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1.
The lowland peatlands of south‐east Asia represent an immense reservoir of fossil carbon and are reportedly responsible for 30% of the global carbon dioxide (CO 2) emissions from Land Use, Land Use Change and Forestry. This paper provides a review and meta‐analysis of available literature on greenhouse gas fluxes from tropical peat soils in south‐east Asia. As in other parts of the world, water level is the main control on greenhouse gas fluxes from south‐east Asian peat soils. Based on subsidence data we calculate emissions of at least 900 g CO 2 m ?2 a ?1 (~250 g C m ?2 a ?1) for each 10 cm of additional drainage depth. This is a conservative estimate as the role of oxidation in subsidence and the increased bulk density of the uppermost drained peat layers are yet insufficiently quantified. The majority of published CO 2 flux measurements from south‐east Asian peat soils concerns undifferentiated respiration at floor level, providing inadequate insight on the peat carbon balance. In contrast to previous assumptions, regular peat oxidation after drainage might contribute more to the regional long‐term annual CO 2 emissions than peat fires. Methane fluxes are negligible at low water levels and amount to up to 3 mg CH 4 m ?2 h ?1 at high water levels, which is low compared with emissions from boreal and temperate peatlands. The latter emissions may be exceeded by fluxes from rice paddies on tropical peat soil, however. N 2O fluxes are erratic with extremely high values upon application of fertilizer to wet peat soils. Current data on CO 2 and CH 4 fluxes indicate that peatland rewetting in south‐east Asia will lead to substantial reductions of net greenhouse gas emissions. There is, however, an urgent need for further quantitative research on carbon exchange to support the development of consistent policies for climate change mitigation. 相似文献
2.
Microbial oxidation in aerobic soils is the primary biotic sink for atmospheric methane (CH 4), a powerful greenhouse gas. Although tropical forest soils are estimated to globally account for about 28% of annual soil CH 4 consumption (6.2 Tg CH 4 year ?1), limited data are available on CH 4 exchange from tropical montane forests. We present the results of an extensive study on CH 4 exchange from tropical montane forest soils along an elevation gradient (1,000, 2,000, 3,000 m) at different topographic positions (lower slope, mid-slope, ridge position) in southern Ecuador. All soils were net atmospheric CH 4 sinks, with decreasing annual uptake rates from 5.9 kg CH 4–C ha ?1 year ?1 at 1,000 m to 0.6 kg CH 4–C ha ?1 year ?1 at 3,000 m. Topography had no effect on soil atmospheric CH 4 uptake. We detected some unexpected factors controlling net methane fluxes: positive correlations between CH 4 uptake rates, mineral nitrogen content of the mineral soil and with CO 2 emissions indicated that the largest CH 4 uptake corresponded with favorable conditions for microbial activity. Furthermore, we found indications that CH 4 uptake was N limited instead of inhibited by NH 4 +. Finally, we showed that in contrast to temperate regions, substantial high affinity methane oxidation occurred in the thick organic layers which can influence the CH 4 budget of these tropical montane forest soils. Inclusion of elevation as a co-variable will improve regional estimates of methane exchange in these tropical montane forests. 相似文献
3.
为探索华南地区尾巨桉人工林和马占相思人工林地表温室气体的季节排放规律、排放通量和主控因子,采用静态箱-气相色谱法,对两种林型地表3种温室气体(CO_2、CH_4、N_2O)通量进行为期1年的逐月测定。结果表明:(1)尾巨桉人工林和马占相思人工林均为CO_2和N_2O的排放源,CH_4的吸收汇。马占相思林地表N_2O通量显著(P0.01)高于尾巨桉林,CO_2通量和CH_4通量无明显差异。(2)两种林型3种温室气体通量有着相似季节变化规律,地表CO_2通量均呈现雨季高旱季低的单峰规律;地表CH_4吸收通量表现为旱季高雨季低的单峰趋势;地表N_2O通量呈现雨季高旱季低且雨季内有两个峰值的排放规律。(3)地表CO_2、N_2O通量和土壤5 cm温度呈极显著(P0.01)正相关,3种温室气体地表通量同土壤含水量呈极显著(P0.01)或显著相关(P0.05)。(4)尾巨桉林和马占相思林温室气体年温室气体排放总量为31.014 t/hm~2和28.782 t/hm~2,均以CO_2排放占绝对优势(98.46%—99.15%),CH_4和N_2O处于次要地位。 相似文献
4.
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
5.
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
6.
