N2O Flux Rates Research Articles

Understory vegetation had important impact on soil microbial characteristics than canopy tree under N addition in a Pinus tabuliformis plantation

Forest ecosystem is a complex community, and its soil microbes play a vital role in global matter cycling. However, the patterns of rhizosphere soil microbial characteristics among tree-shrub-grass and their responses to nitrogen (N) deposition are still unclear. This study evaluated the microbial biomasses, processes (gas fluxes), and enzyme activities in the rhizosphere soils of tree (Pinus tabuliformis), shrub (Rosa xanthina), and grass (Carex lanceolata) and their responses to N addition (0, 3, 6, 9 g N m−2 y−1 corresponding to N0, N3, N6, N9) in a P. tabuliformis plantation. (1) Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) contents, as well as CO2, CH4 flux rates in the rhizosphere soil of C. lanceolata were significantly higher than those in the rhizosphere soils of P. tabuliformis and R. xanthina (P < 0.05). The activities of alkaline phosphatase (ALT), leucine aminopeptidase (LAP), β-glucosidase (BG), D-cellulosidase (CBH), N-acetyl-glucosaminidase (NAG), and xylosidase (XYL) in the rhizosphere soils of C. lanceolata and R. xanthina were significantly higher than those in the rhizosphere soil of P. tabuliformis. (2) Soil MBC content, N2O, and CH4 flux rates increased after N addition, while the CO2 flux rate decreased. MBP content initially increased and then reduced with N additions, and the maximum values observed in N3 or N9 treatments. (3) In the rhizosphere soil of P. tabuliformis, N addition enhanced the NAG, BG, CBH, and XYL activities. While low N increased and high N decreased these enzyme activities in the rhizosphere soils of C. lanceolata and R. xanthina, with the maximum values obtained in N3 treatment. (4) N addition directly reduced the CO2 flux rate and indirectly enhanced the gas flux rate by increasing soil MBC and MBP contents. Species change indirectly affected the microbial biomass and enzyme activity by altering soil chemical properties, which eventually affected gas flux rates. Our study emphasizes the effects of tree-shrub-grass on soil microbial characteristics, which can improve the evaluation of soil ecological processes and responses to N deposition in forest ecosystems.

Nitrogen fertilization and irrigation types do not affect the overall N2O production potential of a sandy soil, but the microbial community structure and the quantity of functional genes related to the N cycle

Nitrous oxide (N2O), one of the major greenhouse gases, features a 273-fold higher global warming potential compared to carbon dioxide (CO2). Soil-born N2O emissions are based on microbial processes, while the microbial processes are affected by environmental factors and agronomic management measures. The objective of this study was the exploration of the effects of different irrigation and nitrogen (N) fertilization regimes on N2O emissions in relation to the microbial community structure and the quantities of genes involved in the N cycle. The following four treatments were investigated in a sandy soil during the potato cropping season in 2019 in Brandenburg, Germany: drip irrigation without N fertilization (DI-ZN), drip irrigation with broadcasted N fertilization (DI-N), simultaneous application of dissolved N in irrigation water, the so-called fertigation (F), and fertigation without crops (F-ZC). N2O fluxes were measured with the closed chamber method. Microbial biomass was analyzed using phospholipid fatty acids (PLFAs). The bacterial functional genes amoA (ammonium monooxygenase), nxrB (nitrite oxidoreductase), narG (nitrate reductase), nirS/nirK (nitrite reductase), and nosZ (N2O reductase) were determined using quantitative real-time polymerase chain reaction (qPCR). N2O fluxes varied over the season and could mainly be explained by temperature changes. The fertilized treatments showed slightly higher area-related cumulative N2O emissions (DI-ZN: 1.13 kg N2O-N ha−1, DI-N: 1.28 N2O-N ha−1, F: 1.26 N2O-N ha−1, median values). Additionally, N2O flux rates as well as the area- and yield-related N2O emissions of DI-N and F were approximately at the same level, even though the quantities and correlation patterns of the investigated functional genes differed. Highest seasonal median flux rates were detected under DI-N (15.0–100.1 μg N2O-N m−2 h−1), where a greater influence of a nirS/nosZ harboring microbial community was found. In contrast, under F more diverse correlation patterns were found, especially regarding a predominance of nirK and nirS/nosZ harboring microbial community. F-ZC showed the lowest N2O flux rates (−8.7–44.2 μg N2O-N m−2 h−1), which might be explained by the lack of plant carbon sources, particularly root exudates. To conclude, the applied treatments affected the microbial community structure and their genetically determined potential for N2O production, whereby the overall N2O flux rates and hence N2O emissions remained unaffected. Although fertigation is considered to be more demand-based particularly in terms of N fertilization, this study indicates that agronomic management measures according to good faming practice might feature an oversupply of N, neglecting the real N demand of cultivated crops and hence hindering the mitigation of N2O emissions.

