Search

Soil respiration and photosynthesis are the two largest carbon dioxide ( CO2) fluxes between terrestrial ecosystems and the atmosphere and, therefore, the dominant processes influencing the oxygen isotopic composition of atmospheric CO2. The characterization of temporal and spatial variations of plant and soil-related fluxes of different oxygen isotopologues of CO2 ( 12C16O2; 12C16O18O) is relevant to constraining the global carbon budget. The oxygen isotopic composition of soil-respired CO2 is controlled by its release rate, the degree of isotopic equilibrium with soil water and the diffusional transport of CO2. The hypothesis of this study was that, as well as soil moisture, the soil particle size, the presence of an organic litter layer and the enzyme carbonic anhydrase ( CA) would have a significant impact on the oxygen isotopic composition of soil-released CO2. We tested this hypothesis with soil microcosm experiments on columns of medium and fine sand. Soil water content and soil texture influenced the isotopic composition of soil-released CO2 significantly. A litter layer had a significant effect on the isotopic composition of water vapour but not on CO2 released from soil. In the absence of CA, oxygen isotope equilibration between the CO2 invasion flux and soil water was insignificant, whereas in the presence of CA about 55% of the CO2 invading the soil exchanged oxygen isotopes with soil water. Our findings highlight the importance of small-scale variability of soil attributes for the oxygen isotopic composition of soil-released CO2 as well as the strong impact of CA activity in soils. [ABSTRACT FROM AUTHOR]

Besides agricultural soils, temperate forest soils have been identified as significant sources of or sinks for important atmospheric trace gases (N2O, NO, CH4, and CO2). Although the number of studies for this ecosystem type increased more than tenfold during the last decade, studies covering an entire year and spanning more than 1-2 years remained scarce. This study reports the results of continuous measurements of soil-atmosphere C- and N-gas exchange with high temporal resolution carried out since 1994 at the Höglwald Forest spruce site, an experimental field station in Southern Germany. Annual soil N2O, NO and CO2 emissions and CH4 uptake (1994-2010) varied in a range of 0.2- 3.0 kgN2O-N ha-1 yr-1, 6.4-11.4 kg NO-N ha-1 yr-1, 7.0- 9.2 t CO2-C ha-1 yr-1, and 0.9-3.5 kgCH4-C ha-1 yr-1, respectively. The observed high fluxes of N-trace gases are most likely a consequence of high rates of atmospheric nitrogen deposition (>20 kgNha-1 yr-1) of NH3 and NOx to our site. For N2O, cumulative annual emissions were ≥0.8 kgN2O-N ha-1 yr-1 in years with freeze-thaw events (5 out 14 of years). This shows that long-term, multi-year measurements are needed to obtain reliable estimates of N2O fluxes for a given ecosystem. Cumulative values of soil respiratory CO2 fluxes tended to be highest in years with prolonged freezing periods, i.e. years with below average annual mean soil temperatures and high N2O emissions (e.g. the years 1996 and 2006). Furthermore, based on our unique database on trace gas fluxes we analyzed if soil temperature, soil moisture measurements can be used to approximate trace gas fluxes at daily, weekly, monthly, or annual scale. Our analysis shows that simple-to-measure environmental drivers such as soil temperature or soil moisture are suitable to approximate fluxes of NO and CO2 at weekly and monthly resolution reasonably well (accounting for up to 59% of the variance). However, for CH4 we so far failed to find meaningful correlations, and also for N2O the predictive power is rather low. This is most likely due to the complexity of involved processes and counteracting effects of soil moisture and temperature, specifically with regard to N2O production and consumption by denitrification and microbial community dynamics. At monthly scale, including information on gross primary production (CO2, NO), and N deposition (N2O), increased significantly the explanatory power of the obtained empirical regressions (CO2: r2 = 0.8; NO: r² = 0.67; N2O, all data: r² = 0.5; N2O, with exclusion of freeze-thaw periods: r² = 0.65). [ABSTRACT FROM AUTHOR]

