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1.
In this study, we quantify the impacts of climate and land use on soil N 2O and CH 4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured greenhouse gases (GHG) fluxes from 12 different ecosystems along climate and land‐use gradients at Mt. Kilimanjaro, combining long‐term in situ chamber and laboratory soil core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N 2O and CH 4 respectively. N 2O emissions correlated positively with soil moisture and total soil nitrogen content. CH 4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N 2O emissions of tropical montane forests were generally low (<1.2 kg N ha ?1 year ?1), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha ?1 year ?1). Forest soils with well‐aerated litter layers were a significant sink for atmospheric CH 4 (up to 4 kg C ha ?1 year ?1) regardless of low mean annual temperatures at higher elevations. Land‐use intensification significantly increased the soil N 2O source strength and significantly decreased the soil CH 4 sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non‐CO 2 GHG emissions following land‐use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N 2O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land‐use change. 相似文献
2.
The influence of forest stand age in a Picea sitchensis plantation on (1) soil fluxes of three greenhouse gases (GHGs – CO 2, CH 4 and N 2O) and (2) overall net ecosystem global warming potential (GWP), was investigated in a 2‐year study. The objective was to isolate the effect of forest stand age on soil edaphic characteristics (temperature, water table and volumetric moisture) and the consequent influence of these characteristics on the GHG fluxes. Fluxes were measured in a chronosequence in Harwood, England, with sites comprising 30‐ and 20‐year‐old second rotation forest and a site clearfelled (CF) some 18 months before measurement. Adjoining unforested grassland (UN) acted as a control. Comparisons were made between flux data, soil temperature and moisture data and, at the 30‐year‐old and CF sites, eddy covariance data for net ecosystem carbon (C) exchange (NEE). The main findings were: firstly, integrated CO 2 efflux was the dominant influence on the GHG budget, contributing 93–94% of the total GHG flux across the chronosequence compared with 6–7% from CH 4 and N 2O combined. Secondly, there were clear links between the trends in edaphic factors as the forest matured, or after clearfelling, and the emission of GHGs. In the chronosequence sites, annual fluxes of CO 2 were lower at the 20‐year‐old (20y) site than at the 30‐year‐old (30y) and CF sites, with soil temperature the dominant control. CH 4 efflux was highest at the CF site, with peak flux 491±54.5 μg m −2 h −1 and maximum annual flux 18.0±1.1 kg CH 4 ha −1 yr −1. No consistent uptake of CH 4 was noted at any site. A linear relationship was found between log CH 4 flux and the closeness of the water table to the soil surface across all sites. N 2O efflux was highest in the 30y site, reaching 108±38.3 μg N 2O‐N m −2 h −1 (171 μg N 2O m −2 h −1) in midsummer and a maximum annual flux of 4.7±1.2 kg N 2O ha −1 yr −1 in 2001. Automatic chamber data showed a positive exponential relationship between N 2O flux and soil temperature at this site. The relationship between N 2O emission and soil volumetric moisture indicated an optimum moisture content for N 2O flux of 40–50% by volume. The relationship between C : N ratio data and integrated N 2O flux was consistent with a pattern previously noted across temperate and boreal forest soils. 相似文献
3.
Greenhouse gases (GHG) can be affected by grazing intensity, soil, and climate variables. This study aimed at assessing GHG emissions from a tropical pasture of Brazil to evaluate (i) how the grazing intensity affects the magnitude of GHG emissions; (ii) how season influences GHG production and consumption; and (iii) what are the key driving variables associated with GHG emissions. We measured under field conditions, during two years in a palisade-grass pasture managed with 3 grazing intensities: heavy (15 cm height), moderate (25 cm height), and light (35 cm height) N 2O, CH 4 and CO 2 fluxes using static closed chambers and chromatographic quantification. The greater emissions occurred in the summer and the lower in the winter. N 2O, CH 4, and CO 2 fluxes varied according to the season and were correlated with pasture grazing intensity, temperature, precipitation, % WFPS (water-filled pores space), and soil inorganic N. The explanatory variables differ according to the gas and season. Grazing intensity had a negative linear effect on annual cumulative N 2O emissions and a positive linear effect on annual cumulative CO 2 emissions. Grazing intensity, season, and year affected N 2O, CH 4, and CO 2 emissions. Tropical grassland can be a large sink of N 2O and CH 4. GHG emissions were explained for different key driving variables according to the season. 相似文献
4.
