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Mangrove ecosystems are significant sources of greenhouse gases (GHG) that is attributed to microbial activity. However, it is still unknown how the sediment microbial populations affect GHG emissions in mangrove ecosystem. Since little is known about microbial populations of mangroves, the present study was aimed to understand the structure and function of microbial communities in the Indian part of the Sundarban mangrove ecosystem in relation to environmental variables and variation of GHG emissions during three seasons: pre-monsoon (March–June), monsoon (July–October) and post-monsoon (November–February). Seasonal variations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) gas samples were taken from the mangrove bed. Culture methods were used to detect twelve different types of microbes such as heterotrophic (Htp), N2 fixing (Nfix), nitrifying (Ntfn), sulfur oxidizing (Soxd), Gram-negative (GMn), Gram-positive (GMp), spore forming (Sfor), denitrifying (DNtfn), anaerobic (Anrb), phosphate solubilizing (Psol), cellulose degrading (Cdeg) bacteria and actinomycetes (Actm). In the monsoon, populations of the Htp, Anrb, Psol, and Cdeg bacteria were more prevalent, whereas populations of the GMn, GMp, Ntfn, DNtfn bacteria, and Actm bacteria were more prevalent in the post-monsoon. Monsoonal CO2 and CH4 fluxes were larger than pre-monsoon and post-monsoon, resulting in increased microbial soil respiration and breakdown of soil organic carbon. Because of higher denitrification and soil temperature, N2O flux was higher in the pre-monsoon period, followed by monsoon and post-monsoon periods. A univariate statistical correlation was employed to assess the relationships between environmental variables and different microbial populations. An ANN (artificial neural network) model was proposed to evaluate the relevance of microbial population contribution to GHG emissions, and it indicated that the Htp, Anrb, and Dntfn microbial populations were most relevant for CO2, CH4, and N2O emissions. The suggested model would be used to assess the drivers behind GHG emission in the mangroves located at different parts of the world.

The “Grain-for-Green” project on the Loess Plateau is the largest revegetation program in the world. However, revegetation-induced land use changes can influence both water and carbon cycles, and the diverse consequences were not well understood. Therefore, the reasonability and sustainability of revegetation measures are in question. This study quantifies the impacts of revegetation-induced land use conversions on the water and carbon cycles in a typical watershed on the Loess Plateau and identifies suitable areas where revegetation of forest or grassland could benefit both soil and water conservation and carbon sequestration. We used a coupled hydro-biogeochemical model to simulate the changes of a few key components in terms of water and carbon by designing a variety of hypothetical land use conversion scenarios derived from revegetation policy. Compared to the baseline condition (land use in 2000), both sediment yield and water yield decreased substantially when replacing steep cropland with forest or grassland. Converting cropland with slopes >25°, 15°, and 6° to forest (CTF) would enhance the carbon sequestration with a negligible negative effect on soil water content, while replacing cropland with grassland (CTG) would result in a decline in net primary production but with a substantial increase in soil water content (3.8%–14.9%). Compared to the baseline, the soil organic carbon would increase by 0.9%–3.2% in CTF and keep relatively stable in CTG. Through testing a variety of hypothetical revegetation scenarios, we identified potential priority areas for CTF and CTG, where revegetation may be appropriate and potentially beneficial to conserving soil and water and enhancing carbon sequestration. Our study highlights the challenges in future water and carbon coupling management under revegetation policy, and our quantitative results and identification of potential areas for revegetation could provide information to policy makers for seeking optimal management on the Loess Plateau.

Concurrent ground-level ozone (O3) pollution and anthropogenic nitrogen (N) deposition can markedly influence dynamics and productivity in forests. Most studies evaluating the functional traits responses of rapid-turnover organs to O3 have specifically examined leaves, despite fine roots are another major source of soil carbon and nutrient input in forest ecosystems. How elevated O3 levels impact fine root biomass and biochemistry remains to be resolved. This study was to assess poplar leaf and fine root biomass and biochemistry responses to five different levels of O3 pollution, while additionally examining whether four levels of soil N supplementation were sufficient to alter the impact of O3 on these two organs. Elevated O3 resulted in a more substantial reduction in fine root biomass than leaf biomass; relative to leaves, more biochemically-resistant components were present within fine root litter, which contained high concentrations of lignin, condensed tannins, and elevated C:N and lignin: N ratios that were associated with slower rates of litter decomposition. In contrast, leaves contained more labile components, including nonstructural carbohydrates and N, as well as a higher N:P ratio. Elevated O3 significantly reduced labile components and increased biochemically-resistant components in leaves, whereas they had minimal impact on fine root biochemistry. This suggests that O3 pollution has the potential to delay leaf litter decomposition and associated nutrient cycling. N addition largely failed to affect the impact of elevated O3 levels on leaves or fine root chemistry, suggesting that soil N supplementation is not a suitable approach to combating the impact of O3 pollution on key functional traits of poplars. These results indicate that the significant differences in the responses of leaves and fine roots to O3 pollution will result in marked changes in the relative belowground roles of these two litter sources within forest ecosystems, and such changes will independently of nitrogen load.

The stability of soil organic carbon (SOC), as it relates to resistance to decomposition, is important for greenhouse gas emission and climate change. However, the SOC stabilization and its related influencing factors subjected to water erosion remain uncertain. The objective of the current study was to determine the SOC stability under long-term water erosion and to investigate the link between SOC stability and edaphic factors. Soil samples from eroded, depositional, and control sites in a closed watershed in subtropical China were collected. The SOC concentration, carbon functional groups, soil physicochemical properties, and thermal stability of SOC were determined. The study results showed that the primary component of the SOC functional groups was O-alkyl carbon (reached 40%), and its proportion has no significant difference among different sites. The TG-T50 (the temperature at which 50% of the soil organic matter is lost) values indicated that the SOC thermal stability in the eroded topsoil was higher than that of the deposited topsoil. The carbon functional groups were lack of relation with SOC thermal stability (p > 0.05). However, the TG-T50 was significantly positively correlated with the cation exchange capacity and silt, but remarkably negatively correlated with SOC, dissolved organic carbon, total nitrogen, sand, clay, pH, aluminum, specific surface area, and iron oxides. These results indicated that the edaphic factors, which were strongly affected by micro-environment, are the main factors affecting thermal stability of organic carbon. The SOC stabilization under the effects of long-term water erosion should be addressed from the perspective of the ecosystem.

Land management is one of the most important factors affecting the protection and carbon sequestration of natural ecosystems. If the ecosystem is maintained naturally, it will have suitable vegetation and soil stability. One of the important factors that affects land management is livestock grazing. In order to evaluate the impact of exclosure rangeland on carbon sequestration (CS) in salty rangelands, the study was carried out in Inchehboroun rangelands of Golestan province, Iran. The main purpose of current research was to evaluate the effectiveness of management of salt rangeland on CS by topsoil and halophytes species. For this purpose, 40 plots (with 2 m2 area) were located along 8 transects of 100 m in exclosure rangeland (ER) and grazing rangeland (GR) sites. The sampling method was randomized-systematic. In the area sampled, plant biomass was estimated. In addition, the content of above ground and underground biomass carbon, litter carbon, and soil organic carbon were determined for both ER and GR. The difference between the means was compared using Duncan test and t-test at P

Soil Organic Carbon (SOC) is a measure of the total carbon content of the soil and is a vital soil health indicator. Over the decades, SOC has been estimated using sampling followed by rigorous laboratory-based testing methods. Spaceborne Microwave/Synthetic Aperture RADAR (SAR) remote sensing has proven to be a versatile tool for various soil study applications. However, there have been very few studies conducted for SOC estimation using SAR remote sensing. This study utilises time-series, C-band remotely sensed SAR data from Sentinel-1 A satellite for SOC estimation and compared the performances of Random Forest (RF) and Ordinary Least Squares (OLS) Regression models over agricultural areas of Rupnagar district of Punjab in India. A set of 96 soil samples were collected from 32 different agricultural field locations in Rupnagar district between November 2019 to January 2020. SAR backscatter of Vertically emitted and Vertically received (VV) and Vertically emitted and Horizontally received (VH) polarisation channels, from Sentinel-1, soil moisture, electrical conductivity, pH, temperature and SOC from the laboratory-based testing methods were used as regression parameters. The RF regression gave a Root Mean Square Error (RMSE) of 0.78 and R2 statistics of 0.887, while the OLS method performed better with an RMSE of 0.53 and an R2 value of 0.907. It was also observed that the backscatter from VV and VH polarisation channels, when used synergistically with field data, have the highest Feature Importance (FI) score in both RF and OLS regression models for SOC estimation.