Tropical forests on upland soils are assumed to be a methane (CH 4) sink and a weak source of nitrous oxide (N 2O), but studies of wetland forests have demonstrated that tree stems can be a substantial source of CH 4, and recent evidence from temperate woodlands suggests that tree stems can also emit N 2O. Here, we measured CH 4 and N 2O fluxes from the soil and from tree stems in a semi‐evergreen tropical forest on upland soil. To examine the influence of seasonality, soil abiotic conditions and substrate availability (litter inputs) on trace greenhouse gas (GHG) fluxes, we conducted our study during the transition from the dry to the wet season in a long‐term litter manipulation experiment in Panama, Central America. Trace GHG fluxes were measured from individual stem bases of two common tree species and from soils beneath the same trees. Soil CH 4 fluxes varied from uptake in the dry season to minor emissions in the wet season. Soil N 2O fluxes were negligible during the dry season but increased markedly after the start of the wet season. By contrast, tree stem bases emitted CH 4 and N 2O throughout the study. Although we observed no clear effect of litter manipulation on trace GHG fluxes, tree species and litter treatments interacted to influence CH 4 fluxes from stems and N 2O fluxes from stems and soil, indicating complex relationships between tree species traits and decomposition processes that can influence trace GHG dynamics. Collectively, our results show that tropical trees can act as conduits for trace GHGs that most likely originate from deeper soil horizons, even when they are growing on upland soils. Coupled with the finding that the soils may be a weaker sink for CH 4 than previously thought, our research highlights the need to reappraise trace gas budgets in tropical forests. 相似文献
7.
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
8.
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
9.
Wetlands contribute considerably to the global greenhouse gas (GHG) balance. In these ecosystems, groundwater level (GWL) and temperature, two factors likely to be altered by climate change, exert important control over CO 2, CH 4 and N 2O fluxes. However, little is known about the temperature sensitivity ( Q10) of the combined GHG emissions from hydromorphic soils and how this Q10 varies with GWL. We performed a greenhouse experiment in which three different (plant‐free) hydromorphic soils from a temperate spruce forest were exposed to two GWLs (an intermediate GWL of ?20 cm and a high GWL of ?5 cm). Net CO 2, CH 4 and N 2O fluxes were measured continuously. Here, we discuss how these fluxes responded to synoptic temperature fluctuations. Across all soils and GWLs, CO 2 emissions responded similarly to temperature and Q10 was close to 2. The Q10 of the CH 4 and N 2O fluxes also was similar across soil types. GWL, on the other hand, significantly affected the Q10 of both CH 4 and N 2O emissions. The Q10 of the net CH 4 fluxes increased from about 1 at GWL = ?20 cm to 3 at GWL = ?5 cm. For the N 2O emissions, Q10 varied around 2 for GWL = ?20 cm and around 4 for GWL = ?5 cm. This substantial GWL‐effect on the Q10 of CH 4 and N 2O emissions was, however, hardly reflected in the Q10 of the total GHG emissions (which varied around 2), because the contribution of these gases was relatively small compared to that of CO 2. 相似文献
10.
Agricultural drainage is thought to alter greenhouse gas emissions from temperate peatlands, with CH 4 emissions reduced in favor of greater CO 2 losses. Attention has largely focussed on C trace gases, and less is known about the impacts of agricultural conversion on
N 2O or global warming potential. We report greenhouse gas fluxes (CH 4, CO 2, N 2O) from a drained peatland in the Sacramento-San Joaquin River Delta, California, USA currently managed as a rangeland (that
is, pasture). This ecosystem was a net source of CH 4 (25.8 ± 1.4 mg CH 4-C m −2 d −1) and N 2O (6.4 ± 0.4 mg N 2O-N m −2 d −1). Methane fluxes were comparable to those of other managed temperate peatlands, whereas N 2O fluxes were very high; equivalent to fluxes from heavily fertilized agroecosystems and tropical forests. Ecosystem scale
CH 4 fluxes were driven by “hotspots” (drainage ditches) that accounted for less than 5% of the land area but more than 84% of
emissions. Methane fluxes were unresponsive to seasonal fluctuations in climate and showed minimal temporal variability. Nitrous
oxide fluxes were more homogeneously distributed throughout the landscape and responded to fluctuations in environmental variables,
especially soil moisture. Elevated CH 4 and N 2O fluxes contributed to a high overall ecosystem global warming potential (531 g CO 2-C equivalents m −2 y −1), with non-CO 2 trace gas fluxes offsetting the atmospheric “cooling” effects of photoassimilation. These data suggest that managed Delta
peatlands are potentially large regional sources of greenhouse gases, with spatial heterogeneity in soil moisture modulating
the relative importance of each gas for ecosystem global warming potential. 相似文献
11.
