Soil Carbon Turnover Research Articles

Chemical Composition of Plant Residues Regulates Soil Organic Carbon Turnover in Typical Soils with Contrasting Textures in Northeast China Plain

Soil organic carbon (SOC) turnover plays a pivotal role in achieving C neutrality, promoting C retention and increasing soil fertility. Residue biochemistry and soil texture essentially determine SOC distribution (including CO2 mineralization and stock in soil) in farmland. However, less is known about allocation of residue-C with contrasting biochemistry and the fate of residue-C in soil under two different textures. This study was conducted in a 61-day aerobic incubation with two Black soils with distinct texture (clay loam vs. sandy loam) in Northeast China. Chemical composition of seven residue parts (soybean roots, leaves, and stems and maize roots, leaves and top and bottom stem parts) was characterized using solid-state 13C nuclear magnetic resonance spectroscopy. The results showed that leaves of both two crops contained significantly higher nitrogen (N), carbonyl and aryl concentrations and lower carbon (C) and lignin concentrations than other parts, resulted in faster decomposition in soils, especially in the clay loam. Stems contained higher O-alkyl and di-O-alkyl concentrations, C/N and lignin/N, while roots contained higher aromaticity. Maize top stem parts with larger slow C pool and longer half-life had higher contribution to SOC accumulation than other parts. Soil textures also induced great impact on SOC turnover. The clay loam favored SOC sequestration due to significantly longer half-life of slow C pool than the sandy loam. Generally, the alkyl/O-alkyl ratio showed the most significant correlation with SOC, CO2 emission and soil biochemical factors in the clay loam; whereas in sandy loam, the lignin/N was the pivotal indicator for SOC accumulation. This study provides insights into the differences in chemical composition among various residue parts, and highlights the significant effects of both residue chemical composition and soil texture on residue decomposition and SOC accumulation.

Content of soil organic carbon and labile fractions depend on local combinations of mineral-phase characteristics

Abstract. Soil organic matter (SOM) is an indispensable component of terrestrial ecosystems. Soil organic carbon (SOC) dynamics are influenced by a number of well-known abiotic factors such as clay content, soil pH, or pedogenic oxides. These parameters interact with each other and vary in their influence on SOC depending on local conditions. To investigate the latter, the dependence of SOC accumulation on parameters and parameter combinations was statistically assessed that vary on a local scale depending on parent material, soil texture class, and land use. To this end, topsoils were sampled from arable and grassland sites in south-western Germany in four regions with different soil parent material. Principal component analysis (PCA) revealed a distinct clustering of data according to parent material and soil texture that varied largely between the local sampling regions, while land use explained PCA results only to a small extent. The PCA clusters were differentiated into total clusters that contain the entire dataset or major proportions of it and local clusters representing only a smaller part of the dataset. All clusters were analysed for the relationships between SOC concentrations (SOC %) and mineral-phase parameters in order to assess specific parameter combinations explaining SOC and its labile fractions hot water-extractable C (HWEC) and microbial biomass C (MBC). Analyses were focused on soil parameters that are known as possible predictors for the occurrence and stabilization of SOC (e.g. fine silt plus clay and pedogenic oxides). Regarding the total clusters, we found significant relationships, by bivariate models, between SOC, its labile fractions HWEC and MBC, and the applied predictors. However, partly low explained variances indicated the limited suitability of bivariate models. Hence, mixed-effect models were used to identify specific parameter combinations that significantly explain SOC and its labile fractions of the different clusters. Comparing measured and mixed-effect-model-predicted SOC values revealed acceptable to very good regression coefficients (R2=0.41–0.91) and low to acceptable root mean square error (RMSE = 0.20 %–0.42 %). Thereby, the predictors and predictor combinations clearly differed between models obtained for the whole dataset and the different cluster groups. At a local scale, site-specific combinations of parameters explained the variability of organic carbon notably better, while the application of total models to local clusters resulted in less explained variance and a higher RMSE. Independently of that, the explained variance by marginal fixed effects decreased in the order SOC > HWEC > MBC, showing that labile fractions depend less on soil properties but presumably more on processes such as organic carbon input and turnover in soil.

