Plant and Soil 04/2012; 343(1):1-3. · 2.73 Impact Factor
ABSTRACT: Sheepfolds represent significant hot spot sources of greenhouse gases (GHG) in semi-arid grassland regions, such as Inner
Mongolia in China. However, the annual contribution of sheepfolds to regional GHG emissions is still unknown. In order to
quantify its annual contribution, we conducted measurements of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) fluxes at two sheepfold sites in the Baiyinxile administrative region of Inner Mongolia for 1year, using static opaque
chamber and gas chromatography methods. Our data show that, at an annual scale, both sheepfolds functioned as net sources
of CO2, CH4 and N2O. Temperatures primarily determined the seasonal pattern of CO2 emission; 60–84% of the CO2 flux variation could be explained by temperature changes. High rates of net CH4 emissions from sheepfold soils were only observed when animals (sheep and goats) were present. While nitrous oxide emissions
were also stimulated by the presence of animals, pulses of N2O emissions were also be related to rainfall and spring-thaw events. The total annual cumulative GHG emissions in CO2 equivalents (CO2: 1; CH4: 25; and N2O: 298) were quantified as 87.4 ± 18.4tha−1 for the sheepfold that was used during the non-grazing period (i.e., winter sheepfold) and 136.7 ± 15.9tha−1 used during the grazing period (i.e., summer sheepfold). Of the annual total GHG emissions, CH4 release accounted for approximately 1% of emissions, while CO2 and N2O emissions contributed to approximately 59% and 40%, respectively. The total GHG emission factor (CO2 + CH4 + N2O) per animal for the sheepfolds investigated in this study was 30.3kg CO2 eqyr−1 head−1, which translates to 0.3, 18.8 and 11.2kg CO2 eqyr−1 head−1 for CH4, CO2 and N2O, respectively. Sheepfolds accounted for approximately 34% of overall N2O emissions in the Baiyinxile administrative region, a typical steppe region within Inner Mongolia. The contribution of sheepfolds
to the regional CO2 or CH4 exchange is marginal.
KeywordsCarbon dioxide–Methane–Nitrous oxide–Sheepfold–Semi-arid grassland–Xilin River catchment
Plant and Soil 04/2012; 340(1):291-301. · 2.73 Impact Factor
ABSTRACT: Fire is a major disturbance in shrubland ecosystems of the Mediterranean basin, with high potential to alter ecosystem nitrogen
(N) stocks and N cycling. However, postfire effects on gross rates of soil N turnover (ammonification, nitrification, microbial
immobilization, denitrification) have rarely been investigated. We determined gross rates of N turnover including nitrous
oxide fluxes and dinitrogen emissions in the mineral soil of unburned and burned shrublands of Southern Italy 6months after
a natural fire. In soil of burned plots, both gross ammonification and gross nitrification were significantly higher than
in soil of unburned plots (2.2 ± 0.3 versus 0.6 ± 0.1mgN kg−1 sdw day−1 for ammonification and 1.1 ± 0.1 versus 0.5 ± 0.1mgN kg−1 sdw day−1 for nitrification). Microbial immobilization, in particular of nitrate, could not compensate for the increase in inorganic
N production, therefore soil nitrate concentrations were considerably higher at the burned plots. Soil microbial biomass carbon
and nitrogen concentrations were significantly lower in soils of burned plots than in soils of unburned plots. Dinitrogen
was the dominant end product of denitrification and emitted at higher rates from the unburned plots than from the burned plots
(0.094 ± 0.003 versus 0.004 ± 0.002mgN kg−1 sdw day−1, while there was no net nitrous oxide flux (burned plots) or slight net nitrous oxide uptake (control plots). These results
show that postfire patterns of gross N turnover in soil can exhibit a significant reduction of both microbial N retention
and N gas losses via denitrification.
