Soil Organic Carbon Content Research Articles

Molecular-level insight into the effect of fertilization regimes on the chemodiversity of dissolved organic matter in tropical cropland

Fertilization is a critical agronomic measure for croplands in tropical regions, owing to their low fertility. However, the effects of fertilization on the quantity and chemodiversity of latosolic dissolved organic matter (DOM) in tropical regions remain largely unknown. Therefore, in this study, the variations in latosol DOM concentrations and chemodiversity induced by inorganic fertilization and the co-application of inorganic fertilization with straw return, sheep manure, biochar, and vermicompost fertilizers at a molecular level were systematically investigated using multispectral techniques and ultrahigh-resolution mass spectrometry. In line with our expectations, the results showed that combined inorganic-organic fertilization improved soil quality by increasing soil organic carbon content compared to that under inorganic fertilization. However, as the most active and bioavailable organic carbon pool, dissolved organic carbonconcentrations between the fertilization treatments were not significantly different (p = 0.07). However, the dissolved organic carbon concentrations under combined inorganic-organic fertilization treatment (NPK plus straw return, 263.45 ± 37.51 mg/kg) were lower than those under inorganic fertilization treatment (282.10 ± 18.57 mg/kg). Spectral analysis showed that the DOM in the combined inorganic-organic fertilization treatments had a higher degree of humification and lower autogenetic contributions. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry analysis indicated that the combined inorganic-organic fertilization increased the chemodiversity of latosolic DOM and promoted the production of large, oxidized, and stable molecules, including lignin, aromatic, and tannin compounds, which potentially benefits soil carbon sequestration in tropical regions. This study could provide a theoretical basis for elucidating on the potentially relevant ecological functions and environmental effects of DOM under fertilization regimes.

Spatio-temporal Dynamics of Land Use/Cover Change and Associated Carbon Stocks in Kanyabaha Wetland in Rukiga District, Uganda

Wetlands play an important ecological function of sequestering atmospheric carbon dioxide and thereby moderating adverse impacts of climate change. It is therefore important to understand the dynamics of carbon stocks in wetland vegetation and soils. This study investigated the spatio-temporal dynamics of aboveground, belowground, and total carbon stocks in Kanyabaha Wetland, located in Rukiga District, Uganda, spanning from 1990 to 2021. Through field sampling and laboratory analysis, aboveground carbon stocks were assessed by harvesting vegetation biomass and converting it to carbon stock using established conversion factors. Soil samples collected at different depths (0-20cm, 20-50cm, 50-100cm) were analyzed for soil organic carbon content to determine belowground carbon stocks. The study reveals variable spatio-temporal patterns of carbon stocks across land use types, with papyrus-dominated areas exhibiting the highest aboveground carbon stocks (49.66 tC/ha), followed by small-scale farmlands (33.73 tC/ha) and tree plantations (23.01 tC/ha). Conversely, built-up areas exhibit the lowest carbon stocks (1.29 tC/ha). Temporal analysis reveals fluctuating patterns in carbon stocks, with increases observed in built-up areas and small-scale farmlands, and decreases in grasslands and tree plantations that could be due to changes in hydrological cycle. Belowground carbon stocks follow similar trends, with papyrus areas maintaining the highest stocks (39.96 tC/ha), particularly at deeper soil depths that exhibit the highest carbon accumulation due to its extensive network of papyrus rhizome. Changes in land use, especially reclamation of the wetlands for farming and settlements affected carbon capture and storage in the wetland ecosystem. These findings highlight the importance of targeted conservation of natural wetlands and sustainable land management strategies in the Kanyabaha Wetland catchment for enhanced carbon sequestration. Further, in depth studies in the variability of carbon stocks due to various eco-climatic factors and anthropogenic activities are necessary to support sustainable wetland land management practices in Uganda.