Tropical peatlands are vital ecosystems that play an important role in global carbon storage and cycles. Current estimates of greenhouse gases from these peatlands are uncertain as emissions vary with environmental conditions. This study provides the first comprehensive analysis of managed and natural tropical peatland GHG fluxes: heterotrophic (i.e. soil respiration without roots), total CO 2 respiration rates, CH 4 and N 2O fluxes. The study documents studies that measure GHG fluxes from the soil ( n = 372) from various land uses, groundwater levels and environmental conditions. We found that total soil respiration was larger in managed peat ecosystems (median = 52.3 Mg CO 2 ha ?1 year ?1) than in natural forest (median = 35.9 Mg CO 2 ha ?1 year ?1). Groundwater level had a stronger effect on soil CO 2 emission than land use. Every 100 mm drop of groundwater level caused an increase of 5.1 and 3.7 Mg CO 2 ha ?1 year ?1 for plantation and cropping land use, respectively. Where groundwater is deep (≥0.5 m), heterotrophic respiration constituted 84% of the total emissions. N 2O emissions were significantly larger at deeper groundwater levels, where every drop in 100 mm of groundwater level resulted in an exponential emission increase (exp(0.7) kg N ha ?1 year ?1). Deeper groundwater levels induced high N 2O emissions, which constitute about 15% of total GHG emissions. CH 4 emissions were large where groundwater is shallow; however, they were substantially smaller than other GHG emissions. When compared to temperate and boreal peatland soils, tropical peatlands had, on average, double the CO 2 emissions. Surprisingly, the CO 2 emission rates in tropical peatlands were in the same magnitude as tropical mineral soils. This comprehensive analysis provides a great understanding of the GHG dynamics within tropical peat soils that can be used as a guide for policymakers to create suitable programmes to manage the sustainability of peatlands effectively. 相似文献
5.
To investigate the effects of multiple environmental conditions on greenhouse gas (CO 2, N 2O, CH 4) fluxes, we transferred three soil monoliths from Masson pine forest (PF) or coniferous and broadleaved mixed forest (MF) at Jigongshan to corresponding forest type at Dinghushan. Greenhouse gas fluxes at the in situ (Jigongshan), transported and ambient (Dinghushan) soil monoliths were measured using static chambers. When the transported soil monoliths experienced the external environmental factors (temperature, precipitation and nitrogen deposition) at Dinghushan, its annual soil CO 2 emissions were 54% in PF and 60% in MF higher than those from the respective in situ treatment. Annual soil N 2O emissions were 45% in PF and 44% in MF higher than those from the respective in situ treatment. There were no significant differences in annual soil CO 2 or N 2O emissions between the transported and ambient treatments. However, annual CH 4 uptake by the transported soil monoliths in PF or MF was not significantly different from that at the respective in situ treatment, and was significantly lower than that at the respective ambient treatment. Therefore, external environmental factors were the major drivers of soil CO 2 and N 2O emissions, while soil was the dominant controller of soil CH 4 uptake. We further tested the results by developing simple empirical models using the observed fluxes of CO 2 and N 2O from the in situ treatment and found that the empirical models can explain about 90% for CO 2 and 40% for N 2O of the observed variations at the transported treatment. Results from this study suggest that the different responses of soil CO 2, N 2O, CH 4 fluxes to changes in multiple environmental conditions need to be considered in global change study. 相似文献
6.
