Soil Heterotrophic Respiration Rates Research Articles

Responses of soil heterotrophic respiration and microbial biomass to organic and conventional production systems

The effects of organic and conventional production systems on crop productivity have been greatly explored, but their effects on soil microbial processes were often neglected. A comparative field study of organic and conventional production systems was conducted at the Tennessee State University research farm to determine soil heterotrophic respiration and microbial biomass carbon. Leafy green vegetables were grown in a conventional production system in an open field, and they were grown in an organic production system, using three different row covers (agribon cloth, insect net, and plastic), and in an open field. Soil samples (0-15cm) were collected from the two production systems. Soil heterotrophic respiration rate (RH), microbial biomass carbon (MBC), and biomass-specific heterotrophic respiration rate (the inverse is used as a proxy for microbial carbon use efficiency) were quantified. The results showed that the conventional production system significantly increased RH relative to the organic system. Organic production system, however, significantly enhanced MBC and reduced biomass-specific respiration rate indicating an increase in carbon use efficiency. Although MBC remained unchanged among the row covers, insect net increased RH and biomass-specific heterotrophic respiration rate. Our results suggest that the organic production system not only promoted soil microbial abundance but also limited soil heterotrophic respiration to the atmosphere governed by the elevated carbon use efficiency.

Changes in the non-growing season soil heterotrophic respiration rate are driven by environmental factors after fire in a cold temperate forest ecosystem

Key messageDuring the non-growing season, environmental factors changed after fire, leading to significantly increased non-growing season soil heterotrophic respiration (Rh) and potentially decreasing the amount of net C stored in cold temperate forest ecosystems of China.ContextIntensifying forest fire regimes are likely to influence future C budgets of forest ecosystems. However, the mechanism of fire disturbance on the components of non-growing season soil respiration rate (Rs) and its environmental factors are not fully understood, creating uncertainties for future C sink estimates under climate change scenarios.AimsThis study examined the effects of recent fire on non-growing season (November 2017 to April 2018) Rs, its heterotrophic (Rh) and autotrophic (Ra) components, and Q10 in a cold temperate forest in northeast China.MethodsSoil CO2 effluxes (including Rh and Ra) were measured using an Li-8100 portable automatic measuring system for soil C flux (Li-Cor, Inc.; Lincoln, NE, USA). Soil temperature and moisture were measured using a temperature probe (Licor p/n8100–201) and soil volumetric water content probe (ECH20 167 EC-5; p/n 8,100,202), respectively, at a depth of 5 cm; snowpack depth was measured with a ruler.ResultsDuring the non-growing season, fire significantly increased the Rh by approximately 47% in burned stands. The Q10 of Rh significantly increased from 2.39 in the unburned stands to 3.12 in the burned stands. An interaction between soil temperature and snowpack depth was the driving environmental factor controlling the non-growing season soil respiration and its components after fire disturbance.ConclusionFire is a potent factor on the components of the soil respiration and should not be ignored in forest ecosystem C cycling, especially during the non-growing season as it is vulnerable to micro-environmental variation. Long-term studies involving diverse ecosystems are required to better elucidate mechanisms that have been found during the non-growing season Rs under an increasing trend of fire occurrence.

