Variation In Soil CO2 Efflux Research Articles

Biochar Addition Increased Soil Carbon Storage but Did Not Exacerbate Soil Carbon Emission in Young Subtropical Plantation Forest

Forests play a crucial role in mitigating global warming, contributing approximately 46% of the global terrestrial carbon sink. However, it remains uncertain whether the addition of biochar to forests enhances the ecosystem’s carbon sink capacity. This study aims to address this scientific question by investigating whether biochar application increases carbon storage, potentially leading to an overall rise in carbon emissions by influencing soil respiration and identifying the underlying mechanisms. A controlled experiment was conducted in a young plantation forest that had grown for three years, where soil CO2 efflux rate and physicochemical properties, photosynthesis, and plant growth traits were measured across varying biochar addition rates (0, 5, and 10 t/ha) over five seasons. Then, statistical methods including one-way ANOVA, regression analysis, and structural equation modeling (SEM) were employed to assess differences in biological and abiotic factors among biochar addition gradients and understand the influencing mechanisms of soil CO2 efflux change. The findings revealed that biochar addition significantly increased the contents of soil organic carbon (SOC) and microbial biomass carbon (MBC), consequently promoting photosynthesis and plant growth (p < 0.05). Biochar addition accounted for 73.8% of the variation in soil CO2 efflux by affecting soil physicochemical properties, photosynthesis, and plant basal diameter growth. However, the net effect of biochar addition on soil CO2 efflux was found to be low. The positive effects of biochar addition on soil CO2 efflux via factors such as soil bulk density, total nitrogen (TN), MBC, and photosynthesis were counteracted by its negative impact through soil total phosphorus (TP), water content, pH, SOC, and plant basal diameter growth. Overall, our findings indicate that there was no significant increase in soil CO2 efflux in the short term (totaling 16 months) over the biochar addition gradient. However, we observed a substantial increase in soil carbon storage and an enhancement in the soil’s capacity to act as a carbon sink. Therefore, adding biochar to forests may be a feasible strategy to increase carbon sinks and mitigate global climate change.

Temporal patterns of fine‐root dynamics have little influence on seasonal soil CO2 efflux in a mixed, mesic forest

AbstractAmong the contributors to soil CO2 efflux, there remains uncertainty about the contribution of root activity to the overall soil efflux. Soil water and temperature frequently have been used to predict a large portion of the variation in soil CO2 efflux. We hypothesized that fine‐root dynamics explain most of the remaining variability in soil CO2 efflux that cannot be explained by soil temperature and water content. We anticipated that seasonal increases in root production, mortality via decomposition, and standing crop would result in corresponding increases in soil CO2 efflux. We tested our hypotheses by collecting and analyzing two years of minirhizotron and soil chamber CO2 flux data from plots distributed throughout the Shale Hills Catchment of the Susquehanna‐Shale Hills Critical Zone Observatory in Central Pennsylvania, USA. Here we showed that: (1) seasonal fluctuations in fine‐root dynamics yielded only a very small increase in the predictability of soil CO2 efflux; (2) fine‐root mortality effects on soil CO2 efflux were strongly tied to soil temperature; (3) fluctuations in fine‐root presence or standing mass independent of temperature and moisture had little effect on soil CO2 efflux; and (4) new fine‐root length and root length mortality had limited impacts on soil CO2 efflux rates. We conclude that, at least in temperate forests on rocky soils, characterizing fine‐root dynamics may provide only limited improvement in the estimation of soil CO2 efflux.

Soil CO2 efflux fluctuates in three different annual seasons in a semideciduous tropical forest in Yucatan, Mexico

Tropical forest soils store a third of the global terrestrial carbon and control carbon dioxide (CO2) terrestrial effluxes to the atmosphere produced by root and microbial respiration. Soil CO2 efflux varies in time and space and is known to be strongly influenced by soil temperature and water content. However, little is known about the influence of seasonality on soil CO2 efflux, especially in tropical dry forests. This study evaluated soil CO2 efflux, soil temperature, and soil volumetric water content in a semideciduous tropical forest of the Yucatan Peninsula under two sites (flat areas close to and far from hills), and three seasons: dry, wet, and early dry (a transition between the rainy and dry seasons) throughout a year. Additionally, six 24-h periods of soil CO2 efflux were measured within these three seasons. The mean annual soil CO2 efflux was 4±2.2 μmol CO2 m-2 s-1, like the mean soil CO2 efflux during the early dry season. In all seasons, soil CO2 efflux increased linearly with soil moisture, which explained 45% of the spatial-temporal variation of soil CO2 efflux. Soil CO2 efflux was higher close to than far from hills in some months. The daily variation of soil CO2 efflux was less important than its spatial and seasonal variation likely due to small diel variations in temperature. Transition seasons are common in many tropical dry forests, and they should be taken into consideration to have a better understanding of the annual soil CO2 efflux, especially under future climate-change scenarios.

