Initial Organic Carbon Research Articles

Impact of Microbial Inoculants and Additives on Rice Straw Composting

Rice straw is a lignocellulosic waste, which is recalcitrant in nature and contains high lignin content. A recalcitrant property provides resistance from natural degradation thus, decomposition of lignocellulosic waste becomes a difficult task. Composting of rice straw is a sustainable practice that benefits environment, agriculture and economy by turning the agricultural waste into valuable resource that might otherwise be burnt or left to decompose inefficiently. This study investigated the effect of different additives on composting of rice straw with combination of microbial consortium (bacteria and fungi). The addition of organic supplements (i.e., biogas slurry, rock phosphate and green waste) significantly raised the initial temperature of compost treatments, and microbial consortium accelerated lignocellulose decomposition during composting. Organic carbon was found to decrease in all the treatments with the progression of decomposition and least i.e. 29.50% was observed in treatment T5 [rice straw + biogas slurry + rock phosphate + green waste (4:1:1:1) + microbial consortium] at the end of composting which had initial organic carbon of 44.80%. A comparative increase in nitrogen content was observed in all the treatments with the commencement of decomposition. After 90 days of composting, treatment T5 contained the highest total nitrogen (1.36%) ultimately led to decrease in C/N ratio. Among all the treatments, T5 showed noticeably increased degradation rate of cellulose, hemicellulose and lignin content. Moreover, humic acid in compost from T5 was also found to be highest (108 mg g-1). The use of additives seems to improve the stability of rice straw compost as well as use of microbial consortium was found to reduce the time of decomposition of substrates. The research findings will be helpful in optimizing the use of organic waste materials by turning them into nutrient rich compost more quickly and effectively.

Partitioning denitrification pathways in N2O emissions from re-flooded dry paddy soils

In flooded paddy fields, peak greenhouse gas nitrous oxide (N2O) emission after rewetting the dry soils is widely recognised. However, the relative contribution of biotic and abiotic factors to this emission remains uncertain. In this study, we used the isotope technique (δ18O and δ15NSP) and molecular-based microbial analysis in an anoxic incubation experiment to evaluate the contributions of bacterial, fungal, and chemical denitrification to N2O emissions. We collected eight representative paddy soils across southern China for an incubation experiment. Results show that during the 10-day incubation period, the net N2O emissions were mainly produced by fungal denitrification, which accounted for 58–77% in six of the eight investigated flooded paddy soils. In contrast, bacterial denitrification contributed 6–15% of the net N2O emissions. Moreover, around 11–35% of the total N2O emissions were derived from chemical denitrification in all soil types. Variation partitioning analysis (VPA) and principal component analysis (PCA) demonstrated that initial soil organic carbon (OC) concentrations were the primary regulator of N2O source patterns. Soils with relatively lower OC concentration (7–15 mg g−1) tend to be dominated by fungal denitrification, which accounted for the net N2O production at the end of the incubation period. Overall, these findings highlight the dominance of the fungal denitrification pathway for N2O production in flooded paddy soils, which predominates in soils with relatively lower OC content. This suggests that fungal contribution should be considered when optimizing agricultural management system timing to control N2O emissions in flooded paddy soil ecosystems, and for the relevant establishment of predictive numerical models in the future.

Cyanobacteria-ferrihydrite aggregates, BIF sedimentation and implications for Archaean- Palaeoproterozoic seawater geochemistry