Impact of a warmer cold season on soil nitrogen and carbon cycling in High Arctic wet sedge tundra

Soil available nitrogen (N) pools in the High Arctic are expected to increase due to permafrost thaw and elevated microbial activity stimulated by atmospheric warming and subsequent changes in soil moisture regimes. The cold season, or the period between soil freeze-up in fall and thaw in spring, is warming relatively faster compared to the growing season, which may increase the insulating snow cover and microbial degradation of soil organic matter. Changes in temperature and available N levels can stimulate soil CO₂, CH4, and N₂O flux rates which could trigger further warming. Despite the potential importance of the cold season, the influence of variability in cold season temperatures on the release and accumulation of inorganic N and greenhouse gases is poorly understood in High Arctic environments. We conducted a 50-day laboratory incubation study that mimics the annual soil temperature cycle to investigate the effects of different minimum cold season temperatures (- 10˚C, −15˚C, −20˚C, −25˚C) on spring and growing season N and carbon (C) cycling in the soil.We measured inorganic N pools, net N cycling rates, and CO₂, CH4, and N₂O fluxes throughout the study. Over the coldest period of the annum, the warmest and coldest soils displayed greatest net N mineralization rates (-0.035 mg kg−1 d-1 and −0.049 mg kg−1 d-1 respectively). During the thaw period, we found that soils treated with −10˚C resulted in a spring NO3–-N flush that was ∼ 700% larger than −15 ˚C, −20 ˚C, −25 ˚C treatments, which were relatively consistent with each other, suggesting a cold-temperature inhibition of nitrification. Although cold season fluxes of CH4 and CO₂ differed with temperature, there was no treatment effect on subsequent flux rates during the growing season. We conclude that changes in cold season temperatures can play a crucial role in soil N biogeochemistry in High Arctic wet-sedge communities and have a potential to disrupt surrounding downstream ecosystems. The impact of cold season warming, however, does not appear to be linear for all processes with temperature change.

A grass–legume cover crop maintains nitrogen inputs and nitrous oxide fluxes from an organic agroecosystem

AbstractLegume cover crops are central to an ecological nutrient management approach that can reduce nitrogen (N) losses from agriculture. Diversifying cropping systems with a legume–grass cover crop mixture could further reduce N losses by increasing soil N assimilation and synchronizing N mineralization with N uptake by the following crop. We established four winter cover crop treatments (crimson clover, cereal rye, clover–rye mixture, and weedy fallow control) in an organic grain agroecosystem that had been managed for 30 years with a legume cover crop as the only external N source. We hypothesized that the legume–grass mixture would provide similar inputs of biologically fixed N2 compared with the sole legume, while reducing N2O emissions during decomposition following tillage. We measured cover crop aboveground biomass C:N and clover N2 fixation, soil inorganic N and N2O fluxes throughout the corn growing season following cover crop tillage, and corn N assimilation at harvest. Even with a reduced clover seeding rate in mixture, the clover and mixture treatments had similar fixed N inputs, litter N and C:N, and no differences in cumulative N2O emissions. During the first peak flux, N2O emissions were 2–5 times higher in clover and mixture relative to rye and fallow, with no differences between clover and mixture. There were no treatment differences at the second N2O peak, which followed the first major rain event. We contextualized these findings by calculating a 6‐year partial N mass balance for this agroecosystem, which was slightly negative (−6.8 ± 0.8 kg N ha−1 year−1) when accounting for historical mean annual N2O emissions and nitrate leaching. Overall, N inputs and harvested N exports were approximately in balance for this legume‐based crop rotation, suggesting that the legacy of ecological nutrient management has promoted efficient N cycling. However, results from our field experiment indicate that short‐term N2O flux rates following cover crop incorporation can be high even for a legume–grass mixture. Additional strategies to reduce soil disturbance are therefore needed to further tighten N cycling in organic grain agroecosystems.

