Article

Assessments of Atmospheric Interchanges of Green House Gas Emissions from the Cultivated Land: Study Based on Edaphic Gradients of Plantations in Semi Arid Region of Gujarat, India

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  • Institute of Science & Technology for Advanced Studies & Research (ISTAR)
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Abstract

The study of the magnitude of temporal and spatial patterns of Greenhouse Gases (GHG) fluxes from the cultivated land of subtropical regions of India is still an uncharted territory. The paper contributes towards the improvement of actual estimate and investigates the seasonal variation of greenhouse gases (GHGs) emissions (N O, CH and CO ) For the purpose three mono specific plantation viz. Manilkara zapota, Mangifera indica, Dendrocalumus stictus, and Mixed plantation are studied in semi arid region of central Gujarat, India to assess the extent of GHG fluxes in response to their soils and the comparative analysis presented to understand the atmospheric interchanges. The research contributes in building a framework for plantation approach for carbon sequestration by analyzing the patterns of GHGs emission under different ecosystem.

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We investigated soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) exchanges in an age-sequence (4, 17, 32, 67 years old) of eastern white pine (Pinus strobus L.) forests in southern Ontario, Canada, for the period of mid-April to mid-December in 2006 and 2007. For both CH4 and N2O, we observed uptake and emission ranging from −160 to 245 μg CH4 m−2 h−1 and −52 to 21 μg N2O m−2 h−1, respectively (negative values indicate uptake). Mean fluxes from mid-April to mid-December across the 4, 17, 32, 67 years old stands were similar for CO2 fluxes (259, 246, 220, and 250 mg CO2 m−2 h−1, respectively), without pattern for N2O fluxes (−3.7, 1.5, −2.2, and −7.6 μg N2O m−2 h−1, respectively), whereas the uptake rates of CH4 increased with stand age (6.4, −7.9, −10.8, and −23.3 μg CH4 m−2 h−1, respectively). For the same period, the combined contribution of CH4 and N2O exchanges to the global warming potential (GWP) calculated from net ecosystem exchange of CO2 and aggregated soil exchanges of CH4 and N2O was on average 4%, <1%, <1%, and 2% for the 4, 17, 32, 67 years old stand, respectively. Soil CO2 fluxes correlated positively with soil temperature but had no relationship with soil moisture. We found no control of soil temperature or soil moisture on CH4 and N2O fluxes, but CH4 emission was observed following summer rainfall events. LFH layer removal reduced CO2 emissions by 43%, increased CH4 uptake during dry and warm soil conditions by more than twofold, but did not affect N2O flux. We suggest that significant alternating sink and source potentials for both CH4 and N2O may occur in N- and soil water-limited forest ecosystems, which constitute a large portion of forest cover in temperate areas.
Article
N2O, CH4 and CO2 soil-atmosphere exchange and controlling environmental factors were studied for a 3-month period (dry-wet season transition) at the Kakamega Rain forest, Kenya, Africa, using an automated measurement system. The mean N2O emission was 42.9 +/- 0.7 mug N m-2 h-1 (range: 1.1-324.8 mug N m-2 h-1). Considering the duration of dry and wet season the annual N2O emission was estimated at 2.6 +/- 1.2 kg N ha-1 yr-1. Large pulse emissions of N2O were observed after the first rainfall events of the wet season, and the magnitude of N2O emissions steadily declined thereafter. A comparable trend in soil CO2 emissions (mean: 71.8 +/- 0.3 mg C m-2 h-1) indicates that the rapid mineralization of litter accumulated during the dry period produced the high N2O emissions at the start of the wet season. Manual N2O emission measurements at four additional rain forest sites were comparable to those measured at the main site, whereas N2O emissions measured at a regrowth site were significantly lower. Spatial differences in N2O emissions could be explained by differences in soil texture and topsoil C:N-ratio (CO2: subsoil C and N concentrations), whereas the temporal variability of N2O and CO2 emissions was primarily driven by soil moisture. Soils predominantly acted as sinks for CH4 (-56.4 +/- 0.8 mug C m-2 h-1). For some chamber positions, episodes of net CH4 release were observed, which could be due to high WFPS and/or termite activity. CH4 fluxes were weakly correlated with soil moisture levels but showed no relation to temperature, texture, pH, carbon or nitrogen contents.
Article
Emissions of nitrous oxide from intensively managed agricultural fields were measured over 3 years. Exponential increases in flux occurred with increasing soil water- filled pore space (WFPS) and temperature; increases in soil mineral N content due to fertilizer application also stimulated emissions. Fluxes were low when any of these variables was below a critical value. The largest fluxes occurred when WFPS values were very high (70-90%), indicating that denitrification was the major process responsible. The relationships with the driving variables showed strong similarities to those reported for very different environments: irrigated sugar cane crops, pastures, and forest in the tropics. Annual emissions varied widely (0.3-18.4 kg N2O-N ha-1). These variations were principally due to the degree of coincidence of fertilizer application and major rainfall events. It is concluded therefore that several years' data are required from any agricultural ecosystem in a variable climate to obtain a robust estimate of mean N2O fluxes. The emissions from small-grain cereals (winter wheat and spring barley) were consistently lower (0.2-0.7 kg N2O-N per 100 kg N applied) than from cut grassland (0.3-5.8 kg N2O- N per 100 kg N). Crops such as broccoli and potatoes gave emissions of the same order as those from the grassland. Although these differences between crop types are not apparent in general data comparisons, there may well be distinct regional differences in the relative and absolute emissions from different crops, due to local factors relating to soil type, weather patterns, and agricultural management practices. This will only be determined by more detailed comparative studies.