Soil hydraulic properties are important aspects of the bamboo plantation's eco-hydrological processes as they affect the runoff, soil erosion, and water balance. This study assessed the effect of four commercially important sympodial bamboo species viz., Bambusa vulgaris, Bambusa balcooa, Dendrocalamus hamiltonii, and Dendrocalamus strictus on surface soil saturated and near-saturated hydraulic conductivity (NSHC), macropore characteristics, and the factors influencing the soil hydrological processes. The surface soil hydraulic conductivity at 0, -10, and -30 mm pressure heads and macropore characteristics were estimated from measured steady-state infiltration using a tension (hood) infiltrometer. Soil organic carbon, bulk density, aggregate mean weight diameter (MWD), root biomass, and litterfall was correlated with saturated hydraulic conductivity (SHC) to determine these parameters' relationship with the hydraulic properties. D. hamiltonii showed significantly higher SHC, NSHC, and water-conducting macroporosity than the rest of the species. The correlation analysis revealed that root biomass and soil aggregate MWD were the major determinants of soil hydraulic conductivity characteristics. Bulk density, soil organic carbon, and leaf litter were weakly correlated with SHC. Among the species evaluated, D. hamiltonii was found to be a highly promising species for improvement of soil hydro-physical property and, therefore, can be recommended for increasing infiltration, reducing runoff, controlling soil erosion, and improving groundwater recharge.

Rangelands account for a large portion of global carbon stocks and have high potential for carbon sequestration if managed properly. Grazing has variable effects on soil organic carbon depending on climate, geography, and soil type; therefore, grazers in various regions may need to be managed differently to ensure optimum carbon sequestration. This study aimed to assess the impacts of cattle grazing on soil carbon in seminatural subtropical humid rangelands in Florida. We measured root biomass, bulk density, soil organic carbon (SOC), and total carbon (TC) concentrations and used the equivalent soil mass method to assess organic carbon stock (OCS) and total carbon stock at three depths (0−5 cm, 5−15 cm, and 15−30 cm) inside and outside of five 15-yr-old grazing exclosures. We also surveyed the vegetation at each sampling location and litter biomass inside and outside of exclosures. We found that grazing increased bulk density, decreased root biomass, but did not affect litter amount. SOC and TC concentrations did not differ significantly between ungrazed and grazed plots. On an equivalent soil mass basis, we found greater soil carbon stocks in grazed plots within the shallower part of the soil (0−5 cm). Removal of grazing resulted in a clear difference in vegetation composition between grazed and ungrazed plots, with grazed plots having higher grass cover (on average 60% in grazed vs. 13% in ungrazed) and ungrazed having higher forb cover (on average 78% in ungrazed vs. 32% in grazed). Results provide evidence that grazing increased soil carbon stocks in the top layer of soil, but longer-term studies are needed to assess the impact of grazing on SOC concentrations. To further clarify the impact of grazing on drivers of soil carbon in subtropical humid seminatural grasslands, we recommend further study of grazing impacts on productivity, root production and turnover, and microbial responses.

To better understand interglacial paleosol development by quantifying the paleosol development processes on the Chinese Loess Plateau (CLP), we need a soil genesis model calibrated for long timescales. Here, we calibrate a process-based soil genesis model, SoilGen2, by confronting simulated and measured soil properties for the Holocene and MIS-13 paleosols formed in the CLP for various parameter settings. The calibration was made sequentially on three major soil process formulations, including decalcification, clay migration and soil organic carbon, which are represented by various process parameters. The order of the tuned parameters was based on sensitivity analyses performed previously on the loess in West European and the CLP. After the calibration of the intrinsic soil process parameters, the effect of uncertainty of dust deposition rate on calibration results was assessed. Our results show that the simulated soil properties are very sensitive to ten reconstructed dust deposition scenarios, reflecting the propagation of uncertainty of dust deposition in model simulations. Our results also show the equal importance of calibrating soil process parameters and defining correct external forcings in the future use of soil models. Our calibrated model allows interglacial soil simulation in the CLP over long timescales.

The mid-Paleozoic colonization of land by plants induced profound changes in the Earth’s surface environments. However, it remains poorly understood how the earliest vascular plants, arising during the Silurian and Devonian periods, adapted to and functioned in ancient drylands. Today, drylands occupy ~45% of the Earth’s land surface and support diverse ecosystems forming the Earth’s most extensive biome. By contrast, only sparse records of dryland systems have been documented from Silurian- and Devonian-aged deposits, and furthermore, in most cases, the evidence for recognizing major plant types is compromised by poor preservation potential of organic matter in such dry environments. Here, we recognize an Early Devonian dryland river system represented by the Guijiatun Formation, Qujing, Yunnan, South China, based on an integrative study combining paleopedology, geochemistry, and paleobotany. This formation contains diverse and abundant redbed calcareous paleosols, most being classified as Calcisols. Such paleosols are interpreted as developing within well-drained landscapes that experienced a semiarid climate with seasonal wet-dry cycles, and are geochemically characterized by the subsurface accumulation and reorganization of pedogenic carbonates. Extensive plant traces are preserved in most of the paleosols observed in the Guijiatun Formation and show K- or H-shaped branching structures that are morphometrically comparable to the belowground rhizomes of zosterophyllopsids and early lycopsids. These plant-bearing paleosols provide direct evidence for the development of primitive vegetation on drylands. The soil inorganic carbon (SIC) contents stored as Ca-Mg carbonates in the Guijiatun paleosols are estimated at 38 ± 8 g C kg-1, comparable to the highest levels of present-day dryland ecosystems. We argue that dryland floras could have been a significant component of the Early Devonian landscapes, controlling the retention of both mobile elements (Ca and Mg) and fine-grained sediment on land, and mantling and protecting buried soil carbon against erosion.

In permafrost peatlands, the degradation of permafrost soil can raise soil temperature and alter moisture conditions, which increases the rate of loss of soil organic carbon (SOC). Here we selected three typical permafrost types that have very different active layer thicknesses but with soil originating from the same vegetation and which exist under comparable climatic conditions in the Da Xing’an mountain range: continuous permafrost, island permafrost, and island melting permafrost. To quantify the relative importance of control elements on SOC stabilization in these different permafrost types, we used correlation analysis to assess the relationship between organic carbon, physical and chemical properties and microorganisms, and explored the contribution of these factors to the accumulation of organic carbon. This study shows that the interaction between clay or silt, iron oxides and microorganisms have an important influence on the stability of organic carbon in permafrost peatlands.

Soil inorganic carbon (SIC) is an important reservoir of carbon (C) in arid, semi-arid, and semi-humid regions. However, knowledge is incomplete on the dynamics of SIC and its relationship with soil organic C (SOC) under different land use types in the semi-humid region, particularly in coastal zones impacted by soil salinization. We collected 170 soil samples from 34 profiles across various land use types (maize-wheat, cotton, paddy, and reed) in the middle-lower Yellow River Delta (YRD), China. We measured soil pH, electrical conductivity (EC), water-soluble salts, and SOC and SIC contents. Our results showed significant differences in both SOC and SIC among land use types. The dry cropland (maize-wheat and cotton) soils had significantly higher SOC and SIC densities (4.71 and 15.46 kg C m–2, respectively) than the paddy soils (3.28 and 14.09 kg C m–2, respectively) in the 0–100 cm layer. Compared with paddy soils, reed soils contained significantly higher SOC (4.68 kg C m–2) and similar SIC (15.02 kg C m–2) densities. There was a significant positive correlation between SOC and SIC densities over a 0–100 cm soil depth in dry cropland soils, but a negative relationship in the paddy soils. On average, SOC and SIC densities under maize-wheat cropping were 15% and 4% lower, respectively, in the salt-affected soils in the middle-lower YRD than the upper YRD. This study indicated that land use types had great influences on both SOC and SIC and their relationship, and salinization had adverse effect on soil C storage in the YRD.