Soil carbon stocks and nutrient stratification in a volcanically active coffee-dominated landscape in south-central Guatemala

The volcanoclastic mountains of Central America offer elevations ideal for coffee production. Both vulcanism and land use can have significant impacts on soil formation and properties. We evaluated how the interactive impacts of soil formation and coffee-dominated land use modulate soil storage and vertical distribution of organic carbon and nutrient elements in a volcanically active landscape dominated by coffee agriculture in south-central Guatemala. Thirty-seven pedons under coffee production (n = 29), forest cover (n = 5) and pasture (n = 3) were characterized and classified, and concentrations and stocks of organic carbon and macronutrient and micronutrient elements were quantified across genetic horizons. Additionally, soil organic carbon (SOC) stock values calculated using the fixed depth (FD) and equivalent soil mass (ESM) methodologies were compared. The active stratovolcano in the region had a strong effect on the development of andic properties and soil horizon burial, with thirty-one pedons classified as Andisols, three as Inceptisols and three as Entisols. Land use management practices and soil horizon burial by deposition of volcanic material were partly reflected in the vertical distribution of SOC concentrations and stocks. The vertical distribution of macronutrients was generally more sensitive to land use than the vertical distribution micronutrients, which could potentially reflect differences in inputs via fertilizers and vegetation cover and in outputs with biomass harvest. Soil organic carbon stocks were similar when calculated by FD and ESM, reflecting relatively consistent depth-wise bulk density. These results demonstrate that in volcanically active landscapes, land use should be considered in concert with soil-forming factors to comprehensively understand organic carbon and nutrient element storage in soils.

Effects of Different Straw Return Methods on the Soil Structure, Organic Carbon Content and Maize Yield of Black Soil Farmland

Straw return is an effective measure to increase soil sustainability. However, few studies have examined the effects of different straw return methods on soil structure, soil organic carbon content and maize yield or the potential relationships between those variables. Therefore, we developed a field orientation experiment to study the effects of different straw return methods on soil porosity, soil aggregate stability, the soil organic carbon content and maize yield. Four treatments were established: flat no-tillage with full straw mulching (FM), ridge no-tillage with full straw mulching (LM), rotary tillage with full straw incorporation (LX), and conventional tillage without straw (CK) as the control treatment. Compared with those of the CK treatment, the soil porosities (f) in the FM, LM and LX treatments significantly increased by 6.7%, 8.8% and 7.9%, respectively; the soil aggregate destruction rates (PAD) decreased by 17.3%, 34.3% and 16.9%, respectively. In addition, the FM, LM and LX treatments effectively increased the mean mass diameters (MWDs) of the soil aggregates and the soil organic carbon content. Compared with those in the CK treatment, the three-year average yields in the FM, LM and LX treatments significantly increased by 5.2%, 7.2% and 4.1%, respectively. Moreover, the f, MWD, soil organic carbon content and corn yield were positively correlated. Our study indicates that the LM treatment was most effective in improving soil structure and increasing soil organic carbon content with corn yield.

Influence of thinning on carbon storage mediated by soil physicochemical properties and microbial community composition in large Chinese fir timber plantation

BackgroundThinning practices are useful measures in forest management and play an essential role in maintaining ecological stability. However, the effects of thinning on the soil properties and microbial community in large Chinese fir timber plantations remain unknown. The purpose of this study was to investigate the changes in soil physicochemical properties and microbial community composition in topsoil (0–20 cm) under six different intensities (i.e., 300 (R300), 450 (R450), 600 (R600), 750 (R750) and 900 (R900) trees per hectare and 1650 (R1650) as a control) in a large Chinese fir timber plantation.ResultsCompared with the CK treatment, thinning significantly altered the contents of soil organic carbon (SOC) and its fractions but not in a linear fashion; these indicators were highest in R900. In addition, thinning did not significantly affect the soil microbial community diversity indices but significantly affected the relative abundance of the core microbial community. Proteobacteria, Acidobacteria, and Actinobacteria were the dominant bacterial phyla; the relative abundances of Proteobacteria and Acidobacteria were highest in R900, and that of Actinobacteria was lowest in R900. The dominant fungal phyla were Ascomycota, Basidiomycota and Mucoromycota; the relative abundance of Ascomycota was lowest in R900, and that of Mucoromycota was highest in R900. The fungal microbial community composition was more sensitive than the bacterial community composition. The activity of the carbon-cycling genes was not linearly correlated with thinning, and the abundance of C-cycle genes was highest in R900.ConclusionsThese findings are important because they show that SOC and its fractions and the abundance of the soil microorganism community in large Chinese fir timber plantations can be significantly altered by thinning, thus affecting the capacity for carbon storage. These results may advance our understanding of how the density of large timber plantations could be modified to promote soil carbon storage.