Article
Factors influencing the rates of production and emission of CH4, CH4 oxidation and rates of SO42− reduction, were measured in the peat of an ombrotrophic bog in New Galloway, Scotland. Vertical concentration profiles of CH4 and O2 showed that the water table essentially represented the oxic-anoxic boundary in the peat. This boundary was usually at the surface in the case of peat-bog hollows, but up to 20 cm of oxic peat occurred above the water table in peat-bog hummocks. Penetration of O2 into the peat increased under illumination when photosynthesis was active, but decreased in the dark. Emission of CH4 from the peat surface was faster from peat-bog hollows than from hummocks, where most CH4 was reoxidized before emission. CH4 emission rates also varied seasonally, being greatest during summer. For most of the year the amount of organic C oxidized to CO2 by SO42− reduction by anaerobic bacteria exceeded that being transformed to CH4 by methanogenic bacteria, except during summer when SO42− reduction became SO42− limited. Laboratory experiments showed that the addition of SO42− to peat inhibited CH4 formation, confirming that there was competitive inhibition of CH4 formation by active SO42− reduction, as demonstrated in other environments. The degree of acid rain deposition of SO42− onto peat bogs may therefore be extremely important in regulating the production and emission of CH4 from peat. CH4 formation was most active in the strata of peat 5–15 cm below the water table, although actual rates of CH4 formation were slower in the peat beneath hummocks than that below hollows. In contrast, CH4 oxidation occurred nearer the peat surface (only 3–7 cm below the water table) where the methanotrophic bacteria could intercept vertically migrating CH4. Surprisingly, the peak for CH4 oxidation potential occurred at about 5 cm below the water table, in peat which was apparently anoxic. This may reflect either a transiently oxic peat environment, in which aerobic CH4-oxidizing bacteria persisted, or the presence of a community of facultatively anaerobic CH4-oxidizing bacteria which, in anoxic conditions, metabolized substrates other than CH4. There was no evidence of anaerobic CH4 oxidation.
Article
A review of the salient features of N 2 O emissions from agricultural soils was done to assess our current understanding and associated problems. Nitrous oxide is an important globe warming gas and a destructive agent of ozone in the stratosphere. A major concern is the increasing contribution of chemical fertilizers to atmospheric N 2 O buildup. There is only a limited understanding of the contributions from manures, biological N 2 fixation and crop residues. A recent estimate suggests that agriculture's share of N 2 O emissions is 80% although such estimates are highly uncertain because of imprecise data and the physical and biological complexities of the production process. As a product of the nitrification and denitrification process in soils, a major problem is our understanding of the proportion of N 2 O produced, i.e. the product ratios, although there is a good general understanding of the processes involved. Measurements of N 2 O emissions from the soil surface fail to take into account N 2 O flux from the bottom of the root zone into the subsoil and aquifers although they are generally considered to be significant. There is a need to apply newly available methodology and for combining this methodology and modelling together to predict N 2 O emissions on the landscape (or field) scale taking climate, soil and cropping variables into account. There is enough information available now to exercise some control of N 2 O emissions from cultivated soils. It is suggested that this be done focusing on factors that directly affect the soil microbes involved with the nitrification (NH 4 ⁺ , O 2 ) and denitrification (NO 3 ⁻ , C, O 2 ) processes. Cropping practices and some soil characteristic amendments are suggested herein for this purpose. Key words: Denitrification, nitrification, emission control, gas ratios
Article
Combining improved injector, gas line and valve-driving models, a gas chromatograph (GC) equipped with Hydrogen Flame Ionization Detector (FID) and Electron Capture Detector (ECD), can measure CH4, CO2, and N2O simultaneously in an air sample in four minutes. Test results show that the system has high sensitivity, resolution, and precision; the linear response range of the system meets the requirement of flux measurements in situ. The system is suitable for monitoring fluxes of the main greenhouse gases in a short-plant field since it is easy to use, efficacious, and constant and reliable in collecting data.