Previous studies have mainly focused on changes in soil physical and chemical properties to evaluate the reclamation of sodic soils using flue gas desulfurization (FGD) gypsum. However, information on the effects of this reclamation method on microbial-based indicators of soil quality is limited, particularly after many years of FGD gypsum application. This study aimed to investigate the long-term effects of FGD gypsum on soil organic carbon (SOC), nutrients, microbial biomass and enzyme activity. Data were collected from soils of three exchangeable sodium percentage (ESP) classes (i.e., low-, middle- and high-ESP classes of 6.1–20, 20–30 and 30–78.4%, respectively) 17 years after FGD gypsum treatment in Inner Mongolia, China. Averaged across the three ESP classes, FGD gypsum application increased the SOC contents at the 0–20 and 20–40-cm soil depths by 18 and 35%, respectively, and increased available potassium at the 0–20-cm soil depth by 51% compared with the no-gypsum controls. The microbial biomass carbon and microbial biomass nitrogen contents at the 20–40-cm soil depth increased by 69 and 194%, respectively, under FGD gypsum. Except in the high-ESP class, urease activities in the 0–40 cm soil profile were significantly higher in the FGD gypsum treatments than in the controls. A significant increase in alkaline phosphatase activity was concentrated in the 20–40 cm soil layer; few classes showed significant increases in catalase and invertase activities in the 0–20 cm soil layer. Pearson correlation analysis showed that increases in soil fertility and biological activity could be attributed to reductions in electrical conductivity, pH and ESP caused by FGD gypsum application. These results confirm that FGD gypsum application is a viable strategy for reclaiming sodic soils due to its positive effects on soil fertility and biochemistry and that it may contribute to soil ecosystem sustainability.

Mob-grazing involves maintaining high densities of livestock for short periods so that most plants are either eaten or trampled, followed by long rest periods. This practice has been proposed as a mechanism to increase soil carbon (C) storage and range quality. However, mob-grazing has not universally achieved these objectives, possibly because many factors influence the effects of grazing on soil C dynamics and vegetation. This study examines factors that may mediate grazing impacts on soil C by comparing plant cover and the seasonal dynamics of roots, soil variables, and mycorrhizal fungal hyphae in experimental plots treated with traditional grazing, annual mob-grazing or no grazing for 18 yr. Root and soil variables were measured directly underneath a C4 grass, a C3 grass, and a forb up to 5 × during a 13-mo period. Mob-grazing did not influence total soil C, but it significantly increased soil organic matter (SOM), fine particulate organic matter, and nitrogen-15 (δ15N). Furthermore, mob-grazing increased soil compaction, decreased soil aggregate stability, decreased soil moisture, and tended to increase the abundance of two invasive plant species: Salsola tragus and Bromus tectorum. Soil compaction, soil aggregate stability, root biomass, particulate organic matter, and percent soil C and N varied significantly across seasons and among plant species. The density of mycorrhizal fungal hyphae varied with season but not with grazing treatment. A significant grazing by date interaction in root biomass and soil carbon-13 (δ13C) suggests that root dieback and inputs of pulverized plant material with a higher δ13C signature could be the source of higher SOM in mob-grazed plots. Compared with ungrazed plots, traditionally grazed plots had higher SOM without the adverse impacts on vegetation and soil properties observed in the mob-grazed plots. No single management strategy is universally beneficial. Range managers should carefully weigh the pros and cons of mob-grazing because, although it can increase SOM in surface soils, it may also negatively impact soil structure and composition of vegetation.

Managing grasslands to sequester carbon is of global importance, but effects of grazing on soil organic carbon (SOC) stocks remain uncertain. We quantified effects of livestock grazing (grazed or not for 9−26 yr) and soil texture on SOC stocks (kg × m−2) of 20 sites in a temperate grassland. We also quantified the effects of livestock grazing on SOC concentration and bulk density. Percent sand explained a considerable amount of the variation in SOC stock (r2 = 0.45 to 0.59). In addition, SOC stocks were 12% less in areas rested from livestock grazing (i.e., not grazed) than annually grazed. Soil carbon concentrations were also 10% less in rested than grazed areas. Bulk density was 2% less in areas rested from grazing, but bulk density was greater at sites with longer periods of rest. We also detected a grazing treatment and rest duration interaction, indicating that bulk density differences between grazing treatments tended to be greater at sites with longer periods of rest. Compared with no grazing, moderate grazing tended to increase SOC stocks and concentrations. Although compaction (i.e., increase in bulk density) is generally regarded as an indicator of declining soil health, minor compaction may help reduce mineralization of SOC and ultimately increase SOC stocks. We discuss methodological improvements needed for a next generation of grazing land experiments to better resolve how best to manage livestock and sequester carbon.

Terrestrial species are predicted to migrate northward under global warming conditions, yet little is known about the direction and magnitude of change in microbial distribution patterns. In this continental-scale study with more than 1600 forest soil samples, we verify the existence of core microbiota and lump them into a manageable number of eco-clusters based on microbial habitat preferences. By projecting the abundance differences of eco-clusters between future and current climatic conditions, we observed the potential warming-driven migration of the core microbiota under warming, partially verified by a field warming experiment at Southwest China. Specifically, the species that favor low pH are potentially expanding and moving northward to medium-latitudes (25°–45°N), potentially implying that warm temperate forest would be under threat of soil acidification with warming. The eco-cluster of high-pH with high-annual mean temperature (AMT) experienced significant abundance increases at middle- (35°–45°N) to high-latitudes (> 45°N), especially under Representative Concentration Pathway (RCP) 8.5, likely resulting in northward expansion. Furthermore, the eco-cluster that favors low-soil organic carbon (SOC) was projected to increase under warming scenarios at low-latitudes ( 45°N) the changes in relative abundance of this eco-cluster is inversely related with the temperature variation trends, suggesting microbes-mediated soil organic carbon changes are more responsive to temperature variation in colder areas. These results have vital implications for the migration direction of microbial communities and its potential ecological consequences in future warming scenarios.

Increased anthropogenic nitrogen (N) deposition is driving N-limited ecosystems towards phosphorus (P) limitation. Plants have evolved strategies to respond to P limitation which affect N cycling in plant‐soil systems. A comprehensive understanding of how plants with efficient P‐acquisition or ‐use strategies influence carbon (C) and N cycling remains elusive. We highlight how P‐acquisition/-use strategies, particularly the release of carboxylates into the rhizosphere, accelerate soil organic matter (SOM) decomposition and soil N mineralisation by destabilising aggregates and organic‐mineral associations. We advocate studying the effects of P-acquisition/-use strategies on SOM formation, directly or through microbial turnover.

Soil microorganisms are known to significantly contribute to climate change through soil carbon (C) cycle feedbacks. However, it is challenging to incorporate these feedbacks into predictions of future patterns of terrestrial C cycling, largely because of the vast diversity of soil microorganisms and their responses to environmental conditions. Here, we show that the composition of the bacterial community can provide information about the microbial community-level thermal response (MCTR), which drives ecosystem-scale soil C-climate feedbacks. The dominant taxa from 169 sites representing a gradient from tropical to boreal forest mainly belonged to the phyla Actinobacteria and Acidobacteria. Moreover, we show that the MCTR in warm biomes and acidic soils was linked primarily to bacteria, whereas the MCTR in cold biomes and alkaline soils was primarily associated with fungi. Our results provide strong empirical evidence of linkages between microbial composition and the MCTR across a wide range of forests, and suggest the importance of specific microorganisms in regulating soil C-climate feedbacks.

Soils store an important amount of carbon (C), mostly in the form of organic matter in different decomposing stages. Hence, understanding the factors that rule the rates at which decomposed organic matter is incorporated into the soil is paramount to better understand how C stocks will vary under changing atmospheric and land use conditions. We studied the interactions between vegetation cover, climate and soil factors using the Tea Bag Index in 16 different ecosystems (eight forests, eight grasslands) along two contrasting gradients in the Spanish province of Navarre (SW Europe). Such arrangement encompassed a range of four climate types, elevations from 80 to 1420 m.a.s.l., and precipitation (P) from 427 to 1881 mm year–1. After incubating tea bags during the spring of 2017, we identified strong interactions between vegetation cover type, soil C/N and precipitation affecting decomposition rates and stabilization factors. In both forests and grasslands, increasing precipitation increased decomposition rates (k) but also the litter stabilization factor (S). In forests, however, increasing the soil C/N ratio raised decomposition rates and the litter stabilization factor, while in grasslands higher C/N ratios caused the opposite effects. In addition, soil pH and N also affected decomposition rates positively, but for these factors no differences between ecosystem types were found. Our results demonstrate that soil C flows are altered by complex site-dependent and site-independent environmental factors, and that increased ecosystem lignification will significantly change C flows, likely increasing decomposition rates in the short term but also increasing the inhibiting factors that stabilize labile litter compounds. This work was supported by the Public University of Navarre; the Spanish Ministry of Science [grant numbers AGL2016-76035-C2, PID2020-116786RB-C32] and the Spanish Ministry of Economy and Competitiveness [grant BES-2017-080326]. Open access funding provided by the Public University of Navarre.