Envirotyping helps in better understanding the root cause of success and limitations of rainfed production systems

The current diagnostic agronomy study of the Bankura region of West Bengal, India, examined the variations in crop yields through a socio-ecological analysis of multiple production system components. Envirotyping for root cause analysis was employed to delve into the variables that affect the performance of rainfed production systems. Mother Earth, man, machine, management, and materials (5Ms concept) were the five indicators under which the variables were grouped. Findings demonstrated the fragility of the region’s soils due to its undulating terrain, unpredictable rainfall patterns, and frequent drought scenarios. The LULC’s NDVI showed that the agricultural area is about 60% and 43% of the total geographical area in the Hirbandh and Ranibandh blocks, respectively. Soils are acidic and diagnosed with deficiency of both macro and micronutrients (phosphorous, sulfur, and boron) having poor water holding capacity (35 to 55 mm for a 50 cm soil depth). The sand and soil organic carbon contents ranged between 43.04%–82.32% and 0.17%–1.01%, respectively with a low bacterial population. These factors are the root cause for low cropping intensity (106%) and low paddy productivity (3,021 kg/ha). Overall, the study contributes to designing and scaling-up of sustainable landscape management practices that could ensure higher cropping intensity and system productivity in similar agro-ecologies with limited evidence.

Spatial Estimation of Soil Organic Carbon Content Utilizing PlanetScope, Sentinel-2, and Sentinel-1 Data

The accurate prediction of soil organic carbon (SOC) is important for agriculture and land management. Methods using remote sensing data are helpful for estimating SOC in bare soils. To overcome the challenge of predicting SOC under vegetation cover, this study extracted spectral, radar, and topographic variables from multi-temporal optical satellite images (high-resolution PlanetScope and medium-resolution Sentinel-2), synthetic aperture radar satellite images (Sentinel-1), and digital elevation model, respectively, to estimate SOC content in arable soils in the Wuling Mountain region of Southwest China. These variables were modeled at four different spatial resolutions (3 m, 20 m, 30 m, and 80 m) using the eXtreme Gradient Boosting algorithm. The results showed that modeling resolution, the combination of multi-source remote sensing data, and temporal phases all influenced SOC prediction performance. The models generally yielded better results at a medium (20 m) modeling resolution than at fine (3 m) and coarse (80 m) resolutions. The combination of PlanetScope, Sentinel-2, and topography factors gave satisfactory predictions for dry land (R2 = 0.673, MAE = 0.107%, RMSE = 0.135%). The addition of Sentinel-1 indicators gave the best predictions for paddy field (R2 = 0.699, MAE = 0.114%, RMSE = 0.148%). The values of R2 of the optimal models for paddy field and dry land improved by 36.0% and 33.4%, respectively, compared to that for the entire study area. The optical images in winter played a dominant role in the prediction of SOC for both paddy field and dry land. This study offers valuable insights into effectively modeling soil properties under vegetation cover at various scales using multi-source and multi-temporal remote sensing data.

The long-term nitrogen fertilizer management strategy based on straw return can improve the productivity of wheat-maize rotation system and reduce carbon emissions by increasing soil carbon and nitrogen sequestration

ProblemFacing the multiple objectives of increasing production, carbon sequestration, and nitrogen reduction in farmland, optimizing straw and nitrogen fertilizer management to achieve a balance between grain production and ecological safety in the wheat-maize rotation system has become increasingly critical and urgent. MethodsThis study conducted a five-year field experiment in the Guanzhong Plain of China from 2017 to 2021 to investigate the effects and synergistic regulatory mechanisms of straw disposal methods (straw return, no-straw return) and nitrogen application rates (0, 150, 225, 300 kg ha−1) during the maize season on soil greenhouse gas (GHG) emissions, crop yield, and soil organic carbon (SOC) and soil toatl nitrogen (STN) content. ResultsThe results showed that under the scenario of no-straw return, fertilization increased soil nitrous oxide (N2O) emissions by 35.9–64.0 %, and annual total crop yield by 16.4–22.8 %; however, under the straw return scenario, the increase in soil N2O emissions due to fertilization decreased to 26.7–62.0 %, while the yield increase rose to 19.5–25.9 %. The interaction effect between straw return and nitrogen application was significant, with straw return boosting the contribution rate of nitrogen application to yield (2.2–4.4 %) and simultaneously reducing the contribution rate of nitrogen application to N2O emissions (3.0–27.5 %). The study also indicated that the yield-increasing effect of straw return continued to increase with the duration of straw return, with the contribution rate to yield reaching 9.9 % after three years of continuous straw return, while the contribution rate of nitrogen application to yield increased by an average of 3.0 % per year. This suggests that there is significant potential for coupling straw return with reduced nitrogen application. Straw return combined with nitrogen fertilizer increased SOC content by 7.9–40.1 % and 3.7–12.5 %, STN content by 1.0–22.8 % and 6.1–13.9 %, respectively, compared to sole nitrogen application and sole straw return. Pathway analysis indicated that straw return combined with nitrogen fertilizer mainly enhanced soil carbon-nitrogen sequestration, improved fertilizer utilization efficiency and crop nutrition levels, reduced net global warming potential (GWP) and greenhouse gas intensity (GHGI), and synergistically regulated to increase yield while reducing GHG emissions. ConclusionThe study highlights that straw return lowers the threshold for nitrogen application levels, suggesting that regulating nitrogen application levels between 224 and 256 kg ha−1 during the maize season, and maintaining a nitrogen application level of 195 kg ha−1 during the wheat season, is beneficial for long-term stable production and emission reduction in the wheat-maize rotation system farmland.