Abstract Precambrian banded iron formations (BIFs) are iron- and silica-rich (bio)chemical sediments that are widely believed to have been precipitated by microbial oxidation of dissolved Fe(II). The by-product of these metabolisms – insoluble ferric iron – would have settled through the water column, often as aggregates with the cell biomass. While the mineralogy, composition and physical properties of cell-iron mineral aggregates formed by anaerobic Fe(II)-oxidising photoferrotrophic bacteria have been extensively studied, there are limited studies that characterise cyanobacteria-iron mineral aggregates that formed during oxygenic photosynthesis. This gap in knowledge is important because it impacts sedimentation velocities and the Fe(III) to organic carbon (Corg) ratios in the marine sediment pile. Here, we used a recently introduced approach to precisely measure the sedimentation velocity of cyanobacteria-ferrihydrite aggregates and the Fe(III):Corg ratios of the cyanobacteria-ferrihydrite aggregates over a wide range of pH and initial Fe(II) concentrations under predicted Palaeoproterozoic atmospheric conditions. Our results indicate that it was highly unlikely BIFs formed at pH <7 via chemical oxidation due to the insufficient sedimentation velocity, even at the maximum predicted Fe(II) concentration of 1800 μM with excess oxygen. Instead, large Banded Iron Formation (BIF) deposits, such as those associated with the ca. 2.47 Ga Kuruman Formation in South Africa, would only had been deposited at minimum Fe(II) concentrations of 500 μM at pH 7 or 250 μM at pH 8. The Fe:Corg ratios in cyanobacteria-ferrihydrite sediments formed during initially anoxic Fe(II) oxidation experiments represent the maximum values under each condition because we specifically extracted samples after all Fe(II) was oxidised. The Fe(III) to organic carbon ratio was consistently below 4, which is also the ratio required for dissimilatory Fe(III) reduction (DIR). This result indicates that biomass in this case was in excess, which contradicts the low organic carbon content seen in most BIFs. Thus, we suggest that biomass was either physically separated from ferrihydrite aggregates during sedimentation under the influence of ocean currents and waves, or it was degraded prior to DIR. The mineralogical and geochemical evidences of both oxide and carbonate facies from the Kuruman Iron Formation (IF) suggest that ferrihydrite was most likely the precursor along with a significant initial organic carbon input, supporting the proposed cyanobacterially-mediated BIF depositional model and experimental results.

Simulation and parameter determination of the net sorption of phenanthrene by sediment particles

The distribution of polycyclic aromatic hydrocarbons (PAHs) in the ocean is affected by the sorption-desorption process of sediment particles. This process is determined by the concentration of PAHs in seawater, water temperature, and organic matter content of sediment particles. Quantitative relationships between the net sorption rates (=the difference of sorption and desorption rates) and these factors have not been established yet and used in PAH transport models. In this study, phenanthrene was chosen as the representative of PAHs. Three groups of experimental data were collected to address the dependence of the net sorption processes on the initial concentration, water temperature, and organic carbon content representing organic matter content. One-site and two-compartment mass-transfer models were tested to represent the experimental data using various parameters. The results showed that the two-compartment mass-transfer model performed better than the one-site mass-transfer model. The parameters of the two-compartment mass-transfer model include the sorption rate coefficients kafand kas (L g−1 min−1), and the desorption rate coefficients kdf and kds (min−1). The parameters at different temperatures and organic carbon contents were obtained by numerical simulations. Linear relationships were obtained between the parameters and water temperature, as well as organic carbon content. kaf, kas and kdf decreased linearly, while kds increased linearly with temperature. kaf, kas and kdf increased linearly, while kds decreased linearly with organic carbon content. The r2 values between the simulation results based on the relationships and the experimental results reached 0.96–0.99, which supports the application of the model to simulate sorption-desorption processes at different water temperatures and organic carbon contents in a realistic ocean.

Global synthesis on the response of soil microbial necromass carbon to climate-smart agriculture.

Climate-smart agriculture (CSA) supports the sustainability of crop production and food security, and benefiting soil carbon storage. Despite the critical importance of microorganisms in the carbon cycle, systematic investigations on the influence of CSA on soil microbial necromass carbon and its driving factors are still limited. We evaluated 472 observations from 73 peer-reviewed articles to show that, compared to conventional practice, CSA generally increased soil microbial necromass carbon concentrations by 18.24%. These benefits to soil microbial necromass carbon, as assessed by amino sugar biomarkers, are complex and influenced by a variety of soil, climatic, spatial, and biological factors. Changes in living microbial biomass are the most significant predictor of total, fungal, and bacterial necromass carbon affected by CSA; in 61.9%-67.3% of paired observations, the CSA measures simultaneously increased living microbial biomass and microbial necromass carbon. Land restoration and nutrient management therein largely promoted microbial necromass carbon storage, while cover crop has a minor effect. Additionally, the effects were directly influenced by elevation and mean annual temperature, and indirectly by soil texture and initial organic carbon content. In the optimal scenario, the potential global carbon accrual rate of CSA through microbial necromass is approximately 980 Mt C year-1, assuming organic amendment is included following conservation tillage and appropriate land restoration. In conclusion, our study suggests that increasing soil microbial necromass carbon through CSA provides a vital way of mitigating carbon loss. This emphasizes the invisible yet significant influence of soil microbial anabolic activity on global carbon dynamics.