为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO 2、CH 4和N 2O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季(6月-9月)对3种恢复方式(人工更新、天然更新和人工促进天然更新)林地土壤温室气体CO 2、CH 4、N 2O通量进行了原位观测。研究结果表明:(1)3种恢复方式林地土壤在生长季均为大气CO 2、N 2O的源,CH 4的汇;生长季林地土壤CO 2排放通量大小关系为人工促进天然更新((634.40±246.52)mg m -2 h -1) > 人工更新((603.63±213.22)mg m -2 h -1) > 天然更新((575.81±244.12)mg m -2 h -1),3种恢复方式间无显著差异;人工更新林地土壤CH 4吸收通量显著高于人工促进天然更新;天然更新林地土壤N 2O排放通量显著高于其他两种恢复方式。(2)土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N 2O通量有极显著影响( P < 0.01);3种恢复方式林地土壤CO 2通量与大气湿度具有极显著的响应( P < 0.01);土壤pH仅与天然更新林地土壤CO 2通量显著相关( P < 0.05);土壤全氮含量仅与人工促进天然更新林地土壤CH 4通量显著相关( P < 0.05)。(3)基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新(1.83×10 4 kg CO 2/hm 2) > 人工更新(1.74×10 4 kg CO 2/hm 2) > 天然更新(1.67×10 4 kg CO 2/hm 2)。(4)阿木尔地区林地土壤年生长季CO 2和N 2O排放量为8.85×10 6 t和1.88×10 2 t,CH 4吸收量为1.05×10 3 t。 相似文献
12.
Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0–10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO 2, CH 4, and N 2O fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO 3 ?), and polymerase chain reaction–denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO 2 (Wetland), >23,000% for CH 4 (Creek), and >110,000% for N 2O (Forest Soils) following pulse events. The Creek soil produced the highest soil CO 2 emissions, the Wetland soil produced the highest CH 4 emissions, and the Forest soils produced the highest N 2O emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large N 2O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes. 相似文献
13.
There are limited data for greenhouse gas (GHG) emissions from smallholder agricultural systems in tropical peatlands, with data for non-CO 2 emissions from human-influenced tropical peatlands particularly scarce. The aim of this study was to quantify soil CH 4 and N 2O fluxes from smallholder agricultural systems on tropical peatlands in Southeast Asia and assess their environmental controls. The study was carried out in four regions in Malaysia and Indonesia. CH 4 and N 2O fluxes and environmental parameters were measured in cropland, oil palm plantation, tree plantation and forest. Annual CH 4 emissions (in kg CH 4 ha −1 year −1) were: 70.7 ± 29.5, 2.1 ± 1.2, 2.1 ± 0.6 and 6.2 ± 1.9 at the forest, tree plantation, oil palm and cropland land-use classes, respectively. Annual N 2O emissions (in kg N 2O ha −1 year −1) were: 6.5 ± 2.8, 3.2 ± 1.2, 21.9 ± 11.4 and 33.6 ± 7.3 in the same order as above, respectively. Annual CH 4 emissions were strongly determined by water table depth (WTD) and increased exponentially when annual WTD was above −25 cm. In contrast, annual N 2O emissions were strongly correlated with mean total dissolved nitrogen (TDN) in soil water, following a sigmoidal relationship, up to an apparent threshold of 10 mg N L −1 beyond which TDN seemingly ceased to be limiting for N 2O production. The new emissions data for CH 4 and N 2O presented here should help to develop more robust country level ‘emission factors’ for the quantification of national GHG inventory reporting. The impact of TDN on N 2O emissions suggests that soil nutrient status strongly impacts emissions, and therefore, policies which reduce N-fertilisation inputs might contribute to emissions mitigation from agricultural peat landscapes. However, the most important policy intervention for reducing emissions is one that reduces the conversion of peat swamp forest to agriculture on peatlands in the first place. 相似文献
14.
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
15.
中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。 相似文献
16.
A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO 2) and methane (CH 4) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO 2 emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO 2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO 2 m ?2 and less than 1.36±0.57 g CH 4 m ?2. On the basis of the carbon emitted, CO 2 is clearly a more important greenhouse gas than CH 4. CO 2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering. 相似文献
17.
The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO 2, methane—CH 4 and nitrous oxide—N 2O) remains poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO 2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH 4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N 2O and N 2O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns. 相似文献
18.
Willow coppice, energy maize and Miscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha ?1 yr ?1 for the perennial crops and 240 kg N ha ?1 yr ?1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH 4, CO 2 and N 2O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO 2 emissions, with highest emissions being found for the N‐fertilized Miscanthus plots (annual mean: 50 mg C m ?² h ?1). Significant differences between the cropping systems were found in soil N 2O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N 2O emissions by far, which accumulated to 3.6 kg N 2O ha ?1 yr ?1. The contribution of CH 4 fluxes to the total soil greenhouse gas subsumption was very small compared with N 2O and CO 2. CH 4 fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH 4. To identify the system providing the best ratio of yield to soil N 2O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N 2O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N 2O emissions than unfertilized Miscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N 2O emissions in the field. 相似文献
19.