帽儿山3种森林生态系统土壤动物与土壤呼吸及其相互关系研究

PDF HTML阅读 XML下载 导出引用 引用提醒 帽儿山3种森林生态系统土壤动物与土壤呼吸及其相互关系研究 DOI: 10.5846/stxb201911252555 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31670619，41101048）；黑龙江省留学归国人员科学基金（LC2018011）；哈尔滨师范大学硕士研究生创新项目（HSDSSCX2019-01） Analysis on soil animals, soil respiration and the correlation in three forest ecosystems in Maoershan Author: Affiliation: Fund Project: Project of National Natural Science Foundation of China (31670619,41101048); Science Foundation of returned students of Heilongjiang Province (LC2018011); Innovation Project of postgraduates of Harbin normal University (HSDSSCX2019-01) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:土壤呼吸是森林生态系统碳循环的关键过程，土壤动物可通过自身代谢及影响微生物活动调控土壤呼吸，因此研究土壤动物与土壤呼吸的相互关系对进一步揭示生态系统碳循环的规律和机理具有重要意义。通过野外定点，以帽儿山3种森林生态系统的土壤呼吸及土壤动物为研究对象，探讨不同森林生态系统的土壤呼吸、土壤动物个体密度和生物量的时间变化规律及二者相互关系。结果表明：（1）3种森林生态系统土壤总呼吸速率与土壤异养呼吸速率均呈现先增强后减弱的时间动态变化（P<0.05），且不同森林生态系统土壤异养呼吸速率差异显著（P<0.05），表现为硬阔叶林最高，红松人工林最低；（2）3种森林生态系统土壤动物生物量也具有显著的时间动态变化（P<0.05），均在9月份达到最大，且不同森林生态系统土壤动物个体密度显著不同（P<0.05），蒙古栎林土壤动物个体密度显著小于红松人工林与硬阔叶林；（3）通过回归分析可得，土壤动物数量及生物量的增加抑制了土壤呼吸速率，尤其在生长季初期、末期。研究表明土壤动物可通过抑制微生物生命活动和降低根系呼吸从而对土壤总呼吸及异养呼吸产生负反馈作用，三者是不可分割的整体，与土壤温度、水分等环境因子共同调控着土壤呼吸。 Abstract:Forest ecosystem is the largest organic carbon pool in terrestrial ecosystem, and its slight changes may cause significant variations in global climate. Soil respiration is the key ecological process of carbon cycle in forest ecosystem, which has a great influence on global climate change. Soil animals, as the important consumers of material cycle in the ecosystem, can regulate soil respiration the help of their own metabolism and affecting microbial activities. Therefore, study of the correlation of soil animals and soil respiration is of great significance to further reveal the law and mechanism of carbon cycle in ecosystem. Based on field experiment and indoor analysis, we chose soil respiration and soil animals in three forest ecosystems of Korean pine plantation forest (HS), Mongolian oak forest (MGL), and Hard-wood forest (YK) in Maoershan as the research object, and discuss the temporal variation and correlation between soil respiration as well as individual density or biomass of soil animals in different forest ecosystems. The results showed that: (1) the total soil respiration rate of the three forest ecosystems increased at first and then decreased (P<0.05), with the lowest value appearing in October. The soil heterotrophic respiration rate also showed significantly temporal dynamic change (P<0.05). The difference of soil heterotrophic respiration rate among different forest ecosystems was significant (P<0.05), which was the highest in Hard-wood forest and the lowest in Korean pine plantation forest. (2) The soil animal biomass and individual density of the three forest ecosystems also had notable temporal dynamic changes (P<0.05). The change trends of soil animal biomass and individual density were different, but they all had the maximum values in September. The individual density of soil animals in Mongolian oak forest was much lower than that in Korean pine plantation forest and Hard-wood forest. (3) Through regression analysis, the increase of the number and biomass of soil animals inhibited the soil respiration rate, especially at the beginning and end of the growing season. And the correlation between soil respiration and soil animals in Korean pine plantation forest was different from that in Mongolian oak forest and Hard-wood forest. It could be concluded that soil animals could produce negative feedback on total soil respiration and heterotrophic respiration by inhibiting microbial life activities and reducing root respiration. Soil animals, soil microorganisms and plant roots are an inseparable whole, which together with soil temperature, water and other environmental factors regulate soil respiration. 参考文献 相似文献 引证文献

Rainfall intensification increases the contribution of rewetting pulses to soil heterotrophic respiration

Abstract. Soil drying and wetting cycles promote carbon (C) release through large heterotrophic respiration pulses at rewetting, known as the “Birch” effect. Empirical evidence shows that drier conditions before rewetting and larger changes in soil moisture at rewetting cause larger respiration pulses. Because soil moisture varies in response to rainfall, these respiration pulses also depend on the random timing and intensity of precipitation. In addition to rewetting pulses, heterotrophic respiration continues during soil drying, eventually ceasing when soils are too dry to sustain microbial activity. The importance of respiration pulses in contributing to the overall soil heterotrophic respiration flux has been demonstrated empirically, but no theoretical investigation has so far evaluated how the relative contribution of these pulses may change along climatic gradients or as precipitation regimes shift in a given location. To fill this gap, we start by assuming that heterotrophic respiration rates during soil drying and pulses at rewetting can be treated as random variables dependent on soil moisture fluctuations, and we develop a stochastic model for soil heterotrophic respiration rates that analytically links the statistical properties of respiration to those of precipitation. Model results show that both the mean rewetting pulse respiration and the mean respiration during drying increase with increasing mean precipitation. However, the contribution of respiration pulses to the total heterotrophic respiration increases with decreasing precipitation frequency and to a lesser degree with decreasing precipitation depth, leading to an overall higher contribution of respiration pulses under future more intermittent and intense precipitation. Specifically, higher rainfall intermittency at constant total rainfall can increase the contribution of respiration pulses up to ∼10 % or 20 % of the total heterotrophic respiration in mineral and organic soils, respectively. Moreover, the variability of both components of soil heterotrophic respiration is also predicted to increase under these conditions. Therefore, with future more intermittent precipitation, respiration pulses and the associated nutrient release will intensify and become more variable, contributing more to soil biogeochemical cycling.