In-field measurements of direct soil greenhouse gas (GHG) emissions provide critical data for quantifying the net energy efficiency and economic feasibility of crop residue-based bioenergy production systems. A major challenge to such assessments has been the paucity of field studies addressing the effects of crop residue removal and associated best practices for soil management (i.e., conservation tillage) on soil emissions of carbon dioxide (CO 2), nitrous oxide (N 2O), and methane (CH 4). This regional survey summarizes soil GHG emissions from nine maize production systems evaluating different levels of corn stover removal under conventional or conservation tillage management across the US Corn Belt. Cumulative growing season soil emissions of CO 2, N 2O, and/or CH 4 were measured for 2–5 years (2008–2012) at these various sites using a standardized static vented chamber technique as part of the USDA-ARS’s Resilient Economic Agricultural Practices (REAP) regional partnership. Cumulative soil GHG emissions during the growing season varied widely across sites, by management, and by year. Overall, corn stover removal decreased soil total CO 2 and N 2O emissions by -4 and -7 %, respectively, relative to no removal. No management treatments affected soil CH 4 fluxes. When aggregated to total GHG emissions (Mg CO 2?eq ha ?1) across all sites and years, corn stover removal decreased growing season soil emissions by ?5?±?1 % (mean?±?se) and ranged from -36 % to 54 % ( n?=?50). Lower GHG emissions in stover removal treatments were attributed to decreased C and N inputs into soils, as well as possible microclimatic differences associated with changes in soil cover. High levels of spatial and temporal variabilities in direct GHG emissions highlighted the importance of site-specific management and environmental conditions on the dynamics of GHG emissions from agricultural soils. 相似文献
7.
Despite the increasing impact of atmospheric nitrogen (N) deposition on terrestrial greenhouse gas (GHG) budget, through driving both the net atmospheric CO 2 exchange and the emission or uptake of non-CO 2 GHGs (CH 4 and N 2O), few studies have assessed the climatic impact of forests and grasslands under N deposition globally based on different bottom-up approaches. Here, we quantify the effects of N deposition on biomass C increment, soil organic C (SOC), CH 4 and N 2O fluxes and, ultimately, the net ecosystem GHG balance of forests and grasslands using a global comprehensive dataset. We showed that N addition significantly increased plant C uptake (net primary production) in forests and grasslands, to a larger extent for the aboveground C (aboveground net primary production), whereas it only caused a small or insignificant enhancement of SOC pool in both upland systems. Nitrogen addition had no significant effect on soil heterotrophic respiration ( RH) in both forests and grasslands, while a significant N-induced increase in soil CO 2 fluxes ( RS, soil respiration) was observed in grasslands. Nitrogen addition significantly stimulated soil N 2O fluxes in forests (76%), to a larger extent in grasslands (87%), but showed a consistent trend to decrease soil uptake of CH 4, suggesting a declined sink capacity of forests and grasslands for atmospheric CH 4 under N enrichment. Overall, the net GHG balance estimated by the net ecosystem production-based method (forest, 1.28 Pg CO 2-eq year −1 vs. grassland, 0.58 Pg CO 2-eq year −1) was greater than those estimated using the SOC-based method (forest, 0.32 Pg CO 2-eq year −1 vs. grassland, 0.18 Pg CO 2-eq year −1) caused by N addition. Our findings revealed that the enhanced soil C sequestration by N addition in global forests and grasslands could be only marginally offset (1.5%–4.8%) by the combined effects of its stimulation of N 2O emissions together with the reduced soil uptake of CH 4. 相似文献
8.