Climate change and air pollution, interact with altering forest management and landuse change to produce short and long-term changes to forest in Europe. The impact of these changes on the forest greenhouse gas (GHG) balance is currently difficult to predict. To improve the mechanistic understanding of the ongoing changes, we studied the response of GHG (N2O, CH4) exchange from forest soils at twelve experimental or natural gradient forest sites, representing anticipated future forest change. The experimental manipulations one or more per site included nitrogen (N) addition (4 sites), changes of climate (temperature, 1 site; precipitation, 2 sites), soil hydrology (3 sites), harvest intensity (1 site), wood ash fertilization (1 site), pH gradient in peat (1 site) and afforestation of cropland (1 site). In most of the investigated treatments N2O emissions increased by 7±3 (range 0-30) µg N2O-N m-2 h-1 across all treatments on mineral soils, but by up to 10 times the mineral soil maximum on an acidic organic soil. Soil moisture together with mineral soil C/N ratio and pH were found to significantly influence N2O emissions across all treatments. Emissions increased with N availability and decreased with soil C/N ratio, especially in interaction with increased soil moisture. High pH reduced the formation of N2O, even under otherwise favourable soil conditions. Oxidation (uptake) of CH4 was reduced from 16±2 to 4±6 µg CH4-C m-2 h-1 by the investigated treatments. The CH4 exchange was significantly influenced by soil moisture and soil C/N ratio across all treatments, and CH4 emissions occurred only in wet or water-saturated conditions. For most of the investigated forest manipulations or natural gradients, the response of both N2O and CH4 fluxes was towards reducing the overall GHG forest sink. The most resilient forests were dry Mediterranean forests, as well as forests with high soil C/N ratio or high soil pH. Mitigation strategies may focus on (I) sustainable management of wet forest areas and forested peat lands, (ii) continuous forest cover management, (iii) reducing atmospheric N input and, thus, N availability, and (iv) improving neutralisation capacity of acid soils (e.g. wood ash application). [ABSTRACT FROM AUTHOR]

Besides agricultural soils, temperate forest soils have been identified as significant sources of or sinks for important atmospheric trace gases (N2O, NO, CH4, and CO2). Although the number of studies for this ecosystem type increased more than tenfold during the last decade, studies covering an entire year and spanning more than 1-2 yr remained scarce. This study reports the results of continuous measurements of soil-atmosphere C- and N-gas exchange with high temporal resolution carried out since 1994 at the Höglwald Forest spruce site, an experimental field station in Southern Germany. Annual soil N2O emission, NO emission, CH4 uptake, and CO2 emission (1994-2010) varied in a range of 0.2-3.2 kg N2O-N ha-1 yr-1, 6.4-11.4 kg NO-N ha-1 yr-1, 0.9-3.5 kg CH4-C ha-1 yr-1, and 7.0-9.2 t CO2-C ha-1 yr-1, respectively. The observed high fluxes of N-trace gases are most likely a consequence of high rates of atmospheric nitrogen deposition (> 20 kg N ha-1 yr-1) of NH3 and NOx to our site. For N2O cumulative annual emissions were > 0.8 kg N2O-N ha-1 yr-1 high in years with freeze-thaw events (5 out 14 yr). This shows that long-term, multi-year measurements are needed to obtain reliable estimates of N2O fluxes for a given ecosystem. Cumulative values of soil respiratory CO2 fluxes were highest in years with prolonged freezing periods e.g. the years 1996 and 2006, i.e. years with below average annual mean soil temperatures and high N2O emissions. The results indicate that long freezing periods may even drive increased CO2 fluxes not only during soil thawing but also throughout the following growing season. Furthermore, based on our unique database on GHGs we analyzed if soil temperature, soil moisture, or precipitation measurements can be used to approximate GHGs at weekly, monthly, or annual scale. Our analysis shows that simple-to-measure environmental drivers such as soil temperature or soil moisture are suitable to approximate fluxes of NO and CO2 in weekly and monthly scales with a reasonable uncertainty (accounting for up to 80% of the variance). However, for N2O and CH4 we so far failed to find meaningful correlations and, thus, to provide simple regression models to estimate fluxes. This is most likely due to the complexity of involved processes and counteracting effects of soil moisture and temperature, specifically with regard to N2O production and consumption by denitrification and microbial community dynamics. [ABSTRACT FROM AUTHOR]