Increasing microbial carbon use efficiency with warming predicts soil heterotrophic respiration globally.

The degree to which climate warming will stimulate soil organic carbon (SOC) losses via heterotrophic respiration remains uncertain, in part because different or even opposite microbial physiology and temperature relationships have been proposed in SOC models. We incorporated competing microbial carbon use efficiency (CUE)-mean annual temperature (MAT) and enzyme kinetic-MAT relationships into SOC models, and compared the simulated mass-specific soil heterotrophic respiration rates with multiple published datasets of measured respiration. The measured data included 110 dryland soils globally distributed and two continental to global-scale cross-biome datasets. Model-data comparisons suggested that a positive CUE-MAT relationship best predicts the measured mass-specific soil heterotrophic respiration rates in soils distributed globally. These results are robust when considering models of increasing complexity and competing mechanisms driving soil heterotrophic respiration-MAT relationships (e.g., carbon substrate availability). Our findings suggest that a warmer climate selects for microbial communities with higher CUE, as opposed to the often hypothesized reductions in CUE by warming based on soil laboratory assays. Our results help to build the impetus for, and confidence in, including microbial mechanisms in soil biogeochemical models used to forecast changes in global soil carbon stocks in response to warming.

Stable isotopic constraints on global soil organic carbon turnover

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates on large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (176 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration rates by SOC pools. ln( − β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln( − β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.76; p &lt; 0.001) linear relationship between ln( − β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

Asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures

Periodic changes in temperature commonly occur diurnally and seasonally. However, the response of soil heterotrophic respiration to rising and decreasing temperatures during these periods remains poorly understood; thus the feedback between climate change and carbon (C) cycling requires further investigation. In this study, soils from three grasslands in the Qinghai-Tibet Plateau were incubated separately at rising (from 5 °C to 31 °C) and decreasing (from 31 °C to 5 °C) temperatures modes over 161 days, to explore how soil heterotrophic respiration rates (RS) respond to different temperature changes. The parameters of RS and temperature sensitivity (Q10) were used for the analyses. In addition, microbial biomass C (MBC), microbial biomass nitrogen (N) (MBN), dissolved organic C (DOC), and other soil properties were measured. The results indicated a pronounced hysteresis of RS for both rising and decreasing temperatures. Furthermore, the hysteresis loops differed in the different sites. RS values were significantly higher for rising temperature (2.71 μg C g−1 d−1) versus decreasing temperature (1.75 μg C g−1 d−1) in all three alpine grasslands. The Q10 values were significantly higher for decreasing temperature (2.42) versus increasing temperature (1.55), with these differences being observed over the 161-d incubation period. Furthermore, soil microbes (specifically, MBC and MBC/MBN) explained 46–77% of the total variation in Q10, followed by substrate and other properties. Our results provide experimental evidence for the asymmetric responses of soil heterotrophic respiration to rising and decreasing temperatures. In addition, the microbial effect was primarily associated with soil heterotrophic respiration, suggesting strong asymmetric responses to rising and decreasing temperatures that require investigation in future studies.

Simulating denitrification and nitrous oxide emissions from subtropical maize-winter wheat rotations in Southwestern China using NOEv2 model