The greenhouse gas (GHG) balance of European grasslands (EU‐28 plus Norway and Switzerland), including CO 2, CH 4 and N 2O, is estimated using the new process‐based biogeochemical model ORCHIDEE‐GM over the period 1961–2010. The model includes the following: (1) a mechanistic representation of the spatial distribution of management practice; (2) management intensity, going from intensively to extensively managed; (3) gridded simulation of the carbon balance at ecosystem and farm scale; and (4) gridded simulation of N 2O and CH 4 emissions by fertilized grassland soils and livestock. The external drivers of the model are changing animal numbers, nitrogen fertilization and deposition, land‐use change, and variable CO 2 and climate. The carbon balance of European grassland (NBP) is estimated to be a net sink of 15 ± 7 g C m ?2 year ?1 during 1961–2010, equivalent to a 50‐year continental cumulative soil carbon sequestration of 1.0 ± 0.4 Pg C. At the farm scale, which includes both ecosystem CO 2 fluxes and CO 2 emissions from the digestion of harvested forage, the net C balance is roughly halved, down to a small sink, or nearly neutral flux of 8 g C m ?2 year ?1. Adding CH 4 and N 2O emissions to net ecosystem exchange to define the ecosystem‐scale GHG balance, we found that grasslands remain a net GHG sink of 19 ± 10 g C‐CO 2 equiv. m ?2 year ?1, because the CO 2 sink offsets N 2O and grazing animal CH 4 emissions. However, when considering the farm scale, the GHG balance (NGB) becomes a net GHG source of ?50 g C‐CO 2 equiv. m ?2 year ?1. ORCHIDEE‐GM simulated an increase in European grassland NBP during the last five decades. This enhanced NBP reflects the combination of a positive trend of net primary production due to CO 2, climate and nitrogen fertilization and the diminishing requirement for grass forage due to the Europe‐wide reduction in livestock numbers. 相似文献
9.
Biochar has been widely researched as an important technology for climate smart agriculture, yet work is still necessary to identify the magnitude of potential greenhouse gas (GHG) mitigation and mechanisms involved. This study measured slow‐pyrolysis wood‐derived biochar's impact on GHG efflux, mineral N dynamics, and soil organic C in a series of two incubations across fertilized and unfertilized agricultural soils and soil moisture regimes. This research explored the magnitude of biochar's full GHG mitigation potential and drivers of such impacts. Results of this incubation indicate slow‐pyrolysis wood‐derived biochar has potential to provide annual emission reductions of 0.58–1.72 Mg CO 2‐eq ha ?1 at a 25 Mg ha ?1 biochar application rate. The greatest GHG mitigation potential was from C sequestration and nitrous oxide (N 2O) reduction in mineral N fertilized soils, with minimal impacts on N 2O emissions in unfertilized soils, carbon dioxide (CO 2) emissions, and methane (CH 4) uptake. Analysis of mineral N dynamics in the bulk soil and on biochar isolates indicated that neither biochar impacts on net mineralization and nitrification nor retention of ammonium () on biochar isolates could explain biochar's N 2O reduction. Instead, biochar amendments exhibited consistent N 2O emission reductions relative to the N 2O emission in the control soil regardless of soil type and fertilization. Results across a soil moisture gradient suggest that woody biochar may aerate soils shifting redox conditions and subsequent N 2O production. Understanding the magnitude of biochar's GHG reduction potential and the mechanisms driving these effects can help inform biochar modeling efforts, explain field results and identify agricultural applications that maximize biochar's full GHG mitigation potential. 相似文献
10.
