Phyllosphere of senescent crops as a microbial N2O source

Landfills are a unique "terrestrial ecosystem" and serve as a significant carbon sink. Microorganisms convert biodegradable substances in municipal solid waste (MSW) to CH4, CO2, and microbial biomass, consisting of the carbon cycling in landfills. Microbial-mediated N and S cycles are also the important biogeochemical process during MSW decomposition, resulting in N2O and H2S emission, respectively. Meanwhile, microbial-mediated N and S cycles affect carbon cycling. How microbial community structure and function respond to C, N, and S cycling during solid waste decomposition, however, are not well-characterized. Here, we show the response of bacterial and archaeal community structure and functions to C, N, and S cycling during solid waste decomposition in a long-term (265days) operation laboratory-scale bioreactor through 16S rRNA-based pyrosequencing and metagenomics analysis. Bacterial and archaeal community composition varied during solid waste decomposition. Aerobic respiration was the main pathway for CO2 emission, while anaerobic C fixation was the main pathway in carbon fixation. Methanogenesis and denitrification increased during solid waste decomposition, suggesting increasing CH4 and N2O emission. In contract, fermentation decreased along solid waste decomposition. Interestingly, Clostridiales were abundant and showed potential for several pathways in C, N, and S cycling. Archaea were involved in many pathways of C and N cycles. There is a shift between bacteria and archaea involvement in N2 fixation along solid waste decomposition that bacteria Clostridiales and Bacteroidales were initially dominant and then Methanosarcinales increased and became dominant in methanogenic phase. These results provide extensive microbial mediation of C, N, and S cycling profiles during solid waste decomposition.

We evaluated the effect of chemical fertilizer and manure applications on N2O emission from a managed grassland by establishing three treatment plots of chemical N fertilizer (chemical fertilizer), manure combined with chemical N fertilizer (manure) and no N fertilizer (control) at the Shizunai Experimental Livestock Farm in southern Hokkaido, Japan. The N2O fluxes from the soils were measured using a closed-chamber method from May 2005 to April 2008. Soil denitrifying enzyme activity (DEA) in the root-mat layer (0–2.5 cm) and in the mineral soil layer (2.5–5 cm) of each treatment plot was measured using an acetylene inhibition method after treatment with NO3 −-N addition, glucose addition, both NO3 −-N and glucose addition or neither NO3 −-N nor glucose addition. Annual N2O emission ranged from 0.6 to 4.9 kg N2O-N ha−1year−1, with the highest emission observed in the manure plot and the lowest in the control plot. The chemical fertilizer induced emission factor (EF) (range: 0.85–1.32%) was significantly higher than the manure-induced EF (range: 0.35–0.85%). The denitrification potential of the soil horizons was measured with the addition of both NO3 −-N and glucose, and was significantly higher in root-mat soil than in mineral soil. Soil DEA in the root mat with the addition of NO3 −-N with and without the addition of glucose had a significantly positive correlation with soil pH (P < 0.05). Soil pH was significantly influenced by N source, which was significantly lower in the chemical fertilizer plot than in the control and manure plots. For a fixed quantity of available N, the application of manure could result in higher N2O emission compared with chemical fertilizer, owing to higher soil pH values under manure application than under chemical fertilizer application.