We measured denitrification and nitrous oxide (N2O) emissions from subtropical maize-winter wheat cropping systems in the Sichuan Basin, Southwestern China between 2005 and 2006, providing a dataset that enabled us to comprehensively test the non-linear empirical NOEv2 model. The primary aims were to (i) quantify annual denitrification and N2O emissions from intensively managed agroecosystems, (ii) parameterize the denitrification sub-model in NOEv2 with site-specific measurements and incubations and (iii) evaluate NOEv2 in a subtropical area in particular. Field measurements were conducted at two adjacent sites (hereafter named NR and NF, respectively). At site NR, soils were fertilized with urea at 150 (NR-150) and 250 (NR-250) kgNha−1 crop−1. At site NF, soils were fertilized with urea (NF-U), ammonium sulphate (NF-AS) and potassium nitrate (NF-KN) at 150kgNha−1 crop−1. Set-aside soils were incubated in laboratory to determine two biological parameters of the NOEv2 model namely the potential denitrification rate (Dp) and the maximal fraction of N2O production through denitrification (rmax). With respect to subtropical climate, we modified the response function linked to soil temperature using an equation based on temperature sensitivity (Q10). The incubated Dp and rmax were 2.96kgNha−1d−1 and 0.60, respectively. A Q10 value of 2.95 was estimated from the exponential relationship between soil heterotrophic respiration rates and soil temperature (5cm depth) throughout the experimental period (r2=0.84, n=96, p=0.000). Varying across the treatments, the observed and simulated denitrification rates ranged from 10.95 to 15.38 and from 12.47 to 14.91kgNha−1yr−1, respectively. The simulations were averagely 3% larger than the observations (ranging from −20 to 27%). Accordingly, the observed and simulated N2O emissions ranged from 1.45 to 2.72 and from 1.38 to 2.21kgNha−1yr−1, respectively. The simulations were averagely 9% lower than the observations (ranging from −19 to 7%). We conclude that NOEv2 is applicable to the studied subtropical area with site-specific parameterization. Modification of the response function linked to soil temperature seems essential to apply the model to a wide range of climate conditions.

Soil organic carbon loss from carbon dioxide and methane emissions, as well as runoff and leaching on a hillslope of Regosol soil in a wheat–maize rotation

Soil carbon dioxide (CO2) and methane (CH4) emissions, as well as runoff and leaching are major pathways of soil organic carbon (SOC) loss, which affect SOC sequestration in croplands. However, fluxes and relationships of the four pathways are still poorly understood. Static chamber-GC techniques were used to measure soil heterotrophic respiration rate and CH4 emission flux on hillslope upland of Regosol soil in Southwest China under traditional mineral fertilizer treatment from 2010 to 2012. Synchronously, SOC loss flux via overland flow, leaching and sediment was measured using free-drained lysimeters (8 m × 4 m). Average annual cumulative soil CO2 emission and CH4 uptake fluxes were 462.8 ± 52.2 and −1.1 ± 0.16 g cm−2. Average annual cumulative dissolved organic carbon (DOC) loss fluxes via overland flow and leaching were 0.16 ± 0.03 and 0.92 ± 0.08 g cm−2, respectively and organic C loss via sediment was 2.2 ± 0.3 g cm−2. Relationship between DOC loss fluxes and soil heterotrophic respiration rates under natural rainfall events could be described by a significant exponential decay function (R = −0.63, P < 0.01). Moreover, a significantly negative correlation was also found between DOC loss flux and soil DOC content in topsoil at 15 cm depth (R = −0.75, P < 0.05). In conclusion, DOC loss decreases soil DOC content and is an underrated negative regulating factor of soil CO2 emission, especially in the regions where high DOC losses occur.

The effect of fire disturbance on short-term soil respiration in typical forest of Greater Xing’an Range, China

We investigated the effect of fire disturbance on short-term soil respiration in birch (Betula platyphylla Suk.) and larch (Larix gmelinii Rupr.) forests in Greater Xing’an range, northeastern China for further understanding of its effect on the carbon cycle in ecosystems. Our study show that post-fire soil respiration rates in B. platyphylla and L. gmelinii forests were reduced by 14% and 10%, respectively. In contrast, the soil heterotrophic respiration rates in the two types of forest were similar in post-fire and control plots. After fire, the contribution of root respiration to total soil respiration was dramatically reduced. Variation in soil respiration rates was explained by soil moisture (W) and soil temperature (T) at a depth of 5 cm. Exponential regression fitted T and W models explained Rs rates in B. platyphylla control and post-fire plots (83.1% and 86.2%) and L. gmelinii control and post-fire plots (83.7% and 88.7%). In addition, the short-term temperature coefficients in B. platyphylla control and post-fire plots were 5.33 and 5, respectively, and 9.12, and 5.26 in L. gmelinii control and post-fire plots, respectively. Our results provide an empirical baseline for studying the effect of fire disturbance on soil carbon balance and estimation of soil carbon flux in boreal forest.