Productivity and Seasonality Drive Total Soil Respiration in Semi-Arid Juniper Woodlands (Juniperus thurifera L., Southern Spain)

We analyzed the relationship between forest productivity (joint effect of forest maturity and soil quality) and total soil respiration (µmol CO2 m−2 s−1) in semi-arid juniper woodlands (young woodlands growing in abandoned farmlands with deeper soils, and mature woodlands in lithic soils), and investigated the seasonal variation in soil CO2 efflux as a function of soil temperature and the soil water content. We measured the soil CO2 efflux from twelve cylinders in the soil over a three-year period using LI-6400 equipment. The results show that, in the more productive site (young woodland), soil CO2 efflux was higher due to greater respiration, mainly in the driest periods. Soil respiration followed a seasonal trend, being higher in spring and decreasing in cold periods. In both juniper woodlands and especially in the older forest, the CO2 efflux rates were low (<2.5 for Q10), typical of slow-growing species. Soil respiration was controlled by soil temperature without drought and in the temperate-warm season, whereas respiration showed sensitivity to soil water content in periods when edaphic humidity was low (but only in the more productive, young forest, which seemed to show better adaptation to drought), and under high soil moisture (soil water > 25%) for both woodlands, coinciding with warm temperatures in the spring. This period also corresponded to the highest CO2 efflux recorded in both woodlands. The accumulation of organic C seems to also be important to maintain elevated soil respiration in summer, especially in young woodlands. Thus, apart from microclimatic conditions, factors related to productivity regulate respiratory activity.

Effects of Warming and Precipitation on Soil CO2 Flux and Its Stable Carbon Isotope Composition in the Temperate Desert Steppe

The stable carbon (C) isotope of soil CO2 efflux (δ13CO2e) is closely associated with soil C dynamics, which have a complex feedback relationship with climate. Three levels of warming (T0: ambient temperature (15.7 °C); T1: T0 + 2 °C; T2: T0 + 4 °C) were combined with three levels of increased precipitation (W0: ambient precipitation (245.2 mm); W1: W0 + 25%; W2: W0 + 50%) in order to quantify soil CO2 flux and its δ13CO2e values under nine treatment conditions (T0W0, T0W1, T0W2, T1W0, T1W1, T1W2, T2W0, T2W1, and T2W2) in desert steppe in an experimental beginning in 2015. A non-steady state chamber system relying on Keeling plots was used to estimate δ13CO2e. The temperature (ST) and moisture (SM) of soil as well as soil organic carbon content (SOC) and δ13C values (δ13Csoil) were tested in order to interpret variations in soil CO2 efflux and δ13CO2e. Sampling was carried out during the growing season in 2018 and 2019. During the experiment, the ST and SM correspondingly increased due to warming and increased precipitation. CO2 flux ranged from 37 to 1103 mg m−2·h−1, and emissions peaked in early August in the desert steppe. Warming of 2 °C to 4 °C stimulated a 14% to 30.9% increase in soil CO2 efflux and a 0.4‰ to 1.8‰ enrichment in δ13CO2e, respectively. Increased precipitation raised soil CO2 efflux by 14% to 19.3%, and decreased δ13CO2e by 0.5‰ to 0.9‰. There was a positive correlation between soil CO2 efflux and ST and SOC indicating that ST affected soil CO2 efflux by changing SOC content. Although the δ13CO2e was positively correlated with ST, it was negatively correlated to SM. The decline of δ13CO2e with soil moisture was predominantly due to intensified and increased diffusive fractionation. The mean δ13CO2e value (−20.2‰) was higher than that of the soil carbon isotope signature at 0–20 cm (δ13Csoil = −22.7‰). The difference between δ13CO2e and δ13Csoil (Δe-s) could be used to evaluate the likelihood of substrate utilization. 13C enriched stable C pools were more likely to be utilized below 20 cm under warming of 2 °C in the desert steppe. Moreover, the interaction of T × W neither altered the CO2 emitted by soil nor the δ13CO2e or Δe-s, indicating that warming combined with precipitation may alleviate the SOC oxidation of soil enriched in 13C in the desert steppe.