It is well known that agricultural and forest ecosystems serve as vital carbon sinks in terrestrial ecosystems. Understanding the fundamental processes and mechanisms of ecosystem carbon cycles in face of climate change is critical for quantifying the carbon sinks of terrestrial ecosystems. Ecosystem carbon cycles cannot be separated from water and nitrogen cycles and thus the response and adaptation of carbon-water-nitrogen processes in agricultural and forest ecosystems to climate change demand further studies. This research topic published 10 papers to gain novel insights into the underlying mechanisms and processes of carbon-water-nitrogen interactions in agricultural and forest ecosystems in response to climate change.Litter decomposition is a pivotal biogeochemical process, which profoundly influences carbon and nitrogen cycling in forest and grassland ecosystems. Climatic factors can significantly impact litter decomposition rates, carbon sequestration, and the emissions of greenhouse gases such as CO2 and N2O. Liu et al. conducted a comprehensive meta-analysis of 351 samples from 37 published studies to explore the interactive effects of solar radiation and precipitation on litter decomposition and CO2 emission on a global scale. They found that the solar radiation significantly increased litter decomposition which was dependent on precipitation regimes. Meanwhile, Li et al. investigated the effects of warming and reclamation on N2O emission flux through a long-term manipulative warming experiment on the Qinghai-Tibetan Plateau. Their results demonstrated that reclamation amplified the warming effects on N2O emissions by enhancing soil nitrification and related enzymatic activities in alpine meadows. Additionally, Lin et al. examined the long-term spatiotemporal variations in aboveground carbon sequestration rates in the eastern Tibetan Plateau using a forest landscape model under different climate change scenarios. Their study highlighted the variability in aboveground carbon sequestration rates across various forest types in response to climate warming.The escalating frequency and duration of drought events under climate change have prompted heightened scrutiny of their impacts on temporal and spatial variations in evapotranspiration and water use efficiency. Yang et al. analyzed the inter-annual variations of evapotranspiration with eddy covariance fluxes in an urban forest in Beijing, China, revealing that spring and mid-summer droughts primarily drove inter-annual variations in evapotranspiration due to the reduced stomatal conductance. Furthermore, Xu et al. employed the ensemble empirical mode decomposition method to investigate spatial variations and mechanisms influencing the stability of water use efficiency in China. Their findings explored the role of precipitation and soil moisture in promoting stable water use efficiency, with unstable trends primarily driven by positive or negative reversals. In addition, Jiang et al. presented an in-depth analysis of the impact of seasonal drought on root distribution and water utilization patterns of forests in south China. Their findings highlighted the critical role of deep fine roots in utilizing deep soil water during the dry season, constituting a substantial portion of total water consumption.Leaf photosynthesis, reliant on both photochemical and carboxylation processes, is central to terrestrial carbon fluxes. Accurate estimation of photochemical parameters and maximum carboxylation rates is essential for predicting carbon fluxes of terrestrial ecosystems. The article by Liu et al. found that the inferred values of the photochemical redox parameters varied with leaf macronutrient contents. The work of Li et al. evaluated the relationships between the leaf maximum rate of carboxylation and both leaf Narea and photosynthetic pigments of winter wheat in a farmland ecosystem in China. One of the study’s notable findings was the strongest correlation between leaf Vcmax and leaf Chlarea. Their findings suggest that photosynthetic pigment content serves as a predictor for estimating Vcmax, offering a novel approach for spatially continuous Vcmax estimation and enhancing simulation accuracy in ecological models.In addition to the above articles from field studies, two papers elucidated the mitigated effects of elevated CO2 concentrations on environmental stressors such as drought and nutrient deficiency. Based on manipulative experiment with environmental growth chambers, Chang et al. examined the effects of elevated CO2 concentration and temperature on plant growth and leaf gas exchange of winter wheat along a soil water gradient, and found that elevated CO2 concentration substantially enhanced leaf photosynthesis by about 30% under water deficiency, suggesting the negative impacts of water deficiency on winter wheat might be partially mitigated by elevated CO2 concentration. Li et al. reported findings that the plant growth and leaf photosynthesis of annual ryegrass under phosphorus deficiency were enhanced by elevated CO2 concentration, indicating the impacts of phosphorus deficiency on annual ryegrass may be alleviated by elevated CO2 concentration under climate change.This research topic presents the latest studies on how climate change affects the carbon-water-nitrogen processes of agricultural and forest ecosystems. Meanwhile, this research topic highlights the importance and uncertainty of ecosystem functioning in response to climate change. Therefore, fully exploring the potential mechanisms and processes of agriculture and forests to climate change is pivotal to projecting the potential risk of climate change on global grain yield and forest carbon sequestrations.