Residue retention and precision nitrogen management effects on soil physicochemical properties and productivity of maize-wheat-mungbean system in Indo-Gangetic Plains

Maize-based crop systems are promoted in large scale in South Asia because they are more sustainable and efficient than rice-based systems. In the present study, using two combinations of crop residue management practices (CRM) with four precision nitrogen (N) management (PNM) systems, we assessed the impacts on soil physicochemical characteristics [soil organic carbon (SOC), bulk density (BD), soil penetration resistance (PR)] and crop yields in 6 years old continuous zero tillage (ZT) practices under maize-wheat-mungbean cropping system in a sandy loam soil of northwestern India. The highest SOC (5.73 g/kg) was observed in Zero Tillage with Residue Retention (ZT + R) plots. Zero-tillage with residue retention (ZT + R) significantly reduced the bulk density over the zero-tillage with no residue retention (ZT-R) across the soil depth. The bulk density in ZT + R was 6.5 and 10.7% lower at 0–15 cm and 15–30 cm soil depth, respectively, than under ZT-R. The penetration resistance (PR) was significantly lower in ZT + R than in ZT-R across the soil depth. Soil organic carbon (SOC) in ZT + R was 7.4% higher at 0–15 cm depth and 11.9% higher at 15–30 cm depth than under ZT-R treatment. Among PNM treatments, the sequence of treatments in SOC content was 50%N + Green Seeker (GS) >33%N + GS > RDN > 70%N + GS. The system productivity (maize equivalent yield) under ZT + R in combination with 50%BN + GS was 15.0% higher than crops grown under ZT-R with RDN. The wheat equivalent yield under the ZT + R treatment is found to be higher (5.97) in the 50%BN + GS, which was 18% higher than the recommended dose of nitrogen treatment (5.04) and 28% higher than the 70%BN + GS treatment (4.68). Results demonstrated that plots with residue retention performed better, showing a 10% increase in system productivity. The study concludes that a ZT-based system with maize-based crop rotations (MWMb) with crop residue retention and precision nitrogen management can improve soil properties and system productivity in northwestern India.

Serendipita indica: A Promising Biostimulant for Improving Growth, Nutrient Uptake, and Sugar Accumulation in Camellia oleifera

Serendipita indica is a very promising root-associated endophytic fungus that is widely used on various plants; however, whether it affects the growth and physiological activity of an oilseed crop (Camellia oleifera) under field conditions remains unclear. In this study, we analyzed the effects of S. indica inoculation on root colonization rate, growth rate, photosynthetic parameters, mineral element concentrations and related gene expression, and sugar concentrations and expression of their transporter genes in four-year-old C. oleifera trees in the field. The results showed that the root colonization rate of C. oleifera increased from 3.37% to 9.42% following being inoculated with S. indica. Inoculation with S. indica significantly increased the plant height (46.81%), net photosynthetic rate (69.16%), nitrogen balance index (14.44%), chlorophyll index (21.08%), leaf K (7.4%), leaf Ca (13.52%), root P (17.75%), root K (12.80%), soil NH4+-N (17.78%), available K (26.66%), Olsen-P (184.30%), easily extractable glomalin-related soil protein (39.26%), and soil organic carbon (16.25%) concentrations compared to the uninoculated treatment. Inoculation with S. indica also significantly up-regulated the expression of CoHKT1;1 and CoCAX1;2 in the leaves and roots and CoPht1;1, CoPht1;2, and CoPht1;3 in the leaves. Plants inoculated with S. indica also presented significantly higher leaf glucose, fructose, and sucrose concentrations, accompanied by up-regulated expression of CoSWEET2a, CoSWEET7, CoSWEET9b, CoSWEET17a, and CoSWEET17b. These results suggest that S. indica has significant potential as a biostimulant for enhancing the growth and nutritional profile of C. oleifera, thereby contributing to sustainable oilseed production.