Nitrogen use efficiency and N2O emissions vary according to seasonal water supply across different cereal production systems of south eastern Australia

Application of nitrogen (N) fertiliser is vital to the productivity of grains production systems. However, losses can result in negative environmental impacts as well as having a significant impact on farmer profitability. Such losses can vary significantly, therefore it is important to benchmark nitrogen use efficiency (NUE) across a range of environments to better understand opportunities for improvement. Using a combination of 15N mass balance and monitoring for gaseous N2O flux we undertook an assessment of NUE at 29 sites spread across a range of management systems in semi-arid and temperate environments of south eastern Australia. An N rate experiment was established at each site, testing three different in-season application rates with N surface applied as urea. Timing and rates were determined in relation to farmer practice for the broader paddock. Loss of fertiliser N averaged 29% (ranging from 5 to 54%) and while daily N2O flux rates represented a fraction of this, peak flux rates ranged from 52 to 132 to 376 g N2O-N/ha/day across low/ medium rainfall, high rainfall and irrigated regions respectively. Crop recovery of applied N ranged from 3 to 65% and was positively correlated with agronomic efficiency of N application.

Rapid nitrate reduction produces pulsed NO and N2O emissions following wetting of dryland soils

Soil drying and wetting cycles can produce pulses of nitric oxide (NO) and nitrous oxide (N2O) emissions with substantial effects on both regional air quality and Earth’s climate. While pulsed production of N emissions is ubiquitous across ecosystems, the processes governing pulse magnitude and timing remain unclear. We studied the processes producing pulsed NO and N2O emissions at two contrasting drylands, desert and chaparral, where despite the hot and dry conditions known to limit biological processes, some of the highest NO and N2O flux rates have been measured. We measured N2O and NO emissions every 30 min for 24 h after wetting soils with isotopically-enriched nitrate and ammonium solutions to determine production pathways and their timing. Nitrate was reduced to N2O within 15 min of wetting, with emissions exceeding 1000 ng N–N2O m−2 s−1 and returning to background levels within four hours, but the pulse magnitude did not increase in proportion to the amount of ammonium or nitrate added. In contrast to N2O, NO was emitted over 24 h and increased in proportion to ammonium addition, exceeding 600 ng N–NO m−2 s−1 in desert and chaparral soils. Isotope tracers suggest that both ammonia oxidation and nitrate reduction produced NO. Taken together, our measurements demonstrate that nitrate can be reduced within minutes of wetting summer-dry desert soils to produce large N2O emission pulses and that multiple processes contribute to long-lasting NO emissions. These mechanisms represent substantial pathways of ecosystem N loss that also contribute to regional air quality and global climate dynamics.

Effects of nitrogen deposition and biochar application on soil N2O fluxes in a Moso bamboo plantation

In July 2019-July 2020, we conducted a field trial to examine the effects of nitrogen addition (60 kg N·hm-2·a-1), biochar application (10 t·hm-2), and their combination on soil N2O emission and the relationship between soil N2O emission and environmental factors in a typical Moso bamboo (Phyllostachys edulis) plantation in Hangzhou City of Zhejiang Province. Soil N2O flux of Moso bamboo plantation was measured by the static chamber-gas chromatography technique. The results showed that nitrogen addition treatment increased the annual cumulative N2O emission by 14.6%, while biochar application and the combination treatment reduced it by 20.8% and 10.6%, respectively. Soil N2O flux rate was significantly correlated with soil temperature, NO3--N concentration, urease and protease activities, and soil NH4+-N concentration across all treatments. In conclusion, under the background of nitrogen deposition, the application of biochar would have a significant reduction effect on soil N2O fluxes in Moso bamboo plantations.