Diel and seasonal patterns of soil CO2 efflux in a temperate tidal marsh

Tidal marshes store large amounts of carbon; however, little is known about the patterns, magnitudes, and biophysical drivers that regulate CO2 efflux from these ecosystems. Due to harsh environmental conditions (e.g., flooding), it is difficult to measure continuous soil CO2 efflux in tidal marshes. These data are necessary to inform empirical and process-based models and to better quantify carbon budgets. We performed automated (30 min) and manual (bi-monthly) soil CO2 efflux measurements, for ~20 months, at two sites in a temperate tidal marsh: tall Spartina (TS; dominated by S. cynosuroides) and short Spartina (SS; dominated by S. alterniflora). These measurements were coupled with water quality, canopy spectral reflectance, and meteorological measurements. There were no consistent diel patterns of soil CO2 efflux, suggesting a decoupling of soil CO2 efflux with diel variations in temperature and tides (i.e., water level) showing a hysteresis effect. Mean soil CO2 efflux was significantly higher at SS (2.15 ± 1.60 μmol CO2 m−2 s−1) than at TS (0.55 ± 0.80 μmol CO2 m−2 s−1), highlighting distinct biogeochemical spatial variability. At the annual scale, air temperature explained >50% of the variability in soil CO2 efflux at both sites; and water level and salinity were secondary drivers of soil CO2 efflux at SS and TS, respectively. Annual soil CO2 efflux varied from 287-876 to 153-211 g C m−2 y−1 at SS and TS, respectively, but manual measurements underestimated the annual flux by <67% at SS and <23% at TS. These results suggest that measuring and modeling diel soil CO2 efflux variability in tidal marshes may be more challenging than previously expected and highlight large discrepancies between manual and automated soil CO2 efflux measurements. New technical approaches are needed to implement long-term automated measurements of soil CO2 efflux across wetlands to properly estimate the carbon balance of these ecosystems.

Spatio-temporal variability in soil CO2 efflux and regulatory physicochemical parameters from the tropical urban natural and anthropogenic land use classes

Urban ecosystems, the heterogeneous and rapidly changing landscape, showed a considerable impact on the global C cycle. However, studies encompassing the spatial differences in urban land uses on soil C dynamics are limited in tropical ecosystems. In this study, seasonal and temporal variability in soil CO2 efflux (SCE) and its regulatory physicochemical variables under five urban land use classes viz., Bare (BAR), Agriculture (AGR), Plantation (PLT), Grassland (GRA) and Lawns (LAW) were assessed from 2014 to 2016. Bare land use was considered as the reference for observing the variation for different land uses. Seasonal measurements of SCE, soil temperature, moisture content, pH, ammonium-N, nitrate-N and microbial biomass C (MBC) were performed whereas soil organic C (SOC), soil N, and soil physical properties were measured annually. Our results showed a significant (P < 0.01) increase in SCE by 89%, 117%, 132% and 166% for land use types from BAR to AGR, PLT, GRA and LAW, respectively. The results revealed a two-fold increase in SCE from anthropogenically managed urban lawns as compared to bare soil. PLT and LAW land use classes showed higher SOC and N contents. SCE was found positively correlated with temperature, moisture, SOC, soil N and MBC whereas negatively correlated with ammonium-N and nitrate-N (at P < 0.05) for the overall dataset. Soil moisture, temperature, SOC, porosity and pH were identified as the major determinant of urban SCE by explaining 63% of the variability in overall SCE. Further, temperature for BAR and LAW; moisture for PLT; ammonium-N for GRA; and nitrate-N for AGR were identified as the major regulators of SCE for different land use classes. The findings revealed that the interaction of soil temperature and moisture with nutrient availability regulates overall and seasonal variability in SCE in an urban ecosystem. Since these variables are highly affected by climate change, thus, the soil C source-sink relationships in tropical urban ecosystems may further change and induce a positive global warming potential from urban ecosystems.