Understanding the mechanism of soil organic carbon (SOC) sequestration is of paramount importance in sustaining crop productivity and mitigating climate change. Long-term trials were employed to investigate the responses of total SOC and its pools, i.e., mineral-associated OC (MOC), particulate OC (POC, containing Light-POC and Heavy-POC), to fertilization regimes at Yangling (25-year), Tianshui (35-year) and Pingliang (37-year) under a rain-fed cropping system in the Loess Plateau. The fertilization regimes in each trial included three treatments, i.e., control (no nutrient input, CK), chemical fertilizers (CF), and organic manure plus chemical fertilizers (MCF). Relative to the CK, long-term fertilization appreciably increased SOC storage by 134, 89 and 129 kg ha−1 yr−1 under CF, and 418, 153 and 384 kg ha−1 yr−1 under MCF in plough layer soils (0–20 cm), respectively, at the Yangling, Tianshui and Pingliang sites. The MOC pools accounted for 72, 67 and 64% of the total SOC at the above three sites with sequestration rates of 76, 57 and 83 kg ha−1 yr−1 under CF and 238, 118 and 156 kg ha−1 yr−1 under MCF, respectively. Moreover, the MOC pool displayed a saturation behavior under MCF conditions. The POC accordingly constituted 27, 33 and 36% of SOC, of which Light-POC accounted for 11, 17 and 22% and Heavy-POC for 17, 16 and 15% of SOC, respectively. The sequestration rates of POC were 58, 32 and 46 kg ha−1 yr−1 under CF, and 181, 90 and 228 kg ha−1 yr−1 under MCF at the three respective sites, in which Light-POC explained 59, 81 and 72% of POC under CF, and 60, 40 and 69% of POC under MCF, with Heavy-POC accounting for the balance. Compared with CK, the application of CF alone did not affect the proportions of MOC or total POC to SOC, whereas MCF application markedly reduced the proportion of MOC and increased the POC ratio, mainly in the Light-POC pool. The distribution of SOC among different pools was closely related to the distribution and stability of aggregates. The present study confirmed that organic manure amendment not only sequestered more SOC but also significantly altered the composition of SOC, thus improving SOC quality, which is possibly related to the SOC saturation level.

Significant interest exists in the potential for specialized grazing systems, including adaptive multipaddock (AMP) grazing, to enhance grassland health and function. However, specific pasture management practices associated with AMP grazing at the ranch level remain poorly understood in comparison with more regionally representative management systems. As part of a larger study examining grazing effects on soil carbon, greenhouse gases, and other ecosystem attributes, here we report on differences in disturbance history and grazing management practices on a sample of AMP operators and their neighboring (n-AMP) ranches at 32 paired sites across the prairie provinces of western Canada. Most ranches studied (77.5%) relied on pastures composed of introduced (seeded) forage. On average, the AMP ranches surveyed were larger in size, supported greater animal numbers, and were more likely to use seeded forages comprising diverse mixes. Relative to n-AMP ranches, AMP ranches used 18.6-fold higher average stock densities in smaller paddocks (22.3 vs. 120.7 ha) while grazing over a grazing season that was 76 d longer, although computed stocking rates remained similar (P ≥ 0.10). AMP operators specifically used much shorter grazing periods (2.8 d) during the early growing season (i.e., before August 1) that were followed by a prolonged rest period (69 d) and could be used to compute a rest-to-grazing ratio for the first half of the grazing season for all ranches. This ratio, along with cattle stock density computed at the pasture scale, exhibited the greatest potential to differentiate the two groups of ranchers. Finally, both groups, and in particular ranchers within the AMP group, demonstrated high variability in management practices among individual operators, highlighting the importance of using specific management metrics rather than generalized descriptors of “grazing system type” to interpret their influence.

Today, there is a greater appreciation for the importance of the physical protection of carbon (C) through interactions with mineral surfaces, isolation from microbes, and the important role of transport in shaping soil properties and controlling moisture limitations on decomposition. As our paradigm for soil organic carbon (SOC) preservation changes, so too should our representation of the underlying processes in soil models. Reactive transport models (RTMs) provide a framework capable of assessing the interactive influence of soil chemistry and transport processes on the accumulation and turnover of SOC. In this study, we present new developments in the isotopically enabled RTM “CrunchTope,” which is capable of explicitly tracking the three isotopes of carbon (12C, 13C, and 14C) and their fractionation between multiple coexisting and interacting solid, liquid and gas phases. This modeling framework opens the door to new applications of depth-resolved RTM models in application to SOC and deeper subsurface carbon reservoirs. Here, we demonstrate SOC accumulation and radiocarbon aging for long-timescale models of soil development in CrunchTope. Our goal is to assess advantages and limitations of such an approach and to identify the type and complexity of reaction networks that are required to adequately apply this model to SOC dynamics. We assess the behavior of this model relative to a high-resolution dataset of SOC content, stable isotope composition, and radiocarbon ages as well as physical and hydrologic data measured from a chronosequence of soils located near Santa Cruz, California. Starting from a previously published model using a simplified reaction network with a single class of carbon, we sequentially incorporate multiple carbon reservoirs subject to both reactivity and transport pathways. Our results indicate that multiple SOC pools with different mean ages of C do not inherently emerge as a result of including reactions which are conventionally expected to provide a diversity of transit times, i.e., sorption and complexation of SOC on mineral surfaces. Instead, transit times emerge as a result of the timescales of the reactions represented in the reaction network. For mineral associated C, the RTM framework imposes dynamic equilibrium with the fluid phase dissolved organic carbon, such that no distinction in radiocarbon ages is achieved between these pools. Aged C can be produced by including a solid-phase carbon reservoir, with a rate-limited solubilization coefficient. Aging of SOC in this way is more akin to selective preservation than to mineral protection and, while such a mechanism may be at play in many soils, mineral protection is thought to be at least as important. As such, our results indicate that additional parameterization is required to reproduce the heterogeneity of carbon transit times that result from organo-mineral interactions. These efforts show the promise of a modeling approach where the varied transit time of soil C emerges from the dynamic physical and hydrologic properties of the model rather than from the a priori assignment of operationally defined pools.

The use of green manures contributes to sustainable soil and nutrient management in agriculture; however, the responses of soil microbial communities to different fertilization regimes at the regional scale are uncertain. A study was undertaken across multiple sites and years in Hunan, Jiangxi, Anhui, Henan, Hubei, and Fujian provinces of South China to investigate the effects of green manuring on the structure and function of soil bacterial communities in rice-green manure cropping systems. The study included four treatments: winter fallow with no chemical fertilizer as a control (NF), milk vetch as green manure without chemical fertilizer (GM), winter fallow and chemical fertilizer (CF), and a combination of chemical fertilizer and milk vetch (GMCF). Significant differences were found in the responses of soil microbial communities at different sites, with sampling sites explaining 72.33% (F = 36.59, P = 0.001) of the community composition variation. The bacterial communities in the soils from Anhui, Henan, and Hubei were broadly similar, while those from Hunan were distinctly different from other locations. The analysis of Weighted UniFrac distances showed that milk vetch changed soil microbial communities compared with winter fallow. Proteobacteria and Chloroflexi predominated in these paddy soils; however, the application of green manures increased the relative abundance of Actinobacteria. There was evidence showing that the functional microbes which play important roles in the cycling of soil carbon, nitrogen (N), and sulfur (S) changed after several years of milk vetch utilization (linear discriminant analysis score > 2). The abundance of methane-oxidizing bacteria and S-reducing bacteria increased, and microbes involved in N fixation, nitrification, and denitrification also increased in some provinces. We concluded that the application of milk vetch changed the bacterial community structure and affected the functional groups related to nutrient transformation in soils at a regional scale.