KeywordsMaquis–Fire–N cycling–Ammonification–Nitrification–Denitrification–Nitrous oxide–Dinitrogen–Microbial biomass–He flow soil core technique
Plant and Soil 04/2012; 343(1):5-15. · 2.73 Impact Factor
ABSTRACT: Simulation of decomposition and inorganic nitrogen release in complex biogeochemical models can be based on different principles.
A major problem is the link between carbon and nitrogen mineralization and a description of microbial growth dynamics in dependence
of a suite of possible substrates. This contribution considers a first order decomposition model with several carbon pools
and one nitrogen pool to investigate how the decomposition of plant types and mineralization of nitrogen is related to carbon
quality. The model structure assumes that nitrogen is mobilised with the rate at which the lignin compounds decompose. The
decomposition module is coupled with microbial dynamics by adjusted Michaelis Menten equations that relate microbial growth
to the availability of various substrates. The model was calibrated using Markov Chain Monte Carlo (MCMC) applied to measured
litter remnants, concentrations of lignin, cellulose and nitrogen from 30 in situ incubations of foliage litters. Additionally,
data from a laboratory incubation experiment were used to analyse the formation of microbial biomass, dissolved organic nitrogen,
ammonium (NH4+) and microbial respiration. Parameter sensitivity was analysed according to the rate of acceptance of various settings in
the MCMC calibration chain. The most important parameters for the decomposition process were the decomposition rate of lignin,
and the temperature response parameter Q10. The most important parameters for the formation of microbial biomass, dissolved organic nitrogen, ammonium and microbial
respiration, were the potential growth rate of the microbial population and the rate of microbial decay. Estimated optimal
decomposition rates for field experiments are 0.003 ± 0.002 d−1 for lignin like compounds, 0.006 ± 0.004 d−1 for cellulose like compounds and 0.0286 ± 0.052 d−1 for solutes. The temperature response parameter Q10 is 3.2 ± 0.6 and the optimum decomposition temperature is 28.1 ± 4.3°C. Important model parameters on microbial biomass and
nitrification are the maximum microbial growth rate μMAX = 0.13 ± 0.82 gCmic gCmic−1d−1 or the rate of microbial decay D = 0.006 ± 0.014 gCmic gCmic−1d−1. The model performance was tested for independent datasets. Generally, correlations between modelled and measured values,
expressed in R2, were high for the remaining tissue dry weight, or concentrations of lignin, cellulose and solutes or organic nitrogen (R
2 > 0.84). Due to uncertainties in measurements of DON and NH4+ concentrations, microbial biomass or basal respiration and significant site variability in these parameters, the model performance
for these parameters as expressed as R2 was somewhat lower, but statistically highly significant, and in the range of 0.1-0.96.
Plant and Soil 04/2012; 328(1):271-290. · 2.73 Impact Factor
ABSTRACT: Microbial respiratory reduction of nitrous oxide (N2O) to dinitrogen (N2) via denitrification plays a key role within the global N-cycle since it is the most important process for converting reactive
nitrogen back into inert molecular N2. However, due to methodological constraints, we still lack a comprehensive, quantitative understanding of denitrification
rates and controlling factors across various ecosystems. We investigated N2, N2O and NO emissions from irrigated cotton fields within the Aral Sera Basin using the He/O2 atmosphere gas flow soil core technique and an incubation assay. NH4NO3 fertilizer, equivalent to 75kg ha−1 and irrigation water, adjusting the water holding capacity to 70, 100 and 130% were applied to the incubation vessels to
assess its influence on gaseous N emissions. Under soil conditions as they are naturally found after concomitant irrigation
and fertilization, denitrification was the dominant process and N2 the main end product of denitrification. The mean ratios of N2/N2O emissions increased with increasing soil moisture content. N2 emissions exceeded N2O emissions by a factor of 5 ± 2 at 70% soil water holding capacity (WHC) and a factor of 55 ± 27 at 130% WHC. The mean ratios
of N2O/NO emissions varied between 1.5 ± 0.4 (70% WHC) and 644 ± 108 (130% WHC). The magnitude of N2 emissions for irrigated cotton was estimated to be in the range of 24 ± 9 to 175 ± 65kg-N ha−1season−1, while emissions of NO were only of minor importance (between 0.1 to 0.7kg-N ha−1 season−1). The findings demonstrate that for irrigated dryland soils in the Aral Sera Basin, denitrification is a major pathway of
N-loss and that substantial amounts of N-fertilizer are lost as N2 to the atmosphere for irrigated dryland soils.