Nitrous Oxide Emissions from an Alpine Grassland as Affected by Nitrogen Addition

Nitrogen (N) addition is an important nutrient strategy for alpine grassland in northwestern China to improve productivity for livestock needs. A field experiment was conducted in a semi-arid alpine grassland in northwestern China to investigate the effect of N addition rates on soil N2O emissions over the growing seasons of 2017 and 2018. Treatments included six N addition rates (0, 10, 30, 60, 120, 240 kg N ha−1 y−1), which were applied before each growing season. The N2O fluxes increased with N addition rates and showed different episodic changes between the two growing seasons. In 2017, the maximum N2O flux rate occurred within 2 weeks following N addition. In 2018, however, the maximum N2O flux rate occurred later in the growing season due to a heavy rainfall event. Growing season cumulative N2O emissions ranged between 0.32 and 1.11 kg N ha−1, and increased linearly with N addition rates. Increasing N addition rates over 60 kg N ha−1 yr−1 did not further increase plant above-ground biomass. The inter-annual variability of N2O flux suggests the importance of soil moisture in affecting N2O emissions. It is particularly important to avoid over-applying N nutrients beyond plant needs to reduce its negative effect on the environment while maintaining livestock productivity. The N2O flux rate increased with soil dissolved organic carbon (DOC) and soil pH. These results suggest the optimal N addition rate to the livestock grassland in this region should be 60 kg N ha−1 yr−1.

Incapability of biochar to mitigate biogas slurry induced N2O emissions: Field investigations after 7 years of biochar application in a poplar plantation

Nitrous oxide (N2O) is a potent atmospheric greenhouse gas that is largely emitted from soils due to the enhanced use of reactive nitrogen in agriculture and plantations. In this study, we evaluated the N2O mitigation ability of biochar after 7 years of application in a poplar plantation. The field experiment was based on combinations of three biochar (0, 80, and 120 t ha−1) and four biogas slurry (0, 125, 250, and 375 m3 ha−1) rates following a factorial design. N2O flux rates were measured for seven consecutive months using in situ static chambers. Soil physicochemical characteristics, potential nitrification rate (PNR), denitrification (DEA), and N2O reduction were recorded once each in September 2019 and January 2020 via lab incubations. In addition, qPCR assays were used to assess the abundance of key nitrifying and denitrifying functional genes. Biochar application after 7 years had no significant effects on N2O flux rates, PNR, and DEA rates. However, a triggering effect of biogas slurry on soil N2O emission was observed, although there was no correlation between biogas slurry rates and N2O emission rates. Factorial ANOVA showed a significant effect of biogas slurry and its interaction with biochar on the relative abundance of bacterial denitrifying and nitrifying functional genes. Additionally, significant correlations of N2O emission rates with PNR rates and NO3− concentration indicated that nitrification was the dominant pathway of N2O emission. Thus, a single biochar application did not mitigate N2O emission rates induced by biogas slurry on a long-term scale.

Greenhouse gas fluxes from turfgrass systems: Species, growth rate, clipping management, and environmental effects.

Turfgrass systems can be an important source or sink for greenhouse gases (GHG), including carbon dioxide (CO2 ), nitrous oxide (N2 O), and methane (CH4 ). Further research is required in turfgrass systems; therefore, our objectives were to evaluate the effects of turfgrass species, growth rate, clipping management, and environmental conditions on GHG emissions. Greenhouse gas fluxes were measured in two separate field experiments in West Lafayette, IN. Experiment 1 investigated GHG flux in three cool-season (C3 ) and two warm-season (C4 ) turfgrass species during two growing seasons. Experiment 2 investigated fluxes in two C3 cultivars with varying growth rates and under different clipping management regimes. The C3 turfgrasses had the highest mean CO2 flux rates ranging from 0.373 to 0.431g CO2 -C m-2 h-1 compared with 0.273 to 0.361g CO2 -C m-2 h-1 for C4 turfgrasses. Mean hourly N2 O flux rates ranged from 43.3 to 50.9μg N2 O-N m-2 h-1 for C3 compared with 11.1 to 14.4μg N2 O-N m-2 h-1 for C4 turfgrasses. Methane flux was more variable across time, but overall C4 turfgrasses were more likely to be a CH4 source, whereas C3 turfgrasses were often a CH4 sink. Growth rate and grass clipping management treatments had negligible impact on measured GHG flux. The differences in management practices specific to C3 and C4 turfgrasses had the largest impact on GHG flux. Results indicate the impact and importance of turfgrass species selection on GHG flux and also provide more information on our overall understanding on carbon and nitrogen cycling in urban soils.