This paper critically reviewed the current knowledge and challenges of rice husk biochar (RHB) production and its effects on soil properties, plant growth, immobilization of heavy metals, reduction of nutrient leaching and mitigation of greenhouse gas emissions. The characteristics of RHBs produced at various pyrolysis temperatures were discussed and compared to biochars derived from other agro- industrial wastes. RHBs produced at higher pyrolysis temperatures show lower hydrogen/carbon ratio, which suggests the presence of higher aromatic carbon compounds. The increase of pyrolysis temperature also results in production of RHBs with higher ash content, lower yield and higher surface area. RHB usually has higher silicon and ash contents and lower carbon content compared to biochars derived from other feedstocks at the same pyrolysis conditions. Although it depends on soil type, RHB application can improve soil organic carbon content, cation exchange capacity, available K concentration, bulk density and microbial activity. The effect of RHB on soil aggregation mainly depends on soil texture. The growth of different crops is also enhanced by application of RHB. RHB addition to soil can immobilize heavy metals and herbicides and reduce their bioavailability. RHB application shows a significant capacity in reduction of nitrate leaching, although its magnitude depends on the biochar application rate and soil biogeochemical characteristics. Use of RHB, especially in paddy fields, shows a promising mitigation effect on greenhouse gas (CH4, CO2 and N2O) emissions. Although RHB characteristics are also related to other factors such as pyrolysis heating rate and residence time, its performance for specific applications (e.g. carbon sequestration, pH amendment) can be manipulated by adjusting the pyrolysis temperature. More research is needed on long-term field applications of RHB to fully understand the advantages and disadvantages of RHB as a soil amendment.

In agroecosystems, temporal diversification creates a sequence of short-lived habitats through time. Crop species as well as the diversity of crops grown in sequence might affect soil biodiversity and nutrient cycling processes. In the present study, we focused on a long-term crop rotation established in 2006 in Lower Saxony, Germany on a Luvisol. Winter wheat (WW) and silage maize (SM) were grown in continuous cultivation as well as in rotations. WW rotations span up to six years (including silage maize, sugar beet, winter rape and/or grain pea). Over two years, microbial biomass carbon (MBC) as well as kinetics (Michaelis-Menten Vmax and Km) of extracellular hydrolytic enzymes (β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG) and acid phosphomonoesterase (AP)) were measured in topsoil (0–10 cm depth) three times during the growing season. Continuous wheat increased soil microbial parameters compared to continuous maize as indicated by the higher microbial biomass to soil organic carbon ratio and higher potential enzymes activities involved in the C- and N-cycles (Vmax of BG and NAG). The efficiency of these enzymes was lowest in continuous maize (highest Km of BG and NAG). Maize and sugar beet as preceding crop of WW significantly decreased MBC in the 1st year but not in the 2nd year WW. Sugar beet decreased BG activity as well as its substrate affinity (increased Km). The effect of sugar beet on MBC and enzyme kinetics depended on the preceding crop and lessened with grain pea as the preceding crop. Soil microorganisms in the wheat phase benefited from winter rape as the preceding crop, shown by an increased biomass and efficiency to turn over chitin and peptidoglycan (decreased Km of NAG). Differences between cultivated crops, cropping history and fluctuations within the year in soil microbial biomass and enzyme kinetics are shown.

Biochar application for soil and agro-environmental development has attracted great attention due to its numerous advantages: improving the soil, mitigating greenhouse gas emissions, increasing crop productivity, and augmenting soil carbon storage. However, during the pyrolytic conversion of waste biomass, polycyclic aromatic hydrocarbons (PAHs), a category of toxic organic pollutants, are inescapably generated and linger on the residual solid coproduct called biochar. Therefore, it is crucial to assess the environmental persistence, bioavailability, effects of biochar-borne PAHs on plant growth and soil microbial community dynamics, food safety, and human health after application into soils. This review highlights the basic need to unravel critical mechanisms driving PAH formation in biochar and the dynamics between the sorbent (biochar) and soil microbes, along with the possible mitigation strategies. Current research gaps, including the influence of biochar application on the short and long-term fate of PAHs, as well as the proper control measures for biochar quality and associated risks, will be discussed herein. The key research findings from this script will lead to proposals in technological and quality control measures during biochar production to ensure they are clean and safe.

Approximately one third of California is grazed by livestock, with most forage produced on annual rangelands, the common term for rangelands with a significant annual herbaceous component. Given the state's interest in mitigating climate change and growing public attention on grazing systems that enhance carbon sequestration, we investigate the impact of grazing management on soil carbon cycling on California annual rangelands, drawing on soil science, rangeland management, and policy analysis literature. We conclude that using managed grazing for augmenting soil organic carbon on California annual rangelands presents significant challenges. Challenges include the heterogeneity, biogeochemical characteristics, and nonequilibrium nature of California's Mediterranean region, where ecological site conditions, soil type and texture, and climate moderate carbon sequestration. Enduring unknowns in the science underlying soil carbon and the dearth of relevant California-based studies further obscure the potential climate change mitigation effects of grazing systems. Given this, grazing management on California annual rangelands should not be prioritized as a climate change mitigation strategy, unless it is for the purposes of data collection and research. Alternative climate change mitigation opportunities on these landscapes include preventing rangeland conversion and enhancing soil carbon stocks through the suite of range management practices known to augment soil organic carbon or prevent erosion, including marginal cropland restoration, riparian restoration, organic amendments, and silvopasture. In this review, we argue that single-purpose management is generally not fitting for the diverse portfolio of social-ecological services produced on California's vast and varied rangelands. When assessing the value of grazing systems for augmenting soil organic carbon, policymakers, landowners, and other decision makers should consider the potential impacts on the numerous ecosystem services supported by the landscape. The multidisciplinary method presented in this review provides a critical framework for evaluating the appropriateness of working lands carbon policies as Natural Climate Solutions for climate change mitigation are developed in California and other geographies.

Soil Organic Carbon (SOC) dynamics study in arable land use at different agro-ecological zones is important for recommendation of sustainable land use management practices against detrimental practices. This will provide insight on how to enhance SOC sequestration, improve soil quality and mitigate impact of climate change in different agro-ecological zones. This study was conducted at two agro-ecological zones of Nigeria; upland rainforest (Ado-Ekiti) and southern guinea savanna (Kabba) to evaluate SOC sequestration under arable land use. From the two agro-ecological zones, 1 ha (ha) of land was marked out, five soil samples were randomly collected at four different depths (0–15, 15–30, 30–45, and 45–60 cm) for SOC sequestration study. Higher SOC concentration and stock were observed at Ado-Ekiti site over Kabba site was due to best soil management practices like soil organic and inorganic fertilizers application and incorporation of crop residues. SOC concentration distribution varied greatly (%CV > 35%) and decreased with depth at the two agro-ecological zones. SOC stocks ranged from 6.59 t ha−1 to 24.97 t ha−1 and decreased with depth in similar trend with SOC concentration. Generally, at both sites, soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) decrease with increasing depth especially to 45 cm depth while soil pH increase with increasing depth. Both SOC concentration and stock were observed to have significant positive correlation (P

Land degradation is becoming a serious problem in the west coast region of India where one of the world's eight biodiversity hotspots, the ‘Western Ghats’, is present. Poor land management practices and high rainfall have led to increasing problems associated with land degradation. A long-term (13-year) experiment was done to evaluate the impact of soil and water conservation measures on soil carbon sequestration and soil quality at three different depths under cashew nut cultivation on a 19% slope. Five soil and water conservation measures - continuous contour trenches, staggered contour trenches, half-moon terraces, semi-elliptical trenches, and graded trenches all with vegetative barriers of Stylosanthes scabra and Vetiveria zizanoides and control were evaluated for their influence on soil properties, carbon sequestration, and soil quality under cashews. The soil and water conservation measures improved significantly the soil organic carbon, soil organic carbon stock, carbon sequestration rate and microbial activity compared to the control condition (without any measures). Among the measures tested, continuous contour trenches with vegetative barriers outperformed the others with respect to soil organic carbon stock, sequestration rate, and microbial activity. The lower metabolic quotient with the measures compared to the control indicated alleviation of environmental stress on microbes. Using principal component analysis and a correlation matrix, a minimum dataset was identified as the soil available nitrogen, bulk density, basal soil respiration, soil pH, acid phosphatase activity, and soil available boron and these were the most important soil properties controlling the soil quality. Four soil quality indices using two summation methods (additive and weighted) and two scoring methods (linear and non-linear) were developed using the minimum dataset. A linear weighted soil quality index was able to statistically differentiate the effect of soil and water conservation measures from that of the control. The highest value of the soil quality index of 0.98 was achieved with continuous contour trenches with a vegetative barrier. The results of the study indicate that soil and water conservation measures for cashews are a potential strategy to improve the soil carbon sequestration and soil quality along with improving crop productivity and reducing the erosion losses.