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Is indirect N2O emission a significant contributor to the agricultural greenhouse gas budget? A case study of a rice paddy-dominated agricultural watershed in eastern China

Variability in the emission factors of nitrous oxide (N2O) associated with the application of chemical fertilizer (EFF) and organic matter (EFO) were analyzed in two onion fields (GL, Gray Lowland soil [Gleysol; Food and Agriculture Organization/UNESCO]; BL, Brown Lowland soil [Fluvisol; Food and Agriculture Organization/UNESCO]) in Mikasa, Hokkaido, Japan. Nitrous oxide flux was measured using a closed chamber technique in four treatments (FOP, chemical nitrogen fertilization and organic matter application, with plants; F, chemical nitrogen fertilization only, without plants; OP, organic matter application only, with plants; C, control, no fertilization or organic matter application, without plants) for 4 years in GL (2000, 2003–2005) and for 1 year in BL (2005). The application rate of chemical fertilizer nitrogen ranged from 237 to 242 kg N ha−1 year−1 in GL and was 284 kg N ha−1 year−1 in BL; organic matter nitrogen ranged from 81 to 117 kg N ha−1 year−1 in GL and was 181 kg N ha−1 year−1 in BL. The emission factors (EF) were calculated using the equations: EFF (%) = (N2O emission in FOP–N2O emission in OP)/(applied chemical nitrogen fertilizer) × 100 and EFO (%) = (N2O emission in FOP–N2O emission in F)/(applied organic matter nitrogen) × 100. The annual N2O emissions for treatments FOP, F, OP and C were 7.2–17, 5.7–17, 3.2–9.9 and 2.0–12 kg N ha−1 year−1, respectively, in GL and 5.6, 2.8, 1.9 and 1.8 kg N ha−1 year−1, respectively, in BL. The EFF ranged from 1.3% to 5.5% in GL and was 1.3% in BL. The EFF was positively correlated with the mean annual air temperature (P < 0.01), suggesting that N2O emission derived from chemical nitrogen fertilizer increases as air temperature rises. The EFO, however, differed greatly between GL (ranging from −5.2% to 9.1%) and BL (1.5%). The EFO was positively correlated with the mean annual relative humidity, although the correlation was not significant (P = 0.23). This finding suggests that much wetter climatic conditions may increase N2O emissions derived from organic matter nitrogen. The estimated N2O emissions based on these EF values and the rate of nitrogen application coincided well with the measured N2O emissions in the FOP treatment in both soils.

Abstract. Fertilised soils are a significant source of nitrous oxide (N2O), a highly active greenhouse gas and a stratospheric ozone depleter. Nitrogen (N) fertilisers, while boosting crop yield, also lead to N2O emissions into the atmosphere, impacting global warming. We investigated relationships between mineral N fertilisation rates and additional manure amendment with different crop types through the analysis of abundances of N cycle functional genes, soil N2O and N2 emissions, nitrogen use efficiency (NUE), soil physicochemical analysis and biomass production. Our study indicates that N2O emissions are predominantly dependent on the mineral N fertilisation rate and enhance with an increased mineral N fertilisation rate. Crop type also has a significant impact on soil N2O emissions. Higher N2O emissions were attained with the application of manure in comparison to mineral fertilisation. Manure amendment also increased the number of N cycle genes that are significant in the variations of N2O. The study indicates that N2O emissions were mainly related to nitrification in the soil. Quantification of nitrogen cycle functional genes also showed the potential role of denitrification, comammox (complete ammonia oxidation) and dissimilatory nitrate reduction to ammonium (DNRA) processes as a source of N2O. Our study did not find soil moisture to be significantly linked to N2O emissions. The results of the study provide evidence that, for wheat, a fertilisation rate of 80 kg N ha−1 is closest to the optimal rate for balancing biomass yield and N2O emissions and achieving a high NUE. Sorghum showed good potential for cultivation in temperate climates, as it showed a similar biomass yield compared to the other crop types and fertilisation rates but maintained low N2O emissions and N losses in a mineral N fertilisation rate of 80 kg N ha−1.

The influence of the incorporation of fresh sugarbeet ( Beta vulgaris L.) plant residues (green weight, 36.5 t ha −1 ; N content, 113 kg ha −1 ) on microbial activity, soil redox potential, and N 2 O emissions was studied using soil microcosms with an automated registration of N 2 O and CO 2 emissions. The experiment was conducted in well‐drained soil columns (water‐filled pore space 63%) and in soil columns with temporary water‐logging (water‐filled pore space continuously increased to 81‐89% for 5 to 7 d). The cumulative CO 2 losses during 45 d were equal for the well‐drained and the temporarily water‐logged soils and amounted to ≈30% of the total residue C added. For the well drained soils, the total N 2 O‐N emission during 45 d was 35‐fold higher than for the control without added plant residues and amounted to 0.37% of the residue‐bound N. Water logging increased the N 2 O‐N losses to ≈1% of the N added with the sugarbeet residues. The period of increasing N 2 O release coincided with the starting net mineralization of the residue N and decreasing redox potentials in the vicinity of the plant material. The greater availability of NO − 3 combined with enhanced metabolic activity led to the formation of anaerobic microenvironments within and around the plant residues, providing favorable conditions for denitrification. The results emphasize the importance of anoxic zones in the soil caused by respiratory O 2 consumption for N 2 O production in well‐aerated soils and indicate that N 2 O emission from N‐rich plant residues could be in the same order of magnitude as reported for mineral N fertilizers.