施肥方式对紫色土土壤异养呼吸的影响

Recent studies have shown that soil respiration is the critical importance in determining the carbon balance of terrestrial ecosystems. Respiration from soils is comprised of both the heterotrophic respiration of microorganisms( soil bacteria,fungi,and fauna) and autotrophic respiration from roots and mycorrhizae. Precise assessment of these components is important for calculating the carbon budgets of vegetation and the turnover rate of soil organic matter,as well as for understanding sources and sinks of carbon in terrestrial ecosystems in the face of global climate change. Although soil heterotrophic respirations have received considerable attention in recent decades,much less is known about the effects of various natural or artificial factors such as temperature,precipitation or fertilization etc. on it. The field study was conducted at a sloping cropland in Yanting Agro-ecological Station of Purple Soil,Chinese Academy of Science under Chinese Ecosystem Research Network( CERN),situated at N31°16°,E105°28',with the altitude of 400 to 600 meters in the middle of Sichuan Basin,where a set of long-term research plots is located. Three plots were randomly assigned to oneof the following treatments: conventional chemical fertilizer( NPK),organic manure( pig slurry,OM) and crop residue with chemical fertilizer( RSDNPK). Total nitrogen for each fertilization treatment was applied at the same rate with 130 and150 kgN /hm2 for wheat and maize seasons,respectively. The results showed that soil heterotrophic respiration exhibited pronounced seasonal variations that clearly reflected those of soil temperature,with minimum values in winter and maximum values in summer. There was a pulse of soil heterotrophic respiration induced by fertilization at the 5th day after fertilization. The peak rate for OM treatment was 2356. 8 mgCO2m-2h-1and it was significantly higher than that for both RSDNPK and NPK treatments( P0. 01). Meanwhile,the respiration rate and the annual cumulative CO2 emission in OM and RSDNPK treatments were higher than those in NPK treatment. During wheat growing season,average respiration rate for NPK,OM and RSDNPK treatments were 212. 9,285. 8 and 305. 8 mgCO2m-2h-1,respectively,which were all lower than that in maize growing season. The cumulative soil CO2 emissions from NPK,OM and RSDNPK were 255. 1,342. 3and 369. 5 gC /m2 for wheat season,and 344. 7,542. 8 and 376. 9 gC /m2 for maize season,while 599. 8,885. 1 and 746. 4gCm-2for the whole year,respectively. The results implied that lower C /N ratio organic material was the primary driving force for increasing soil heterotrophic rate and cumulative soil CO2 emissions. The values of temperature sensitivity( Q10)for soil heterotrophic respiration in wheat season and maize season were also measured. The results showed that Q10 values in wheat season always higher than that in maize season at all plots. During the whole experiment time,the magnitudes of Q10 both followed the order of OM NPK RSDNPK,which was clearly reflected that Q10 was sensitive to lower C /N organic materials. Q10 values obtained from soil temperature at soil surface( 0 cm) and soil 5 cm depth in OM and RSDNPK were2. 64,2. 77 and 1. 88,1. 99,respectively. It indicated that the Q10 values for soil heterotrophic respiration rates were higher at lower temperatures and lower at higher temperature.

Sustained large stimulation of soil heterotrophic respiration rate and its temperature sensitivity by soil warming in a cool-temperate forested peatland

We conducted a soil warming experiment in a cool-temperate forested peatland in northern Japan during the snow-free seasons of 2007–2011, to determine whether the soil warming would change the heterotrophic respiration rate and its temperature sensitivity. We elevated the soil temperature by 3°C at 5-cm depth by using overhead infrared heaters and continuously measured hourly soil CO2 fluxes with a 15-channel automated chamber system. The 15 chambers were divided into three groups each with five replications for the control, unwarmed-trenched and warmed-trenched treatments. Soil warming enhanced heterotrophic respiration by 82% (mean of four seasons (2008–2011) observation±SD, 6.84±2.22 µmol C m−2 s−1) as compared to the unwarmed-trenched treatment (3.76±0.98 µmol C m−2 s−1). The sustained enhancement of heterotrophic respiration with soil warming suggests that global warming will accelerate the loss of carbon substantially more from forested peatlands than from other upland forest soils. Soil warming likewise enhanced temperature sensitivity slightly (Q10, 3.1±0.08 and 3.3±0.06 in the four-season average in unwarmed- and warmed-trenched treatments, respectively), and significant effect was observed in 2009 (p<0.001) and 2010 (p<0.01). However, there was no significant difference in the basal respiration rate at 10°C (R10, 2.2±0.52 and 2.8±1.2 µmol C m−2 s−1) between treatments, although the values tended to be high by warming throughout the study period. These results suggest that global warming will enhance not only the heterotrophic respiration rate itself but also its Q10 in forests with high substrate availability and without severe water stress, and predictions for such ecosystems obtained by using models assuming no change in Q10 are likely to underestimate the carbon release from the soil to the atmosphere in a future warmer environment.