Thinning is an important forest management practice that has great potential to influence regional soil carbon storage and dynamics. The present study measured soil respiration (RS, the efflux of CO2 emitted) and its two components (heterotrophic (RH) and autotrophic (RA) respiration) from soil 42 years after thinning in comparison to un-thinning (control). Autotrophic respiration was significantly greater in the thinning plot, approximately 44% higher compared to the control, while both R s and RH were slightly, but not significantly, higher in the thinning plot. Higher fine root biomass might have contributed to the higher R a in the thinning plot. Both R s and RH showed clear soil temperature-dependent seasonal patterns, whereas R a was less responsive to changes in temperature, especially within one specific season. The annual and season-specific temperature sensitivities of RS and RH were lower in the thinning plot, specifically during the mid-growing season. Furthermore, variations in the season-specific temperature sensitivity of R s and RH were less intense in the thinning plot. We conclude that forest thinning can reduce the temperature sensitivity of RS and RH during the mid-growing season and increase soil CO2 emission in the long term.

Hydrogen (H2) has been proposed as an alternative energy carrier to reduce the carbon footprint and associated radiative forcing of the current energy system. Here, we describe the representation of H2 in the GFDL-AM4.1 model including updated emission inventories and improved representation of H2 soil removal, the dominant sink of H2. The model best captures the overall distribution of surface H2, including regional contrasts between climate zones, when vd(H2) is modulated by soil moisture, temperature, and soil carbon content. We estimate that the soil removal of H2 increases with warming (2–4% per K), with large uncertainties stemming from different regional response of soil moisture and soil carbon. We estimate that H2 causes an indirect radiative forcing of 0.84 mW m−2/(Tg(H2)yr−1) or 0.13 mW m−2 ppbv−1, primarily due to increasing CH4 lifetime and stratospheric water vapor production.

Soil heterotrophic respiration and its temperature sensitivity are affected by various climatic and environmental factors. However, little is known about the combined effects of concurrent climatic and environmental changes, such as climatic warming, changing precipitation regimes, and increasing nitrogen (N) deposition. Therefore, in this study, we investigated the individual and combined effects of warming, wetting, and N addition on soil heterotrophic respiration and temperature sensitivity. We incubated soils collected from a temperate forest in South Korea for 60 d at two temperature levels (15 and 20 °C, representing the annual mean temperature of the study site and 5 °C warming, respectively), three moisture levels (10%, 28%, and 50% water-filled pore space (WFPS), representing dry, moist, and wet conditions, respectively), and two N levels (without N and with N addition equivalent to 50 kg N ha–1 year–1). On day 30, soils were distributed across five different temperatures (10, 15, 20, 25, and 30 °C) for 24 h to determine short-term changes in temperature sensitivity (Q10, change in respiration with 10 °C increase in temperature) of soil heterotrophic respiration. After completing the incubation on day 60, we measured substrate-induced respiration (SIR) by adding six labile substrates to the three types of treatments. Wetting treatment (increase from 28% to 50% WFPS) reduced SIR by 40.8% (3.77 to 2.23 µg CO2-C g–1 h–1), but warming (increase from 15 to 20 °C) and N addition increased SIR by 47.7% (3.77 to 5.57 µg CO2-C g–1 h–1) and 42.0% (3.77 to 5.35 µg CO2-C g–1 h–1), respectively. A combination of any two treatments did not affect SIR, but the combination of three treatments reduced SIR by 42.4% (3.70 to 2.20 µg CO2-C g–1 h–1). Wetting treatment increased Q10 by 25.0% (2.4 to 3.0). However, warming and N addition reduced Q10 by 37.5% (2.4 to 1.5) and 16.7% (2.4 to 2.0), respectively. Warming coupled with wetting did not significantly change Q10, while warming coupled with N addition reduced Q10 by 33.3% (2.4 to 1.6). The combination of three treatments increased Q10 by 12.5% (2.4 to 2.7). Our results demonstrated that among the three factors, soil moisture is the most important one controlling SIR and Q10. The results suggest that the effect of warming on SIR and Q10 can be modified significantly by rainfall variability and elevated N availability. Therefore, this study emphasizes that concurrent climatic and environmental changes, such as increasing rainfall variability and N deposition, should be considered when predicting changes induced by warming in soil respiration and its temperature sensitivity.

In rice-wheat rotation systems, changes in soil phosphorus (P) pools and microorganisms in rice-growing seasons have been studied; however, further investigations are required to test whether these indexes exhibit different responses in wheat-growing seasons. Additionally, such studies need to include potential variations in soil carbon (C) structure and microbial community composition. In this study, a long-term rice-wheat rotation P-input reduction experiment was conducted to observe the variations in soil P pools and C composition in the 7th wheat season and to investigate the responses of soil enzyme activity and microbial communities. Four P fertilization treatments were included in the experiment, i.e., P application for rice season only (PR), for wheat season only (PW), and for both rice and wheat seasons (PR+W) and no P application in either season (Pzero). Compared with PR+W treatment, Pzero treatment significantly decreased (P

Drylands play major roles in the terrestrial carbon cycle and mitigation of climate change. Understanding the dynamics of soil organic carbon (SOC) stocks under land use change and management is essential for achieving soil C sequestration through land-based solutions for drylands. In this paper, we briefly reviewed the literature to evaluate the impact of land use change and management on dryland SOC stocks. While the site-level field measurements of SOC stocks under different types of land use change and land management are remarkable, we found that the impact is hardly quantified at the regional level using selected soil datasets or process models and may be due to insufficient data quality, representativeness and information availability, which are among the major challenges of upscaling from field measurements to estimating regional SOC stocks. Therefore, we proposed a comprehensive framework following the IPCC inventory approach to improve future studies, which underlines the needs of data collection from multiple sources, meta-analysis for calculating SOC stock change factors, and matching land and soil datasets.

Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant (NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment (800 d), > 96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils; very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth (25 cm) in both soils. Three phases on the vertical migration rate (v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement (0–355 d, v = 219 ± 17 mm year–1), followed by a steady movement (355–577 d, v = 150 ± 24 mm year–1) and a very slow movement (577–800 d, v = 107 ± 7 mm year–1). In contrast, its migration rate in the brown soil (v = 133 ± 17 mm year–1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon (SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer (0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface (20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades. Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.

Sweet orange has great socioeconomic value in India and other parts of the world for their important role in human diet and other properties like sweet flavour, sweet aroma, source of vitamin C etc. Despite its numerous commercial values, and large acreages under cultivation little has been studied on the role of sweet orange orchards in carbon management and environmental sustainability. Therefore, the present study was conducted to (1) develop appropriate models for estimation of sweet orange tree biomass, and (2) assess biomass and ecosystem carbon stock for sweet orange orchards in North East India. Allometric models for biomass estimation were developed using data from 58 harvested orange trees. The height-diameter relationships and allometric scaling between above-ground biomass (AGB), culm height (H) and diameter at breast height (D) were examined using various models. Total biomass carbon and soil organic carbon stock of the sweet orange orchard were estimated at 7.69 and 100.2 Mg C ha−1 respectively. Our finding on biomass carbon stock of the sweet orange orchard was comparable with other fruit orchards across the world. However, the age of the orchard and management systems are two major determinants for carbon sink potential of such systems. We recommend upscaling of sweet orange based agroforestry for restoration of degraded shifting cultivated lands in North East India for environmental sustainability and socioeconomic upliftment of the farmers.

Long-term straw return is an important carbon source for improving soil organic carbon (SOC) stocks in croplands, and straw removal through burning is also a common practice in open fields in South China. However, the specific effects of long-term rice straw management on SOC fractions, the related enzyme activities and their relationships, and whether these effects differ between crop growing seasons remain unknown. Three treatments with equal nitrogen, phosphorus, and potassium nutrient inputs, including straw/ash and chemical nutrients, were established to compare the effects of straw removal (CK), straw return (SR), and straw burned return (SBR). Compared to CK, long-term SR tended to improve the yield of early season rice (P=0.057), and significantly increased total organic carbon (TOC) and microbial biomass carbon (MBC) in double-cropped rice paddies. While SBR had no effect on TOC, it decreased light fraction organic carbon (LFOC) in early rice and easily oxidizable organic carbon (EOC) in late rice, significantly increased dissolved organic carbon (DOC), and significantly decreased soil pH. These results showed that MBC was the most sensitive indicator for assessing changes of SOC in the double-cropped rice system due to long-term straw return. In addition, the different effects on SOC fraction sizes between SR and SBR were attributed to the divergent trends in most of the soil enzyme activities in the early and late rice that mainly altered DOC, while DOC was positively affected by β-xylosidase in both early and late rice. We concluded that straw return was superior to straw burned return for improving SOC fractions, but the negative effects on soil enzyme activities in late rice require further research.