Predicting Soil Organic Carbon Mineralization Rates Using δ13C, Assessed by Near-Infrared Spectroscopy, in Depth Profiles Under Permanent Grassland Along a Latitudinal Transect in Chile

Carbon (C) mineralization and turnover in soil rely on complex interactions among environmental variables that differ along latitudinal gradients. This study aims to quantify the relationship between the variation in δ13C signature with soil depth (∆δ13C) and soil C turnover across a large geo-climatic gradient. Thirteen grassland sites were sampled along a 4000 km latitudinal gradient in Chile. Maximizing climatic and physicochemical soil’s diversity to test the index with the widest range of application. We used near-infrared spectroscopy (NIRS) to estimate δ13C of SOC at several soil depths. To assess soil C mineralization rates (CMR) and specific potential respiration (SPR) as proxies for C mineralization and turnover, using ∆δ13C, soil incubations were performed. Highest 13C isotope abundance was found at low latitude (− 22.57‰, 35.5°S) and lowest at high latitude (− 27.43‰, 53.2°S). Our results show 13C’s enrichment in parallel with decreasing C content with depth. The analysis of the relationship between ∆δ13C values versus CMR and SPR showed a significant positive relationship across all data points (p < 0.0001, R2 = 0.62; p < 0.01, R2 = 0.29, respectively). Partial correlation analysis of control variables indicates a relationship between ∆δ13C with CMR and SPR when controlling for climatic and soil physicochemical variables. ∆δ13C calculated from NIRSs may serve as a proxy to research the potential degradability of SOM and its interaction with soil geochemistry. Uncertainty and variability in the prediction power of our model reveals the importance of considering the latitudinal changeability in soil types as a control on properties controlling ∆δ13C.

Can Regenerative Agriculture increase national soil carbon stocks? Simulated country-scale adoption of reduced tillage, cover cropping, and ley-arable integration using RothC

Adopting Regenerative Agriculture (RA) practices on temperate arable land can increase soil organic carbon (SOC) concentration without reducing crop yields. RA is therefore receiving much attention as a climate change mitigation strategy. However, estimating the potential change in national soil carbon stocks following adoption of RA practices is required to determine its suitability for this. Here, we use a well-validated model of soil carbon turnover (RothC) to simulate adoption of three regenerative practices (cover cropping, reduced tillage intensity and incorporation of a grass-based ley phase into arable rotations) across arable land in Great Britain (GB). We develop a modelling framework which calibrates RothC using studies of these measures from a recent systematic review, estimating the proportional increase in carbon inputs to the soil compared to conventional practice, before simulating adoption across GB. We find that cover cropping would on average increase SOC stocks by 10 t·ha−1 within 30 years of adoption across GB, potentially sequestering 6.5 megatonnes of carbon dioxide per year (MtCO2·y−1). Ley-arable systems could increase SOC stocks by 3 or 16 t·ha−1, potentially providing 2.2 or 10.6 MtCO2·y−1 of sequestration over 30 years, depending on the length of the ley-phase (one and four years, respectively, in these scenarios). In contrast, our modelling approach finds little change in soil carbon stocks when practising reduced tillage intensity. Our results indicate that adopting RA practices could make a meaningful contribution to GB agriculture reaching net zero greenhouse gas emissions despite practical constraints to their uptake.

Intense wet-dry cycles weakened the carbon sequestration of soil aggregates in the riparian zone