Changes in Soil Aggregate Carbon Components and Responses to Plant Input during Vegetation Restoration in the Loess Plateau, China.

Vegetation restoration is an effective measure to cope with global climate change and promote soil carbon sequestration. However, during vegetation restoration, the turnover and properties of carbon within various aggregates change. The effects of plant source carbon input on surface soil and subsurface soil may be different. Thus, the characteristics of carbon components in aggregates are affected. Therefore, the research object of this study is the Robinia pseudoacacia forest located in 16-47a of the Loess Plateau, and compared with farmland. The change characteristics of organic carbon functional groups in 0-20 cm, 20-40 cm, and 40-60 cm soil layers were analyzed by Fourier near infrared spectroscopy, and the relationship between the chemical structure of organic carbon and the content of organic carbon components in soil aggregates was clarified, and the mechanism affecting the distribution of organic carbon components in soil aggregates was revealed in the process of vegetation restoration. The results show the following: (1) The stability of surface aggregates is sensitive, while that of deep aggregates is weak. Vegetation restoration increased the surface soil organic carbon content by 1.97~3.78 g·kg-1. (2) After vegetation restoration, the relative contents of polysaccharide functional groups in >0.25 mm aggregates were significantly reduced, while the relative contents of aromatic and aliphatic functional groups of organic carbon were significantly increased. The opposite is true for aggregates smaller than 0.25 mm. (3) With the increase in soil depth, the effect of litter on organic carbon gradually decreased, while the effect of root input on the accumulation of inert carbon in deep soil was more lasting.

Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes

Abstract Large grazers modify vegetated ecosystems and are increasingly viewed as keystone species in trophic rewilding schemes. Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resilience. Previous work in diverse European saltmarshes found that, despite changing plant and invertebrate community structure, grazers do not suppress below‐ground properties, including soil organic carbon (SOC). We hypothesised that, in contrast, eastern US saltmarshes would be sensitive to large grazers as extensive areas are dominated by a single grass, Spartina alterniflora. We predicted that grazers would reduce above‐ and below‐ground Spartina biomass, suppress invertebrate densities, shift soil texture and ultimately reduce SOC concentration. We tested our hypotheses using a replicated 51‐month large grazer (horse) exclusion experiment in Georgia, coupled with observations of 14 long‐term grazed sites, spanning ~1000 km of the eastern US coast. Grazer exclusion quickly led to increased Spartina height, cover and flowering, and increased snail density. Changes in vegetation structure were reflected in modified soil texture (reduced sand, increased clay) and elevated root biomass, yet we found no response of SOC. Large grazer exclusion also reduced drought‐associated vegetation die‐off. We also observed vegetation shifts in sites along the eastern US seaboard where grazing has occurred for hundreds of years. Unlike in the exclusion experiment, long‐term grazing was associated with reduced SOC. A structural equation model implicated grazing by revealing reduced stem height as a key driver of reduced soil organic carbon. Synthesis: These results illustrate the context dependency of large grazer impacts on ecosystem properties in coastal wetlands. In contrast to well‐studied European marshes, eastern US marshes are dominated and structured by a single foundational grass species resulting in vegetation and soil properties being more sensitive to grazing. Coastal systems characterised by a single foundation species might be inherently vulnerable to large grazers and lack resilience in the face of other disturbances, underlining that frameworks to explain and predict large grazer impacts must account for geographic variation in ecosystem structure.