In order to study the history of natural fires under warming scenarios and to evaluate the possible incidence of fires in the future, we analyzed the carbon concentration and carbon isotope composition of black carbon within the loess-paleosol sequence of the Chinese Loess Plateau. Notably, the interglacials in this East Asian monsoon region were abnormally warm. The results from the interval of L5-S5 of the studied Xifeng section suggest that the principal factors controlling natural fires in an interglacial period (S5) and a glacial period (L5) were fuel load and fuel moisture level, respectively. The difference between the carbon isotope composition of black carbon and soil organic carbon during S5LL1 (marine oxygen isotope stage (MIS) 14) was due to the fact that the former records the more positive carbon isotope values of C3 plants caused by drought and low temperatures in the fire season, while the latter records the carbon isotope of plants throughout the year. The optimum temperature and humidity conditions during S5SS1 (MIS 13) were the most conducive to fires during the interglacial period of S5. However, when the temperature and humidity decreased to a specific range (mean annual temperature 2-12 °C, mean annual precipitation 200–700 mm) during the glacial period of L5, the fire occurrence reached its highest level.

Intraspecific leaf trait variations are becoming a topic of interest for many ecologists because individual-based traits are essentially the drivers of variations at the community level. Six coexisting major tree species in an old-growth temperate forest, Northeast China (i.e., Abies nephrolepis, Pinus koraiensis, Acer mono, Fraxinus mandshurica, Tilia amurensis, and Ulmus laciniata) were sampled, and three habitat types (i.e., Hab I: high soil organic carbon with a moderate slope; Hab II: low soil organic carbon with a gentle slope; and Hab III: low soil organic carbon with a strong slope) were used in the plot. We performed a two-way ANOVA to compare the specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), and leaf carbon content (LCC) between saplings (1

Homegarden agroforestry system has potential to sequester carbon while simultaneously producing agriculture yield and tree products. This study analyzed relationship between homegarden size and soil organic carbon stock (SCS) along an altitudinal gradient in Central Himalaya, India. Homegardens were selected at four altitudes (very low, low, mid and high) and categorized into three size classes viz. small, medium and large. Soil samples from surface (0–15 cm) and sub surface soils (15–30 cm) were collected seasonally and analyzed. Results indicated that SCS ranged between 22.56 and 81.51 t C ha−1 and increased with increasing altitude for small homegardens. For medium and large homegardens, it increased up to mid altitude and then decreased in high altitude homegardens. At each altitude, maximum SCS (38.56–66.16 t C ha−1) was recorded for medium sized homegardens except at high altitude where it was maximum (66.01 t C ha−1) for small homegardens. Seasonal variation in SCS showed inconsistent pattern along the altitudinal gradient. The differences in SCS due to size and altitude recorded in the present study are possibly caused by distinct quality of plant material and management practices.

The Land Degradation Neutrality Initiative of the UN Convention to Combat Desertification (UNCCD) encourages each of the 123 signatory countries to stabilise or reduce their extent of degraded land. Land degradation is assessed using the methods described in the Good Practice Guidance (GPG) document for Sustainable Development Goal (SDG) Indicator 15.3.1 (the proportion of land that is degraded over total land area), using three sub-indicators: land cover change, land productivity and soil organic carbon (SOC) stocks (as a proxy for carbon stocks above and below ground). The GPG identifies degraded areas by aggregating the sub-indicator assessments using a one-out-all-out (1OAO) approach, in which an area is identified as degraded if any one or more of the sub-indicators shows degradation i.e. a land cover transition defined as degradation, a reduction in productivity, and/or a reduction in SOC stocks. Under some circumstances, however, the 1OAO method can result in a counterintuitive degradation assessment, such as where the removal of invasive plant species reduces plant biomass, which would normally suggest degradation of net primary production, but which in this circumstance is considered a positive change in the context of land remediation activities. Each country has the opportunity to report areas within its sovereign bounds as an error of ‘false positive’ or ‘false negative’ degradation with sufficient justification, however it is vital that this is done in a way that ensures consistency of reporting amongst countries at regional and global scales. This paper describes scenarios in which the 1OAO process can lead to a counterintuitive degradation assessment, focusing on the potential impacts of invasive plants, woody encroachment (i.e. bush encroachment), and land remediation activities on SOC stocks as examples. We present an interpretation matrix to assist with determining how to report degradation in these cases, and help identify the drivers of degradation and potential remediation activities. Increased clarity around degradation labelling and interpretation could improve reporting consistency and transparency, and increase the efficiency and effectiveness of land degradation remediation actions.

Tillage practices on sloping ground often result in unsustainable soil losses impairing soil functions such as crop productivity, water and nutrients storage, and soil organic carbon (SOC) sequestration. A sloping olive grove (10%) was planted in shallow gypsiferous soils in 2004. It was managed by minimum tillage; the most frequent management practice in central Spain. The consequences of erosion were studied in soil samples (at 0–10, 10–20, and 20–30 cm depths) by analyzing SOC, available water and gypsum content, and by detecting spectral signatures using an ASD FieldSpecPro® VIS/NIR-spectroradiometer. The Brightness index (BI), Shape index (FI), and Normalized Difference Vegetation Index (NDVI) were derived from the ASD spectral signatures and from remote sensing (Sentinel-2 image) data. The development of these young olive trees was estimated from the measured diameter of the trunks (17 ± 18 cm diameter). In 20–30 cm of the soil, the carbon stock (38 ± 18 Mg ha−1) as well as the available water content (12 ± 6%) was scarce, affecting the productivity of the olive grove. The above-mentioned indices obtained from the laboratory samples and the pixels of the Sentinel-2 image were significantly (p

Mixed grass pastures which occupy the eolian sand dunes of the southern Great Plains provide stabilizing soil cover, soil carbon (C) storage, and are a critical resource for livestock production. Large areas of dunes cover the American Great Plains, were active 700–1000 years ago during periods of frequent drought and have the potential to reactivate under forecasted climate scenarios and poor management. This study determined the soil age and development of eolian sandy soils and evaluated long-term grazing of native and improved pasture on root carbon, soil organic C (SOC), stable isotopes of soil fractions, and other soil properties. Pasture treatments included grazed and ungrazed (50 + yrs), improved pastures (28–50 yrs), and winter wheat (Triticum aestivum) or go-back grass (for 28–30yrs). Improved pasture grass species included both native (switchgrass (Panicum virgatum L.), and sand bluestem (Andropogon hallii Hack.) and non-native (weeping lovegrass (Eragrostis curvula (Schrad.) Nees)), and caucasian bluestem (Bothriochloa bladhii (Retz.) S.T. Blake) species. The Eda soil age was very recent and ranged from present at the surface to

There is limited information on changes cause by nitrogen (N) fertilizers and biochar (BC) application in soil carbon and nitrogen availability, leaching and microbial activity at different growth stages in rice. This is first comprehensive study conducted in early and late seasons during 2019 to evaluate efficiency of various traditional N fertilizers (i) Urea (ii) Ammonium nitrate and (iii) Ammonium sulfate (315 kg N ha−1) with or without biochar (30 t ha−1). Results illustrated that all N fertilizers sources applied with biochar significantly increased soil organic carbon (SOC) content by an average 48.44% and 50.63%, soil total nitrogen (Nt) by 4.56% and 4.94%, reduction in total nitrogen leaching by 42.63% and 76.16%, while dissolved organic carbon leaching (DOC) augmented by 39.87% and 38.38% than non-applied treatments in early and late season, respectively. Additionally, soil microbial biomass C and N progressively increased with growth stages and was found higher than non-applied treatments in both seasons. Furthermore, combined application of N fertilizers and biochar, facilitated soil N transformation and the net concentration of NH4+–N and NO3−–N was relatively higher than non-charred treatments. Similarly, in both early and late seasons, urease enzyme activity increased by an average 13.52% and 13.55%, β-glucosidase by 15.99% and 19.27% however, catalase activity decreased by 14.58% and 12.38%, correspondingly. Moreover, no significant difference (p

