Soil Total Carbon Content Research Articles

Mangrove wetland recovery enhances soil carbon sequestration capacity of soil aggregates and microbial network stability in southeastern China

Mangrove wetlands are highly productive ecosystems in tropical and subtropical coastal zones, play crucial roles in water purification, biodiversity maintenance, and carbon sequestration. Recent years have seen the implementation of pond return initiatives, which have facilitated the gradual recovery of mangrove areas in China. However, the implications of these initiatives for soil aggregate stability, microbial community structure, and network interactions remain unclear. This study assesses the impacts of converting ponds to mangroves—both in natural and artificially restored settings—on soil aggregate stability and microbial networks at typical mangrove restoration sites along China's southeastern coast. Our observations confirmed our hypothesis that pond-to-mangrove conversions resulted in an increase in the proportion of large aggregates (>0.25 mm), improved soil aggregate structural stability, and increased carbon sequestration. However, mangrove recovery led to a decrease in the abundance and diversity of soil fungi communities. In terms of co-occurrence networks, naturally restored mangrove wetlands exhibited more nodes and edges. The naturally recovered mangrove wetlands demonstrated a higher level of community symbiosis compared to those that were manually restored. Conversely, bacterial networks showed a different pattern, with significant shifts in key taxa related to carbon sequestration functions. For instance, the proportion of bacterial Desulfobacterota and fungi Basidiomycota in natural recovery mangrove increased by 15.03 % and 7.82 %, respectively, compared with that in aquaculture ponds. Soil fungi and bacteria communities, as well as carbon sequestration by aggregates, were all positively correlated with soil total carbon content (P < 0.05). Both bacterial and fungal communities contributed to soil aggregate stability. Our study highlights the complex relationships between soil microbial communities, aggregate stability, and the carbon cycle before and after land-use changes. These findings underscore the potential benefits of restoring mangrove wetlands, as such efforts can enhance carbon storage capacity and significantly contribute to climate change mitigation.

Soil organic carbon fractions and storage potential in Finnish arable soils

AbstractUnderstanding the factors affecting the total amount and distribution of soil organic carbon (OC) across different functional carbon pools is important to better define the future management of soil OC stocks. The interactions between soil management practices, local physicochemical soil properties and climate are essential for determining the OC content of the soil. Nevertheless, how these factors affect the total amount of OC and its distribution across carbon pools, i.e., more labile particulate (POC) and more stable mineral‐associated (MAOC) organic carbon, is only partly known. In this study, we assessed topsoil (0–20 cm) samples from 93 arable farms in the southern half of Finland to determine the total amount of OC, and its distribution in MAOC and POC, along with relevant soil properties (amount of clay and silt, aluminium and iron oxides and pH), climate (precipitation and temperature) and fertilization (mineral versus organic). The fertilization did not affect the total soil carbon content (12–58 g OC kg−1 soil). The share of OC in the MAOC fraction (on average 86% of total OC) was relatively stable across the large range of OC contents and clay contents (2%–68%). We assessed the highest feasible MAOC of the soils with boundary line analyses and their OC saturation state with Hassink's equation (Hassink, 1997). Only soils with the lowest clay content (&lt;10% clay) were assumed to be carbon‐saturated, suggesting that most of the studied soils have a capacity to accrue more MAOC. Simple linear regression showed that clay, aluminium and iron oxides explained 9%, 21% and 22% of the variation in MAOC, respectively. Multiple regression analyses including the amount of clay, clay+silt, aluminium and iron oxides, pH, type of fertilization, precipitation and temperature as explanatory variables explained 33%–53% of the variation in OC and MAOC. In all soils, aluminium oxides were important explanatory variable for MAOC, whereas Fe oxides were significant only in soils with higher clay content (&gt;30%). In soils with a low clay content (&lt;30%), pH had added value in explaining MAOC. Altogether, it seems that various climatic, edaphic and soil management‐related factors are context‐dependently controlling OC and that soil textural information alone is not necessarily an adequate predictor to assess the MAOC saturation state of the soil.