Plant and Soil 04/2012; 314(1):273-283. · 2.73 Impact Factor
Plant and Soil 04/2012; 340(1):1-6. · 2.73 Impact Factor
ABSTRACT: Combined measurements of nitrification activity and N2O emissions were performed in a lowland and a montane tropical rainforest ecosystem in NE-Australia over a 18months period
from October 2001 until May 2003. At both sites gross nitrification rates, measured by the BaPS technique, showed a strong
seasonal pattern with significantly higher rates of gross nitrification during wet season conditions. Nitrification rates
at the montane site (1.48 ± 0.24–18.75 ± 2.38mg N kg−1 day−1) were found to be significantly higher than at the lowland site (1.65 ± 0.21–4.54 ± 0.27mg N kg−1 day−1). The relationship between soil moisture and gross nitrification rates could be described best by O’Neill functions having
a soil moisture optimum of nitrification at app. 65% WFPS. At the lowland site, for which continuous measurements of N2O emissions were available, nitrification was positively correlated with N2O emission. Nitrification contributed significantly to N2O formation during dry season (app.85%) but less (app. 30%) during wet season conditions. In average 0.19‰ of the N metabolized
by nitrification was released as N2O. The N2O fraction loss for nitrification was positively correlated with changes in soil moisture and varied slightly between 0.15
and 0.22‰. Our results demonstrate that combined N2O emission and microbial N turnover studies covering prolonged observation periods are needed to clarify and quantify the
role of the microbial processes nitrification and denitrification for annual N2O emissions from soils of terrestrial ecosystems.
Plant and Soil 04/2012; 309(1):105-117. · 2.73 Impact Factor
ABSTRACT: Plant-microbe interactions are crucial regulators of belowground nitrogen cycling in terrestrial ecosystems. However, such
interactions have mostly been excluded from experimental setups for the investigation of gross inorganic N fluxes and N partitioning
to plants and microorganisms. Ungulate grazing is likely to feed back on soil N fluxes, and hence it is of special importance
to simultaneously investigate grazing effects on both plant and microbial N fluxes in intact plant-soil systems, where plant-microbe
interactions persist during the experimental incubation. Based on the homogenous 15NH4+ labelling of intact plant-soil monoliths we investigated how various stocking rates (0, 2.35, 4.8 and 7.85 sheep ha−1 grazing season−1) in steppe of Inner Mongolia feedback on gross rates of N mineralization and short-term inorganic N partitioning between
plant, microbial and soil N pools. Our results showed that the effect of grazing on gross N mineralization was non-uniform.
At low stocking rate gross N mineralization tended to decrease but increased with higher grazing pressure. Hence, there was
no significant correlation between stocking rate and gross N mineralization across the investigated grazing intensities. Grazing
decreased 15N recovery both in plant and microbial N pools but strongly promoted NO3− accumulation in the soil and thus negatively affected potential ecosystem N retention. This appeared to be closely related
to the grazing-induced decline in easily degradable soil C availability at increasing stocking rate.
KeywordsSteppe–Grazing–N mineralization–Microbial biomass–Plant-microbe competition–Nitrate–Plant N uptake–Intact plant–soil system
Plant and Soil 04/2012; 340(1):127-139. · 2.73 Impact Factor
ABSTRACT: Eurasian steppe ecosystems are nitrogen-limited and suffer additionally from high grazing intensities in many areas. Soil
surface-bound cyanobacteria are able to fix nitrogen and can be the major source of plant available nitrogen in such ecosystems.
