Stable isotope discrimination during soil denitrification: Production and consumption of nitrous oxide

Measuring the stable isotope composition of nitrous oxide ( N(2)O) evolved from soil could improve our understanding of the relative contributions of the main microbial processes ( nitrification and denitrification) responsible for N(2)O formation in soil. However, interpretation of the isotopic data in N(2)O is complicated by the lack of knowledge of fractionation parameters by different microbial processes responsible for N(2)O production and consumption. Here we report isotopic enrichment for both nitrogen and oxygen isotopes in two stages of denitrification, N(2)O production and N(2)O reduction. We found that during both N(2)O production and reduction, enrichments were higher for oxygen than nitrogen. For both elements, enrichments were larger for N(2)O production stage than for N(2)O reduction. During gross N(2)O production, the ratio of delta(18)O- to-delta(15)N differed between soils, ranging from 1.6 to 2.7. By contrast, during N(2)O reduction, we observed a constant ratio of delta(18)O- to-delta(15)N with a value near 2.5. If general, this ratio could be used to estimate the proportion of N(2)O being reduced in the soil before escaping into the atmosphere. Because N(2)O- reductase enriches N(2)O in both isotopes, the global reduction of N(2)O consumption by soil may contribute to the globally observed isotopic depletion of atmospheric N(2)O

Tree species and moisture effects on soil sources of N2O: Quantifying contributions from nitrification and denitrification with O-18 isotopes

Nitrous oxide (N2O) is an important greenhouse gas and participates in the destruction of stratospheric ozone. Soil bacteria produce N2O through denitrification and nitrification, but these processes differ radically in substrate requirements and responses to the environment. Understanding the controls over N2O efflux from soils, and how N2O emissions may change with climate warming and altered precipitation, require quantifying the relative contributions from these groups of soil bacteria to the total N2O flux. Here we used ammonium nitrate (NH4NO3, including substrates for both processes) in which the nitrate has been enriched in the stable isotope of oxygen, O-18, to partition microbial sources of N2O, arguing that a molecule of N2O carrying the O-18 labeled will have been produced by denitrification. We compared the influences of six common tree species on the relative contributions of nitrification and denitrification to N2O flux from soils, using soils from the Siberian afforestation experiment. We also altered soil water content, to test whether denitrification becomes a dominant source of N2O when soil water content increases. Tree species altered the proportion of nitrifier and denitrifier-derived N2O. Wetter soils produced more N2O from denitrification, though the magnitude of this effect varied among tree species. This indicates that the roles of denitrification and nitrification vary with tree species, and, that tree species influence soil responses to increased water content

Forest Soil Carbon and Climate Changes

Forest soil carbon is an important component of the global carbon cycle, and the changes of its accumulation and decomposition, stabilization and destabilization directly affect the atmospheric CO2 concentration and global warming [...

Stable isotope discrimination during soil denitrification: Production and consumption of nitrous oxide

Measuring the stable isotope composition of nitrous oxide ( N(2)O) evolved from soil could improve our understanding of the relative contributions of the main microbial processes ( nitrification and denitrification) responsible for N(2)O formation in soil. However, interpretation of the isotopic data in N(2)O is complicated by the lack of knowledge of fractionation parameters by different microbial processes responsible for N(2)O production and consumption. Here we report isotopic enrichment for both nitrogen and oxygen isotopes in two stages of denitrification, N(2)O production and N(2)O reduction. We found that during both N(2)O production and reduction, enrichments were higher for oxygen than nitrogen. For both elements, enrichments were larger for N(2)O production stage than for N(2)O reduction. During gross N(2)O production, the ratio of delta(18)O- to-delta(15)N differed between soils, ranging from 1.6 to 2.7. By contrast, during N(2)O reduction, we observed a constant ratio of delta(18)O- to-delta(15)N with a value near 2.5. If general, this ratio could be used to estimate the proportion of N(2)O being reduced in the soil before escaping into the atmosphere. Because N(2)O- reductase enriches N(2)O in both isotopes, the global reduction of N(2)O consumption by soil may contribute to the globally observed isotopic depletion of atmospheric N(2)O