Divergent changes of carbon and nitrogen in the density fractions of soil organic matter after revegetation in the Tengger Desert, north China

AbstractRevegetation is an effective measure to enhance soil organic carbon (OC) and nitrogen (N) storage in drylands, but the underlying processes remain poorly understood. Based on density fractionation, the free light fraction (fLF), the occluded light fraction (oLF), and a heavy fraction (HF) were extracted from a chronosequence of revegetated sites aged 10, 22, 34, 48, and 65 years. A mobile sand dune (MSD) was used as the reference site (aged 0 years). The OC and N contents of different fractions and the bulk soils were determined to evaluate the impacts of revegetation and clarify post‐revegetation stabilization mechanisms for the OC and N. The results showed that the dry mass of fLF and oLF in established shrublands were 17.16–31.30 and 17.68–44.87 times greater than those in the MSD, respectively, while the amount of HF decreased by 1.09%–2.51% in 65 years. The contents and stocks of OC and N and C:N ratio in each fraction significantly increased over time but decreased with soil depth, and these three variables decreased sequentially from fLF to oLF to HF. The OC and N contents and their ratios in each fraction were positively and linearly correlated with their corresponding values in the bulk soil. The OC and N percentages contained in the fLF and oLF increased significantly, but those in the HF decreased with increasing site age. Despite this, more than 55.08% of OC and 80.59% of N were remained in the HF across all the sites, indicating that the enhancement of OC and N stocks in SOM following revegetation were mainly derived from an increase in OC and N in protected fractions. Biological and physicochemical factors including microbial biomass C and N, the availability of N, P, and K, bulk density, and clay and silt contents, were the key factors regulating the OC and N dynamics in the density fractions. The initial OC and N accumulation after revegetation occurs mainly in the HF, while vegetation development shifts the OC and N from stable to labile pools. The OC and N accumulation in revegetated soils is attributed to the changes in both the LF and HF whereas OC and N in the light fraction become increasingly important over time. Stabilization by forming aggregates and mineral associations may dominate the long‐term OC and N sequestration in restored ecosystems.

Acid rain reduced soil carbon emissions and increased the temperature sensitivity of soil respiration: A comprehensive meta-analysis

Soil respiration the second-largest carbon flux in terrestrial ecosystems, has been extensively studied across a wide range of biomes. Surprisingly, no consensus exist on how acid rain (AR) impacts the spatiotemporal pattern of soil respiration. Therefore, we conducted a meta-analysis using 318 soil respiration and 263 soil respiration temperature sensitivity (Q10) data points obtained from 48 studies to assess the impact of AR on soil respiration components and their Q10. The results showed that AR reduced soil total respiration (Rt) and soil autotrophic respiration (Ra) by 7.41 % and 20.75 %, respectively. As the H+ input increased, the response rates of Ra to AR (RR-Ra) and soil heterotrophic respiration (Rh) to AR (RR-Rh) decreased and increased, respectively. With increased AR duration, the RR-Ra increased, whereas the RR-Rh did not change. AR increased the Q10 of Rt (Rt-Q10) and Rh (Rh-Q10) by 1.92 % and 9.47 %, respectively, and decreased the Q10 of Ra (Ra-Q10) by 2.77 %. Increased mean annual temperature, mean annual precipitation, and initial soil organic carbon increased the response rate of Ra-Q10 to AR (RR-Ra-Q10) and decreased the response rate of Rh-Q10 to AR (RR-Rh-Q10). However, as the AR frequency and initial soil pH increased, both RR-Ra-Q10 and RR-Rh-Q10 also increased. In summary, AR decreased Rt but increased Q10, likely due to soil acidification (soil pH decreased by 7.84 %), reducing plant root biomass (decreased by 5.67 %) and soil microbial biomass (decreased by 5.67 %), changing microbial communities (increased fungi to bacteria ratio of 15.91 %), and regulated by climate, vegetation, soil and AR regimes. To the best of our knowledge, this is the first study to reveal the large-scale, varied response patterns of soil respiration components and their Q10 to AR. It highlights the importance of applying the reductionism theory in soil respiration research to enhance our understanding of soil carbon cycling processes with in the context of global climate change.