Increasing the frequency and magnitude of wet-dry cycles can fundamentally affect soil carbon (C) turnover. However, the response of soil respiration to intense wet-dry cycles in the riparian zone is unclear. Hence, this study aimed to identify whether soil respiration and soil aggregates in different land use types were affected by different flooding intensities in the riparian zone of the Three Gorges Reservoir, China, and determine the responses of soil organic carbon (SOC) sequestration by soil aggregates to wet-dry cycles in the riparian zone. At the Wuyangwan of the Pengxi River, a tributary of the Yangtze River in the Three Gorges Reservoir, soil respiration and soil aggregates were investigated at different elevations of the riparian zone with representative land use types, namely a cornfield (173C) and a paddy field (173P), both at an elevation of 173 m above sea level, and two paddy fields, 168 m and 163 m above sea level (168P and 163P). The results showed that soil aggregate stability increased (e.g., the mean weight diameter increased by 38% and 18% for 173C and 173P, respectively) in the low flooding intensity sites and decreased (e.g., the mean weight diameter decreased by 44% and 33% for 168P and 163P, respectively) in strong flooding intensity sites after four wet-dry cycles in the riparian zone of the Three Gorges Reservoir. Moreover, the wet-dry cycles increased soil respiration (i.e., the soil respiration increased by 36%, 218%, 129%, and 31% for 173C, 173P, 168P, and 163P, respectively). In addition, soil aggregate stability had a direct negative effect on soil respiration (namely, the mitigation of CO2 emissions), and the negative effect weakened after four intense wet-dry cycles (pathway coefficient was −0.76 in 2014 and −0.28 in 2018). Thus, the carbon sequestration of soil aggregates was weakened in the riparian zone. The size of the soil aggregate fractions and their organic carbon contents directly or indirectly affected soil respiration. Most notably, the proportion of microaggregates and their associated nitrogen and organic carbon contents strongly influenced soil respiration. Finally, from the perspective of maintaining soil aggregate stability and SOC sequestration, we suggest that agricultural activities should be prohibited in areas with high flooding intensity in the riparian zones.

Soil Carbon Turnover and Changes in Soil Nitrogen under the Agropastoral System in Brazilian Savannas (Cerrados)

Soil Carbon Turnover and Changes in Soil Nitrogen under the Agropastoral System in Brazilian Savannas (Cerrados)

Differential Responses of Soil Organic Carbon Fractions and Carbon Turnover Related Enzyme Activities to Wheat Straw Incorporation in Subtropical China

Soil organic carbon (SOC) fractions and C turnover related enzyme activities are essential for nutrient cycling. This is because they are regarded as important indicators of soil fertility and quality. We measured the effects of wheat straw incorporation on SOC fractions and C turnover related enzyme activities in a paddy field in subtropical China. Soil samples were collected from 0–10 cm and 10–20 cm depths after rice harvesting. The total SOC concentrations were higher in the high rate of wheat straw incorporation treatment (NPKS2) than in the not fertilized control (CK) (P

Divergences of soil carbon turnover and regulation in alpine steppes and meadows on the Tibetan Plateau

The grasslands of the Tibetan Plateau store approximately 2.5% of global soil organic carbon (SOC) and considerable soil inorganic carbon (SIC) and have the potential to become a vast carbon source or sink as climate change progresses. However, the soil carbon (C) sequestration mechanisms that occur across large-scale natural gradients remain unclear. Here, humic substances (HS) were utilized to trace soil C turnover at 0–20 cm, and we compared divergences among three main grassland types (alpine meadow, alpine steppe, and artificial plantation) using structural equation modeling (SEM). The results showed that the alpine meadows sequestered the most soil C (63.99 ± 4.41 g kg−1 SOC and 4.11 ± 0.63 g kg−1 SIC), sequestering 2–3 times more than the alpine steppe ecosystems (19.78 ± 1.98 g kg−1 SOC and 9.21 ± 0.66 g kg−1 SIC). The alpine steppe and artificial plantation regions have strong C sink potential due to their low C/N ratios (P < 0.05). Importantly, SIC played an important role in the alpine steppes, accounting for nearly 26–37% of soil C. The ratios of recalcitrant HS to SOC were estimated as 46.50%, 65.09%, and 78.17% in the alpine meadow, alpine steppe, and artificial plantation ecosystems, respectively, indicating that SOC in the alpine meadow was the most sensitive to climate change. Fulvic acid (FA) accounted for 50.86% of SOC in the 0–20-cm interval, contributing most to the formation of SOC in all vegetation types. In addition, in contrast to climatic controls on soil C turnover in the alpine meadow, climate conditions rarely controlled C turnover in the alpine steppe. Moreover, sand and silt were the main soil minerals involved in C turnover in alpine meadow and alpine steppe ecosystems, respectively. Our study improves understanding of the mechanism by which soil C sinks form on the Tibetan Plateau under warming and wetting conditions.