Impact of biocrust on soil nitrogen maintenance and microbial composition in citrus orchards under varying urea application rates

Biocrust communities and their effects on soil nitrogen (N) content in natural drylands have been extensively studied. However, their significance in citrus orchards, which are typically managed with N fertilizer, remains unclear. To address this, an investigation was conducted in a citrus orchard subjected to varying levels of urea application (0 %, 70 %, and 100 % of the local N fertilizer application) over three years. The study focused on biocrust communities dominated by bryophytes, examining their community and individual characteristics, and comparing the properties and microbial communities of soils with and without biocrust cover. The results showed that biocrust had the highest percent coverage (56.1 %) in the plot with 70 % local N fertilizer application. Dicranella heteromalla was the dominant biocrust species across all treatments, exhibiting greener and longer leaves with 70 % local N fertilizer application. Biocrust cover significantly (P < 0.01) influenced soil total nitrogen content, soil water content, soil total carbon content, and soil dissolved organic carbon content. In contrast, fertilizer application had non-significant effects on the physicochemical properties of soils, regardless of biocrust cover. A notable difference in bacterial phyla composition was observed between soils with and without biocrust cover (PERMANOVA, P = 0.001), although fertilization did not significantly affect the bacterial diversity index. Additionally, biocrust cover significantly (P < 0.01) influenced predicted soil bacterial functional groups, including ureolysis and nitrogen fixation, while fertilizer application had a weaker impact on these bacterial functional groups. In conclusion, nitrogen application altered the community and dominant species characteristics of biocrust but did not overshadow the effects of biocrust on soil N dynamics. In the citrus orchard with varying levels of urea application, biocrust played a crucial role in soil water retention, N maintenance, and predicted microbial ecological functions related to N cycling.

Response Mechanism of cbbM Carbon Sequestration Microbial Community Characteristics in Different Wetland Types in Qinghai Lake.

Carbon-sequestering microorganisms play an important role in the carbon cycle of wetland ecosystems. However, the response mechanism of carbon-sequestering microbial communities to wetland type changes and their relationship with soil carbon remain unclear. To explore these differences and identify the main influencing factors, this study selected marsh wetlands, river wetlands and lakeside wetlands around Qinghai Lake as research subjects. High-throughput sequencing was employed to analyze the functional gene cbbM of carbon-sequestering microorganisms. The results revealed that the alpha diversity of cbbM carbon-sequestering microorganisms mirrored the trend in total carbon content, with the highest diversity observed in marsh wetlands and the lowest in lakeside wetlands. The dominant bacterial phylum was Proteobacteria, with prevalent genera including Thiothrix, Acidithiobacillus, and Thiodictyon. Acidithiobacillus served as a biomarker in lakeside wetlands, while two other genera were indicative of marsh wetlands. The hierarchical partitioning analysis indicated that the diversity of cbbM carbon-fixing microorganisms was primarily influenced by the total nitrogen content, while the community structure was significantly affected by the soil total carbon content. Moreover, an increased soil temperature and humidity were found to favor the carbon fixation processes of Thiomicrospira, Thiomonas, Polaromonas, and Acidithiobacillus. In summary, changes in wetland types seriously affected the characteristics of cbbM carbon sequestration in microbial communities, and a warm and humid climate may be conducive to wetland carbon sequestration.

Effect of Different kharif Paddy Straw Management Options and Nitrogen Levels on Soil Organic Carbon and Soil Total Carbon and Nitrogen

A field experiment was conducted during rabi 2020-21, at Regional Agricultural Research Station, Polasa, Jagtial, PJTSAU to study the effect of paddy straw burning and incorporation on soil organic carbon, total carbon and nitrogen and soil C:N ratio. The results of the investigation reported that incorporation of paddy straw whose C:N ratio was 71:1 showed that soil organic carbon was significantly higher under paddy straw incorporated treatments. Total carbon content of soil in paddy straw burnt treatments was 1.07 times higher than initial and in paddy straw incorporated treatments 1.51 times higher over initial was observed. Soil total nitrogen decreased with crop duration. At harvest soil total nitrogen was 2606 kg ha-1, 2693 kg ha-1 and 1931 kg ha-1 in paddy straw burning, paddy straw incorporation without phosphorus, paddy straw incorporation with phosphorus respectively. C:N ratio of soil is not influenced by paddy straw management options, nitrogen levels and the interaction between them.