Effects of microplastics exposure on soil inorganic nitrogen: A comprehensive synthesis

Microplastics, a growing environmental concern, impact soil inorganic nitrogen (N) transformation, specifically affecting water-extractable nitrate N (NO3−−N) and ammonium N (NH4+−N). However, inconsistencies among relevant findings necessitate a systematic analysis. Accordingly, the present meta-analysis addresses these discrepancies by evaluating the effects of microplastics on soil inorganic N and identifying key influencing factors. Our meta-analysis of 216 paired observations from 47 studies demonstrates microplastics exposure causes an overall significant reduction of 7.89% in soil NO3−−N concentration, but has no significant impact on NH4+−N concentration. Subgroup analysis further revealed effects of microplastics on soil inorganic N were modulated by microplastics characteristics, experimental conditions (exposure time, experimental temperature, plant effects), and soil properties (soil texture, initial soil pH, initial soil organic carbon, soil total N concentration). We found that microplastics exposure above 27 ℃ enhances soil NO3−−N concentration, a finding linked to specific soil properties and conditions, underscoring the impacts of global warming. Importantly, the microplastics polymer type was the most influential predictor of effects on soil NO3−−N concentration, while soil NH4+−N concentration was primarily affected by soil texture and microplastics type. These findings illuminate the complex effects of microplastics on soil inorganic N, informing soil management amid increasing microplastics pollution.

Commercial scale production of Yamabushitake mushroom (Hericium erinaceus (Bull.) Pers. 1797) using rubber and bamboo sawdust substrates in tropical regions

Yamabushitake (Hericium erinaceus) is one of the most sought out mushrooms that is widely used for both direct consumption and medicinal purposes. While its demand increases worldwide, cultivation of the mushroom is limited to temperate areas and its production in tropical regions has never been explored. The aim of this study was to test the utilization of rubber and bamboo sawdust, alone or as a substrate mixture, for industrial scale Yamabushitake mushroom production. Five substrate treatments with various ratios of the two sawdust were compared for their physicochemical properties in relation to mushroom productivity. The highest mushroom fresh and dry (113.22 and 23.25 g, respectively), biological efficiency (42.61%), and cap size (9.53 cm) were obtained from the substrates containing 100% rubber sawdust, with the mushroom yield decreasing proportional to the ratio of bamboo sawdust. The 100% rubber sawdust substrate provided a higher initial organic matter and carbon content together with C:N ratio at 63.2%, 36.7% and 65.48, respectively, whereas the 100% bamboo sawdust provided higher nitrogen content (1.03%), which was associated with lower mushroom yield but higher number of fruiting bodies. As in the 100% rubber sawdust substrate, a comparable mushroom yield and growth attributes were also obtained in the 3:1 rubber-bamboo sawdust mixture substrate. Principle component analysis of the measured variables indicated a strong influence of substrate C:N ratio before spawning and the change in substrate electrical conductivity and N content after cultivation to the variation in mushroom productivity among the treatments. The results demonstrate the applicability of rubber sawdust and its combination with up to 25% of bamboo sawdust for Yamabushitake mushroom cultivation and provide the basis for substrate optimization in the tropical Yamabushitake mushroom industry through a circular economy framework.

Positive effects of crop rotation on soil aggregation and associated organic carbon are mainly controlled by climate and initial soil carbon content: A meta-analysis