Microbial Necromass in Soils—Linking Microbes to Soil Processes and Carbon Turnover

The organic matter of living plants is the precursor material of the organic matter stored in terrestrial soil ecosystems. Although a great deal of knowledge exists on the carbon turnover processes of plant material, some of the processes of soil organic matter (SOM) formation, in particular from microbial necromass, are still not fully understood. Recent research showed that a larger part of the original plant matter is converted into microbial biomass, while the remaining part in the soil is modified by extracellular enzymes of microbes. At the end of its life, microbial biomass contributes to the microbial molecular imprint of SOM as necromass with specific properties. Next to appropriate environmental conditions, heterotrophic microorganisms require energy-containing substrates with C, H, O, N, S, P, and many other elements for growth, which are provided by the plant material and the nutrients contained in SOM. As easily degradable substrates are often scarce resources in soil, we can hypothesize that microbes optimize their carbon and energy use. Presumably, microorganisms are able to mobilize biomass building blocks (mono and oligomers of fatty acids, amino acids, amino sugars, nucleotides) with the appropriate stoichiometry from microbial necromass in SOM. This is in contrast to mobilizing only nutrients and consuming energy for new synthesis from primary metabolites of the tricarboxylic acid cycle after complete degradation of the substrates. Microbial necromass is thus an important resource in SOM, and microbial mining of building blocks could be a life strategy contributing to priming effects and providing the resources for new microbial growth cycles. Due to the energy needs of microorganisms, we can conclude that the formation of SOM through microbial biomass depends on energy flux. However, specific details and the variability of microbial growth, carbon use and decay cycles in the soil are not yet fully understood and linked to other fields of soil science. Here, we summarize the current knowledge on microbial energy gain, carbon use, growth, decay, and necromass formation for relevant soil processes, e. g. the microbial carbon pump, C storage, and stabilization. We highlight the factors controlling microbial necromass contribution to SOM and the implications for soil carbon use efficiency (CUE) and we identify research needs for process-based SOM turnover modelling and for understanding the variability of these processes in various soil types under different climates.

Organic Amendments Alter Long-Term Turnover and Stability of Soil Carbon: Perspectives from a Data-Model Integration

Organic amendment (OA) additions may profoundly regulate the turnover behaviours of soil organic carbon (SOC). Explicit understanding of such role of OA is crucial for accurately assessing the potential of carbon sequestration in agricultural soils. To explore the effects of OA additions on the detailed SOC stabilization and destabilization processes, we collected SOC measurements from 29 trials with experimental duration ranging from 14 to 85 years across the globe. Using these datasets, we constrained a soil carbon model to analyse SOC turnover and built-up processes as impacted by OA additions. We found that OA generally decreases microbial carbon use efficiency (CUE) and the fraction of inert SOC that is resistant to decomposition (finert), but has divergent effects on the decay rate of humic SOC (khum). Across the sites, there was great variability in the effects of OA on CUE, khum, and finert, which can be largely explained by local soil and climate conditions and the quantity and quality of OA. Long-term simulations suggested that, without considering the effects of OA on CUE, khum, and finert, the effectiveness of OA additions for carbon sequestration could be largely overestimated. Our results suggest that the strong site-specific regulations of OA on SOC dynamics as demonstrated in this study must be properly considered and better constrained by observational data when assessing SOC sequestration in agricultural soils under the management of OA additions.

Overestimation of global soil heterotrophic respiration

The new estimate of Rh (represented by red lines) in Ciais et al (2020) is generally far smaller than that from the Trendy (16 out of 17) and the MsTMIP (8 out of 12) models as well as the ensemble means of all models (represented by blue dashed lines). The overestimated Rh in global land-carbon cycle models could possibly give rise to inaccurate simulations of soil carbon turnover, and the global land-atmospheric carbon exchange.

Plant input does not exert stronger control on topsoil carbon persistence than climate in alpine grasslands.

Chen et al. (Ecology Letters, 2021, 24, 1018) concluded that plant input governs topsoil carbon persistence in alpine grasslands. We demonstrated that the excluded direct effect of precipitation on topsoil Δ14 C in their analysis was significant and strong. Our results provide an alternative viewpoint on the drivers of soil carbon turnover.