Impact of climate and land degradation on soil carbon fluxes in dry semiarid grasslands in SE Spain

This study investigates how precipitation, temperature and seasonality (as a proxy of plant productivity) affect the temporal and spatial variability of soil CO2 efflux in two dry semiarid grasslands with different degrees of land degradation. We measured soil CO2 efflux over four years under plant, biological soil crust and bare soil patches and estimated annual soil carbon losses in both, a natural and a degraded grassland, by means of generalised additive mixed models considering temporal autocorrelation in the data. Soil CO2 efflux ranged from 0.08 to 3.70 and from 0.10 to 3.01 μmol CΟ2 m−2 s−1 in the natural and degraded grasslands, respectively. Daily soil CO2 efflux was mostly affected by moisture in the degraded grassland (25.4%), while in the natural grassland was affected jointly by seasonality, temperature and moisture (27.5%). Overall, the highest soil carbon fluxes were measured in soils covered by biological soil crusts (1.24 ± 0.02 and 1.10 ± 0.02) and the lowest in bare soils (1.11 ± 0.02 and 0.82 ± 0.02 μmol CΟ2 −2 s−1) in the natural and degraded sites, respectively. Cumulative soil carbon fluxes were mainly driven by temperature and previous precipitation (over three months). The highest soil carbon losses were estimated in the driest year (2009) and the lowest in the wettest (2010) with almost twice the amount of rainfall. The main difference between these years was the timing of the events that mostly occurred in the moments of maximum plant activity with optimum temperatures in spring in the dry year. Changes in precipitation patterns will affect soil carbon fluxes more than rainfall amount, particularly in degraded grasslands. Therefore, considering all climate drivers together with plant activity is essential to predict how climate change will affect soil biological processes in drylands.

How Simulations of the Land Carbon Sink Are Biased by Ignoring Fluvial Carbon Transfers: A Case Study for the Amazon Basin

Summary Land-surface models are important tools for simulation of the past, present, and future capacity of terrestrial ecosystems to absorb anthropogenic CO2 emissions. However, fluvial carbon (C) transfers are presently neglected in these models. Using the Amazon basin as a case study, we show that this negligence leads to significant underestimation of the net uptake of atmospheric C while terrestrial C storage changes are overestimated. These biases arise from the fact that C—in reality, leached from soils and exported through the river network—is instead represented as partly being respired and partly being stored in soils. Moreover, these biases scale mainly to the fluvial C export to the coast, despite aquatic CO2 emission to the atmosphere being the major pathway of riverine C exports. We further show that fluvial C transfers may change significantly in response to changes in either hydrology or in atmospheric C uptake by vegetation.

Temporal variations in soil CO2 efflux in an alpine meadow site on the Qinghai–Tibetan Plateau

AbstractTemporal variations in soil CO2 efflux and its direct links to soil microbial biomass and environmental factors in high‐elevation regions are poorly understood. In this study, I investigated the variations in soil CO2 efflux over time and their relationships to soil organic matter, soil microbial biomass and environmental factors in an alpine meadow site on the Qinghai–Tibetan Plateau. The results showed notable monthly to seasonal changes in soil CO2 efflux in alpine meadows. The soil CO2 efflux was lower overall from January to May and from October to December than from June to September (p &lt; 0.05); on a seasonal basis, the soil CO2 efflux was lower during the spring, autumn and winter than during the summer (p &lt; 0.05). In addition, linear regression analysis showed that the temporal variations in soil CO2 efflux over the whole year decreased with soil microbial biomass carbon content (p &lt; 0.05). Soil CO2 efflux was also positively related to air temperature and snow cover depth (p &lt; 0.05). Multiregression and principal component regression analyses indicated that temporal variations in soil CO2 efflux were mainly caused by monthly and seasonal changes in air temperature and soil microbial biomass.