Understanding the global patterns and controls on soil aggregation and associated organic carbon (OC) is essential to improve soil carbon storage and mitigate climate warming. Crop rotation is an important feature of sustainable agricultural management and influences multiple soil properties. However, the effects of crop rotation on soil aggregation and associated OC remain poorly understood. We conducted a meta-analysis of 2199 paired observations from 53 studies to quantitatively analyze crop rotation-induced changes in soil aggregation and associated OC and elucidate optimal climatic, edaphic, and agronomic factors. Overall, crop rotation improved the proportions of macroaggregates (> 0.25 mm) by 7–14%, aggregate stability by 7–9%, and OC contents in all sizes of aggregates by 7–8% relative to continuous monoculture. Crop rotation increased soil aggregation and associated OC mainly in regions with mean annual temperature between 8 and 15℃, mean annual precipitation between 600 and 1000 mm, and also in topsoil (0–20 cm) with loamy textures and medium levels of initial soil OC (10–15 g kg−1), total nitrogen (0.75–1.50 g kg−1), and pH (6−8). Greater increases in soil aggregation and associated OC induced by crop rotation were associated with sub-soiling, no-till, straw retention, combined manure-inorganic fertilizers, and a lower nitrogen fertilization input rate with more rotation cycles and longer rotation length. Crop rotation effects were especially strong when the previously cultivated crop was soybean. The variance partitioning analysis revealed that variations in crop rotation-induced changes in soil aggregation and associated OC were mainly explained by climate (26–35%) and soil properties (17–34%). The random forest model indicated that climate (mean annual temperature and precipitation) and initial soil OC were the predominant controls on the effects of crop rotation. Overall, these findings suggest that the use of crop rotation can help sequester carbon by improving soil aggregation and associated OC, and highlight the importance of climate and initial soil OC in site-specific crop rotation systems to the sustainability of agroecosystems.

Impact of organic and integrated production systems on yield and seed quality of rainfed crops and on soil properties.

Mineral and vitamin deficiencies together affect a greater number of human populations in the world than does protein malnutrition. Organic farming is reported to improve nutritional quality of food grains while also improving soil health. However, sufficient scientific information on several aspects of organic farming based on long-term studies is lacking particularly under rainfed conditions of India. The purpose of this study was to assess the long-term impact of organic and integrated production systems on crops yield and quality, economic returns and soil properties. The study was conducted with three crops, sunflower (Helianthus annuus L.), pigeonpea (Cajanus cajan L.), and greengram [Vigna radiata (L.) Wilczek] under three different production systems, control (use of chemical inputs alone), organic and integrated. The results of the 10-year study revealed that, the average production of integrated system was on par with organic management and recorded significantly higher pigeonpea equivalent yield (PEY) (827 kg ha-1) compared to control (chemical inputs) (748 kg ha-1). In general, the yield gap between organic and integrated production systems declined from fourth year for greengram and eighth year for sunflower, during the 10-year experimental period whereas the pigeonpea yield was similar under both production systems from first year. Plots under organic management had significantly lower bulk density (1.18 mg m-3), higher water holding capacity (38.72%) and porosity (53.79%) compared to integrated production system and control (chemical inputs). The soil organic C (SOC) content in the plots under organic production system was 32.6% more than the initial organic carbon of the soil (0.43%), with higher soil N (205.2 kg ha-1). Plots under integrated production system, however, had higher soil P (26.5 kg ha-1) compared with other treatments. The dehydrogenase activity (5.86 μg TPF g-1 soil h-1) and microbial biomass carbon (317.3 μg g-1 soil) content was higher in the plots under organic production system than under other systems. Organically produced pigeonpea and greengram seeds had similar protein content with that of integrated system, and higher K and micronutrient (Fe, Zn, Cu, and Mn) contents than other treatments. The results show the potential of organic production system in improving crop yields, soil properties and produce quality in semiarid rainfed areas.

Soil carbon and nitrogen sequestration and associated influencing factors in a sustainable cultivation system of fruit trees intercropped with cover crops

We comprehensively quantified the influence of cover crops on soil carbon and nitrogen storage in Chinese orchards by a meta-analysis based on the literature published during 1990 to 2020. The factors influencing soil carbon and nitrogen storage were also analyzed. The results showed that compared with clean tillage, soil carbon and nitrogen storage under the cultivation of cover crops considerably increased by 31.1% and 22.8%, respectively. Intercropping legumes enhanced soil organic carbon storage by 4.0% and total nitrogen storage by 3.0% compared with non-legumes. The effect of mulching duration was most prominent at 5-10 years, with 58.5% and 32.8% increases in soil carbon and nitrogen storage, respectively. The largest increase in soil carbon and nitrogen storage (32.3% and 34.1%, respectively) occurred in areas with low initial organic carbon (<10 g·kg-1) and total nitrogen (<1.0 g·kg-1). In addition, suitable mean annual temperature (10-13 ℃) and precipitation (400-800 mm) markedly contributed to soil carbon and nitrogen storage in the middle and lower reaches of the Yellow River. The findings indicated that multiple factors influence the synergistic changes in soil carbon and nitrogen storage in orchards, while intercropping with cover crops is an effective strategy for enhancing soil carbon and nitrogen sequestration.