Stocks and fluxes of carbon associated with land use change in Southeast Asian tropical peatlands: A review

[1] The increasing and alarming trend of degradation and deforestation of tropical peat swamp forests may contribute greatly to climate change. Estimates of carbon (C) losses associated with land use change in tropical peatlands are needed. To assess these losses we examined C stocks and peat C fluxes in virgin peat swamp forests and tropical peatlands affected by six common types of land use. Phytomass C loss from the conversion of virgin peat swamp forest to logged forest, fire-damaged forest, mixed croplands and shrublands, rice field, oil palm plantation, and Acacia plantation were calculated using the stock difference method and estimated at 116.9 ± 39.8, 151.6 ± 36.0, 204.1 ± 28.6, 214.9 ± 28.4, 188.1 ± 29.8, and 191.7 ± 28.5 Mg C ha−1, respectively. Total C loss from uncontrolled fires ranged from 289.5 ± 68.1 Mg C ha−1 in rice fields to 436.2 ± 77.0 Mg C ha−1 in virgin peat swamp forest. We assessed the effects of land use change on C stocks in the peat by looking at how the change in vegetation cover altered the main C inputs (litterfall and root mortality) and outputs (heterotrophic respiration, CH4 flux, fires, and soluble and physical removal) before and after conversion. The difference between the soil input-output balances in the virgin peat swamp forest and in the oil palm plantation gave an estimate of peat C loss of 10.8 ± 3.5 Mg C ha−1 yr−1. Peat C loss from other land use conversions could not be assessed due to lack of data, principally on soil heterotrophic respiration rates. Over 25 years, the conversion of tropical virgin peat swamp forest into oil palm plantation represents a total C loss from both biomass and peat of 427.2 ± 90.7 Mg C ha−1 or 17.1 ± 3.6 Mg C ha−1 yr−1. In all situations, peat C loss contributed more than 63% to total C loss, demonstrating the urgent need in terms of the atmospheric greenhouse gas burden to protect tropical virgin peat swamp forests from land use change and fires.

Soil Carbon Stocks and Soil Carbon Quality in the Upland Portion of a Boreal Landscape, James Bay, Quebec

As part of a multidisciplinary project on carbon (C) dynamics of the ecosystems characterizing the Eastmain Region Watershed (James Bay, Quebec), the objective of this study is to compare the soil C stocks and soil organic matter quality among the main upland vegetation types in a boreal region subjected to a high fire frequency. On average, the organic layer contained twice the amount of C than the mineral soil. Closed canopy vegetation types had greater C stocks both in the mineral and in the organic layers than the other more open canopy vegetation types. Landscape features such as drainage and surficial deposit could not discriminate between vegetation types although closed vegetation types were on average found on wetter site conditions. Average soil C contents varied more than 2-fold across vegetation types. On the opposite, except for the organic layer C:N ratio, which was smaller in closed vegetation types, other measured soil organic matter properties (namely specific rate of evolved C after a long-term incubation, hydrolysis acid-resistant C as well as the rate of changes in soil heterotrophic respiration with increasing temperature (Q10)) remained within a narrow range between vegetation types. Therefore, total soil C stocks were a major determinant of both labile C and estimated summer soil heterotrophic respiration rate. The homogeneity of soil organic matter quality across the vegetation types could be attributable to the positive relationship between soil C storage and soil C fluxes observed in this landscape experiencing a high fire frequency. The low variability in soil C quality could help simplify the modelling of soil C fluxes in this environment.