Temporal and spatial variability in soil CO2 efflux in the patagonian steppe

Soil respiration is a major flux of CO2 to the atmosphere. Despite its significance there is a limited understanding of its magnitude, controlling factors and how it varies over time and space in arid ecosystems. We evaluated the temporal pattern of soil CO2 efflux and their response to rain pulses in a patagonian steppe, taking into account the spatial heterogeneity (bare soil and vegetated patches). We measured soil CO2 efflux in bare soil and vegetated patches along the year. We also analyzed physical and chemical soil traits, root density and heterotrophic bacterial count. Soil water content and temperature exhibited seasonal variability and it was larger in bare soil patches than in vegetated patches. Root density, organic matter and phosphorus were higher in vegetated patches than in bare soil. CO2 efflux was 48% higher in vegetated patches than in bare soil patches. Soil CO2 efflux decreased from summer to winter, reaching its maximum value (about 0.6 μmol m2 s−1) in spring. In both patch types, soil CO2 efflux was explained by the interaction between soil temperature and soil water content. Soil CO2 efflux also was positively correlated with soil root density. Bare soil and vegetated patches exhibited distinct response to a rain pulses. Vegetated patches were highly sensitive to rainfall events, generating a large CO2 pulse, returning to previous values after three days. Bare soil CO2 efflux did not exhibit significant changes after a rain pulse. In patagonian arid ecosystems, the seasonal variation in soil respiration is explained mainly by the interaction between soil temperature and water content. Bare soil patches had higher water content but lower root density resulting in lower soil CO2 respiration than vegetated patches. However, at ecosystem level the contribution of bare soil to total soil CO2 efflux was similar to the contribution of vegetated patches because bare soil cover is 65% in the study area. Changes in the number of small rain events as well as changes in plant cover could have large consequences on soil ecology and biochemistry in dry and heterogeneous ecosystems.

Geomorphologic heterogeneity influences dry-season soil CO2 efflux by mediating soil biophysical variables in a tropical river valley

Riparian landscapes are characterized by heterogeneous geomorphological structures such as erosive and depositional habitats, and therefore, may have variable soil biophysical properties. The heterogeneity in geomorphological structures and related biophysical properties would exert spatial variations in the soil CO2 efflux (SCE). However, studies assessing the relative control of biophysical variables on the SCE under such complex landscapes of dry tropical ecosystems are limited. Therefore, we assessed the effect of heterogeneity in geomorphological structures on SCE, and identified the key biophysical variables governing SCE along the riparian landscapes. The SCE, soil organic C (SOC), microbial biomass C (MBC) and pH were found to vary significantly (P < 0.05) along riparian habitats, and SCE was found 73% higher at erosive than depositional habitats. SOC was found as a prominent regulator of SCE which alone explained about 80% of the variability in SCE. Moreover, soil moisture, fine particles, pH and MBC also showed strong control on SCE along riparian landscapes. Stepwise regression analysis revealed that after excluding SOC as a main variable, soil moisture explained 32% of the variability in SCE at overall landscape level whereas fine particles and MBC explained 78% and 23% of the variability in SCE at erosive and depositional habitats, respectively. Overall, results indicate that erosive habitats are the major source of SCE, and variation in biophysical variables is greatly affecting the SCE at these habitats. Therefore, further assessment of interactions of SCE, soil biophysical parameters and their regulatory components such as hydrology, vegetation and anthropogenic activities at micro—(site and land-use) as well as macro—(landscape) scales would help to understand the soil C dynamics along the heterogeneous riparian landscapes under climate change scenarios.

Soil respiration partitioning in afforested temperate peatlands

Understanding and quantifying soil respiration and its component fluxes are necessary to model global carbon cycling in a changing climate as small changes in soil CO2 fluxes could have important implications for future climatic conditions. A soil respiration partitioning study was conducted in eight afforested peatland sites in south-west Ireland. Using trenched points, annual soil CO2 emissions, and the contributions of root and heterotrophic respiration as components of total soil respiration, were estimated. Nonlinear regression models were evaluated to determine the best predictive soil respiration model for each component flux, using soil temperature and water table level as explanatory variables. Temporal variation in soil CO2 efflux was driven by soil temperature at 10 cm depth, with all treatment points also affected by water table level fluctuations. The effect of water table level on soil respiration was best accounted for by incorporating a water level Gaussian function into the soil-temperature–soil-respiration model. Mean root respiration was 44% of mean total soil respiration, varying between 1100 and 2049 g CO2 m−2 year−1. Heterotrophic respiration was divided between peat respiration and litter respiration, which accounted for 35 and 21% of total soil respiration, respectively. While peat respiration varied between 774 and 1492 g CO2 m−2 year−1, litter respiration varied between 514 and 1013 g CO2 m−2 year−1. Although the extrapolation of these results to other sites should be done with caution, the empirical models developed for the entire dataset in this study are a useful tool to predict and simulate CO2 emissions in similar afforested peatlands (e.g. pine and spruce plantations) in temperate maritime climate conditions.