Geospatial prediction of total soil carbon in European agricultural land based on deep learning

Accurate geospatial prediction of soil parameters provides a basis for large-scale digital soil mapping, making efficient use of the expensive and time-consuming process of field soil sampling. To date, few studies have used deep learning for geospatial prediction of soil parameters, but there is evidence that it may provide higher accuracy compared to machine learning methods. To address this research gap, this study proposed a deep neural network (DNN) for geospatial prediction of total soil carbon (TC) in European agricultural land and compared it with the eight most commonly used machine learning methods based on studies indexed in the Web of Science Core Collection. A total of 6209 preprocessed soil samples from the Geochemical mapping of agricultural and grazing land soil (GEMAS) dataset in heterogeneous agricultural areas covering 4,899,602 km2 in Europe were used. Prediction was performed based on 96 environmental covariates from climate and remote sensing sources, with extensive comprehensive hyperparameter tuning for all evaluated methods. DNN outperformed all evaluated machine learning methods (R2 = 0.663, RMSE = 9.595, MAE = 5.565), followed by Quantile Random Forest (QRF) (R2 = 0.635, RMSE = 25.993, MAE = 22.081). The ability of DNN to accurately predict small TC values and thus produce relatively low absolute residuals was a major reason for the higher prediction accuracy compared to machine learning methods. Climate parameters were the main factors in the achieved prediction accuracy, with 23 of the 25 environmental covariates with the highest variable importance being climate or land surface temperature parameters. These results demonstrate the superiority of DNN over machine learning methods for TC prediction, while highlighting the need for more recent soil sampling to assess the impact of climate change on TC content in European agricultural land.

Carbon Storage of Mangrove Forests in Sarawak, Malaysia

The emission of carbon dioxide (CO2) gases into the atmosphere is caused by human activities such as manufacturing, vehicle smoke, open burning, and clearing areas of agriculture or development activities. This is a major contributor to global climate change. Mangrove forest is one of the potential areas for carbon storage. For many years, the number of Mangrove forests in Malaysia has been decreasing due to some anthropogenic activity and the exploitation of them for economic gain. This study aims to compare and measure the carbon storage of two different types of mangroves in Malaysia, namely the WSSM and AALL mangroves. The soil samples were randomly collected using peat augers at depths between 0 and 30 cm, and 40 samples were analyzed with a CHNS analyzer. The total carbon content of the soil samples was found to be 12.11% for WSSM and 2.64% for AALL. The significant results and the total soil carbon of humic acid observed at both study sites as well as the seasonal variation led to the conclusion that the soil of mangrove has carbon sequestration potential. As a wildlife sanctuary, Sibuti Mangrove Forest has higher carbon sequestration due to less anthropogenic activity than AALL Mangrove Forest. The conclusion is that the soil of WSSM Mangrove Forest is better in terms of location effect than the soil of AALL. During seasonal sampling comparison, higher soil total carbon content was observed.

Effects of Organic Liquid Waste Derived from Bioethanol Fermentation on Corn Production

The liquid waste (LW) discharged during bioethanol production needs treatment. In this study, LW was applied to corn, and its effects on corn growth, yield, and nitrogen (N) content, as well as on soil chemical properties, were evaluated. Five treatments were applied during corn cultivation: no fertilizer (NF), chemical fertilizer (CF), LW at a standard application rate (LW1.0), LW at 1.7 times the rate of LW1.0 (LW1.7), and split application of LW1.7 (S-LW1.7) in six replications. The amount of N applied was 30 kg 10a−1 for CF and LW1.0, and 51 kg 10a−1 for LW1.7 and S-LW1.7. N was applied separately three times in CF, LW1.0, and LW1.7 and six times in S-LW1.7. A higher corn yield, corn ear weight, and number of leaves was observed in LW treatments than in CF. N content of the corn plant top was higher in S-LW1.7 than in LW1.7; N availability was 56.9% and 40.5% higher, respectively, indicating that split application improved N availability. Soil total N content increased significantly in LW treatments, and soil total carbon content tended to increase in S-LW1.7. Therefore, application of LW could increase corn yield and soil fertility, and its effect could be enhanced by split application.

Variations in Microbial Residue and Its Contribution to SOC between Organic and Mineral Soil Layers along an Altitude Gradient in the Wuyi Mountains