Background and aims The impact of understory vegetation control or replacement with selected plant species, which are common forest plantation management practices, on soil C pool and greenhouse gas (GHG, including CO 2, CH 4 and N 2O) emissions are poorly understood. The objective of this paper was to investigate the effects of understory vegetation management on the dynamics of soil GHG emissions and labile C pools in an intensively managed Chinese chestnut ( Castanea mollissima Blume) plantation in subtropical China. Methods A 12-month field experiment was conducted to study the dynamics of soil labile C pools and GHG emissions in a Chinese chestnut plantation under four different understory management practices: control (Control), understory removal (UR), replacement of understory vegetation with Medicago sativa L. (MS), and replacement with Lolium perenne L. (LP). Soil GHG emissions were determined using the static chamber/GC technique. Results Understory management did not change the seasonal pattern of soil GHG emissions; however, as compared with the Control, the UR treatment increased soil CO 2 and N 2O emissions and CH 4 uptake, and the MS and LP treatments increased CO 2 and N 2O emissions and reduced CH 4 uptake ( P?<?0.05 for all treatment effects, same below). The total global warming potential (GWP) of GHG emissions in the Control, UR, MS, and LP treatments were 36.56, 39.40, 42.36, and 42.99 Mg CO 2 equivalent (CO 2-e) ha ?1 year ?1, respectively, with CO 2 emission accounting for more than 95 % of total GWP regardless of the understory management treatment. The MS and LP treatments increased soil organic C (SOC), total N (TN), soil water soluble organic C (WSOC) and microbial biomass C (MBC), while the UR treatment decreased SOC, TN and NO 3 ?-N but had no effect on WSOC and MBC. Soil GHG emissions were correlated with soil temperature and WSOC across the treatments, but had no relationship with soil moisture content and MBC. Conclusions Although replacing competitive understory vegetation with legume or less competitive non-legume species increased soil GHG emissions and total GWP, such treatments also increased soil C and N pools and are therefore beneficial for increasing soil C storage, maintaining soil fertility, and enhancing the productivity of Chinese chestnut plantations. 相似文献
11.
Background and aimsThe litter layer is a major source of CO2, and it also influences soil-atmosphere exchange of N2O and CH4. So far, it is not clear how much of soil greenhouse gas (GHG) emission derives from the litter layer itself or is litter-induced. The present study investigates how the litter layer controls soil GHG fluxes and microbial decomposer communities in a temperate beech forest. MethodsWe removed the litter layer in an Austrian beech forest and studied responses of soil CO2, CH4 and N2O fluxes and the microbial community via phospholipid fatty acids (PLFA). Soil GHG fluxes were determined with static chambers on 22 occasions from July 2012 to February 2013, and soil samples collected at 8 sampling events. ResultsLitter removal reduced CO2 emissions by 30 % and increased temperature sensitivity (Q10) of CO2 fluxes. Diffusion of CH4 into soil was facilitated by litter removal and CH4 uptake increased by 16 %. This effect was strongest in autumn and winter when soil moisture was high. Soils without litter turned from net N2O sources to slight N2O sinks because N2O emissions peaked after rain events in summer and autumn, which was not the case in litter-removal plots. Microbial composition was only transiently affected by litter removal but strongly influenced by seasonality. ConclusionsLitter layers must be considered in calculating forest GHG budgets, and their influence on temperature sensitivity of soil GHG fluxes taken into account for future climate scenarios. 相似文献
12.
Nitrogen (N) deposition can alter the rates of microbial N- and C- turnover, and thus can affect the fluxes of greenhouse gases (GHG, e.g., CO 2, CH 4, and N 2O) from forest soils. The effects of N deposition on the GHG fluxes from forest soils were reviewed in this paper. N deposition to forest soils have shown variable effects on the soil GHG fluxes from forest, including increases, decreases or unchanged rates depending on forest type, N status of the soil, and the rate and type of atmospheric N deposition. In forest ecosystems where biological processes are limited by N supply, N additions either stimulate soil respiration or have no significant effect, whereas in “N saturated” forest ecosystems, N additions decrease CO 2 emission, reduce CH 4 oxidation and elevate N 2O flux from the soil. The mechanisms and research methods about the effects of N deposition on GHG fluxes from forest soils were also reviewed in this paper. Finally, the present and future research needs about the effects of N deposition on the GHG fluxes from forest soils were discussed. 相似文献
13.