Subsoil organic carbon turnover is dominantly controlled by soil properties in grasslands across China

Soil organic carbon turnover time (τ, year) is an important indicator of soil carbon stability and a major factor determining soil carbon sequestration capacity. Many previous studies have investigated τ in the topsoil layers, but little is known about subsoil τ and its environmental drivers. We estimated subsoil τ (the ratio of subsoil organic carbon (OC) stock to net primary production) using field observations from the published literatures and employed regression analysis and the structural equation model (SEM) to identify the effects of climate, soil, and vegetation variables on subsoil τ in China’s grasslands. The results showed that the average subsoil τ over 0.2–1 m varied greatly from 5.5 to 702.2 years, with a mean (±standard deviation) of 118.5 ± 97.8 years. Subsoil τ varied significantly among different grassland types, with 164.0 ± 112.0 years for alpine meadow, 107.0 ± 47.9 years for alpine steppe, 177.0 ± 143.0 years for temperate desert steppe, 96.6 ± 88.7 years for temperate meadow steppe, and 101.0 ± 75.9 years for temperate typical steppe. Subsoil τ was significantly negatively correlated (p < 0.05) with normalized difference vegetation index, leaf area index, and gross primary production. Mean annual (air) temperature and precipitation had a negative impact on τ, indicating a faster turnover of soil carbon with a changing climate. Based on SEM, soil properties mainly drove subsoil τ, challenging our current understanding and providing evidence that different factors control topsoil and subsoil τ. In this sense, different environmental factors should be considered to reliably predict soil carbon dynamics at the top of 1 m and subsoils in biogeochemical models or Earth system models at regional or global scales.

Calibration of the EU-Rotate_N model with measured C and N mineralization from potential fertilizers and evaluation of its prediction of crop and soil data from a vegetable field trial

Mechanistic models are useful tools for understanding and taking account of the complex, dynamic processes such as carbon (C) and nitrogen (N) turnover in soil and crop growth. In this study, the EU-Rotate_N model was first calibrated with measured C and N mineralization from nine potential fertilizer resources decomposing at controlled soil temperature and moisture. The materials included seaweeds, wastes from the food industry, food waste anaerobically digested for biogas production, and animal manure. Then the model’s ability to predict soil and crop data in a field trial with broccoli and potato was evaluated. Except for seaweed, up to 68% of added C and 54–86% of added N was mineralized within 60 days under controlled conditions. The organic resources fell into three groups: seaweed, high-N industrial wastes, and materials with high initial content of mineral N. EU-Rotate_N was successfully calibrated for the materials of industrial origin, whereas seaweeds, anaerobically digested food waste and sheep manure were challenging. The model satisfactorily predicted dry matter (DM) and N contents (root mean square; RMSE: 0.11–0.32) of the above-ground part of broccoli fertilized with anaerobically digested food waste, shrimp shell pellets, sheep manure and mineral fertilizers but not algal meal. After adjusting critical %N for optimum growth, potato DM and N contents were also predicted quite well (RMSE: 0.08–0.44). In conclusion, the model can be used as a learning and decision support tool when using organic materials as N fertilizer, preferably in combination with other models and information from the literature.

Micro-scale resolution of carbon turnover in soil - Insights from laser ablation isotope ratio mass spectrometry on water-glass embedded aggregates

Soil aggregates may stabilize carbon at mineral surfaces and in the interior, but resolving such micro-scale carbon (C) turnover at a scale of soil aggregates <2 mm is challenged by C contaminations during sample preparation such as from resin embedding. Here we introduce a novel C-free embedding method using silica gel for water glass formation, and applied it to soil aggregates from a C3/C4 vegetation change soil chronosequence (4, 10 and 19 years of Miscanthus cropping on former C3 soil) for subsequent δ13C and C turnover analyses using laser ablation isotope ratio mass spectrometry (LA-IRMS). We hypothesized that C-free embedding allows for the first time the comparison of C turnover at soil aggregates both in their center and at their outer surface. We found that using water glass embedding enabled δ13C analyses via LA-IRMS in all parts of the sample, free of any contaminations. There was a large micro-scale heterogeneity in δ 13C signals within aggregates, which increased with cropping duration (total range −5.5 to –41.5‰). Noteworthy, after 19 years Miscanthus materials were still found preferentially at soil aggregate surfaces and hardly in interior parts, documenting slow aggregate turnover but also success of the embedding technique for future micro-scale C dynamic analyses in environmental samples.