The emissions of nitrous oxide and methane from natural soil temperature gradients in a volcanic area in southwest Iceland

The effect of abrupt climate warming on biogeochemical cycling and N2O emissions in a terrestrial ecosystem

The relative contribution of different soil organism groups to nutrient cycling has been quantified for a number of ecosystems. Some functions, particularly within the N‐cycle, are carried out by very specific organisms. Others, including those of decomposition and nutrient release from organic inputs are, however, mediated by a diverse group of bacteria, protozoa, fungi and invertebrate animals. Many authors have hypothesized that there is a high degree of equivalence and flexibility in function within this decomposer community and thence a substantial extent of redundancy in species richness and resilience in functional capacity. Three case studies are presented to examine the relationship between soil biodiversity and nitrogen cycling under global change in ecosystem types from three latitudes, i.e. tundra, temperate grassland and tropical rainforest.In all three ecosystems evidence exists for the potential impact of global change factors (temperature change, CO2enrichment, land‐use‐change) on the composition and diversity of the soil community as well as on various aspects of the nitrogen and other cycles. There is, however, very little unequivocal evidence of direct causal linkage between species richness and nutrient cycling efficiency. Most of the changes detected are shifts in the influence of major functional groups of the soil biota (e.g. between microflora and fauna in decomposition). There seem to be few data, however, from which to judge the significance of changes in diversity within functional groups. Nonetheless the soil biota are hypothesized to be a sensitive link between plant detritus and the availability of nutrients to plant uptake. Any factors affecting the quantity or quality of plant detritus is likely to change this link. Rigorous experimentation on the relationships between soil species richness and the regulation or resilience of nutrient cycles under global change thus remains a high priority.

Seasonal agricultural wetlands act as potential source of N2O and CH4 emissions

Regional distribution and environmental regulation mechanism of nitrous oxide in the Bohai Sea and North Yellow Sea: A preliminary study

Anthropogenic activities strongly affect greenhouse gases emissions in coastal wetland. In situ field study was conducted to explore the effects of anthropogenic activities on the N2O emissions, used static, manual stainless steel chambers in four seriously disturbed coastal wetlands (west side of the seawall, WSS; oil field existed, OF; Spartina alterniflora coastal marsh, SCM; and aquaculture pond, ACP) in the Yellow River estuary. Results showed that N2O emissions showed significant seasonal variation (p < 0.05). The maximum values were found in August at WSS and ACP, in December and April at SCM and OF, while minimal values were observed in April, February, October, and August, respectively. The annual average N2O fluxes from WSS, OF, SCM, and ACP were 13.24, 9.83, 8.11 and 2.70 μg N2O m−2 h−1, and the variance analysis results showed that the difference between WSS and ACP reached significant level (p < 0.05). For each month, significant differences were observed between WSS and ACP during June, December and February, WSS and SCM during October, and SCM and ACP during December (p < 0.05). Basing on previous natural wetland measurements, we found that seawall construction and S. alterniflora invasion significantly affected the N2O fluxes in the Yellow River estuary, especially seawall construction which accelerated N2O emissions due to its block of seawater migration, resulting in changes of soil physicochemical properties. Pearson correction analysis showed that significant correlations were observed between N2O emissions and electrical conductivity at WSS and OF, while other environmental factors (temperature, water content, total carbon, total nitrogen, C/N ratio) had no significant effect, which indicated that electrical conductivity was the most important factor that affected N2O emissions in these sampling sites. Our results suggested that there could be considerable changes of N2O emissions as a response of artificial disturbance, particularly seawall construction.

Yield-scaled N2O emissions were effectively reduced by biochar amendment of sandy loam soil under maize - wheat rotation in the North China Plain