The need for renewable energy sources will lead to a considerable expansion in the planting of dedicated fast‐growing biomass crops across Europe. These are commonly cultivated as short‐rotation coppice (SRC), and currently poplar ( Populus spp.) is the most widely planted. In this study, we report the greenhouse gas (GHG) fluxes of carbon dioxide (CO 2), methane (CH 4) and nitrous oxide (N 2O) measured using eddy covariance technique in an SRC plantation for bioenergy production. Measurements were made during the period 2010–2013, that is, during the first two rotations of the SRC. The overall GHG balance of the 4 years of the study was an emission of 1.90 (±1.37) Mg CO 2eq ha ?1; this indicated that soil trace gas emissions offset the CO 2 uptake by the plantation. CH 4 and N 2O contributed almost equally to offset the CO 2 uptake of ?5.28 (±0.67) Mg CO 2eq ha ?1 with an overall emission of 3.56 (±0.35) Mg CO 2eq ha ?1 of N 2O and of 3.53 (±0.85) Mg CO 2eq ha ?1 of CH 4. N 2O emissions mostly occurred during one single peak a few months after the site was converted to SRC; this peak comprised 44% of the total N 2O loss during the two rotations. Accurately capturing emission events proved to be critical for deriving correct estimates of the GHG balance. The nitrogen (N) content of the soil and the water table depth were the two drivers that best explained the variability in N 2O and CH 4, respectively. This study underlines the importance of the ‘non‐CO 2 GHGs’ on the overall balance. Further long‐term investigations of soil trace gas emissions should monitor the N content and the mineralization rate of the soil, as well as the microbial community, as drivers of the trace gas emissions. 相似文献
14.
Sub-Saharan Africa (SSA) must undertake proper cropland intensification for higher crop yields while minimizing climate impacts. Unfortunately, no studies have simultaneously quantified greenhouse gas (GHG; CO 2, CH 4, and N 2O) emissions and soil organic carbon (SOC) change in SSA croplands, leaving it a blind spot in the accounting of global warming potential (GWP). Here, based on 2-year field monitoring of soil emissions of CO 2, CH 4, and N 2O, as well as SOC changes in two contrasting soil types (sandy vs. clayey), we provided the first, full accounting of GWP for maize systems in response to cropland intensifications (increasing nitrogen rates and in combination with crop residue return) in SSA. To corroborate our field observations on SOC change (i.e., 2-year, a short duration), we implemented a process-oriented model parameterized with field data to simulate SOC dynamic over time. We further tested the generality of our findings by including a literature synthesis of SOC change across maize-based systems in SSA. We found that nitrogen application reduced SOC loss, likely through increased biomass yield and consequently belowground carbon allocation. Residue return switched the direction of SOC change from loss to gain; such a benefit (SOC sequestration) was not compromised by CH 4 emissions (negligible) nor outweighed by the amplified N 2O emissions, and contributed to negative net GWP. Overall, we show encouraging results that, combining residue and fertilizer-nitrogen input allowed for sequestering 82–284 kg of CO 2-eq per Mg of maize grain produced across two soils. All analyses pointed to an advantage of sandy over clayey soils in achieving higher SOC sequestration targets, and thus call for a re-evaluation on the potential of sandy soils in SOC sequestration across SSA croplands. Our findings carry important implications for developing viable intensification practices for SSA croplands in mitigating climate change while securing food production. 相似文献
15.
The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO 2, CH 4 and N 2O emissions increased by an average of 3.7%, 0.3%, 24.3% and 91.3% under N enrichment, respectively, and that the soil CH 4 uptake decreased by 6.0%. Furthermore, the percentage increase in N 2O emissions (91.3%) was two times lower than that (215%) reported by Liu and Greaver ( Ecology Letters, 2009, 12:1103–1117). There was also greater stimulation of soil C pools (15.70 kg C ha ?1 year ?1 per kg N ha ?1 year ?1) than previously reported under N deposition globally. The global N deposition results showed that croplands were the largest GHG sources (calculated as CO 2 equivalents), followed by wetlands. However, forests and grasslands were two important GHG sinks. Globally, N deposition increased the terrestrial soil C sink by 6.34 Pg CO 2/year. It also increased net soil GHG emissions by 10.20 Pg CO 2‐Geq (CO 2 equivalents)/year. Therefore, N deposition not only increased the size of the soil C pool but also increased global GHG emissions, as calculated by the global warming potential approach. 相似文献
16.