In this study, the abundance and dinitrogen fixation capacity of the most common soil surface-bound microbial and lichen species
were determined at an ungrazed, a winter-grazed, and a heavily grazed steppe site in the Xilin River catchment, Inner Mongolia,
People’s Republic of China. The microorganisms were identified as Nostoc spec. and the lichen species as Xanthoparmelia camtschadalis (Ach.) Hale by a combination of classical light microscopy, confocal laser scanning microscopy and molecular analysis of
the internal transcribed spacer (ITS1) region of ribosomal RNA. Both species were found exclusively at grazed steppe sites,
with a clear difference in abundance depending on the grazing intensity. At the winter-grazed site, Nostoc was more abundant than Xanthoparmelia; for the heavily grazed site, the opposite was found. N2 fixation was quantified with both the acetylene reduction method and 15N2 incubation. Cyanobacterial colonies of Nostoc fixed N2 vigorously, whereas X. camtschadalis did not at all. The fraction of nitrogen derived from the fixation of molecular nitrogen in Nostoc was 73%, calculated from 15N natural abundance measurements of Nostoc with X. camtschadalis as reference. The conservatively calculated N2 uptake by Nostoc was 0.030–0.033kg N ha−1 for the heavily grazed site and 0.080–0.087kg N ha−1 for the winter-grazed site for the growing seasons of 2004 and 2005, respectively. Together with previous findings, this
study demonstrates that N2 fixation by Nostoc can potentially replace significant amounts, if not all, of the nitrogen lost in the form of N2O and NO soil emissions in this steppe ecosystem.
Biology and Fertility of Soils 04/2012; 45(7):679-690. · 2.32 Impact Factor
ABSTRACT: Organic matter addition is thought to be an important regulator of nitrous oxide (N2O) emissions from croplands. Contradictory effects, however, were reported in previous studies. To investigate the effects
of crop residue management on N2O emissions from rice-wheat rotation ecosystems, we conducted field experiments at three sites (Suzhou, Wuxi and Jiangdu)
in the Yangtze River Delta, using static chamber and gas chromatography methods. Our data show that N2O emissions throughout the rice season from plots treated with wheat straw application at a high rate (WS) prior to rice transplanting
(1.1–2.0kg N ha−1) were significantly lower (P < 0.05) than those from the control plots without organic matter addition or added with wheat straw at a moderate rate (1.6–2.9kg
N ha−1). Furthermore, the WS treatments had a residual inhibitory effect on N2O emissions in the following non-rice season, which consistently resulted in significantly lower emissions (P < 0.05) compared to the control treatments (2.2–3.1 vs. 3.9–5.6kg N ha−1). In comparison to the control treatments, the WS treatments reduced both the seasonal and annual direct emission factors
of the applied nitrogen (EFd) by 50–68% (mean: 57%). The addition of compost (aerobically composted rice or wheat straw harvested in the last rotation)
reduced the seasonal and annual EFds by 29–32%. Over the entire rice-wheat rotation cycle, annual N2O emissions from the fertilized fields at the three sites ranged from 3.3 ± 0.3 to 16.8 ± 0.6kg N ha−1, with a coefficient of variation (CV) of 61%. Similarly, the EFds during the rice-wheat rotation cycle ranged from 0.4% to 2.5%, with a CV of 67%. These high spatial variations might have
been related to: variations in soil properties, such as texture and soil organic carbon; management practices, such as straw
treatments (i.e., compost versus fresh straw) and weather conditions, such as precipitation and rainfall distribution. Our
results indicate that the incorporation of fresh wheat straw at a high rate during the rice season is an effective management
practice for the mitigation of N2O emissions in rice-wheat rotation systems. Whether this practice is also effective in reducing the overall global warming
potential of net N2O, CH4 and CO2 emissions needs to be seen through further studies.
Plant and Soil 04/2012; 327(1):315-330. · 2.73 Impact Factor
ABSTRACT: In order to identify the effects of land-use/cover types, soil types and soil properties on the soil-atmosphere exchange of
greenhouse gases (GHG) in semiarid grasslands as well as provide a reliable estimate of the midsummer GHG budget, nitrous
oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes of soil cores from 30 representative sites were determined in the upper Xilin River catchment in Inner Mongolia.