Tree species and moisture effects on soil sources of N 2

Nitrous oxide (N2O) is an important greenhouse gas and participates in the destruction of stratospheric ozone. Soil bacteria produce N2O through denitrification and nitrification, but these processes differ radically in substrate requirements and responses to the environment. Understanding the controls over N2O efflux from soils, and how N2O emissions may change with climate warming and altered precipitation, require quantifying the relative contributions from these groups of soil bacteria to the total N2O flux. Here we used ammonium nitrate (NH4NO3, including substrates for both processes) in which the nitrate has been enriched in the stable isotope of oxygen, O-18, to partition microbial sources of N2O, arguing that a molecule of N2O carrying the O-18 labeled will have been produced by denitrification. We compared the influences of six common tree species on the relative contributions of nitrification and denitrification to N2O flux from soils, using soils from the Siberian afforestation experiment. We also altered soil water content, to test whether denitrification becomes a dominant source of N2O when soil water content increases. Tree species altered the proportion of nitrifier and denitrifier-derived N2O. Wetter soils produced more N2O from denitrification, though the magnitude of this effect varied among tree species. This indicates that the roles of denitrification and nitrification vary with tree species, and, that tree species influence soil responses to increased water content

Age-Dependent Changes in Soil Respiration and Associated Parameters in Siberian Permafrost Larch Stands Affected by Wildfire

The observed high spatial variation in soil respiration (SR) and associated parameters emphasized the importance of SR heterogeneity at high latitudes and the involvement of many factors in its regulation, especially within fire-affected areas. The problem of estimating CO2 emissions during post-fire recovery in high-latitude ecosystems addresses the mutual influence of wildfires and climate change on the C cycle. Despite its importance, especially in permafrost regions because of their vulnerability, the mutual influence of these factors on CO2 dynamics has rarely been studied. Thus, we aimed to understand the dynamics of soil respiration (SR) in wildfire-affected larch recovery successions. We analyzed 16-year data (1995–2010) on SR and associated soil, biological, and environmental parameters obtained during several field studies in larch stands of different ages (0–276 years) in the Krasnoyarsk region (Russia). We observed a high variation in SR and related parameters among the study sites. SR varied from 1.77 ± 1.18 (mean ± SD) µmol CO2 m−2 s−1 in the 0–10-year-old group to 5.18 ± 2.70 µmol CO2 m−2 s−1 in the 150–276-year-old group. We found a significant increasing trend in SR in the 88–141-year old group during the study period, which was related to the significant decrease in soil water content due to the shortage of precipitation during the growing season. We observed a high spatial variation in SR, which was primarily regulated by biological and environmental factors. Different parameters were the main contributors to SR in each group, an SR was significantly affected by the inter-relationships between the studied parameters. The obtained results can be incorporated into the existing SR databases, which can allow their use in the construction and validation of C transport models as well as in monitoring global fluctuations in the C cycle in response to climate change

Correction to: Soil respiration patterns and rates at three Taiwanese forest plantations: dependence on elevation, temperature, precipitation, and litterfall

Abstract Unfortunately, the original article (Huang et al. 2017) contained some errors. The Fig. 4 displayed incorrectly. The correct figure can be found below

Soil respiration patterns and rates at three Taiwanese forest plantations: dependence on elevation, temperature, precipitation, and litterfall

Abstract Background Soil respiration contributes to a large quantity of carbon emissions in the forest ecosystem. In this study, the soil respiration rates at three Taiwanese forest plantations (two lowland and one mid-elevation) were investigated. We aimed to determine how soil respiration varies between lowland and mid-elevation forest plantations and identify the relative importance of biotic and abiotic factors affecting soil respiration. Results The results showed that the temporal patterns of soil respiration rates were mainly influenced by soil temperature and soil water content, and a combined soil temperature and soil water content model explained 54–80% of the variation. However, these two factors affected soil respiration differently. Soil temperature positively contributed to soil respiration, but a bidirectional relationship between soil respiration and soil water content was revealed. Higher soil moisture content resulted in higher soil respiration rates at the lowland plantations but led to adverse effects at the mid-elevation plantation. The annual soil respiration rates were estimated as 14.3–20.0 Mg C ha−1 year−1 at the lowland plantations and 7.0–12.2 Mg C ha−1 year−1 at the mid-elevation plantation. When assembled with the findings of previous studies, the annual soil respiration rates increased with the mean annual temperature and litterfall but decreased with elevation and the mean annual precipitation. A conceptual model of the biotic and abiotic factors affecting the spatial and temporal patterns of the soil respiration rate was developed. Three determinant factors were proposed: (i) elevation, (ii) stand characteristics, and (iii) soil temperature and soil moisture. Conclusion The results indicated that changes in temperature and precipitation significantly affect soil respiration. Because of the high variability of soil respiration, more studies and data syntheses are required to accurately predict soil respiration in Taiwanese forests