Microbes are crucial components of soil, and their residue carbon plays a significant role in the formation and stabilization of soil carbon pools. However, current research on microbial residue carbon has predominantly focused on surface soils, with limited studies on deep soils. The patterns of variation along soil profiles and their controlling factors remain unclear. Therefore, this study aimed to investigate the soils from different elevations in the Wuyi Mountains, specifically focusing on the organic layers (0–10 cm) and mineral layers (30–40 cm). Amino sugars were utilized as biomarkers for the microbial residue, and the RDA (redundancy analysis) method was employed to analyze the patterns of microbial residue carbon in different soil layers and to identify the factors that control them. The results indicate that there are significant differences in the microbial residue carbon content and its contribution to soil organic carbon (SOC) between the different soil layers. Specifically, between the organic layer and the mineral layer, the microbial residue carbon content exhibited an increasing trend, whereas its contribution to SOC decreased. This finding suggests that soil layer type has a notable impact on microbial residue carbon content and its contribution to SOC. Moreover, fungal residue carbon content was found to be higher than bacterial residue carbon content in both soil layers. However, the ratio of fungal residue carbon to bacterial residue carbon gradually decreased between the organic layer and the mineral layer. This implies that although fungal residue carbon remains dominant, the contribution of bacterial residue carbon to the soil carbon pool increases as the soil transitions to the mineral layer. The total soil carbon content, elevation, and C/N ratio exhibited positive correlations with fungal and bacterial residue carbon, indicating their significant roles in the accumulation of microbial residue carbon in soils. Notably, elevation emerged as a key regulating factor in the accumulation of microbial residue carbon, explaining 85.8% and 67.9% of the variations observed in the organic layer and the mineral layer respectively. These research findings contribute to a better understanding of the soil carbon cycling process and its mechanisms, providing a scientific basis for developing strategies to enhance soil carbon sequestration by manipulating micro-organisms.

Evaluation of the biomass, carbon sequestered and microbiota in a naturally-growing Bambusa vulgaris. Schrad. Ex J.C. Wendl stand

The world is increasingly facing the conflicting pressures of economic growth and environmental protection, and forests have the capacity to sequester carbon from the atmosphere in large amounts. This study evaluated the biomass, carbon content and microbial activities of a naturally growing Bambusa vulgaris stand at the Forestry Research Institute of Nigeria (FRIN), Ibadan, Oyo state. Three clumps were randomly selected for the study and analyzed to obtain the biomass, carbon content and microbial population. After harvesting, the culm samples were divided into leaf, branch and culm components and their respective fresh weights were taken. All the sub-samples were then oven-dried at 65 °C for 48 h and to get the oven-dried weight, a ratio of oven-dry to fresh weight was calculated. The total stand biomass for B. vulgaris was then determined and computed on a per hectare basis, while the microbiota were determined using standard methods. The B. vulgaris stand stored in total 59.37 t/ha carbon of which 30.55 t/ha were stored in the above-ground biomass (culms, branches and leaves), 1.53 t/ha in the below ground biomass and 24.29 t/ha in the soils. The total biomass stored by the stand was 59.42 t/ha, of which 56.59 t/ha was stored above ground and 2.83 t/ha in the below-ground biomass. Total biomass carbon content in B. vulgaris was 32.08 t/ha. The aboveground carbon storage was much higher in culms (16.69 t/ha) than in branches (8.52 t/ha), leaves (5.32 t/ha), in litter fall (0.02 t/ha) or rhizomes (1.53 t/ha). The total soil carbon content was 24.29 t/ha, of which 8.48 t/ha occurred at 0–15 cm depth, 8.19 t/ha at 15–30 cm, and 7.62 t/ha at 30–45 cm depth. A regression model was developed for future predictions of carbon content of B. vulgaris. About 16 microorganisms were identified in the study (10 bacteria and 6 fungi species) with populations ranging with soil depth. The amount of carbon sequestered and the short time needed for bamboo to grow makes it a good carbon sink, thereby helping to mitigate climate change issues.

Revegetation promotes soil microbial network stability in a novel riparian ecosystem

Abstract Soil microorganisms play a crucial role in ecosystem processes and functions, but how their co‐occurrence networks respond to restoration of degraded ecosystems remains poorly understood. Here, we examined the effects of revegetation on the structure and function of the soil microbiome, including soil microbial network complexity and stability, in a novel riparian ecosystem with winter submergence opposite to the natural hydrological regime. We found that extreme flooding intensity (30 m submergence up to 286 days per year) reduced microbial α‐diversity and network stability (robustness) but increased network complexity including network connectivity, connectance and average clustering coefficient over a 3‐year period, and those effects were mitigated by active revegetation in comparison with natural regeneration. Revegetation increased microbial network stability directly by decreasing network complexity, while extreme flooding regulated network stability indirectly by changing the soil total carbon content. Nevertheless, those dynamics of microbial network were coupling with soil microbial functions such as greenhouse gas (e.g. CH4, CO2 and N2O) fluxes and nutrient cycling. Synthesis and applications: This study provides evidence to support the critical role of revegetation in preserving soil microbial network stability and functions under changing hydrological regime.