The soil N2O emissions across all of the investigated sites ranged from 0.18 to 21.8μg N m-2h-1, with a mean of 3.4μg N m-2h-1 and a coefficient of variation (CV, which is given as a percentage ratio of one standard deviation to the mean) as large
as 130%. CH4 fluxes ranged from -88.6 to 2,782.8μg C m-2h-1 (with a CV of 849%). Net CH4 emissions were only observed from cores taken from a marshland site, whereas all of the other 29 investigated sites showed
net CH4 uptake (mean: -33.3 μgC m-2h-1). CO2 emissions from all sites ranged from 3.6 to 109.3mg C m-2h-1, with a mean value of 37.4mg C m-2h-1 and a CV of 66%. Soil moisture primarily and positively regulated the spatial variability in N2O and CO2 emissions (R2 = 0.15–0.28, P < 0.05). The spatial variation of N2O emissions was also influenced by soil inorganic N contents (P < 0.05). By simply up-scaling the site measurements by the various land-use/cover types to the entire catchment area (3,900km2), the fluxes of N2O, CH4 and CO2 at the time of sampling (mid-summer 2007) were estimated at 29 t CO2-C-eq d-1, -26 t CO2-C-eq d-1 and 3,223 t C d-1, respectively. This suggests that, in terms of assessing the spatial variability of total GHG fluxes from the soils at a
semiarid catchment/region, intensive studies may focus on CO2 exchange, which is dominating the global warming potential of midsummer soil-atmosphere GHG fluxes. In addition, average
GHG fluxes in midsummer, weighted by the areal extent of these land-use/cover types in the region, were approximately -30.0μg
C m-2h-1 for CH4, 2.4μg N m-2h-1 for N2O and 34.5mg C m-2h-1 for CO2.
KeywordsGHG fluxes-Land-use/cover-Semi-arid grassland-Xilin River catchment
Plant and Soil 04/2012; 331(1):341-359. · 2.73 Impact Factor
ABSTRACT: The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0±0.1SEμgNm−2h−1. Fluxes of N2O increased from <5μgNm−2h−1 during dry season conditions to up to 24.5μgNm−2h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3±0.7SEμgNm−2h−1 and 4.1±0.5SEμgNm−2h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5±0.3SEμgCm−2h−1), slightly lower at the SF site (−25.6±1.3SEμgCm−2h−1) and lowest for the RP site (−5.7±0.5SEμgCm−2h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2month measurement period, CO2 emissions at the PF site increased significantly from 50mgCm−2h−1 up to 100mgCm−2h−1 (mean value 68.8±0.8SEmgCm−2h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0±1.8SEmgCm−2h−1 (SF) and 34.9±1.1SEmgCm−2h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified.
Plant and Soil 04/2012; 289(1):335-353. · 2.73 Impact Factor
ABSTRACT: Denitrification, the anaerobic reduction of nitrogen oxides to nitrogenous gases, is an extremely challenging process to measure
and model. Much of this challenge arises from the fact that small areas (hotspots) and brief periods (hot moments) frequently
account for a high percentage of the denitrification activity that occurs in both terrestrial and aquatic ecosystems. In this
paper, we describe the prospects for incorporating hotspot and hot moment phenomena into denitrification models in terrestrial
soils, the interface between terrestrial and aquatic ecosystems, and in aquatic ecosystems. Our analysis suggests that while
our data needs are strongest for hot moments, the greatest modeling challenges are for hotspots. Given the increasing availability
of high temporal frequency climate data, models are promising tools for evaluating the importance of hot moments such as freeze-thaw
cycles and drying/rewetting events. Spatial hotspots are less tractable due to our inability to get high resolution spatial
approximations of denitrification drivers such as carbon substrate. Investigators need to consider the types of hotspots and
hot moments that might be occurring at small, medium, and large spatial scales in the particular ecosystem type they are working
in before starting a study or developing a new model. New experimental design and heterogeneity quantification tools can then
be applied from the outset and will result in better quantification and more robust and widely applicable denitrification
Biogeochemistry 04/2012; 93(1):49-77. · 3.07 Impact Factor
ABSTRACT: Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1mgNkg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60μgN2O-Nm−2h−1, equivalent to 0.03–0.14kgN2O-Nha−1y−1, and were considerably lower than previously reported for the same region. NO
flux rates ranged between 0.16 and 0.48μgNO
-Nm−2h−1, equivalent to 0.01–0.04kgNO
-Nha−1y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance.