Quantification of greenhouse gas emissions from managed biofuel plantations in a semi-arid landscape of Southern India

Jatropha curcas L. and Pongamia pinnata (L.) Pierre, are promising biofuel species in peninsular India. We quantified greenhouse gas fluxes from managed 9 year old plantations of these species for all seasons in three consecutive years (2012–2013, 2013–2014 and 2014–2015) using manually-operated closed chamber method. CH4, N2O and CO2 were analysed by using Varian 450-GC based on Gas Chromotography. The mean soil CO2, CH4, and N2O emissions in the Jatropha curcas plantation recorded were 7.720 t ha−1 y−1, 0.023 t ha−1 y−1 and 0.017 t ha−1 y−1, respectively. While in Pongamia pinnata soil CO2, CH4, and N2O emissions were recorded to be 7.633 t ha−1 y−1, 0.008 t ha−1 y−1 and 0.019 t ha−1 y−1, respectively. Our results indicate that Jatropha curcas has higher GHG emissions than Pongamia pinnata. A pronounced seasonal variability was observed in CH4, N2O and CO2 flux rates. The highest emissions for Jatropha curcas occur during rainy season, whereas for Pongamia pinnata it occurs during winter. Soil moisture and temperature being the most influencing factors for CO2 fluxes from soil. We conclude that these plantation has an effect on soil-atmosphere GHG exchanges and can act as a good source of mitigation of greenhouse gases.

Water filled-pore space and soil temperature related to N2O fluxes from shallot cultivated in rainy and dry season

Agricultural soils managed with a large amount of fertilizer generate nitrous oxide (N2O). This study aims to observe the N2O flux rates from four organic matter treatments and examining soil water-filled pore space (WFPS) and soil temperature in rainy and dry seasons. The experimental sites took place on a silt loam soil with four organic matter treatments, i.e., 1). No organic matter (OM), 2). Chicken manure, 3). Cattle manure, and 4). Bio-compost. N2O fluxes were measured bi-weekly during the rainy season and weekly during the dry season. Soil WFPS and soil temperature were both determine at the same time. N2O fluxes from Shallot were significantly different between rainy and dry season (p<0.01), but not between treatments. It is ranged between 3.58 to 20.19 mg N2O m−2 d−1 on the rainy season and between 0.57 to 2.79 mg N2O m−2 d−1 on dry season. The linear regression showed that both soil WFPS and soil temperature only significantly relate to N2O fluxes in the rainy season. Soil WFPS >45% lead to high N2O fluxes and higher soil temperature. This finding showed that water is one of the vital inputs to maintain in order to mitigate N2O emission from agricultural soils, whether in upland or lowland.

Field Application of Organic Fertilizers Triggers N2O Emissions From the Soil N Pool as Indicated by 15N-Labeled Digestates

Anaerobic digestion (AD) can generate biogas while simultaneously producing digestate which can be used as fertilizer. Feedstocks used for AD influence digestate composition, which in turn may affect carbon (C) and nitrogen (N) turn-over in soils and subsequently influence nitrous oxide (N2O) emissions after soil application. Assessment of greenhouse gas emissions from digestates can help to evaluate the overall sustainability of an agricultural production system. The objective of this study was therefore to evaluate and understand the effect of differences in digestate composition on in situ N2O emissions within the 1st weeks after application of seven digestates. The digestates were derived from different feedstocks and 15N-labeled, either in total N or only in ammonium-N. Therefore, the experimental design enabled us to differentiate between potential N2O-N sources (i.e., digestate N or soil N). Furthermore, it allowed to distinguish to some extent between organic-N and ammonium-N as potential N sources for denitrification. Digestates were homogeneously incorporated into the upper 5 cm of microplots in an arable Haplic Luvisol in South Germany at a rate of 170 kg N ha−1. After application, N2O fluxes were measured for ~60 days (May-July) using the closed chamber method in 2 experimental years. Mainly due to higher precipitations in the 1st year, cumulative N2O emissions were higher (312–1,580 g N2O-N ha−1) compared to the emissions (133–690 g N2O-N ha−1) in the 2nd year. Between 16–33% (1st year) and 17–38% (2nd year) of N2O emissions originated from digestate N, indicating that digestate application triggered N2O production and release mainly from soil N. This effect was strongest immediately after digestate application. It was concluded that the first (short term) peak in N2O emissions after digestate application is largely related to denitrification of soil-N. However, the experimental setup does not allow to differentiate between the different denitrification pathways. Weather conditions showed a substantial effect on N2O emissions, where the correlation between N2O and CO2 flux rates hinted on denitrification as main N2O source. The effect of digestate composition, particularly organic N from the digestate, on soil N2O emissions seems to be of minor relevance.

