 to 106.6 μg C m⁻² h⁻¹ and the rate depended largely on seasonal variability in precipitation and temperature. CH₄ uptake was positively correlated with soil temperature, air temperature and to a lesser extent with precipitation, and was negatively correlated with soil moisture and NO₃⁻-N content. The results indicate that between-year variability in CH₄ uptake was impacted by precipitation and temperature and was not sensitive to elevated N deposition in alpine grassland.