Modeling carbon dynamics in two adjacent spruce forests with different soil conditions in Russia

Abstract. Net ecosystem carbon exchange (NEE) was measured with eddy covariance method for two adjacent forests located at the southern boundary of European taiga in Russia in 1999–2004. The two spruce forests shared similar vegetation composition but differed in soil conditions. The wet spruce forest (WSF) possessed a thick peat layer (60 cm) with a high water table seasonally close to or above the soil surface. The dry spruce forest (DSF) had a relatively thin organic layer (5 cm) with a deep water table (&gt;60 cm). The measured multi-year average NEE fluxes (2000 and –1440 kg C ha−1yr−1 for WSF and DSF, respectively) indicated that WSF was a source while DSF a sink of atmospheric carbon dioxide (CO2) during the experimental years. A process-based model, Forest-DNDC, was employed in the study to interpret the observations. The modeled multi-year average NEE fluxes were 1800 and –2200 kg C ha−1yr−1 for WSF and DSF, respectively, which were comparable with observations. The modeled data also showed high soil heterotrophic respiration rates at WSF that suggested that the water table fluctuation at WSF could have played a key role in determining the negative carbon balance in the wetland ecosystem. A sensitivity test was conducted by running Forest-DNDC with varied water table scenarios for WSF. The results indicated that the NEE fluxes from WSF were highly sensitive to the water table depth. When the water table was high, the WSF ecosystem maintained as a sink of atmospheric CO2; while along with the drop of the water table the length of the flooded period reduced and more organic matter in the soil profile suffered from rapid decomposition that gradually converted the ecosystem into a source of atmospheric CO2. The general effect of water table variation on wetland carbon balance observed from this modeling study could be applicable for a wide range of wetland ecosystems that have accumulated soil organic carbon while face hydrological changes under certain climatic or land-use change scenarios.

General model for N2O and N2 gas emissions from soils due to dentrification

Observations of N gas loss from incubations of intact and disturbed soil cores were used to model N2O and N2 emissions from soil as a result of denitrification. The model assumes that denitrification rates are controlled by the availability in soil of NO3 (e− acceptor), labile C compounds (e− donor), and O2 (competing e− acceptor). Heterotrophic soil respiration is used as a proxy for labile C availability while O2 availability is a function of soil physical properties that influence gas diffusivity, soil WFPS, and O2 demand. The potential for O2 demand, as indicated by respiration rates, to contribute to soil anoxia varies inversely with a soil gas diffusivity coefficient which is regulated by soil porosity and pore size distribution. Model inputs include soil heterotrophic respiration rate, texture, NO3 concentration, and WFPS. The model selects the minimum of the NO3 and CO2 functions to establish a maximum potential denitrification rate for particular levels of e− acceptor and C substrate and accounts for limitation of O2 availability to estimate daily N2+N2O flux rates. The ratio of soil NO3 concentration to CO2 emission was found to reliably (r2=0.5) model the ratio of N2 to N2O gases emitted from the intact cores after accounting for differences in gas diffusivity among the soils. The output of the ratio function is combined with the estimate of total N gas flux rate to infer N2O emission. The model performed well when comparing observed and simulated values of N2O flux rates with the data used for model building (r2=0.50) and when comparing observed and simulated N2O+N2 gas emission rates from irrigated field soils used for model testing (r2=0.47).

Generalized model for N2 and N2O production from nitrification and denitrification

We describe a model of N2 and N2O gas fluxes from nitrification and denitrification. The model was developed using laboratory denitrification gas flux data and field‐observed N2O gas fluxes from different sites. Controls over nitrification N2O gas fluxes are soil texture, soil NH4, soil water‐filled pore space, soil N turnover rate, soil pH, and soil temperature. Observed data suggest that nitrification N2O gas fluxes are proportional to soil N turnover and that soil NH4 levels only impact N2O gas fluxes with high levels of soil NH4 (&gt;3 μg N g−1). Total denitrification (N2 plus N2O) gas fluxes are a function of soil heterotrophic respiration rates, soil NO3, soil water content, and soil texture. N2:N2O ratio is a function of soil water content, soil NO3, and soil heterotrophic respiration rates. The denitrification model was developed using laboratory data [Weier et al, 1993] where soil water content, soil NO3, and soil C availability were varied using a full factorial design. The Weier's model simulated observed N2 and N2O gas fluxes for different soils quite well with r2 equal to 0.62 and 0.75, respectively. Comparison of simulated model results with field N2O data for several validation sites shows that the model results compare well with the observed data (r2 = 0.62). Winter denitrification events were poorly simulated by the model. This problem could have been caused by spatial and temporal variations in the observed soil water data and N2O fluxes. The model results and observed data suggest that approximately 14% of the N2O fluxes for a shortgrass steppe are a result of denitrification and that this percentage ranged from 0% to 59% for different sites.