Understanding environmental and physiological controls of the variations in δC of CO respired (δC) from different compartments of an ecosystem is important for separation of CO fluxes and to assess coupling between assimilation and respiration. In a wheat field, over 3 days we characterised the temporal dynamics of δC from shoots and roots, from the soil and from the whole agroecosystem. To evaluate the basis of potential variations in δC, we also measured δC in different organic matter pools, as well as meteorological and gas exchange parameters. We observed strong diel variations up to ca. 6% in shoot, root and soil δC, but not in δC of the putative organic substrates for respiration, which varied by not more than ca. 1% within 24 h. Whole ecosystem-respired CO was least depleted in C in the afternoon and most negative in the early morning. We assume that temporally variable respiratory carbon isotope fractionation and changes in fluxes through metabolic pathways, rather than photosynthetic carbon isotope fractionation, governs the δC of respired CO at the diel scale, and thus provides insights into the metabolic processes related to respiration under field conditions. [ABSTRACT FROM AUTHOR]

Fluxes of greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured during a two month campaign at a drained peatland forest in Finland by the eddy covariance (EC) technique (CO2 and N2O), and automatic and manual chambers (CO2, CH4 and N2O). In addition, GHG concentrations and soil parameters (mineral nitrogen, temperature, moisture content) in the peat profile were measured. The aim of the measurement campaign was to quantify the GHG fluxes before, during and after thawing of the peat soil, a time period with potentially high GHG fluxes, and to compare different flux measurement methods. The forest was a net CO2 sink during the two months and the fluxes of CO2 dominated the GHG exchange. The peat soil was a small sink of atmospheric CH4 but a small source of N2O. Both CH4 oxidation and N2O production took place in the top-soil whereas CH4 was produced in the deeper layers of the peat. During the thawing of the peat distinct peaks in CO2 and N2O emissions were observed. The CO2 peak followed tightly the increase in soil temperature, whereas the N2O peak occurred with an approx. one week delay after soil thawing. CH4 fluxes did not respond to the thawing of the peat soil. The CO2 and N2O emission peaks were not captured by the manual chambers and hence we conclude that automatic chamber measurements or EC are necessary to quantify fluxes during peak emission periods. Sub-canopy EC measurements and chamber-based fluxes of CO2 and N2O were comparable, although the fluxes of N2O measured by EC were close to the detection limit of the EC system. We conclude that if fluxes are high enough, i.e. greater than 5-10 μgNm-2 h-1, the EC method is a good alternative to measure N2O and CO2 fluxes at ecosystem scale, thereby minimizing problems with chamber enclosures and spatial representativeness of the measurements. [ABSTRACT FROM AUTHOR]

The aim of the present work was to estimate the contribution of different point and diffuse sources to the regional N2O emission strength of steppe in the Xilin river catchment, Inner Mongolia, People’s Republic of China. Transect studies showed that the topographic effect on N2O emissions from upland soils was negligible and that upland steppe is only a very weak net source of N2O during the growing season (0.8 ± 0.4 μg N2O–N m−2 h−1). Slightly higher emissions were found for riparian areas (1.8 ± 0.3 μg N2O–N m−2 h−1), which cover ∼4% of the landscape. Even faeces or urine additions stimulated N2O emissions from steppe soils only weakly (<2.5 μg N2O–N m−2 h−1 for a 5 days period). Due to low moisture contents, N2O emissions from dung heaps were also rather low (6.2 ± 0.8 μg N2O–N kg−1 dry matter h−1). In contrast, three orders of magnitude higher N2O emissions were found at sheepfolds (2.45 mg N2O–N m−2 h−1 on average). By calculating N2O emissions on a landscape scale, we show that point sources, and especially sheepfolds, become the dominating regional N2O source during the growing season if stocking rates are >1 sheep ha−1. Our results indicate that the common grazing management in the Xilin river region leads to a translocation of nitrogen from large source areas towards defined spots. This finding is further supported by measurements of NH3 concentrations at different sites. Since most of the nitrogen accumulated in these hot spots is finally lost through burning of the dried excrements by the farmers for heating and cooking purposes, the ecosystem faces a significant human perturbation of regional N cycling, which may contribute to an accelerated degradation of steppe in the Xilin river region. [ABSTRACT FROM AUTHOR]