Enhancement of N2O emissions by grazing is related to soil physicochemical characteristics rather than nitrifier and denitrifier abundances in alpine grassland

Grazing can degrade grassland soil and increase nitrous oxide (N2O) emissions, but the underlying mechanism is poorly understood. We investigated the relationship of soil N2O emission with nitrifying enzyme activity (NEA), denitrifying enzyme activity (DEA), and the abundances of N2O-producing and N2O-reducing functional genes, in response to three grazing intensities (none, light, intensive) over two growing seasons on an alpine grassland on Kunlun Mountain in semi-arid North China. Compared to the non-grazed control, light and intensive grazing treatments increased the 2-yr total N2O emissions by 27.5% and 68.1%, respectively. Daily N2O flux rate correlated positively with soil water-filled pore space (WFPS), temperature, and dissolved organic carbon (DOC) but not with the abundances of nitrifiers (AOB, AOA, Nitrobacter-like nxrA), nitrate reducers (narG) and denitrifiers (nirS, nirK, and nosZ). These results suggest that soil environmental factors rather than nitrifier, N2O-producer and N2O-reducer abundances were more important in determining the grazing enhancement of N2O emissions from the alpine grassland in semi-arid areas. The abundance of AOB and Nitrobacter-like nxrA but not AOA correlated positively with NEA, indicating they are good indicators for the potential nitrification in this arid alpine grassland. Reducing grazing intensity from intensive to light resulted in more above-ground biomass and N uptake in both years and less N2O emissions in 2018. These results highlight the importance of establishing a proper grazing intensity to reduce N2O emissions from the degraded grassland while maintaining productivity for livestock.

Nitrous oxide emissions in proportion to nitrification in moist temperate forests

Chronic elevated nitrogen deposition has increased nitrogen availability in many forest ecosystems globally, and this phenomenon has been suggested to increase soil nitrification. Although it is believed that increased nitrogen availability would also increase nitrous oxide (N2O) emissions from forest ecosystems, its impact on N2O flux is poorly known. In this study, 3-years monitoring of N2O emissions was performed in a forested watershed receiving elevated nitrogen deposition and located in the suburbs of Tokyo, Japan. In addition, a comparative field survey was carried out in nine temperate forest sites with varying nitrogen availabilities. In the intensively studied forest site showing typical nitrogen saturation, the average annual N2O emissions from the whole watershed were estimated to be 0.88 kg N ha−1 year−1, comparable to the highest observed levels for temperate forests except for some very high emission sites in Europe. Although no correlation was found for humid spots with WFPS > 60%, a clear positive correlation was noted between N2O flux and net nitrification rate in situ for plots with water-filled pore space (WFPS) < 60%. The N2O flux varied across nine forest sites almost in proportional to the stream water NO3− concentration in the watershed that ranged from 0.14 to 1.64 mg N/L. We conclude that N2O emissions are related to nitrification in moist temperate forest, which may be associated with the magnitude of nitrogen saturation.