The influence of plant residues on soil aggregation and carbon content: A meta‐analysis

AbstractBackgroundSoil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood.AimIn this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH.MethodsOur meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH).ResultsThe benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage.ConclusionsWhile plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content.

Evaluation of integrated nutrient management on soil health, maize productivity and grain quality

Managing various organic residues produced from agricultural waste is today's prominent need. The present experiment was conducted to evaluate the effect of integrated, chemical, and organic fertilizers on maize productivity. Initially, vermicompost was prepared using different organic residues viz., paddy straw, neem leaves and dhaincha leaves, each in combination with cow dung in 1:1 ratio. Further, prepared vermicompost along with integrated nutrient and chemical fertilizer treatments, were tested on maize productivity. The experiment was carried out in Randomized Block Design. The average two-year data revealed the increased yield and yield attributes of maize with integrated nutrient management followed by the recommended dose of fertilizers and different vermicompost treatments. The least maize productivity was noted with control treatment. The different vermicompost treatments comparatively improved the organic carbon (0.43 to 0.45%) and micronutrient status of the soil in the second year of application (Fe- 10.85 to 13.32 mg kg-1, Zn- 2.95 to 4.18 mg kg-1, Cu- 0.55 to 0.73 mg kg-1, Mn- 10.37 to 15.24 mg kg-1). The result of vermicompost application can be recorded higher in terms of improvement in yield and soil properties in the later years, as the initial organic carbon and nutrient content of the experimental soil was recorded to be low, and, it takes almost three to four years for the positive response of soil to the applied organic amendments. Therefore, long-term experiments are required to evaluate the effects of vermicompost on soil chemical properties and maize productivity. The investigation revealed that integrated nutrient treatment proved better in terms of improving the yield and nutrient status of the soil.

How does uncertainty of soil organic carbon stock affect the calculation of carbon budgets and soil carbon credits for croplands in the U.S. Midwest?

Cropland carbon budget depicts the amount of carbon flowing in and out of agroecosystems and the changes in carbon stocks of soil and living biomass during the same period. Soil carbon credit is the additional change in soil carbon stock under certain farming practices compared with the business-as-usual practices. Accurately calculating cropland carbon budget and soil carbon credit is critical to assessing climate change mitigation potential in agroecosystems. The calculation of cropland carbon budget and soil carbon credit is sensitive to local soil and climatic conditions, especially initial soil organic carbon (SOC) stock, which is determined by both SOC concentration (SOC%) and bulk density (Bulk_Density). SOC stock data are either from soil sampling or gridded public survey data. In agroecosystem models, SOC stock data are a key model input for quantifying cropland carbon budget and soil carbon credit. However, various types and degrees of uncertainties exist in SOC stock datasets, which propagate to the quantification of SOC stock change. In particular, a large discrepancy is found in two widely used SOC stock datasets — Rapid Carbon Assessment dataset (RaCA) and Gridded Soil Survey Geographic Database (gSSURGO) — in the U.S. Midwest, with a relative difference (quantified using Normalized Root Mean Square Error, NRMSE) of 48.0% for 0–30 cm SOC stock between the two datasets. It remains largely unclear how uncertainty in SOC stocks affects the calculation of cropland carbon budget and soil carbon credit. To address this question, we used a well-validated process-based agroecosystem model, ecosys, to assess the impacts of SOC stock uncertainty on carbon budget and soil carbon credit calculation in the U.S. Midwestern corn-soybean rotation systems. Our results reveal the following findings: (1) A sizable discrepancy exists in simulated cropland carbon budget between using gSSURGO and using RaCA for their SOC% and Bulk_Density as model inputs, with a Pearson correlation coefficient (r) of only 0.4 for simulated change of SOC stock (ΔSOC) using these two different soil datasets. (2) Simulated cropland carbon budget components were more sensitive to initial SOC% than to Bulk_Density. For example, the upper and lower quartiles of multi-year averaged ΔSOC were −29.8 and 4.8 gC/m2/year for the selected counties respectively, with an uncertainty of 13.7 and 0.7 gC/m2/year induced by uncertainties in initial SOC% and Bulk_Density, respectively. (3) Both simulated ΔSOC and its uncertainty were negatively correlated with initial SOC%, whereas ΔSOC was negatively correlated with air temperature, and ΔSOC uncertainty was positively correlated with air temperature. (4) The uncertainty of calculated soil carbon credits was much smaller compared with the uncertainty of calculated absolute carbon budgets assuming the same SOC stock uncertainty level in the inputs. Specifically, in our assessment comparing planting cover crops vs no cover crop, the uncertainty of calculated soil carbon credits induced by initial SOC% uncertainty was less than 4% (relative to the quantified value of the soil carbon credits) for 90% of the cases. Our analysis highlights that high accuracy measurement of SOC% as inputs is needed for the calculation of cropland carbon budgets; however, soil carbon credit quantification is much less sensitive to the initial SOC% inputs, and the current publicly available soil datasets (e.g., gSSURGO) are largely suitable for the calculation of soil carbon credits.