The magnitude, temporal, and spatial patterns of soil‐atmospheric greenhouse gas (hereafter referred to as GHG) exchanges in forests near the Tropic of Cancer are still highly uncertain. To contribute towards an improvement of actual estimates, soil‐atmospheric CO 2, CH 4, and N 2O fluxes were measured in three successional subtropical forests at the Dinghushan Nature Reserve (hereafter referred to as DNR) in southern China. Soils in DNR forests behaved as N 2O sources and CH 4 sinks. Annual mean CO 2, N 2O, and CH 4 fluxes (mean±SD) were 7.7±4.6 Mg CO 2‐C ha ?1 yr ?1, 3.2±1.2 kg N 2O‐N ha ?1 yr ?1, and 3.4±0.9 kg CH 4‐C ha ?1 yr ?1, respectively. The climate was warm and wet from April through September 2003 (the hot‐humid season) and became cool and dry from October 2003 through March 2004 (the cool‐dry season). The seasonality of soil CO 2 emission coincided with the seasonal climate pattern, with high CO 2 emission rates in the hot‐humid season and low rates in the cool‐dry season. In contrast, seasonal patterns of CH 4 and N 2O fluxes were not clear, although higher CH 4 uptake rates were often observed in the cool‐dry season and higher N 2O emission rates were often observed in the hot‐humid season. GHG fluxes measured at these three sites showed a clear increasing trend with the progressive succession. If this trend is representative at the regional scale, CO 2 and N 2O emissions and CH 4 uptake in southern China may increase in the future in light of the projected change in forest age structure. Removal of surface litter reduced soil CO 2 effluxes by 17–44% in the three forests but had no significant effect on CH 4 absorption and N 2O emission rates. This suggests that microbial CH 4 uptake and N 2O production was mainly related to the mineral soil rather than in the surface litter layer. 相似文献
17.
Atmospheric nitrogen deposition is anticipated to increase over the next decades with possible implications for future forest-atmosphere
interactions. Increased soil N 2O emissions, depressed CH 4 uptake and depressed soil respiration CO 2 loss is considered a likely response to increased N deposition. This study examined fluxes of N 2O, CH 4 and CO 2 over two growing seasons from soils in unmanaged forest and grassland communities on abandoned agricultural areas in Michigan.
All sites were subject to simulated increased N-deposition in the range of 1–3 g N m −2 annually. Nitrous oxide fluxes and soil N concentrations in coniferous and grassland sites were on the whole unaffected by
the increased N-inputs. It is noteworthy though that N 2O emissions increased three-fold in the coniferous sites in the first growing season in response to the low N treatment, although
the response was barely significant ( p<0.06). In deciduous forests, we observed increased levels of soil mineral N during the second year of N fertilization, however
N 2O fluxes did not increase. Rates of methane oxidation were similar in all sites with no affect of field N application. Likewise,
we did not observe any changes in soil CO 2 efflux in response to N additions. The combination of tillage history and vegetation type was important for the trace gas
fluxes, i.e. soil CO 2 efflux was greater in successional grassland sites compared with the forested sites and CH 4 uptake was reduced in post-tillage coniferous- and successional sites compared with the old-growth deciduous site. Our results
indicate that short-term increased N availability influenced individual processes linked to trace gas turnover in the soil
independently from the ecosystem N status. However, changes in whole system fluxes were not evident and were very likely mediated
by competitive N uptake processes. 相似文献
18.
Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site‐specific management strategies strongly affect the biosphere–atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO 2), nitrous oxide (N 2O), and methane (CH 4). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO 2 exchange, while long‐term N 2O and CH 4 flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO 2, N 2O, and CH 4 fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO 2 sink (−1,783 to −91 g CO 2 m −2 year −1), but a N 2O source (18–638 g CO 2‐eq. m −2 year −1), and either a CH 4 sink or source (−9 to 488 g CO 2‐eq. m −2 year −1). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between −2,761 and −58 g CO 2‐eq. m −2 year −1, with N 2O and CH 4 emissions offsetting concurrent CO 2 uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N 2O and CH 4 fluxes was generally low and varied considerably within years. However, after site‐specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity (“sweet spots”) and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N 2O and CH 4 emissions. The N 2O‐N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%–8.6%). Although grassland management led to increased N 2O and CH 4 emissions, the CO 2 sink strength was generally the most dominant component of the annual GHG budget. 相似文献
19.