Crop intensification with sustainable practices did not increase N2O emissions

Nitrous oxide (N2O) is the most important greenhouse gas produced by agricultural soils and is a byproduct of microbial nitrification and denitrification processes. The N2O emission rates depend on soil, climatic and management factors. The objectives of this study were i) to evaluate N2O emissions during a barley crop period and its subsequent barley-maize interperiod, under two management systems, and ii) to relate the N2O flux rates with soil mineral N content, waterfilled pore space (WFPS) and soil temperature. These periods are part of three-year crop sequence (barley - maize - soybean) of a long-term experiment under two management systems, ecological intensification (EI) and farmer current practices (FP). For the analyzed period, the EI system included a cover crop after barley and higher N rates, with split application, compared to FP. N2O emissions were monitored weekly using a static chambers method. Simultaneously, the mineral N content (NO3--N and NH4+-N), WFPS and soil temperature at 10 cm depth were determined. The flux of N2O-N ranged from 6 to 61 μg of N2O-N m2 h-1 during the barley crop and between 1.5 and 47 μg of N2O-N m2 h-1 during the barley-maize interperiod, without significant differences between management systems. N2O emissions were controlled by soil temperature and %WFPS according to a multiple regression analysis. NH4+-N and NO3--N soil content did not enter into any model as a regulator of N2O flux. During the barley period there was a significant effect of the WFPS × soil temperature interaction since N2O emissions increased with soil temperature only at WFPS > 40 %. During the barley-maize interperiod, there were significant positive effects of WFPS and temperature on N2O emissions with no significant WFPS x temperature interaction. The cumulative emissions of N2O-N were not different between management systems during the barley crop (IE = 646 and FP=757 g N2O-N ha-1) or during barley-maize interperiod (IE = 816 and FP=754 g N2O-N ha-1). Throughout the study period, the combination of management practices in EI increased barley yield and did not increase N2O emissions with respect to FP, despite higher N rates and the inclusion of cover crop in EI. The intensification of crops does not necessarily increase N2O emissions from agricultural soils as long as the crops are conducted with appropriate management practices.

Presence of spring-thaw N2O emissions are not linked to functional gene abundance in a drip-fertigated cropped soil in arid northwestern China

Spring-thaw represents a significant source for nitrous oxide (N2O) emissions from fertilized croplands in temperate regions. In this study, we present surface N2O fluxes, soil-profile N2O concentrations at 5, 15, 30 and 60 cm depths along with the abundance of nitrifiers and denitrifiers over the winter and spring-thaw periods in an arid, drip- fertigated cotton field, which had received spring application of 240 kg N ha−1 as urea alone (Urea), polymer-coated urea (ESN), and urea plus urease and nitrification inhibitors. Nitrous oxide emissions from December to April were generally unaffected by fertilizer treatments with a cumulative average of 186 g N ha−1, accounting for 39% of the annual N2O emissions. Emission peaks occurred at spring-thaw and coincided with increasing soil-profile N2O concentrations at all depths, suggesting the burst in N2O fluxes was due to new N2O production, rather than a physical release of N2O trapped in the soil profiles over winter. The abundance of nitrifier and denitrifier genes changed over the winter and spring-thaw periods but was not affected by fertilizer treatments from the previous spring, suggesting the abundance of N2O-producing microorganism was more controlled by environmental conditions than N sources applied in the previous spring. The daily N2O flux rate from December to April was positively correlated with soil temperature, water-filled pore space, and denitrifying enzyme activity, but not with the gene copy number of AOA, AOB, narG, nirS, nirK and nosZ, indicating that variation in the abundance of these genes was not contributing to the N2O emissions. These results suggest that N2O emissions in spring-thaw are substantial for drip-fertigated croplands in the arid regions and should be considered in the annual budgets. The environmental factors such as soil temperature and moisture are likely more important than the copy-numbers of N2O-producing functional genes in driving the variability in spring-thaw emissions.