Forage and grazing (FG) systems can store a substantial amount of soil organic carbon (SOC) under appropriate land use management and reduce atmospheric CO2 concentrations. Increasing SOC levels along with many interlinked ecosystem services are essential for increased productivity and sustainability of FG lands (FGLs). Although adoption of improved management practices (MPs) that support SOC sequestration (SOCq) is necessary, clear understandings of challenges and opportunities which are sometimes unique to individual FGLs, are also important for implementation of MPs. The objective of this forum paper is to explore the latest scientific knowledge on opportunities to address major challenges for increasing SOCq in FGLs. In intensively managed FGLs where the goal is often to maximize yields, lands are heavily fertilized and thus, usually drive towards SOC loss. Diversifications of both forage and grazing species along with strategic grazing plans have been proven as effective MPs for increasing SOCq. However, challenge of maintaining productivity levels still remains. Implementing improved grazing for nutrient cycling and integrating forage diversification for increased biodiversity are found to improve soil health attributes, which are critical for SOCq. However, to achieve this, we also need to consider site- and soil- specific factors. Extreme climatic events often lead to a decline in soil fertility status, SOCq and overall productivity of FGL systems. To address these challenges, uses of models to simulate the FGL systems and have definite choices of suitable MPs are helpful. However, we must be able to access a wide range of datasets to develop system-level adaption strategies that are effective in mitigating these adverse effects. Ultimately, participatory research with novel views and improved perceptions based on the value of SOCq and long-term benefits of the implementation of the best MPs and developing education and outreach materials to enrich the producers’ knowledge gaps are helpful for climate-resilient FGL systems.

Ecological stoichiometry provides the possibility for linking microbial dynamics with soil carbon (C), nitrogen (N), and phosphorus (P) metabolisms in response to agricultural nutrient management. To determine the roles of fertilization and residue return with respect to ecological stoichiometry, we collected soil samples from a 30-year field experiment on residue return (maize straw) at rates of 0, 2.5, and 5.0 Mg ha−1 in combination with 8 fertilization treatments: no fertilizer (F0), N fertilizer, P fertilizer, potassium (K) fertilizer, N and P (NP) fertilizers, N and K (NK) fertilizers, P and K (PK) fertilizers, and N, P, and K (NPK) fertilizers. We measured soil organic C (SOC), total N and P, microbial biomass C, N, and P, water-soluble organic C and N, KMnO4-oxidizable C (KMnO4-C), and carbon management index (CMI). Compared with the control (F0 treatment without residue return), fertilization and residue return significantly increased the KMnO4-C content and CMI. Furthermore, compared with the control, residue return significantly increased the SOC content. Moreover, the NPK treatment with residue return at 5.0 Mg ha−1 significantly enhanced the C:N, C:P, and N:P ratios in the soil, whereas it significantly decreased the C:N and C:P ratios in soil microbial biomass. Therefore, NPK fertilizer application combined with residue return at 5.0 Mg ha−1 could enhance the SOC content through the stoichiometric plasticity of microorganisms. Residue return and fertilization increased the soil C pools by directly modifying the microbial stoichiometry of the biomass that was C limited.

Understanding how topography-soil-disturbance drives spatial distribution of vegetation is the interest of ecologists. This study was, conducted to investigate the topography-soil-disturbance and vegetation relationships in Abune Yosef mountain range, Ethiopia. A total of 85 nested sample plots measuring 400 m2, 25 m2 and 1 m2 were established for trees, shrubs and herbs respectively. Topographic, soil and disturbance variables were also assessed from each plot. Plant community classification was described and identified by agglomerative hierarchical clustering using Ward's minimum variance clustering methods. Shannon diversity index was employed to determine community diversity. After detecting the length of the first Detrended Correspondence Analysis (DCA) axis, Canonical Correspondence Analysis (CCA) forward and backward stepwise selection of environmental variables was performed based on their p-value by running permutation tests. The first axis explained 43.63% of the overall inertia and is correlated with Elevation, pH, slope aspect, total Nitrogen, soil organic Carbon & Clay. On the other hand, the second axis explained 32.06% of the total inertia and is correlated with bulk density, slope, logging, & available Phosphorus. The present study revealed that topographic variables have a profound influence on vegetation spatial distribution than soil and disturbance factors.

The labile organic carbon (C) and C-related enzymes are sensitive indicators capturing alterations of soil organic matter (SOM), even in a short-time scale. Although the effects of crop husbandry and land use change on these attributes have been well studied, there is no consensus about how plant phenology may impact them. This study aimed to determine the short-term effect of six distinct phenological stages (PS-1: full bloom; PS-2: fruit set; PS-3: pit hardening; PS-4: physiological maturity; PS-5: 60 d after physiological maturity; and PS-6: fall) of peach on the changes in soil organic carbon (SOC) fractions of different oxidizability, labile C pools, and C-cycle enzyme activities in soils, for two consecutive years (2015 and 2016) in the North-Western Himalayas (NWH). Peach rhizosphere soils were sampled at the topsoil (0–15 cm) and subsoil (16–30 cm) layers, along with rhizosphere soils from adjacent perennial grasses, which served as a control. Values for most of the assessed parameters, including very labile C, labile C, microbial biomass C, permanganate oxidizable C, dissolved organic C, mineralizable C, amylase activity, and carboxymethyl-cellulase activity, were significantly (P ≤ 0.05) higher at PS-3 than at other phenological stages of peach. Conversely, a sudden decline in these soil variables was recorded at PS-5, followed by a slight buildup at PS-6, particularly in the topsoil of the peach orchard. Short-term changes in organic C fractions of different oxidizability, influenced by peach phenological stage, significantly (P ≤ 0.05) affected C management index, C pool index, and lability index. Both the C management index and lability index showed their highest values at PS-3 and their lowest values at PS-5, clearly indicating short-term accretion and depletion of SOC, in tandem with the peach phenological events. Principal component analysis suggested that a composite of soil indicators, including microbial biomass C, dissolved organic C, amylase, and invertase, could help detect short-term changes in SOC content. It is concluded that peach phenological events had a major impact on the short-term variations of the studied soil variables, which could be attributed to changes in the above- and belowground plant residues, as well as the extent of nutrients and water acquisition.

Smouldering wildfires in peatlands can last for weeks, resulting in the release of large amount of soil carbon and harmful emissions with detrimental effects on human health and the environment. Despite their importance, smouldering fires are poorly understood. An experimental study was carried out here to measure the spread rate of peat fire in detail, using infrared (IR) imaging. Peat samples with different moisture contents were prepared and burned in an open reactor of 20 × 20 cm2 cross section and 10 cm depth, under laboratory-controlled conditions. In total, twelve experiments were studied, each lasting for 8 h on average. Infrared and visual cameras were synchronised, and images were acquired at a frequency of 1/min, for the duration of the experiment. Profiles of smouldering spread on the free surface of peat were tracked using an image intensity threshold and then used to calculate the horizontal spread rate. Temporally and spatially resolved spread rates are presented and analysed. Increasing the moisture content of the peat resulted in a decrease in spread rate and the smouldering front became increasingly irregular. At high moisture contents, spread at the lower layers of peat is faster compared to top surfaces which leads to formation of overhang, and IR is able to measure the formation of the overhang and its collapse as a step increase in horizontal spread. The overhang becomes more prominent when moisture content is increased. The new tool allows the study of unprecedented details in the spread of peat fires and can be adopted in future experimental studies.

Freshwater influenced wetlands (FIW), wetlands impacted by both freshwater flooding and underground seawater (MIW) and seawater influenced wetlands (SIW) were chosen as sampling sites to investigate the variations in the soil organic carbon content and stock in wetlands with different hydrologic conditions in the Yellow River Delta, China. The results showed that a salinity gradient developed as the hydrologic conditions ranged from freshwater to seawater. In 0–50 cm soils, the mean values of soil organic carbon (SOC), microbial biomass carbon (MBC) and readily oxidized organic carbon (ROOC) were higher in FIW and SIW than those in MIW, while the dissolved organic carbon (DOC) showed a higher mean value in MIW. Along the 0–50 cm soil profile, SOC, MBC, ROOC and DOC decreased as the soil depth increased in FIW and SIW. However, in MIW, soil carbon initially decreased and then increased later. The annual mean values of SOC in 0–50 cm soils were 6.87 g/kg in FIW, 4.92 g/kg in MIW and 5.42 g/kg in SIW, respectively. The soil organic carbon density (SOCD) values for FIW, MIW and SIW were 4.55, 3.26 and 3.84 kg C/m2, respectively. Correlation analysis revealed that SOC, ROOC and DOC were significantly negatively correlated with soil pH, bulk density (BD), sand content, and the C/N ratio, and positively related with water content (WC), silt content, and TN (p