Ecological Status Assessment of Permafrost-Affected Soils in the Nadym Region, Yamalo-Nenets Autonomous District, Russian Arctic

Permafrost-affected regions in the Russian Arctic are a critical study area for studying the sources of metal elements (MEs) in soils originating from geological/pedogenic processes or from anthropogenic sources via atmospheric transport. In the Nadym region of the Yamalo-Nenets Autonomous District, we investigated the contents of soil organic carbon (SOC), total nitrogen (TN), and MEs across different soil types and horizons, explored the source apportionment of MEs, and assessed local ecological risks of potentially toxic elements (PTEs). The results showed that (1) the contents of SOC and TN in Histic Cryosols (8.59% and 0.27%) were significantly higher than in Plaggic Podzols (Arenic, Gelic, and Turbic) (2.28% and 0.15%) and in Ekranic Technosols (Umbric) (1.32% and 0.09%); (2) the concentrations of MEs in the Nadym region were lower than in other Arctic regions; (3) the primary sources of MEs were identified as geological processes (36%), atmospheric transport (23%), agricultural activities (21%), and transportation (20%); and (4) the permafrost-affected soils in the Nadym region exhibited low ecological risks from PTEs. These results underscore the critical role of geological and anthropogenic factors in shaping soil conditions and highlight the relatively low ecological risk from PTEs, providing a valuable benchmark for future environmental assessments and policy development in Yamal permafrost regions.

Vineyard cover crop management strategies and their effect on soil properties across Europe

AbstractVineyard soils are often of inherently poor quality with low organic carbon content. Management can improve soil properties and thus soil fertility. In European wine‐growing regions, a broad range of inter‐row management strategies evolved based on specific local site conditions and the varying effects of management intensities on soil, water balance, yield and grape quality. Accordingly, there is a need to investigate the effects of locally common cover crop management strategies and tillage intensity on soil organic carbon content and soil physical parameters. In this study, we investigated the impact of the most common inter‐row management practices in Austria, France, Romania and Spain. In all countries, we compared paired sites. Each site with cover crops and inter‐row management of low intensity was compared with one site with (temporarily) bare soil and high management intensity. All studied sites with cover crops and low management intensity, except those in Spain, had higher organic carbon contents than the paired more intensively managed vineyards. However, the highly water‐limited Spanish vineyards with temporary cover crops had lower organic carbon contents than the paired sites with bare soil. Sites with more organic carbon had better results for bulk density, percolation stability (PS), hydraulic conductivity and available soil water, with soil hydraulic parameters being less pronounced than others. Country comparison of inter‐row weed control systems showed that PS was particularly low in sampled vineyards in Romania and Spain, where weed control is based on intensive mechanical tillage. Alternating management systems with tillage every second inter‐row showed a decrease in soil structure compared with permanent green cover. Thus, inter‐row management with cover crops and reduced tillage increases soil organic carbon content and improves soil structure compared with bare soil management. If local constraints, such as water scarcity, do not allow year‐round planting, alternating inter‐row management with several years of alternating periods may be an option to mitigate those adverse effects. However, negative impact on the soil structure occurs with the very first tillage operation, whereas negative effects on the carbon balance only appear after long‐term use of tillage.

In-situ prediction of soil organic carbon contents in wheat-rice rotation fields via visible near-infrared spectroscopy

Visible near-infrared (VNIR) spectroscopy is a reliable method for estimating soil properties. However, its effectiveness in accurately predicting soil organic carbon (SOC) contents, particularly in wheat-rice rotation fields, remains uncertain. In this study, we collected 202 samples from wheat-rice fields (0–20 ​cm) in southeastern China and measured in-situ spectra of the vertical surface of the soil cores and the laboratory spectra of the dried and sieved soil samples. Our study focused on evaluating three algorithms - external parameter orthogonalization (EPO), direct standardization (DS), and piecewise direct standardization (PDS) - to address the influence of external factors, particularly soil moisture. To carry out our analysis, the dataset was divided into calibration (141 samples) and validation (61 samples) sets via the Kennard-Stone algorithm. A subset of the corresponding in-situ and laboratory spectra in the calibration set (transfer set) was used to derive the transfer matrix for EPO, DS, and PDS, enabling the conversion of in-situ spectra to laboratory spectra by characterizing their differences. Four machine learning models, including cubist, partial least squares regression (PLSR), random forest (RF), and memory-based learning (MBL), were used to predict the SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) contents based on the laboratory, in-situ, and corrected in-situ spectra. The results revealed that the laboratory spectra outperformed the non-corrected in-situ spectra, with coefficients of determination (R2) of 0.91, 0.75, and 0.80 for SOC, POC, and MAOC, respectively. Among the models, MBL and PLSR exhibited the highest average R2 at 0.85–0.86. EPO marginally improved the prediction accuracy (R2 increased from 0.85 to 0.87 for SOC, 0.64 to 0.69 for POC, and 0.75 to 0.82 for MAOC). These promising prediction accuracies underscore the potential of VNIR spectra for in-situ predictions in wheat-rice fields in Southeast China, offering insights for predicting SOC contents via in-situ spectroscopy.