Seasonal and inter-annual variability of soil CO2 efflux in a Norway spruce forest over an eight-year study

Automated soil CO2 efflux chamber measurements were carried out over a period of eight years in a young Norway spruce forest in the northeast region of the Czech Republic to determine seasonal and inter-annual variables affecting this flux. The data obtained was summarized and analysed with the aims of estimating long-term carbon losses from the soil and comparing selected models to determine the model best describing soil CO2 efflux. Our results show that seasonal variation in soil CO2 efflux was driven mainly by soil temperature, while inter-annual variation showed the closest relationship with precipitation. The total amount of carbon released from the soil into the atmosphere per season varied from 6.4 to 11.2 tC ha−1 over the eight-year record. One of the variables used in the CO2 efflux models, beside environmental variables, was day of year (DOY). Incorporating this variable into models improved the estimation of soil CO2 efflux dynamics. Therefore, we assume that models incorporating DOY could be used effectively to gap-fill measured soil chamber data. These models could also be appropriate for filling longer gaps on a scale from days to weeks, because DOY, as a single parameter, covers up to 80% of variability in the data. This study also demonstrated the different levels of correlation between investigated climate variables and soil CO2 efflux at seasonal and inter-annual time scales. This highlights the importance of different environmental variables in interpreting long-term soil CO2 efflux data and also modelling the complexity of the processes connected with soil CO2 efflux in Norway spruce forest.

Soil CO2 efflux in a warm-temperature and sub-alpine forest in Jeju, South Korea

BackgroundThis study investigated the temporal variation in soil CO2 efflux and its relationship with soil temperature and precipitation in the Quercus glauca and Abies koreana forests in Jeju Island, South Korea, from August 2010 to December 2012. Q. glauca and A. koreana forests are typical vegetation of warm-temperate evergreen forest zone and sub-alpine coniferous forest zone, respectively, in Jeju island.ResultsThe mean soil CO2 efflux of Q. glauca forest was 0.7 g CO2 m−2 h−1 at 14.3 °C and that of A. koreana forest was 0.4 g CO2 m−2 h−1 at 6.8 °C. The cumulative annual soil CO2 efflux of Q. glauca and A. koreana forests was 54.2 and 34.2 t CO2 ha−1, respectively. Total accumulated soil carbon efflux in Q. glauca and A. koreana forests was 29.5 and 18.7 t C ha−1 for 2 years, respectively. The relationship between soil CO2 efflux and soil temperate at 10 cm depth was highly significant in the Q. glauca (r2 = 0.853) and A. koreana forests (r2 = 0.842). Soil temperature was the main controlling factor over CO2 efflux during most of the study period. Also, precipitation may affect soil CO2 efflux that appeared to be an important factor controlling the efflux rate.ConclusionsSoil CO2 efflux was affected by soil temperature as the dominant control and moisture as the limiting factor. The difference of soil CO2 efflux between of Q. glauca and A. koreana forests was induced by soil temperature to altitude and regional precipitation.

Spatial variability of soil CO2 efflux in drip-irrigated old and young citrus orchards and its dependence on biotic and abiotic factors

Quantification of soil respiration (Rs) is an essential step in modelling soil carbon fluxes associated with stand structure and management. This study aims to characterise the spatial variations of Rs at tree scale in adult (AO) and young (YO) drip-irrigated orange orchards, with special focus on abiotic (soil moisture, θs) and biotic (stand age and root traits) factors determining the variability of Rs. Rs, soil temperature (Ts), θs, soil organic carbon content (OC) and root traits were sampled along three transects parallel to the drip-line. Measurements were carried out in autumn, with mean Ts over the sampling area close to 18°C. Heterotrophic respiration (Rh) was determined in undisturbed non-rooted soil, and root-derived (or rhizosphere) respiration (Rr) was estimated from the difference Rs−Rh. Root distribution and root density were closely correlated with θs. Fine-root density appeared to play a major role in the control of Rs, explaining a great part of the spatial variability of Rs. The ratio Rh/Rs, estimated by means of a simple partitioning model, appeared to decrease with stand age (~0.68 and ~0.32 in YO and AO, respectively), indicating the predominance of Rh in the young orchard and of Rr in the old one. The study highlights that stand structure plays a determinant role in driving the spatial variability of Rs and its partitioning between heterotrophic and root-derived respiration in irrigated orchards.