Initial soil organic carbon stocks govern changes in soil carbon: Reality or artifact?

Changes in soil organic carbon (SOC) storage have the potential to affect global climate; hence identifying environments with a high capacity to gain or lose SOC is of broad interest. Many cross-site studies have found that SOC-poor soils tend to gain or retain carbon more readily than SOC-rich soils. While this pattern may partly reflect reality, here we argue that it can also be created by a pair of statistical artifacts. First, soils that appear SOC-poor purely due to random variation will tend to yield more moderate SOC estimates upon resampling and hence will appear to accrue or retain more SOC than SOC-rich soils. This phenomenon is an example of regression to the mean. Second, normalized metrics of SOC change-such as relative rates and response ratios-will by definition show larger changes in SOC at lower initial SOC levels, even when the absolute change in SOC does not depend on initial SOC. These two artifacts create an exaggerated impression that initial SOC stocks are a major control on SOC dynamics. To address this problem, we recommend applying statistical corrections to eliminate the effect of regression to the mean, and avoiding normalized metrics when testing relationships between SOC change and initial SOC. Careful consideration of these issues in future cross-site studies will support clearer scientific inference that can better inform environmental management.

Elevational pattern of soil organic carbon release in a Tibetan alpine grassland: Consequence of quality but not quantity of initial soil organic carbon

Soil organic carbon (SOC) dynamics along elevational gradients are highly uncertain due to our limited knowledge of the underlying mechanisms that determine SOC release. By combining field investigation and laboratory aerobic incubation with multiple soil analytical approaches, we explored the determinants of SOC release along an elevational gradient (3200–4200 m) in the Tibetan alpine grassland. We illustrated that the SOC quantity (i.e., the initial standing SOC stock) and SOC quality (i.e., chemical recalcitrance, physico-chemical protection and biological recalcitrant fraction) increased gradually with elevation, reaching a maximum value at the middle altitude (∼3600 m), while an opposite unimodal distribution pattern was observed in CO2–C release. Our results also showed that SOC quality explained more variance in CO2–C release than did SOC quantity and soil properties. The proportion of stable SOC fractions in larger initial SOC stocks is higher, especially the recalcitrant SOC pool and mineral-associated OC fractions, which could be the potential mechanism behind high initial SOC stocks leading to lower soil CO2–C release. Collectively, our results provide compelling evidence that SOC quality plays a primary role in the elevational pattern of CO2–C release in Tibetan alpine grassland. Our findings highlight the importance of SOC quality in predicting SOC dynamics in the Tibetan alpine grassland under climate change scenarios.

Contribution of species and functional richness to carbon storage in eucalypt woodland restoration