During two intensive field campaigns in summer and autumn 2004 nitrogen (N2O, NO/NO2) and carbon (CO2, CH4) trace gas exchange between soil and the atmosphere was measured in a sessile oak ( Quercus petraea (Matt.) Liebl.) forest in Hungary. The climate can be described as continental temperate. Fluxes were measured with a fully automatic measuring system allowing for high temporal resolution. Mean N2O emission rates were 1.5 µg N m−2 h−1 in summer and 3.4 µg N m−2 h−1 in autumn, respectively. Also mean NO emission rates were higher in autumn (8.4 µg N m−2 h−1) as compared to summer (6.0 µg N m−2 h−1). However, as NO2 deposition rates continuously exceeded NO emission rates (−9.7 µg N m−2 h−1 in summer and −18.3 µg N m−2 h−1 in autumn), the forest soil always acted as a net NO x sink. The mean value of CO2 fluxes showed only little seasonal differences between summer (81.1 mg C m−2 h−1) and autumn (74.2 mg C m−2 h−1) measurements, likewise CH4uptake (summer: −52.6 µg C m−2 h−1; autumn: −56.5 µg C m−2 h−1). In addition, the microbial soil processes net/gross N mineralization, net/gross nitrification and heterotrophic soil respiration as well as inorganic soil nitrogen concentrations and N2O/CH4 soil air concentrations in different soil depths were determined. The respiratory quotient (ΔCO2 resp ΔO) for the uppermost mineral soil, which is needed for the calculation of gross nitrification via the Barometric Process Separation (BaPS) technique, was 0.8978 ± 0.008. The mean value of gross nitrification rates showed only little seasonal differences between summer (0.99 µg N kg−1 SDW d−1) and autumn measurements (0.89 µg N kg−1 SDW d−1). Gross rates of N mineralization were highest in the organic layer (20.1–137.9 µg N kg−1 SDW d−1) and significantly lower in the uppermost mineral layer (1.3–2.9 µg N kg−1 SDW d−1). Only for the organic layer seasonality in gross N mineralization rates could be demonstrated, with highest mean values in autumn, most likely caused by fresh litter decomposition. Gross mineralization rates of the organic layer were positively correlated with N2O emissions and negatively correlated with CH4 uptake, whereas soil CO2 emissions were positively correlated with heterotrophic respiration in the uppermost mineral soil layer. The most important abiotic factor influencing C and N trace gas fluxes was soil moisture, while the influence of soil temperature on trace gas exchange rates was high only in autumn. [ABSTRACT FROM AUTHOR]

Soil emissions of NO and N2O were measured continuously at high frequency for more than one year at 15 European forest sites as part of the EU-funded project NOFRETETE. The locations represent different forest types (coniferous/deciduous) and different nitrogen loads. Geographically they range from Finland in the north to Italy in the south and from Hungary in the east to Scotland in the west. The highest NO emissions were observed from coniferous forests, whereas the lowest NO emissions were observed from deciduous forests. The NO emissions from coniferous forests were highly correlated with N-deposition. The site with the highest average annual emission (82 µg NO-N m-2 h-1) was a spruce forest in South-Germany (Höglwald) receiving an annual N-deposition of 2.9 gm-2. NO emissions close to the detection limit were observed from a pine forest in Finland where the N-deposition was 0.2 gN m-2 y-1. No significant correlation between N2O emission and N-deposition was found. The highest average annual N2O emission (20 µgN2O-Nm-2 h-1) was found in an oak forest in the Mátra mountains (Hungary) receiving an annual N-deposition of 1.6 g m-2. N2O emission was significantly negatively correlated with the C/N ratio. The difference in N-oxide emissions from soils of coniferous and deciduous forests may partly be explained by differences in N-deposition rates and partly by difference in characteristics of the litter layer and soil. NO was mainly derived from nitrification whereas N2O was mainly derived from denitrification. In general, soil moisture is lower at coniferous sites (at least during spring time) and the litter layer of coniferous forests is thick and well aerated favouring nitrification and thus release of NO. Conversely, the higher rates of denitrification in deciduous forests due to a compact and moist litter layer lead to N2O production and NO consumption in the soil. The two factors soil moisture and soil temperature are often explaining most of the temporal variation within a site. When comparing annual emissions on a regional scale, however, factors such as nitrogen deposition and forest and soil type become much more important. [ABSTRACT FROM AUTHOR]