Ecosystems 04/2012; 10(4):623-634. · 3.49 Impact Factor
ABSTRACT: This study provides a combined dataset on N loss pathways and fluxes from sloping cropland in the purple soil area, southwestern China. A lysimeter experiment was conducted to quantify nitrate leaching (May 2004-May 2010) and N(2)O emission (May 2009-May 2010) losses. Nitrate leaching was the dominant N loss pathway and annual leaching fluxes ranged from 19.2 to 53.4 kg N ha(-1), with significant differences between individual observation years (P < 0.05). Direct N(2)O emissions due to N fertilizer use were 1.72 ± 0.34 kg N ha(-1) yr(-1), which corresponds to an emission factor of 0.58 ± 0.12%. However, indirect N(2)O emissions caused by nitrate leaching and surface runoff N losses, may contribute another 0.15-0.42 kg N ha(-1) yr(-1). Our study shows that nitrate leaching lowered direct N(2)O emissions, highlighting the importance for a better understanding of the tradeoff between direct and indirect N(2)O emissions for the development of meaningful N(2)O emission strategies.
Environmental pollution (Barking, Essex: 1987) 03/2012; 162:361-8. · 3.43 Impact Factor
ABSTRACT: Simulations with the process oriented Forest-DNDC model showed reasonable to good agreement with observations of soil water contents of different soil layers, annual amounts of seepage water and approximated rates of nitrate leaching at 79 sites across Germany. Following site evaluation, Forest-DNDC was coupled to a GIS to assess nitrate leaching from German forest ecosystems for the year 2000. At national scale leaching rates varied in a range of 0->80 kg NO(3)-N ha(-1) yr(-1) (mean 5.5 kg NO(3)-N ha(-1) yr(-1)). A comparison of regional simulations with the results of a nitrate inventory study for Bavaria showed that measured and simulated percentages for different nitrate leaching classes (0-5 kg N ha(-1) yr(-1):66% vs. 74%, 5-15 kg N ha(-1) yr(-1):20% vs. 20%, >15 kg N ha(-1) yr(-1):14% vs. 6%) were in good agreement. Mean nitrate concentrations in seepage water ranged between 0 and 23 mg NO(3)-N l(-1).
Environmental pollution (Barking, Essex: 1987) 07/2011; 159(11):3204-14. · 3.43 Impact Factor
ABSTRACT: Based on multi-year measurements of CH(4) exchange in sub-daily resolution we show that clear-cutting of a forest in Southern Germany increased soil temperature and moisture and decreased CH(4) uptake. CH(4) uptake in the first year after clear-cutting (-4.5 ± 0.2 μg C m(-2) h(-1)) was three times lower than during the pre-harvest period (-14.2 ± 1.3 μg C m(-2) h(-1)). In contrast, selective cutting did not significantly reduce CH(4) uptake. Annual mean uptake rates were -1.18 kg C ha(-1) yr(-1) (spruce control), -1.16 kg C ha(-1) yr(-1) (selective cut site) and -0.44 kg C ha(-1) yr(-1) (clear-cut site), respectively. Substantial seasonal and inter-annual variations in CH(4) fluxes were observed as a result of significant variability of weather conditions, demonstrating the need for long-term measurements. Our findings imply that a stepwise selective cutting instead of clear-cutting may contribute to mitigating global warming by maintaining a high CH(4) uptake capacity of the soil.