Biologically diverse forest and woodland restoration can mitigate climate change and biodiversity loss. Understanding the trade-off between carbon storage and biodiversity is important to maximise the value of restoration opportunities. Ecological theory suggests biological diversity contributes positively to carbon storage until the relationship plateaus (i.e., species are added with no effect on carbon storage), and yet in practice, tree monocultures are perceived to sequester more carbon than diverse plantings. Here, we measured the contribution of plant diversity to carbon storage in trees and shrubs ten years after planting for yate (Eucalyptus occidentalis) woodland restoration. We found no evidence for a trade-off between carbon storage and plant diversity. We planted yate with mixes of yate woodland species including native grasses, shrubs, and trees. Ten years after planting, grass establishment was poor, and density of trees and shrubs was patchy. There was some unassisted recruitment of woody species. Diversity was measured as observed species richness and observed functional richness, which incorporated taxonomic diversity, structural diversity, and presence/absence of nitrogen-fixing legumes. Carbon stocks measured were above and belowground tree and shrub biomass, leaf and twig litter biomass, and organic carbon (%) in the topsoil. Across all three carbon stocks diverse yate plantings sequestered as much carbon as yate monocultures. Observed species richness had a weak negative effect on tree and shrub biomass in the best linear mixed model but this effect diminished with the removal of an outlier. Tree density had a positive effect on tree and shrub biomass in models with and without the outlier. There was no effect of diversity on litter biomass and soil organic carbon. Instead, linear mixed models of these stocks showed the influence of soil properties. Litter biomass increased with soil potassium and decreased with soil pH. Soil organic carbon increased with initial soil organic carbon and soil nitrogen. There are potential additional biodiversity benefits of diverse plantings that we did not measure (e.g., soil erosion control, wildlife habitat). We call for more field experiments to explore these potential benefits and to generate the ecological knowledge needed to improve the quality of global forest and woodland restoration efforts.

Carbon cycle in the microbial ecosystems of biological soil crusts

The carbon cycle (C-cycle) is the most important and complex biogeochemical cycle in soil ecosystems, but our understanding of C-cycle at the community level remains limited. Biocrusts are known ecosystem engineers and represent ideal model systems for biogeochemical cycling studies. Here, metagenomic sequencing based on five repeated collections of four types of biocrusts revealed a low abundance of genes related to light-driven inorganic carbon fixation, and high abundance of genes related to the chemical energy-driven degradation of macromolecular organic carbon (OC), fermentation, aerobic respiration, and CO oxidation. For OC decomposition, genes mediating starch/glycogen and cellulose degradation were most abundant during the initial complex OC degradation, as were genes mediating fermentation during terminal steps of OC decomposition. To assess successional changes in carbon cycle, the metagenomic data were combined with absolute quantification via GeoChip, as well as key enzyme activity measurements. Inorganic carbon fixation, fermentation, CH4 oxidation, and both starch/glycogen and peptidoglycan degradation decreased during succession. However, several high efficiency processes, as well as CO oxidation and most types of OC degradation, increased. Co-occurrence networks revealed that C-cycle in biocrusts consists of an assimilation module, akin to primary production, and a dissimilation module, comparable to secondary production; dynamic changes in the relationships between C-cycle pathways and microbial community composition occurred during succession. The two C-cycle modules were connected by the Calvin-Benson-Bassham cycle, as well as ethanol and propionate fermentation; the modules were balanced by drought and salinity. Collectively, these results improve our understanding of C-cycle pathways and regulatory mechanisms in biocrust succession, and provide a basis for future multi-omics studies of these systems.

Structural reconstructions effect on oil and gas formation of the Yenisei-Khatanga trough eastern part

The article presents the results of research on the influence of structural reconstructions on the hydrocarbon systems evaluation in the eastern part of the Yenisei-Khatanga trough. Based on seismic data interpretation and paleoprofiles construction, several stages of structural reconstructions in the geological evolution of the basin are established: at the Middle and Late Triassic boundary, Late Triassic and Jurassic boundary, in the Bathonian-Callovian time, Tithonian-Valanginian time, in the Barremian-Aptian time, in the Aptian-Albian time, in the Cenomanian time, and powerful reconstructions in the Cenozoic era. Based on interpretation of geochemical information of the well-core and outcrops, the characterization of the type of organic matter, the amount of initial organic carbon, the oil and gas source potential for the Late Triassic, Lower Jurassic, Middle Jurassic, Upper Jurassic, Lower Cretaceous oil and gas source rocks is given. The results of exploration of the geological structure of the region, the geochemical features of oil and gas source rocks became the basis for building a 2D basin model, which made it possible not only to identify generation kitchen, migration routes and accumulation zones of hydrocarbon fluids, but also to estimate the start time of generation and emigration of hydrocarbons, as well as the moments of interruption of these processes during periods of uplifting of the territory. Changes of the structural plan transformed the configuration of the basin, which led, on the one hand, to the formation of areas where rich in organic matter interlayers accumulated, and, on the other hand, to the interruption of hydrocarbon systems evaluation, reconfiguration and even destruction of deposits.