This study provides for the first time data on the stratification of NO and N2O production with soil depth under aerobic and anaerobic incubation conditions for different temperate forest sites in Germany (spruce, beech, clear-cut) and the Netherlands (Douglas fir). Results show that the NO and N2O production activity is highest in the forest floor and decreases exponentially with increasing soil depth. Under anaerobic incubation conditions NO and N2O production was in all soil layers up to 2-3 orders of magnitude higher then under aerobic incubation conditions. Furthermore, significant differences between sites could be demonstrated with respect to the magnitude or predominance of NO and N2O production. These were driven by stand properties (beech or spruce) or management (clear-cut versus control). With regard to CH4 the most striking result was the lack of CH4 uptake activity in soil samples taken from the Dutch Douglas fir site at Speulderbos, which is most likely a consequence of chronically high rates of atmospheric N deposition. In addition, we could also demonstrate that CH4 fluxes at the soil surface are obviously the result of simultaneously occurring uptake and production processes, since even under aerobic conditions a net production of CH4 in forest floor samples was found. The provided dataset will be very useful for the development and testing of process oriented models, since for the first time activity data stratified for several soil layers for N2O, NO, and CH4 production/oxidation activity for forest soils are provided. [ABSTRACT FROM AUTHOR]

The article discusses a study on nitrous oxide and nitric oxide emissions from forest soils in Europe. It emphasizes the importance of process-oriented models connected to a geographic information system used in calculating nitrogen-trace gas emissions from soils. It also outlines the materials and methodologies used in the study. Information on soil is being obtained from the Soil Geographical Data Base of Europe.

Trace gas exchange of N2O, NO/NO2 and CH4 between soil and the atmosphere was measured in a typical Mediterranean pine (Pinus pinaster) forest during two intensive field campaigns in spring and autumn 2003. Furthermore, gross and net turnover rates of N mineralization and nitrification as well as soil profiles of N2O and CH4 concentrations were determined. For both seasons a weak but significant N2O uptake from the atmosphere into the soil was observed. During the unusually dry and hot spring mean N2O uptake was -4.32 µg N m-2 h-1, whereas during the wet and mild autumn mean N2O uptake was -7.8 µg N m-2 h-1. The observed N2O uptake into the soil was linked to the very low availability of inorganic nitrogen at the study site. Organic layer gross N mineralization decreased from 5.06 mg N kg-1 SDW d-1 in springtime to 2.68 mg N kg-1 SDW d-1 in autumn. Mean NO emission rates were significantly higher in springtime (9.9 µg N m-2 h-1) than in autumn (1.4 µg N m-2 h-1). A significant positive correlation between NO emission rates and gross N mineralization as well as nitrification rates was found. The negative correlation between NO emissions and soil moisture was explained with a stimulation of aerobic NO uptake under N limiting conditions. Since NO2 deposition was continuously higher than NO emission rates the examined forest soil did function as a net NOx sink. Observed mean net CH4 uptake rates were in spring significantly higher (-73.34 µg C m-2 h-1) than in autumn (-59.67 µg C m-2 h-1). Changes in CH4 uptake rates were strongly negatively correlated with changes in soil moisture. The N2O and CH4 concentrations in different soil depths revealed the organic layer and the upper 10 cm of mineral soil as the most important soil horizons for N2O and CH4 consumption. [ABSTRACT FROM AUTHOR]

The effects of five different tree species common in the temperate zone, i.e. beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), Norway spruce (Picea abies [L.] Karst), Japanese larch (Larix leptolepis [Sichold and Zucc.] Gordon) and mountain pine (Pinus mugo Turra), on soil respiration, gross N mineralization and gross nitrification rates were investigated. Soils were sampled in spring and summer 2002 at a forest trial in Western Jutland, Denmark, where pure stands of the five tree species of the same age were growing on the same soil. Soil respiration, gross rates of N mineralization and nitrification were significantly higher in the organic layers than in the Ah horizons for all tree species and both sampling dates. In summer (July), the highest rates of soil respiration, gross N mineralization and gross nitrification were found in the organic layer under spruce, followed by beech > larch > oak > pine. In spring (April), these rates were also higher under spruce compared to the other tree species, but were significantly lower than in summer. For the Ah horizons no clear seasonal trend was observed for any of the processes examined. A linear relationship between soil respiration and gross N mineralization (r²=0.77), gross N mineralization and gross nitrification rates (r²=0.72), and between soil respiration and gross nitrification (r²=0.81) was found. The results obtained underline the importance of considering the effect of forest type on soil C and N transformations. [ABSTRACT FROM AUTHOR]

Copyright of Oral & Maxillofacial Surgery is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of HNO is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Presents the authors' reply to comments on their study "Pure Stands of Temperate Forest Tree Species Modify Soil Respiration and N Turnover." Key findings of the study; Reply to remarks regarding the presentation of the data; Feasibility of a higher number of sampling dates.