Article
The mineralization of nitrogen and phosphorus from plant residues provides an important input of inorganic nutrients to the soil, which can be taken up by plants. The dynamics of nutrient mineralization or immobilization during decomposition are controlled by different biological and physical factors. Decomposers sequester carbon and nutrients from organic substrates and exchange inorganic nutrients with the environment to maintain their stoichiometric balance. Additionally, physical losses of organic compounds from leaching and other processes may alter the nutrient content of litter. In this work, we extend a stoichiometric model of litter nitrogen mineralization to include (1) phosphorus mineralization, (2) physical losses of organic nutrients, and (3) chemical heterogeneity of litter Substrates. The enhanced model provides analytical mineralization curves for nitrogen and phosphorus as well as critical litter carbon : nutrient ratios (the carbon : nutrient ratios below which net nutrient release occurs) as a function of the elemental composition of the decomposers, their carbon-use efficiency, and the rate of physical loss of organic compounds. The model is used to infer the critical litter carbon : nutrient ratios from observed nitrogen and phosphorus dynamics in about 2600 litterbag samplings from 21 decomposition data sets spanning artic to tropical ecosystems. At the beginning of decomposition, nitrogen and phosphorus tend to be immobilized in boreal and temperate climates (i.e., both C:N and C:P critical ratios are lower than the initial ratios), while in tropical areas nitrogen is generally released and phosphorus may be either immobilized or released, regardless of the typically low phosphorus concentrations. The critical carbon : nutrient ratios we observed were found to increase with initial litter carbon : nutrient ratios, indicating that decomposers adapt to low-nutrient conditions by reducing their carbon-use efficiency. This stoichiometric control on nutrient dynamics appears ubiquitous across climatic regions and ecosystems, although other biological and physical processes also play important roles in litter decomposition. In tropical humid conditions, we found high critical C:P ratios likely due to high leaching and low decomposer phosphorus concentrations. In general, the Compound effects of stoichiometric constraints and physical losses explain most of the variability in critical carbon: nutrient ratios and dynamics of nutrient immobilization and release Lit the global scale.
Article
Soils are the major source of the greenhouse gas nitrous oxide (N2O) to our atmosphere. A thorough understanding of terrestrial N2O production is therefore essential. N2O can be produced by nitrifiers, denitrifiers, and by nitrifiers paradoxically denitrifying. The latter pathway, though well-known in pure culture, has only recently been demonstrated in soils. Moreover, nitrifier denitrification appeared to be much less important than classical nitrate-driven denitrification. Here we studied a poor sandy soil, and show that when moisture conditions are sub-optimal for denitrification, nitrifier denitrification can be a major contributor to N2O emission from this soil. We conclude that the relative importance of classical and nitrifier denitrification in N2O emitted from soil is a function of the soil moisture content, and likely of other environmental conditions as well. Accordingly, we suggest that nitrifier denitrification should be routinely considered as a major source of N2O from soil.
Article
This paper provides an introduction to the Special Issue on "Climate Change and Coupling of Macronutrient Cycles along the Atmospheric, Terrestrial, Freshwater and Estuarine Continuum", dedicated to Colin Neal on his retirement. It is not intended to be a review of this vast subject, but an attempt to synthesize some of the major findings from the 22 contributions to the Special Issue in the context of what is already known. The major research challenges involved in understanding coupled macronutrient cycles in these environmental media are highlighted, and the difficulties of making credible predictions of the effects of climate change are discussed. Of particular concern is the possibility of interactions which will enhance greenhouse gas concentrations and provide positive feedback to global warming.
Article
It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas (GHG) footprint. We compared field emissions of nitrous oxide (N2O), methane (CH4) and soil respiration rates from the C4 grass Miscanthus × giganteus and willow (salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow, Miscanthus, wheat (Triticum aetivum) and oilseed rape (Brassica napus). N2O, CH4 fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N2O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 μg m−2 h−1 N2O-N from wheat and oilseed rape, and 4 and 0.2 μg m−2 h−1 N2O-N from Miscanthus and willow, respectively. Soil CH4 fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO2 was larger for Miscanthus (−770 g C m−2 h−1) than willow (−602 g C m−2 h−1) in the growing season of 2010. N2O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of 15N-labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer-induced increase in N2O emission in both crops. Denitrification rates (N2O + N2) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer.
Article
We compared carbon storage and fluxes in young and old ponderosa pine stands in Oregon, including plant and soil storage, net primary productivity, respiration fluxes, eddy flux estimates of net ecosystem exchange (NEE), and Biome-BGC simulations of fluxes. The young forest (Y site) was previously an old-growth ponderosa pine forest that had been clearcut in 1978, and the old forest (O site), which has never been logged, consists of two primary age classes (50 and 250 years old). Total ecosystem carbon content (vegetation, detritus and soil) of the O forest was about twice that of the Y site (21 vs. 10 kg C m−2 ground), and significantly more of the total is stored in living vegetation at the O site (61% vs. 15%). Ecosystem respiration (Re) was higher at the O site (1014 vs. 835 g C m−2 year−1), and it was largely from soils at both sites (77% of Re). The biological data show that above-ground net primary productivity (ANPP), NPP and net ecosystem production (NEP) were greater at the O site than the Y site. Monte Carlo estimates of NEP show that the young site is a source of CO2 to the atmosphere, and is significantly lower than NEP(O) by c. 100 g C m−2 year−1. Eddy covariance measurements also show that the O site was a stronger sink for CO2 than the Y site. Across a 15-km swath in the region, ANPP ranged from 76 g C m−2 year−1 at the Y site to 236 g C m−2 year−1 (overall mean 158 ± 14 g C m−2 year−1). The lowest ANPP values were for the youngest and oldest stands, but there was a large range of ANPP for mature stands. Carbon, water and nitrogen cycle simulations with the Biome-BGC model suggest that disturbance type and frequency, time since disturbance, age-dependent changes in below-ground allocation, and increasing atmospheric concentration of CO2 all exert significant control on the net ecosystem exchange of carbon at the two sites. Model estimates of major carbon flux components agree with budget-based observations to within ± 20%, with larger differences for NEP and for several storage terms. Simulations showed the period of regrowth required to replace carbon lost during and after a stand-replacing fire (O) or a clearcut (Y) to be between 50 and 100 years. In both cases, simulations showed a shift from net carbon source to net sink (on an annual basis) 10–20 years after disturbance. These results suggest that the net ecosystem production of young stands may be low because heterotrophic respiration, particularly from soils, is higher than the NPP of the regrowth. The amount of carbon stored in long-term pools (biomass and soils) in addition to short-term fluxes has important implications for management of forests in the Pacific North-west for carbon sequestration.