Optical assessment of the spatial variation in total soil carbon using laser-induced breakdown spectroscopy

Soil carbon storage is a substantial factor in the global carbon cycle. Carbon sequestration in agricultural soils, and the assessment and validation of soil carbon storage, are crucial for the mitigation of agricultural greenhouse gas emissions and for steering towards sustainable farming practices. Enforcement and verification of carbon sequestration policies, methods, and models require extensive soil carbon monitoring capability. However, current conventional laboratory-based methods for soil carbon estimation are laborious, expensive, and time-consuming. In this work, we have developed a compact, robust, and field-capable experimental device based on laser-induced breakdown spectroscopy (LIBS) for the rapid assessment of total soil carbon content and its spatial distribution in mineral soils. The carbon content quantification was performed using a spectral line of carbon at a wavelength of 193.1 nm emitted from the laser-induced plasma plume. The LIBS measurements were performed on soil samples collected from 28 different locations and various depths (up to 1 m) of a test field cultivated with a forage legume (red clover - Trifolium pratense, L.) and grass (Timothy - Phleum pratense, L.) mixture in eastern Finland. A calibration model was established based on a limited and randomly chosen sample set and validated by comparing soil carbon estimates obtained from various locations in the test field using the dry combustion (LECO) method. Further, we demonstrate here the usefulness of LIBS methodology for mapping three-dimensional carbon distribution at the test field. We emphasize here that the calibration model can be generalized to other sample areas under similar soil type with a relative error of less than 10 % and possesses potential for fast on-site determination of spatial variation in total soil carbon, reducing substantially the need of time-consuming sample processing in laboratory. Therefore, LIBS enables frequent and extensive spatial and temporal soil carbon mapping and has the potential to become part of the future carbon monitoring network.

Desertification induced changes in soil bacterial and fungal diversity and community structure in a dry-hot valley forest

Increase in aridity is a global phenomenon due to climate change. Understanding soil microbial communities' response to aridity induced desertification is essential to predict the regulation of microbial processes under climate change and to develop feasible restoration plans. Therefore, to elucidate desertification effects, we investigated the changes in soil properties and, shifts and drivers of soil microbial diversity and community composition of a dry-hot valley-based Pinus densata forest located in south-east Tibetan Plateau of China. Amplicon sequencing of bacterial and fungal communities were used to determine soil bacterial and fungal community composition and diversity patterns. The results revealed that soil bacterial and fungal alpha-diversities were lower in desertified P. densata forest soils. Soil total carbon content (TC) was the major predictor of bacterial Pielou index. Whereas fungal Chao 1 and Simpson diversity indices were mainly influenced by total nitrogen contents (TN) of the soil. Differential response between soil bacterial and fungal communities' structures were observed between the desertified and non-desertified soils. Soil pH mainly regulated the overall microbial community structures in addition to TC determining bacterial and TN determining fungal community structures, respectively. Changes in the relative abundance of bacterial phylum Chloroflexi and Actinobacteria, and the ratio of fungal phylum Ascomycota/Basidiomycota were the indicators of intensity of soil desertification in the studied forests. The relative abundance of pathogenic microbial communities in soils was more in desertified soils in comparison to the non-desertified soils of P. densata forests, such as the bacterial genus Conexibacter and fungal genera Penicillium and Ilyonectria. This study evidences the differential response of soil bacterial and fungal communities to changes in soil biotic and abiotic properties indicating differential adaptive mechanism in a forest ecosystem currently experiencing adverse effects of rapid desertification.

Root exudation patterns of Chinese fir after thinning relating to root characteristics and soil conditions

Root exudates are crucial to belowground carbon allocation and nutrient cycling in forest ecosystems. Few studies have focused on the effects of forest management activities, such as thinning, on root exudation rates of mature woody species in subtropical regions. In this study, we aimed to determine three kinds of root exudation rates (i.e., per mass, length, and area) in situ under three thinning intensities: Control (unthinned), light thinning intensity (LIT, felled 30% of individual trees), and heavy thinning intensity (HIT, felled 70% of individual trees), in a 29-year-old Chinese fir plantation. We found that root exudation rates increased after thinning and showed significant seasonal dynamics, with the highest and lowest rates being in summer and winter, respectively. The root exudation rates increased with microbial biomass C and N. Positive relationships between the root exudation rates, number of root tips, and root vitalities were observed. The root exudation rates increased with root diameter and decreasing specific root area, suggesting that resource-conservative roots of Chinese fir were biased toward accelerating root exudation rate for nutrient acquisition, instead of optimizing root morphology. In addition, thinning reduced overall soil total carbon content in a Chinese fir plantation. The soil total C content was higher in HIT than in LIT, indicating that HIT could reduce soil C loss by root exudation rates. These findings elucidate how thinning affects fine root exudation rates by altering soil conditions and root characteristics while contributing to our ability to predict belowground C allocation and nutrient cycling in response to silvicultural treatments.