Afforestation Promotes Soil Organic Carbon and Soil Microbial Residual Carbon Accrual in a Seasonally Flooded Marshland

This study aimed to delve deeper into the alterations in the microbial residual carbon (MRC) accumulation in the Yangtze River’s wetland ecosystems as a consequence of afforestation and to evaluate their impact on soil organic carbon (SOC). The hypothesis posited that afforestation could foster soil aggregation by augmenting arbuscular mycorrhizal fungi (AMF) hyphae and glomalin-related soil protein (GRSP) in deep soil, thereby suppressing the proliferation of genes pivotal to microbial residue decomposition and enhancing MRC accumulation. We collected soil samples at 0–20, 20–40, 40–60, 60–80 and 80–100 cm respectively. Metagenomic sequencing, the quantification of soil amino sugars and MRC, soil aggregate distribution profiling and the measurement of AMF mycelium length density alongside GRSP levels were analyzed. Our findings showed that afforestation notably elevated the concentration of soil amino sugars and the levels of total and fungal MRC, with increases ranging from 53%–80% and 82%–135%, respectively, across the five soil depths examined, in stark contrast to the eroded, non-afforested control. The role of MRC in the SOC was observed to escalate with increasing soil depth, with afforestation markedly amplifying this contribution within the 40–60 cm, 60–80 cm and 80–100 cm soil layers. The study concludes that the SOC content in the deeper soil horizons post-afforestation witnessed a significant rise, paralleled by a substantial increase in both total and fungal MRC, which exhibited a robust positive correlation with the SOC levels. This underscores the pivotal role that amino sugar accumulation from microbial residues plays in the retention of SOC in the deeper soil layers of afforested regions, challenging the conventional wisdom that plant residues are recalcitrant to decomposition within forested SOC matrices.

Impact of planting density and shoot thinning on alstroemeria flowering, soil attributes and cost economics

A field experiment was conducted to assess the impact of various planting densities and levels of shoot thinning on cut flower yield, quality, soil chemical properties and cost economics in the commercially cultivated alstroemeria cultivar 'Capri'. The experiment involved three planting densities (4, 6 and 8 plants/m2) along with three shoot thinning levels (10 %, 20 % and 30 %). It was observed that higher planting density (4 plants/m2) promoted the length of cut stem, early bud formation, and flowering, optimal quality parameters, including maximum stem thickness, cut stem weight, floret quantity/stem, floret size, number of flowering stems/plant (yield) and vase life. Exclusive use of higher vegetative mass removal (30 % shoot thinning) was found to improve quality parameters such as the length of cut stem, number of flowering stems, stem thickness, weight of cut stem, floret quantity/stem, floret size, vase life, and early flowering. Soil samples were collected from each treatment and the consequent lab analysis revealed that the lower planting density and shoot thinning level resulted in maximum soil organic carbon, nitrogen, phosphorous and potassium content. In conclusion, planting density of 4 plants/m2 and 30 % shoot thinning emerged as the optimal combination for enhancing quantitative parameters in commercial alstroemeria cultivation. The study underscores the importance of strategic planting practices and vegetative mass management for maximizing yield and quality in alstroemeria production, along with ensuring higher economic returns.

Distinct features of topsoil carbon fractions across urban forests in eastern China

AbstractRapid urbanization has increased the areas of urban forests that store considerable soil carbon (C). Different soil C fractions may show distinctive contents and spatial patterns in view of their contrasting sensitivities to various drivers. However, current studies on soil C fractions are mostly limited to natural ecosystems and little is known about the large‐scale patterns and drivers of soil C fractions in urban forests. Based on a field survey of urban forests across a north–south transect in eastern China, we analysed the spatial variations and main drivers of topsoil (surface layer, 0–10 cm; subsurface layer, 10–20 cm) C fractions (i.e., soil organic C, SOC; soil inorganic C, SIC; particulate organic C, POC; mineral‐associated organic C, MAOC). Our results showed that topsoil contents of POC, MAOC and SOC changed non‐linearly with latitude, with lowest values occurring in the cities in the warm temperate region. In contrast, SIC content showed the highest values in the warm temperate region. POC instead of MAOC was found to be a major fraction of SOC in urban forests. The spatial variation in topsoil POC content was mainly explained by mean annual temperature, soil clay and silt content, and park age. The spatial variation in MAOC content was mainly explained by soil clay and silt content, mean annual precipitation, mean annual temperature and park age. In contrast, the spatial variation in SIC content was mainly explained by mean annual precipitation and soil pH. These findings demonstrate distinct features of different soil C fractions in urban forests and provide useful implications for urban soil carbon management.