Article
Tree species can affect the sink and source strength of soils for atmospheric methane and nitrous oxide. Here we report soil methane (CH4) and nitrous oxide (N2O) fluxes of adjacent pure and mixed stands of beech and spruce at Solling, Germany. Mean CH4 uptake rates ranged between 18 and 48 μg C m−2 hour−1 during 2.5 years and were about twice as great in both mixed and the pure beech stand as in the pure spruce stand. CH4 uptake was negatively correlated with the dry mass of the O horizon, suggesting that this diminishes the transport of atmospheric CH4 into the mineral soil. Mean N2O emission was rather small, ranging between 6 and 16 μg N m−2 hour−1 in all stands. Forest type had a significant effect on N2O emission only in one mixed stand during the growing season. We removed the O horizon in additional plots to study its effect on gas fluxes over 1.5 years, but N2O emissions were not altered by this treatment. Surprisingly, CH4 uptake decreased in both mixed and the pure beech stands following the removal of the O horizon. The decrease in CH4 uptake coincided with an increase in the soil moisture content of the mineral soil. Hence, O horizons may maintain the gas diffusivity within the mineral soil by storing water which cannot penetrate into the mineral soil after rainfall. Our results indicate that conversion of beech forests to beech–spruce and pure spruce forests could decrease soil CH4 uptake, while the long-term effect on N2O emissions is expected to be rather small.
Article
Based on current climate scenarios, a higher frequency of summer drought periods followed by heavy rainfall events is predicted for Central Europe. It is expected that drying/rewetting events induce an increased matter cycling in soils and may contribute considerably to increased emissions of the greenhouse gas N2O on annual scales. To investigate the influence of drying/rewetting events on N2O emissions in a mature Norway spruce forest in the Fichtelgebirge area (NE Bavaria, Germany), a summer drought period of 46 days was induced by roof installations on triplicate plots, followed by a rewetting event of 66 mm experimental rainfall in 2 days. Three nonmanipulated plots served as controls. The experimentally induced soil drought was accompanied by a natural drought. During the drought period, the soil of both the throughfall exclusion and control plots served as an N2O sink. This was accompanied by subambient N2O concentrations in upper soil horizons. The sink strength of the throughfall exclusion plots was doubled compared with the control plots. We conclude that the soil water status together with the soil nitrate availability was an important driving factor for the N2O sink strength. Rewetting quickly turned the soil into a source for atmospheric N2O again, but it took almost 4 months to turn the cumulative soil N2O fluxes from negative (sink) to positive (source) values. N2O concentration and isotope analyses along soil profiles revealed that N2O produced in the subsoil was subsequently consumed during upward diffusion along the soil profile throughout the entire experiment. Our results show that long drought periods can lead to drastic decreases of N2O fluxes from soils to the atmosphere or may even turn forest soils temporarily to N2O sinks. Accumulation of more field-scale data on soil N2O uptake as well as a better understanding of underlying mechanisms would essentially advance our knowledge of the global N2O budget.
Article
Soils provide the largest terrestrial carbon store, the largest atmospheric CO2 source, the largest terrestrial N2O source and the largest terrestrial CH4 sink, as mediated through root and soil microbial processes. A change in land use or management can alter these soil processes such that net greenhouse gas exchange may increase or decrease. We measured soil–atmosphere exchange of CO2, N2O and CH4 in four adjacent land-use systems (native eucalypt woodland, clover-grass pasture, Pinus radiata and Eucalyptus globulus plantation) for short, but continuous, periods between October 2005 and June 2006 using an automated trace gas measurement system near Albany in southwest Western Australia. Mean N2O emission in the pasture was 26.6 μg N m−2 h−1, significantly greater than in the natural and managed forests (< 2.0 μg N m−2 h−1). N2O emission from pasture soil increased after rainfall events (up to 100 μg N m−2 h−1) and as soil water content increased into winter, whereas no soil water response was detected in the forest systems. Gross nitrification through 15N isotope dilution in all land-use systems was small at water holding capacity < 30%, and under optimum soil water conditions gross nitrification ranged between < 0.1 and 1.0 mg N kg−1 h−1, being least in the native woodland/eucalypt plantation < pine plantation < pasture. Forest soils were a constant CH4 sink, up to −20 μg C m−2 h−1 in the native woodland. Pasture soil was an occasional CH4 source, but weak CH4 sink overall (−3 μg C m−2 h−1). There were no strong correlations (R < 0.4) between CH4 flux and soil moisture or temperature. Soil CO2 emissions (35–55 mg C m−2 h−1) correlated with soil water content (R < 0.5) in all but the E. globulus plantation. Soil N2O emissions from improved pastures can be considerable and comparable with intensively managed, irrigated and fertilised dairy pastures. In all land uses, soil N2O emissions exceeded soil CH4 uptake on a carbon dioxide equivalent basis. Overall, afforestation of improved pastures (i) decreases soil N2O emissions and (ii) increases soil CH4 uptake.