Increases in the concentrations of atmospheric greenhouse gases, carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2O) due to human activities are associated with global climate change. CO 2 concentration in the atmosphere has increased by 33% (to 380 ppm) since 1750 ad, whilst CH 4 concentration has increased by 75% (to 1,750 ppb), and as the global warming potential (GWP) of CH 4 is 25 fold greater than CO 2 it represents about 20% of the global warming effect. The purpose of this review is to: (a) address recent findings regarding biophysical factors governing production and consumption of CH 4, (b) identify the current level of knowledge regarding the main sources and sinks of CH 4 in Australia, and (c) identify CH 4 mitigation options and their potential application in Australian ecosystems. Almost one-third of CH 4 emissions are from natural sources such as wetlands and lake sediments, which is poorly documented in Australia. For Australia, the major anthropogenic sources of CH 4 emissions include energy production from fossil fuels (~24%), enteric fermentation in the guts of ruminant animals (~59%), landfills, animal wastes and domestic sewage (~15%), and biomass burning (~5%), with minor contributions from manure management (1.7%), land use, land-use change and forestry (1.6%), and rice cultivation (0.2%). A significant sink exists for CH 4 (~6%) in aerobic soils, including agricultural and forestry soils, and potentially large areas of arid soils, however, due to limited information available in Australia, it is not accounted for in the Australian National Greenhouse Gas Inventory. CH 4 emission rates from submerged soils vary greatly, but mean values ≤10 mg m ?2 h ?1 are common. Landfill sites may emit CH 4 at one to three orders of magnitude greater than submerged soils. CH 4 consumption rates in non-flooded, aerobic agricultural, pastoral and forest soils also vary greatly, but mean values are restricted to ≤100 μg m ?2 h ?1, and generally greatest in forest soils and least in agricultural soils, and decrease from temperate to tropical regions. Mitigation options for soil CH 4 production primarily relate to enhancing soil oxygen diffusion through water management, land use change, minimised compaction and soil fertility management. Improved management of animal manure could include biogas capture for energy production or arable composting as opposed to open stockpiling or pond storage. Balanced fertiliser use may increase soil CH 4 uptake, reduce soil N 2O emissions whilst improving nutrient and water use efficiency, with a positive net greenhouse gas (CO 2-e) effect. Similarly, the conversion of agricultural land to pasture, and pastoral land to forestry should increase soil CH 4 sink. Conservation of native forests and afforestation of degraded agricultural land would effectively mitigate CH 4 emissions by maintaining and enhancing CH 4 consumption in these soils, but also by reducing N 2O emissions and increasing C sequestration. The overall impact of climate change on methanogenesis and methanotrophy is poorly understood in Australia, with a lack of data highlighting the need for long-term research and process understanding in this area. For policy addressing land-based greenhouse gas mitigation, all three major greenhouse gases (CO 2, CH 4 and N 2O) should be monitored simultaneously, combined with improved understanding at process-level. 相似文献
20.
Most studies of greenhouse gas fluxes from forest soils in the coastal rainforest have considered carbon dioxide (CO 2), whereas methane (CH 4) has not received the same attention. Soil hydrology is a key driver of CH 4 dynamics in ecosystems, but the impact on the function and distribution of the underlying microbial communities involved in CH 4 cycling and the resultant net CH 4 exchange is not well understood at this scale. We studied the growing season variations of in situ CH 4 fluxes, microbial gene abundances of methanotrophs (CH 4 oxidizers) and methanogens (CH 4 producers), soil hydrology, and nutrient availability in three typical forest types across a soil moisture gradient. CH 4 displayed a spatial variability changing from a net uptake in the upland soils (3.9–46 µmol CH 4 m ?2 h ?1) to a net emission in the wetter soils (0–90 μmol CH 4 m ?2 h ?1). Seasonal variations of CH 4 fluxes were related to soil hydrology in both upland and wet soils. Thus, in the upland soils, uptake rates increased with the decreasing soil moisture, whereas CH 4 emission was inversely related to the water table depth in the wet soils. Spatial variability of CH 4 exchange was related to the abundance of genes involved in CH 4 oxidation and production, but there was no indication of a temporal link between microbial groups and CH 4 exchange. Our data show that the abundances of genes involved in CH 4 oxidation and production are strongly influenced by soil moisture and each other and grouped by the upland–wetland classification but not forest type. 相似文献
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