Assessing and mapping of soil organic carbon at multiple depths in the semi-arid Trans-Ural steppe zone

The quantification of soil organic carbon (SOC) and its vertical distribution is crucial for understanding carbon dynamics in terrestrial ecosystems. This study aimed to 2.5D digital mapping of SOC content in the Trans-Ural steppe zone (Russia) using a quantile regression forest (QRF) approach. The study utilized a dataset comprising 2495 SOC measurements collected from 1316 locations across three soil depths: 0–20 cm, 20–40 cm, and 40–60 cm. Environmental covariates were incorporated into the SOC modeling process, capturing major soil formation factors, and the uncertainty of the generated maps was estimated. The results revealed that SOC content ranged from 0.59 to 9.05 % in the topsoil, from 0.5 to 6.61 % in the subsurface layer and from 0.06 to 4.64 % in the subsoil. Based on the error metrics, including root mean square error (RMSE), coefficient of determination (R2), and Nash-Sutcliffe efficiency coefficient (NSE), we found a decrease in prediction accuracy with increasing soil depth. Furthermore, climate and vegetation variables, as well as elevation, emerged as key factors influencing the prediction of SOC concentrations at all depths. We also made an attempt to assess the future change of SOC under the influence of climate and anthropogenic impact. We anticipate that climate aridization and plowing will lead to a decline in SOC content in the Trans-Ural steppe region. Our findings contribute to the existing knowledge of SOC dynamics in steppe ecosystems at several depths, supporting informed decision-making for sustainable land use and climate change mitigation strategies.

The advantage of afforestation using native tree species to enhance soil quality in degraded forest ecosystems

Different vegetation restoration methods have improved soil quality to varying degrees. This study, focused on the forest–grassland–desert transition zone in the Hebei–Inner Mongolia border region, and employed a systematic grid sampling method to establish fixed monitoring plots in the Saihanba Mechanized Forest Farm and the Ulan Buh Grassland. The differences in soil quality evolution across various vegetation restoration methods under the same climatic and soil historical conditions were analyzed, elucidating the roles of these vegetation restoration methods in degraded forest ecosystems, with the aim of providing a reference for ecological restoration under similar land conditions. This study used a grid method to establish sample points in the forest–grassland–desert transitional zone and assessed five methods of vegetation restoration sites: artificial forest composed of native species of Larix principis-rupprechtii (FL), artificial forest composed of exotic Pinus sylvestris var. mongolica (FP), natural secondary broad-leaved forest (FN), open grassland (GO), and enclosed grassland (GC). The differences in soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkaline hydrolysis nitrogen (AN), rapidly available phosphorus (AP) and rapidly available potassium (AK) among the different vegetation restoration sites were compared via variance analysis, and the soil quality index (SQI) was calculated to assess the soil quality at the sample points. The SOC, TN, and AN contents of forest soil were significantly greater than those of grassland, and the TN, TP, AN, AK, and SOC contents of FL, FN, and GC were significantly greater than those of FP and GO. Among them, the TN, TP, and SOC contents were the highest in the FL, reaching 2.74, 0.39, and 47.27 g kg−1, respectively. In terms of ecological stoichiometric characteristics, the average N:P ratio in the study area was 6.68, indicating a serious lack of N in the study area. Among the different types of restoration sites, the effect was stronger in the FP than in the FL, and the TN and AN contents were only 1.48 g kg−1 and 116.69 mg kg−1, respectively. The SQI in the FL was not significantly different from that in the FN or GC, but it was significantly greater than that in the FP and GO. These findings indicate that native tree species restoration in degraded forest ecosystems significantly improved soil quality, while the introduction of exotic tree species for afforestation had a minimal effect on improving soil quality.