Article
From spring 2000 through fall 2001, we measured nitric oxide (NO) and nitrous oxide (N2O) fluxes in two temperate forest sites in Massachusetts, USA that have been treated since 1988 with different levels of nitrogen (N) to simulate elevated rates of atmospheric N deposition. Plots within a pine stand that were treated with either 50 or 150 kg N ha−1 yr−1 above background displayed consistently elevated NO fluxes (100–200 µg N m−2 h−1) compared to control plots, while only the higher N treatment plot within a mixed hardwood stand displayed similarly elevated NO fluxes. Annual NO emissions estimated from monthly sampling accounted for 3.0–3.7% of N inputs to the high-N plots and 8.3% of inputs to the Pine low-N plot. Nitrous oxide fluxes in the N-treated plots were generally < 10% of NO fluxes. Net nitrification rates (NRs) and NO production rates measured in the laboratory displayed patterns that were consistent with field NO fluxes. Total N oxide gas flux was positively correlated with contemporaneous measurements of NR and concentration. Acetylene inhibited both nitrification and NO production, indicating that autotrophic nitrification was responsible for the elevated NO production. Soil pH was negatively correlated with N deposition rate. Low levels (3–11 µg N kg−1) of nitrite () were detected in mineral soils from both sites. Kinetic models describing NO production as a function of the protonated form of (nitrous acid [HNO2]) adequately described the mineral soil data. The results indicate that atmospheric deposition may generate losses of gaseous NO from forest soils by promoting nitrification, and that the response may vary significantly between forest types under similar climatic regimes. The lowering of pH resulting from nitrification and/or directly from deposition may also play a role by promoting reactions involving HNO2.
Article
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 CO2, CH4, and N2O 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 N2O sources and CH4 sinks. Annual mean CO2, N2O, and CH4 fluxes (mean±SD) were 7.7±4.6 Mg CO2-C ha−1 yr−1, 3.2±1.2 kg N2O-N ha−1 yr−1, and 3.4±0.9 kg CH4-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 CO2 emission coincided with the seasonal climate pattern, with high CO2 emission rates in the hot-humid season and low rates in the cool-dry season. In contrast, seasonal patterns of CH4 and N2O fluxes were not clear, although higher CH4 uptake rates were often observed in the cool-dry season and higher N2O 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, CO2 and N2O emissions and CH4 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 CO2 effluxes by 17–44% in the three forests but had no significant effect on CH4 absorption and N2O emission rates. This suggests that microbial CH4 uptake and N2O production was mainly related to the mineral soil rather than in the surface litter layer.
Article
Well-drained forest soils are thought to be a significant sink for atmospheric methane. Recent research suggests that land use change reduces the soil methane sink by diminishing populations of methane oxidizing bacteria. Here we report soil CH4 uptake from ‘natural’ mature beech forests and from mature pine and spruce plantations in two study areas of Germany with distinct climate and soils. The CH4 uptake rates of both beech forests at Solling and Unterlüß were about two–three times the CH4 uptake rates of the adjacent pine and spruce plantations, indicating a strong impact of forest type on the soil CH4 sink. The CH4 uptake rates of sieved mineral soils from our study sites confirmed the tree species effect and indicate that methanotrophs were mainly reduced in the 0–5 cm mineral soil depth. The reasons for the reduction are still unknown. We found no site effect between Solling and Unterlüß, however, CH4 uptake rates from Solling were significantly higher at the same effective CH4 diffusivity. This potential site effect was masked by higher soil water contents at Solling. Soil pH (H2O) explained 71% of the variation in CH4 uptake rates of sieved mineral soils from the 0–5 cm depth, while cation exchange capacity, soil organic carbon, soil nitrogen and total phosphorous content were not correlated with CH4 uptake rates. Comparing 1998–99, annual CH4 uptake rates increased by 69–111% in the beech and spruce stands and by 5–25% in the pine stands, due primarily to differences in growing season soil moisture. Cumulative CH4 uptake rates from November throughout April were rather constant in both years. The CH4 uptake rates of each stand were separately predicted using daily average soil matric potential and a previously developed empirical model. The model results revealed that soil matric potential explains 53–87% of the temporal variation in CH4 uptake. The differences between measured and predicted annual CH4 uptake rates were less than 10%, except for the spruce stand at Solling in 1998 (17%). Based on data from this study and from the literature, we calculated a total reduction in the soil CH4 sink of 31% for German forests due in part to conversion of deciduous to coniferous forests.