Carbon turnover times shape topsoil carbon difference between Tibetan Plateau and Arctic tundra

The Tibetan Plateau (TP) and Arctic permafrost constitute two large reservoirs of organic carbon, but processes which control carbon accumulation within the surface soil layer of these areas would differ due to the interplay of climate, soil and vegetation type. Here, we synthesized currently available soil carbon data to show that mean organic carbon density in the topsoil (0–10 cm) in TP grassland (3.12 ± 0.52 kg C m−2) is less than half of that in Arctic tundra (6.70 ± 1.94 kg C m−2). Such difference is primarily attributed to their difference in radiocarbon-inferred soil carbon turnover times (547 years for TP grassland versus 1609 years for Arctic tundra) rather than to their marginal difference in topsoil carbon inputs. Our findings highlight the importance of improving regional-specific soil carbon turnover and its controlling mechanisms across permafrost affected zones in ecosystem models to fully represent carbon-climate feedback.

Microbial Activity and Root Carbon Inputs Are More Important than Soil Carbon Diffusion in Simulating Soil Carbon Profiles

AbstractIt is well‐known that soil carbon composition and turnover rate vary with soil depth, and the responses of soil carbon to global change in deeper soil layers may differ from those near the surface. Therefore, vertically resolved soil carbon models are needed for accurately predicting future soil carbon under global warming. In this study, we developed a vertically resolved soil carbon model by including vertical transport of soil carbon and using Michaelis‐Menten kinetics for soil carbon decomposition by microbes. The model was calibrated against six sites with the observed profiles of both soil carbon concentration and 14C measurements, and against 91 forest sites with soil carbon concentrations across a wide range of climate and soil conditions for four forest types in Europe and China. Results of independent model validation at another 93 sites showed that the calibrated model explained 40%–94% of the observed variance of soil carbon concentrations at different depths. Model sensitivity analysis showed that microbial activity and root carbon inputs are more important than soil carbon diffusion in simulating soil carbon profile. Results from our study highlight the need for detailed measurements of soil microbial activities and root carbon input at different soil depths in the field.

Tracing plant-environment interactions from organismal to planetary scales using stable isotopes: a mini review.

Natural isotope variation forms a mosaic of isotopically distinct pools across the biosphere and flows between pools integrate plant ecology with global biogeochemical cycling. Carbon, nitrogen, and water isotopic ratios (among others) can be measured in plant tissues, at root and foliar interfaces, and in adjacent atmospheric, water, and soil environments. Natural abundance isotopes provide ecological insight to complement and enhance biogeochemical research, such as understanding the physiological conditions during photosynthetic assimilation (e.g. water stress) or the contribution of unusual plant water or nutrient sources (e.g. fog, foliar deposition). While foundational concepts and methods have endured through four decades of research, technological improvements that enable measurement at fine spatiotemporal scales, of multiple isotopes, and of isotopomers, are advancing the field of stable isotope ecology. For example, isotope studies now benefit from the maturation of field-portable infrared spectroscopy, which allows the exploration of plant-environment sensitivity at physiological timescales. Isotope ecology is also benefiting from, and contributing to, new understanding of the plant-soil-atmosphere system, such as improving the representation of soil carbon pools and turnover in land surface models. At larger Earth-system scales, a maturing global coverage of isotope data and new data from site networks offer exciting synthesis opportunities to merge the insights of single-or multi-isotope analysis with ecosystem and remote sensing data in a data-driven modeling framework, to create geospatial isotope products essential for studies of global environmental change.

Field Application of Organic Fertilizers Triggers N2O Emissions From the Soil N Pool as Indicated by 15N-Labeled Digestates