Greenhouse gas fluxes from human waste management pathways in Haiti

The lack of safely managed sanitation services is a major global public health and ecological sustainability challenge. Ecological sanitation (EcoSan) technologies designed to close the “poop loop” through the capture, treatment, and beneficial reuse of human feces can meet this interconnected challenge. EcoSan has the potential to mitigate climate change through the reduction of greenhouse gas (GHG) emissions, yet the climate impacts of EcoSan are poorly understood. We measured GHG emissions (carbon dioxide, CO2; methane, CH4; and nitrous oxide, N2O) from two EcoSan operations in Haiti, as well as two anaerobic waste stabilization ponds and a grass field where sewage is known to be illegally deposited. Carbon dioxide was the major constituent of total GHG emissions from both EcoSan systems. Nitrous oxide emissions were similar across both EcoSan systems, however CH4 emissions were significantly higher in the system with moister pile conditions. Highest CH4 fluxes were observed during the first two months of composting in both EcoSan systems. In a paired-comparison, we found that piles with a soil lining had four-fold lower CH4 emissions and three-fold lower N2O emissions compared to piles with a cement lining. Overall climate-forcing effects of emissions from EcoSan were favorable relative to waste stabilization ponds and unmanaged disposal on grass fields. In contrast to EcoSan, CH4 emissions dominated net emissions from waste stabilization ponds, accounting for 94% of net emissions, and N2O emissions were negligible. Methane emissions from waste stabilization ponds were up to 250 times higher than those from EcoSan compost piles. The grass field had a significantly higher CH4 flux than EcoSan, and the highest N2O flux rate observed. Our data suggest that EcoSan systems can contribute to climate change mitigation by reducing GHG emissions relative to alternative sanitation pathways, and EcoSan management conditions can be optimized to minimize emissions.

Linking soil N2O emissions with soil microbial community abundance and structure related to nitrogen cycle in two acid forest soils

Tree species and seasonal change influence N2O flux and microbial communities, but the mechanisms are unclear. We studied N2O flux in soils planted with slash pine and oil-seed camellia trees. We sampled on typical days of the four seasons. We tested whether N-cycling communities respond more to tree species or seasonal change. We assessed how tree species affect N2O flux. We used qPCR and RFLP to determine abundance and community composition of amoA-containing bacteria (AOB) and archaea (AOA), and denitrifiers that contain the narG, nirK, nirS, and nosZ genes. N2O flux rate and soil characteristics varied significantly between forest soils and sampling seasons. Abundance of all detected genes, but not of the nirS gene, was significantly affected by tree species. Differences in gene abundance between days in different seasons were found only for narG, nirK, and nosZ. Functional microbial community composition in the soil varied between the tree species for most of the genes studied, but varied, not significantly, slightly among sampling days. Differences in the abundance and community composition of nitrifiers and denitrifiers between tree species depended on soil concentration of NH4+, NO3−, and dissolved organic carbon (DOC). N2O flux rate was affected by community composition, but not abundance of nitrifiers and denitrifiers. Temperature, NO3−, and DOC concentrations significantly affected N2O flux. Tree species influenced N2O flux more than seasonal change, by altering community composition and environmental factors rather than nitrifier/denitrifier abundance.

Abundance of transcripts of functional gene reflects the inverse relationship between CH4 and N2O emissions during mid-season drainage in acidic paddy soil

Agricultural management significantly affects methane (CH4) and nitrous oxide (N2O) emissions from paddy fields. However, little is known about the underlying microbiological mechanism. Field experiment was conducted to investigate the effect of the water regime and straw incorporation on CH4 and N2O emissions and soil properties. Quantitative PCR was applied to measure the abundance of soil methanogens, methane-oxidising bacteria, nitrifiers, and denitrifiers according to DNA and mRNA expression levels of microbial genes, including mcrA, pmoA, amoA, and nirK/nirS/nosZ. Field trials showed that the CH4 and N2O flux rates were negatively correlated with each other, and N2O emissions were far lower than CH4 emissions. Drainage and straw incorporation affected functional gene abundance through altered soil environment. The present (DNA-level) gene abundances of amoA, nosZ, and mcrA were higher with straw incorporation than those without straw incorporation, and they were positively correlated with high concentrations of soil exchangeable NH4+ and dissolved organic carbon. The active (mRNA-level) gene abundance of mcrA was lower in the drainage treatment than in continuous flooding, which was negatively correlated with soil redox potential (Eh). The CH4 flux rate was significantly and positively correlated with active mcrA abundance but negatively correlated with Eh. The N2O flux rate was significantly and positively correlated with present and active nirS abundance and positively correlated with soil Eh. Thus, we demonstrated that active gene abundance, such as of mcrA for CH4 and nirS for N2O, reflects the contradictory relationship between CH4 and N2O emissions regulated by soil Eh in acidic paddy soils.