Article
The magnitude, temporal, and spatial patterns of greenhouse gas (hereafter referred to as GHG) fluxes from soils of plantation in the subtropical area of China are still highly uncertain. To contribute towards an improvement of actual estimates, soil CO 2 , CH 4 , and N 2 O fluxes were measured in two different land-use types in a hilly area of South China. This study showed 2 years continuous measurements (twice a week) of GHG fluxes from soils of a pine plantation and a longan orchard system. Impacts of environmental drivers (soil temperature and soil moisture), litter exclusion and land-use (vegetation versus orchard) were presented. Our results suggested that the plantation and orchard soils were weak sinks of atmospheric CH 4 and significant sources of atmospheric CO 2 and N 2 O. Annual mean GHG fluxes from soils of plantation and orchard were: CO 2 fluxes of 4.70 and 14.72 Mg CO 2 –C ha À1 year À1 , CH 4 fluxes of À2.57 and À2.61 kg CH 4 –C ha À1 year À1 , N 2 O fluxes of 3.03 and 8.64 kg N 2 O–N ha À1 year À1 , respectively. Land use types had great impact on CO 2 and N 2 O emissions. Annual average CO 2 and N 2 O emissions were higher in the orchard than in the plantation, while there were no clear differences in CH 4 emissions between two sites. Our results suggest that afforestation could be a potential mitigation strategy to reduce GHG emissions from agricultural soils if the observed results were representative at the regional scale. CO 2 and N 2 O emissions were mainly affected by soil temperature and soil moisture. CH 4 uptakes showed significant correlation with soil moisture. The seasonal changes in soil CO 2 and N 2 O fluxes followed the seasonal weather pattern, with high CO 2 and N 2 O emission rates in the rainy period and low rates in the dry period. In contrast, seasonal patterns of CH 4 fluxes were not clear. Removal of surface litter reduced soil CO 2 effluxes by 17–25% and N 2 O effluxes by 34–31% in the plantation and orchard in the second sampling year but not in the first sampling year which suggested micro-environmental heterogeneity in soils. Removal of surface litter had no significant effect on CH 4 absorption rates in both years. This suggests that microbial CH 4 uptake was mainly related to the mineral soil rather than in the surface litter layer. # 2007 Elsevier B.V. All rights reserved.
Article
Reforestation is a mitigation option to reduce increased atmospheric carbon dioxide levels as well as its predicted climate change. As a result, several forestry-based carbon storage projects have been introduced in many countries. To quantify the dynamics of ecosystem carbon allocation as affected by different forest management practices, we measured the above-and belowground biomass accumulation over 14 years, as well as the tissue carbon concentrations of trees in four different types: three monospecific plantations of slash pine (Pinus elliottii) (SPP), Chinese fir (Cunninghamia lanceolata) (CFP), and tea-oil camellia (Camellia oleifera) (TCP) and one natural secondary forest (NSF) (Pinus massoniana and Cyclobalanopsis glauca). A regression equation was constructed using the diameter at breast height/basal diameter (DBH/BD) and elements of total tree biomass. The equation was subsequently utilized to estimate tree carbon storage. The carbon storage of understory, forest floor, and soil components was also estimated. Results indicated that NSF stored significantly more carbon (141.99 t/ha) than SPP (104.07 t/ha), CFP (102.95 t/ ha), and TCP (113.09 t/ha). Most of the carbon was found in the soil pool (60.30% in SPP, 70.42% in CFP, 63.87% in TCP, and 59.36% in NSF). In addition, more than 60% of the soil carbon storage at 0–100 cm depth was stored in the upper 40 cm. With the exception of trees, each component of NSF, including the understudy, forest floor, and soil, possessed significantly higher carbon storage than that of the three plantations (p < 0.05). Soil surface disturbance during forest management practices was one of the main factors reducing the soil and understory carbon storage of tree plantation stands. These results suggest that natural restoration is a superior approach for increasing the carbon storage potential in the hilly red soil region in reforestation projects compared to plantations. In addition, reducing soil surface disturbance during forest management practices might also play an important factor in improving carbon sequestration potential in above tree plantations.
Article
Respiration, which is the second most important carbon flux in ecosystems following gross primary productivity, is typically represented in biogeochemical models by simple temperature dependence equations. These equations were established in the 19th century and have been modified very little since then. Recent applications of these equations to data on soil respiration have produced highly variable apparent temperature sensitivities. This paper searches for reasons for this variability, ranging from biochemical reactions to ecosystem-scale substrate supply. For a simple membrane-bound enzymatic system that follows Michaelis–Menten kinetics, the temperature sensitivities of maximum enzyme activity (Vmax) and the half-saturation constant that reflects the affinity of the enzyme for the substrate (Km) can cancel each other to produce no net temperature dependence of the enzyme. Alternatively, when diffusion of substrates covaries with temperature, then the combined temperature sensitivity can be higher than that of each individual process. We also present examples to show that soluble carbon substrate supply is likely to be important at scales ranging from transport across membranes, diffusion through soil water films, allocation to aboveground and belowground plant tissues, phenological patterns of carbon allocation and growth, and intersite differences in productivity. Robust models of soil respiration will require that the direct effects of substrate supply, temperature, and desiccation stress be separated from the indirect effects of temperature and soil water content on substrate diffusion and availability. We speculate that apparent Q10 values of respiration that are significantly above about 2.5 probably indicate that some unidentified process of substrate supply is confounded with observed temperature variation.