Anaerobic digestion (AD) can generate biogas while simultaneously producing digestate which can be used as fertilizer. Feedstocks used for AD influence digestate composition, which in turn may affect carbon (C) and nitrogen (N) turn-over in soils and subsequently influence nitrous oxide (N2O) emissions after soil application. Assessment of greenhouse gas emissions from digestates can help to evaluate the overall sustainability of an agricultural production system. The objective of this study was therefore to evaluate and understand the effect of differences in digestate composition on in situ N2O emissions within the 1st weeks after application of seven digestates. The digestates were derived from different feedstocks and 15N-labeled, either in total N or only in ammonium-N. Therefore, the experimental design enabled us to differentiate between potential N2O-N sources (i.e., digestate N or soil N). Furthermore, it allowed to distinguish to some extent between organic-N and ammonium-N as potential N sources for denitrification. Digestates were homogeneously incorporated into the upper 5 cm of microplots in an arable Haplic Luvisol in South Germany at a rate of 170 kg N ha−1. After application, N2O fluxes were measured for ~60 days (May-July) using the closed chamber method in 2 experimental years. Mainly due to higher precipitations in the 1st year, cumulative N2O emissions were higher (312–1,580 g N2O-N ha−1) compared to the emissions (133–690 g N2O-N ha−1) in the 2nd year. Between 16–33% (1st year) and 17–38% (2nd year) of N2O emissions originated from digestate N, indicating that digestate application triggered N2O production and release mainly from soil N. This effect was strongest immediately after digestate application. It was concluded that the first (short term) peak in N2O emissions after digestate application is largely related to denitrification of soil-N. However, the experimental setup does not allow to differentiate between the different denitrification pathways. Weather conditions showed a substantial effect on N2O emissions, where the correlation between N2O and CO2 flux rates hinted on denitrification as main N2O source. The effect of digestate composition, particularly organic N from the digestate, on soil N2O emissions seems to be of minor relevance.

基于GWR模型的伊河流域土壤有机碳空间分布特征及影响因素分析

土壤有机碳作为陆地碳库主体，其分布特征及与驱动因素的空间关系对土壤碳周转过程有重大影响。通过野外调查、采样和室内分析，基于地理加权回归（GWR）模型结合9个环境和土壤变量，建模分析伊河流域土壤有机碳空间分布状况，以及影响其分布的主要因素。研究发现，流域表层土壤有机碳在3.37-38.34 g/kg之间，上、中、下游有机碳分布存在空间差异，其中上游差异最大，下游差异最小。相关分析表明，有机碳与土壤理化性质相关性显著，与年平均气温以外的环境因子相关性不显著。GWR模型较好地预测了伊河流域土壤有机碳空间分布，局部决定系数在0.49-0.64之间，自下游到上游，决定系数逐步升高，对上游的预测精度最高。分析发现，在海拔较高的中上游区域，土壤有机碳含量主要受立地环境、成土母质和地表覆盖的影响；在中上游低山丘陵区，人类活动和环境因素共同影响了土壤有机碳含量；在中下游平原区农业活动和化肥投入是造成土壤有机碳含量较高的主要因素。研究揭示了各因素对有机碳影响的空间分异特征，可为伊河流域土壤生态系统的合理发展和管理提供依据。;Soil organic carbon (SOC), as the main body of land carbon pool, its distribution characteristics and spatial relationship with driving factors have significant impacts on the process of soil carbon turnover. Through field investigation, sampling and indoor analysis, based on the geographical weighted regression (GWR) model combined with nine environmental and soil variables, the spatial distribution of soil organic carbon and its main affecting factors in the Yihe River Basin were analyzed. The results showed that:(1) the distribution of organic carbon in the surface soil was between 3.37-38.34 g/kg. There were spatial differences in the upper, middle, and lower reaches, among which the difference in the upper reaches was the largest and the difference in the lower reaches was the smallest. (2) Soil organic carbon was closely related to the physical and chemical properties of soil itself, and was less affected by environmental factors other than annual average temperature. (3) The GWR model can predict the spatial distribution of soil organic carbon in the Yihe River Basin, and the local determination coefficient was between 0.49-0.64. From the downstream to the upstream, the determination coefficient increased gradually, and the prediction accuracy of the upstream was the highest. (4) In the middle and upper reaches of high altitude, soil organic carbon contents were mainly affected by site environment, soil parent material, and surface coverage. In the middle and upper reaches of low mountains and hills, human activities and environmental factors jointly affected soil organic carbon content. In the middle and lower reaches of plain area, the agricultural activities and chemical fertilizer input were the main factors causing high soil organic carbon content. This study revealed the spatial differentiation characteristics of the effects of various factors on organic carbon, which could provide a basis for the reasonable development and management of soil ecosystem in the Yihe River Basin.