Spatial variability of soil CO2 efflux in the forest-tundra zone of West Siberia (novy Urengoi): control of abiotic factors.

Spatial variability of soil CO2 efflux in the forest-tundra zone of West Siberia (novy Urengoi): control of abiotic factors.

Вклад абиотических факторов в пространственное варьирование эмиссии СО2 почв лесотундровой зоны Западной Сибири (Новый Уренгой)

Вклад абиотических факторов в пространственное варьирование эмиссии СО2 почв лесотундровой зоны Западной Сибири (Новый Уренгой)

Impacts of water regime and land-use on soil CO2 efflux in a small temperate agricultural catchment

Within the context of climate change, it is necessary to improve our mechanistic understanding of processes that release CO2 to the atmosphere. This study was designed to investigate spatial variation of soil CO2 efflux (FCO2) at the landscape (catchment) scale, which has received less attention so far in comparison to more homogeneous, smaller areas. More specifically, this study investigated the impacts of water regime, land-use and crop rotation on FCO2 in a small temperate agricultural catchment. FCO2 was measured manually with closed dynamic chambers over a 1 year period (36 weekly to bi-weekly measurement dates) at 22 sites that were selected to represent most of the diversity of drainage classes, soil types and land-uses in a small catchment in North-Western France. FCO2 was modelled empirically at each site as a function of soil temperature and soil water content. As a secondary step, impacts of water regime, land-use and crop rotation on heterotrophic respiration (HR) were also sought, with HR being estimated empirically as a fraction of FCO2 on the basis of partitioning coefficients taken from the literature. Results showed that water regime, land-use and crop rotation all had significant impacts on FCO2 on an annual scale. Poorly-drained sites emitted less CO2 than well-drained and moderately-well drained sites, which could be explained by reduced soil CO2 production and/or limitations in soil transport in more saturated environments. In addition, larger annual FCO2 were measured on grasslands compared to croplands (wheat and maize crops), which is likely due to the presence of larger amounts of available soil carbon and nutrients and to the presence or denser rooting systems. Due to the literature-based determination of partitioning coefficients, the results related to HR estimates were affected by more uncertainties than those related to FCO2 but they showed that the water regime tended to impact them similarly as FCO2, while HR was likely less affected by land-use. Altogether, the results of this study, performed at scale of a small agricultural temperate catchment, confirm that specific patterns of FCO2 result from varying soil CO2 production and transport processes, resulting from complex interactions between soil environment characteristics (soil carbon content, water regime,…) and land-use/crop rotations.

Diurnal variation of soil CO2 efflux and its optimal measuring time-window of temperate meadow steppes in western Songnen Plain, China

In order to study the diurnal variation of soil CO2 efflux from temperate meadow steppes in Northeast China, and determine the best time for observation, a field experiment was conducted with a LI-6400 soil CO2 flux system under five typical plant communities (Suaeda glauca (Sg), Chloris virgata (Cv), Puccinellia distans (Pd), Leymus chinensis (Lc) and Phragmites australis (Pa)) and an alkali-spot land (As) at the meadow steppe of western Songnen Plain. The results showed that the diurnal variation of soil CO2 efflux exhibited a single peak curve in the growing season. Diurnal maximum soil respiration (Rs) often appeared between 11:00 and 13:00, while the minimum occurred at 21:00–23:00 or before dawn. Air temperature near the soil surface (Ta) and soil temperature at 10 cm depth (T10) exerted dominant control on the diurnal variations of soil respiration. The time-windows 7:00–9:00 could be used as the optimal measuring time to represent the daily mean soil CO2 efflux at the Cv, Pd, Lc and Pa sites. The daily mean soil CO2 efflux was close to the soil CO2 efflux from 15:00 to 17:00 and the mean of 2 individual soil CO2 efflux from 15:00 to 19:00 at the As and Sg sites, respectively. During nocturnal hours, negative soil CO2 fluxes (CO2 downwards into the soil) were frequently observed at the As and Sg sites, the magnitude of the negative CO2 fluxes were 0.10–1.55 μmol/(m2·s) and 0.10–0.69 μmol/(m2·s) at the two sites. The results implied that alkaline soils could absorb CO2 under natural condition, which might have significant implications to the global carbon budget accounting.