Article
Oxidation by soil bacteria is the only biological sink for atmospheric methane (CH4). There are substantial uncertainties regarding the global size of this sink, in part because the ecological controls of the involved processes are not well understood to date. We have investigated effects of severe summer drought and of nitrogen inputs (ammonium nitrate or cattle urine) on soil CH4 fluxes in a field experiment. Soil moisture was the most important factor regulating the temporal dynamics of CH4 fluxes. Simulated drought episodes altered the soil’s water balance throughout the year, increasing CH4 oxidation by 50% on an annual basis. N fertilizers exerted only small and transient effects at the ecosystem level. Laboratory incubations suggested that effects differed between soil layers, with larger effects of drought and N application in the top soil than in deeper layers. With soil moisture being the primary controlling factor of methanotrophy, a detailed understanding of the ecosystem’s water balance is required to predict CH4 budgets under future climatic conditions. KeywordsAmmonium nitrate–Cattle urine–Drought–Enzymatic inhibition–Grazing
Article
Elevated nitrogen deposition has increased tree growth, the storage of soil organic matter, and nitrate leaching in many European forests, but little is known about the effect of tree species and nitrogen deposition on nitrous oxide emission. Here we report soil N2O emission from European beech, Scots pine and Norway spruce forests in two study areas of Germany with distinct climate, N deposition and soils. N2O emissions and throughfall input of nitrate and ammonium were measured biweekly during growing season and monthly during dormant season over a 28months period. Annual N2O emission rates ranged between 0.4 and 1.3kg N ha−1year−1 among the stands and were higher in 1998 than in 1999 due to higher precipitation during the growing season of 1998. A 2-way-ANOVA revealed that N2O fluxes were significantly higher (p<0.001) at Solling than at Unterlüß while tree species had no effect on N2O emissions. Soil texture and the amount of throughfall explained together 94% of the variance among the stands, indicating that increasing portions of silt and clay may promote the formation of N2O in wet forest soils. Moreover, cumulative N2O fluxes were significantly correlated (r2=0.60, p<0.001) with cumulative NO3− fluxes at 10cm depth as an indicator of N saturation, however, the slope of the regression curve indicates a rather weak effect of NO3− fluxes on N2O emissions. N input by throughfall was not correlated with N2O emissions and only 1.6–3.2% of N input was released as N2O to the atmosphere. Our results suggest that elevated N inputs have little effect on N2O emissions in beech, spruce and pine forests.
Article
Land-use type affects gross nitrogen transformation and this information is particularly lacking under varied low temperature conditions. In this study, the effects of land-use type (forest vs. grassland) and temperature (10 vs. 15°C) on gross N transformation rates under aerobic conditions were investigated using the 15N isotope pool dilution technique in the laboratory. Soils were collected from forest and grassland sites in China and Canada. The results showed that gross N mineralization and immobilization rates were significantly higher in forest soils than in grassland soils, while the reverse was true for gross nitrification rates. The higher TC and lower SOCw concentrations in the Chinese soils relative to the Canadian soils were related to the greater gross N mineralization rates and lower gross N immobilization rates in Chinese soils. The greater gross N mineralization rates and lower gross N immobilization rates resulted in much higher inorganic N accumulation and that may increase the risk of NO 3− leaching in the Chinese soils. Increasing temperature significantly increased gross nitrification rates in grassland soils and gross N immobilization rates in forest soils, suggesting that grassland soils maybe more vulnerable to N loss through NO 3− leaching or denitrification (when conditions for denitrification exist) and that conversion of grassland to forest soils may exert less negative effects on the environment by promoting the retention of N and decreasing the production of NO 3− and subsequently the risk of NO 3− leaching under increasing temperature by global warming.
Article
CO2 efflux plays a key role in carbon exchange between the biosphere and atmosphere, but our understanding of the mechanism controlling its temporal and spatial variations is limited. The purpose of this study is to determine annual soil CO2 flux and assess its variations in arable subtropical soils of China in relation to soil temperature, moisture, rainfall, microbial biomass carbon (MBC) and dissolved organic carbon (DOC) using the closed chamber method. Soils were derived from three parent materials including granite (G), tertiary red sandstone (T) and quaternary red clay (Q). The experiment was conducted at the Ecological Station of Red Soil, The Chinese Academy of Sciences, in a subtropical region of China. The results showed that soil CO2 flux had clear seasonal fluctuations with the maximum value in summer, the minimum in winter and intermediate in spring and autumn. Further, significant differences in soil CO2 flux were found among the three red soils, generally in the order of G>T>Q. The average annual fluxes were estimated as 2.84, 2.13 and 1.41 kg CO2 m−2 year−1 for red soils derived from G, T and Q, respectively. Soil temperature strongly affects the seasonal variability of soil CO2 flux (85.0–88.5% of the variability), followed by DOC (55.8–84.4%) and rainfall (43.0–55.8%). The differences in soil CO2 flux among the three red soils were partly explained by MBC (33.7–58.9% of the variability) and DOC (23.8–33.6%).