Environmental pollution (Barking, Essex: 1987) 07/2011; 159(10):2467-75. · 3.43 Impact Factor
ABSTRACT: Here we describe a newly designed system with three stand-alone working incubation vessels for simultaneous measurements of N(2), N(2)O, NO, and CO(2) emissions from soil. Due to the use of a new micro thermal conductivity detector and the redesign of vessels and gas sampling a so-far unmatched sensitivity (0.23 μg N(2)-N h(-1) kg(-1) ds or 8.1 μg N(2)-N m(-2) h(-1)) for detecting N(2) gas emissions and repeatability of experiments could be achieved. We further tested different incubation methods to improve the quantification of N(2) emission via denitrification following the initialization of soil anaerobiosis. The best results with regard to the establishment of a full N balance (i.e., the changes in mineral N content being offset by simultaneous emission of N gases) were obtained when the anaerobic soil incubation at 25 °C was preceded by soil gas exchange under aerobic conditions at a lower incubation temperature. The ratios of N and C gas emission changed very dynamically following the initialization of anaerobiosis. For soil NO(3)(-) contents of 50 mg N kg(-1) dry soil (ds) and dissolved organic carbon (DOC) concentrations of approximately 300 mg C kg(-1) ds, the cumulative emissions of N(2), N(2)O, and NO were 24.3 ± 0.1, 12.6 ± 0.4, and 10.1 ± 0.3 mg N kg(-1) ds, respectively. Thus, N gas emissions accounted (on average) for 46.2% (N(2)), 24.0% (N(2)O), and 19.2% (NO) of the observed changes in soil NO(3)(-). The maximum N(2) emission reached 1200 μg N h(-1) kg(-1) ds, whereas the peak emissions of N(2)O and NO were lower by a factor of 2-3. The overall N(2):N(2)O and NO:N(2)O molar ratios were 1.6-10.0 and 1.6-2.3, respectively. The measurement system provides a reliable tool for studying denitrification in soil because it offers insights into the dynamics and magnitude of gaseous N emissions due to denitrification under various incubation conditions.
Environmental Science & Technology 06/2011; 45(14):6066-72. · 4.80 Impact Factor
ABSTRACT: Overgrazing-induced degradation of temperate semiarid steppes may affect the soil sink for atmospheric methane (CH4). However, previous studies have primarily focused on the growing season and on single grazing patterns. Thus, the response of annual CH4 uptake by steppes compared with various grazing practices is uncertain. In this study, we investigated the effects of grazing on the annual CH4 uptake by two typical Eurasian semiarid steppes (the Stipa grandis steppe and the Leymus chinensis steppe) located in Inner Mongolia, China. The CH4 fluxes were measured year-round using static chambers and gas chromatography at 12 field sites that differed primarily in grazing intensities. Our results indicated that steppe soils were CH4 sinks throughout the year. The annual CH4 uptake correlated with stocking rates, whereas the seasonality of CH4 uptake was primarily dominated by temperature. The annual CH4 uptake at all sites averaged 3.7±0.7 kg C ha−1 yr−1 (range: 2.3–4.5), where approximately 35% (range: 23–40%) occurred during the nongrowing season. Light-to-moderate grazing (stocking rate≤1 sheep ha−1 yr−1) did not significantly change the annual CH4 uptake compared with ungrazed steppes, but heavy grazing reduced annual CH4 uptake significantly (by 24–31%, P<0.05). These findings imply that easing the pressure of heavily grazed steppes (e.g. moving to light or moderate stocking rates) would help restore steppe soil sinks for atmospheric CH4. The empirical equations based on the significant relationships between annual CH4 uptake and stocking rates, aboveground plant biomass and topsoil air permeability (P<0.01) could provide simple approaches for the estimation of regional CH4 uptake by temperate semiarid steppes.
Global Change Biology 05/2011; 17(9):2803 - 2816. · 6.86 Impact Factor
Ecological Informatics. 01/2011; 6:333-340.