Changes in soil hydration status affect microbial community dynamics and shape key biogeochemical processes. Evidence suggests that local anoxic conditions may persist and support anaerobic microbial activity in soil aggregates (or in similar hot spots) long after the bulk soil becomes aerated. To facilitate systematic studies of interactions among environmental factors with biogeochemical emissions of CO 2, N 2O and CH 4 from soil aggregates, we remolded silt soil aggregates to different sizes and incorporated carbon at different configurations (core, mixed, no addition). Assemblies of remolded soil aggregates of three sizes (18, 12, and 6 mm) and equal volumetric proportions were embedded in sand columns at four distinct layers. The water table level in each column varied periodically while obtaining measurements of soil GHG emissions for the different aggregate carbon configurations. Experimental results illustrate that methane production required prolonged inundation and highly anoxic conditions for inducing measurable fluxes. The onset of unsaturated conditions (lowering water table) resulted in a decrease in CH 4 emissions while temporarily increasing N 2O fluxes. Interestingly, N 2O fluxes were about 80% higher form aggregates with carbon placement in center (anoxic) core compared to mixed carbon within aggregates. The fluxes of CO 2 were comparable for both scenarios of carbon sources. These experimental results highlight the importance of hydration dynamics in activating different GHG production and affecting various transport mechanisms about 80% of total methane emissions during lowering water table level are attributed to physical storage (rather than production), whereas CO 2 emissions (~80%) are attributed to biological activity. A biophysical model for microbial activity within soil aggregates and profiles provides a means for results interpretation and prediction of trends within natural soils under a wide range of conditions. 相似文献
20.
Land‐use/land‐cover change (LULCC) often results in degradation of natural wetlands and affects the dynamics of greenhouse gases (GHGs). However, the magnitude of changes in GHG emissions from wetlands undergoing various LULCC types remains unclear. We conducted a global meta‐analysis with a database of 209 sites to examine the effects of LULCC types of constructed wetlands (CWs), croplands (CLs), aquaculture ponds (APs), drained wetlands (DWs), and pastures (PASs) on the variability in CO 2, CH 4, and N 2O emissions from the natural coastal wetlands, riparian wetlands, and peatlands. Our results showed that the natural wetlands were net sinks of atmospheric CO 2 and net sources of CH 4 and N 2O, exhibiting the capacity to mitigate greenhouse effects due to negative comprehensive global warming potentials (GWPs; ?0.9 to ?8.7 t CO 2‐eq ha ?1 year ?1). Relative to the natural wetlands, all LULCC types (except CWs from coastal wetlands) decreased the net CO 2 uptake by 69.7%?456.6%, due to a higher increase in ecosystem respiration relative to slight changes in gross primary production. The CWs and APs significantly increased the CH 4 emissions compared to those of the coastal wetlands. All LULCC types associated with the riparian wetlands significantly decreased the CH 4 emissions. When the peatlands were converted to the PASs, the CH 4 emissions significantly increased. The CLs, as well as DWs from peatlands, significantly increased the N 2O emissions in the natural wetlands. As a result, all LULCC types (except PASs from riparian wetlands) led to remarkably higher GWPs by 65.4%?2,948.8%, compared to those of the natural wetlands. The variability in GHG fluxes with LULCC was mainly sensitive to changes in soil water content, water table, salinity, soil nitrogen content, soil pH, and bulk density. This study highlights the significant role of LULCC in increasing comprehensive GHG emissions from global natural wetlands, and our results are useful for improving future models and manipulative experiments. 相似文献
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