Article
Methane emission by soils results from antagonistic but correlated microbial activities. Methane is produced in the anaerobic zones of submerged soils by methanogens and is oxidised into CO2 by methanotrophs in the aerobic zones of wetland soils and in upland soils. Methanogens and methanotrophs are ubiquitous in soils where they remain viable under unfavourable conditions. Methane transfer from the soil to the atmosphere occurs mostly through the aerenchyma of aquatic plants, but also by diffusion and as bubbles escaping from wetland soils. Methane sources are mainly wetlands. However 60 to more than 90 % of CH4 produced in the anaerobic zones of wetlands is reoxidised in their aerobic zones (rhizosphere and oxidised soil-water interface). Methane consumption occurs in most soils and exhibits a broad range of values. Highest consumption rates or potentials are observed in soils where methanogenesis is or has been effective and where CH4 concentration is or has been much higher than in the atmosphere (ricefields, swamps, landfills, etc.). Aerobic soils consume atmospheric CH4 but their activities are very low and the micro-organisms involved are largely unknown. Methane emissions by cultivated or natural wetlands are expressed in mg CH4·m–2·h–1 with a median lower than 10 mg CH4·m–2·h–1. Methanotrophy in wetlands is most often expressed with the same unit. Methane oxidation by aerobic upland soils is rarely higher than 0.1 mg CH4·m–2·h–1. Forest soils are the most active, followed by grasslands and cultivated soils. Factors that favour CH4 emission from cultivated wetlands are mostly submersion and organic matter addition. Intermittent drainage and utilisation of the sulphate forms of N-fertilisers reduce CH4 emission. Methane oxidation potential of upland soils is reduced by cultivation, especially by ammonium N-fertiliser application.
Article
Changes in land use and management of tropical systems are considered to be major factors in the recent upsurge in increases in atmospheric nitrous oxide (N2O) and methane (CH4). Studies were initiated in western Puerto Rico grasslands to determine the effect of plowing, or liming and fertilizing an acid Oxisol on the soil–atmosphere exchanges of N2O and CH4. Weekly field flux measurements and field manipulation and laboratory studies were conducted over 22 months during 1993–1995. We found that N2O emissions from an Oxisol acidified to pH 4 were generally lower than from pH 6 Oxisol soils that were used as reference controls. Plowing the grasslands did not change mean N2O emission rates from either pH soil. Liming the acidified Oxisol to pH 6 tended to increase N2O emissions to the rates from the undisturbed grassland. Fertilizing the acidified grassland increased N2O emissions but much less than when these soils were both limed and fertilized. Short-term field studies employing nitrification inhibitors in which we measured nitric oxide (NO) and N2O emissions, demonstrated that nitrification rates generally control N2O emissions; thus these were lower in unlimed soil. It is likely that NO was produced through the chemical decomposition of nitrite, which in turn, was a product of biological nitrification. Soil consumption of atmospheric CH4 in the acidified Oxisol was about one-fourth of that in the pH 6 reference soil. Liming did not restore CH4 consumption in the acid soil to rates comparable to those in the reference Oxisol. We conducted a laboratory induction study to determine if incubation of these limed or unlimed acidified soils with high concentrations of CH4 could induce methanotrophic activity. Comparable uptake rates to the control soils were not induced by these incubations. These studies illustrate that management of soil can considerably affect the soil–atmosphere exchange of such trace gases as N2O and CH4 which can affect global atmospheric properties.
Article
Turkey's demand for energy and electricity is increasing rapidly. Since 1990, energy consumption has increased at an annual average rate of 4.3%. As would be expected, the rapid expansion of energy production and consumption has brought with it a wide range of environmental issues at the local, regional and global levels. With respect to global environmental issues, Turkey's carbon dioxide (CO2) emissions have grown along with its energy consumption. Emissions in 2004 reached 193 million tons. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases (GHGs). State emissions are significant on a global scale. CO2 and carbon monoxide (CO) are the main GHGs associated with global warming. At the present time, coal is responsible for 30–40% of the world CO2 emissions from fossil fuels. Sulfur dioxide (SO2) and NOx contribute to acid rain. Carbon assessments can play an important role in a strategy to control CO2 emissions while raising revenue.
Article
A Chinese fir forest (Cunninghamia lanceolata, CL) and a secondary evergreen broadleaved forest (BF) located in Fujian Province, south-eastern China, were examined before clear-cutting to compare their ecosystem carbon and nitrogen pools (above- and below-ground tree, understorey vegetation and forest floor biomass + 0–100 cm mineral soil layer). The ecosystem pools of C and N in the CL before clear-cutting were 257 Mg ha−1 and 8605 kg ha−1, respectively. The corresponding values for the BF were 336 Mg ha−1 of C and 10,248 kg ha−1 of N. For the two forests, most of the C was in the trees, whereas most of the N pool was in the soil. C and N pools in understorey vegetation and forest floor were small in the two forests (about 2% of ecosystem pools). During clear-cutting, 117 Mg ha−1 C and 307 kg ha−1 N in stem wood with bark and coarse branches (>2 cm) were removed from the CL compared to 159 Mg ha−1 C and 741 kg ha−1 N from the BF. Two days after slash burning, C removal from logging residues (including forest floor material) was estimated at 10 Mg ha−1 for CL and 23 Mg ha−1 for BF, and N removal was 233 and 490 kg ha−1 in the CL and BF, respectively. Compared with the pre-burn levels in the CL, contents of topsoil organic C and total N 2 days after burning were reduced by 17 and 19%, respectively. In the BF, the corresponding proportions were 27% (C) and 25% (N). Our results indicate that clear-cutting and slash burning had caused marked short-term changes in ecosystem C and N in the two forests. How long these changes will persist needs further study.