Pelletized Straw Incorporation in Sandy Soil Increases Soil Aggregate Stability, Soil Carbon, and Nitrogen Stocks

In China, increasing the quantity and quality of total carbon and nitrogen stocks in sandy soil used for crop production is an important research issue. Soil amendment with pelletized straw could improve both soil physical structure and fertility in sandy soils, but these aspects remain understudied. The present pot and field experiments examined the dynamic changes in sandy soil water holding capacity, soil bulk density, soil total carbon and nitrogen stocks, and the distribution of water-stable aggregates and soil total carbon stocks related to aggregates across the following treatments: no fertilization (i.e., study control (CK)), normal fertilizer rate (NM), soil amendment at 150 Mg ha−1 (S150), manure amendment at 150 Mg ha−1 (M150), pelletized straw amendment at 75 Mg ha−1 (PS75), and pelletized straw amendment at 150 Mg ha−1 (PS150). The results show that the pelletized straw incorporation significantly increased water holding capacity and decreased soil bulk density. PS150 notably increased the large macroaggregates (&gt;2000 μm) proportion and decreased the ratio of &lt;250 μm aggregate size fractions in comparison with CK, NM, S150, and M150 at 0–20 and 20–40 cm soil depths. Compared with the CK treatment, the bulk soil carbon and nitrogen stocks in the 0–20 cm layers under the PS150 treatment were significantly increased by 85.2% and 302.9%, and in the 20–40 cm layers those increased by 136.4% and 257.1%, respectively. The PS150 treatment resulted in higher soil organic carbon (SOC) and particulate organic carbon content than the CK and PS75 treatments, whereas the PS75 treatment achieved maximum soil inorganic carbon content. The pelletized straw treatment increased the large macroaggregate-associated soil total carbon content at 0–20 and 20–40 cm soil depths. The maximum soil total carbon stocks were in the small macroaggregates (250 &lt; WSA &lt; 2000 μm) rather than in the large macroaggregate and microaggregates under the PS75 and PS150 treatments. Additionally, the pelletized straw and manure amendments increased the yield of silage corn, which was dependent on the increase in soil total carbon and nitrogen content in the macroaggregates, whereas the soil and manure amendments did not facilitate sandy soil aggregation and soil total carbon stock increases. In conclusion, PS150 was found to be the optimal amendment for maintaining sandy soil profile physico-chemical properties through macroaggregate stabilization. These results will be beneficial for arid and semi-arid regions, thus contributing to soil carbon and nitrogen conservation.

Impacts of microplastics and heavy metals on the earthworm Eisenia fetida and on soil organic carbon, nitrogen, and phosphorus

Microplastics (MPs) are increasingly being studied because they have become ubiquitous in aquatic and terrestrial environments. However, little is known about the negative effects of co-contamination by polypropylene microplastic (PP MPs) and heavy metal mixtures on terrestrial environment and biota. This study assessed the adverse effects of co-exposure to PP MPs and heavy metal mixture (Cu2+, Cr6+, and Zn2+) on soil quality and the earthworm Eisenia fetida. Soil samples were collected in the Dong Cao catchment, near Hanoi, Vietnam, and analyzed for changes in extracellular enzyme activity and carbon, nitrogen, and phosphorus availability in the soil. We determined the survival rate of earthworms Eisenia fetida that had ingested MPs and two doses of heavy metals (the environmental level - 1 × - and its double - 2 ×). Earthworm ingestion rates were not significantly impacted by the exposure conditions, but the mortality rate for the 2 × exposure conditions was 100%. Metal-associated PP MPs stimulated the activities of β-glucosidase, β-N-acetyl glucosaminidase, and phosphatase enzymes in soil. Principle component analysis showed that these enzymes were positively correlated with Cu2+ and Cr6+ concentrations, but negatively correlated with microbial activity. Zn2+ showed no correlation with soil extracellular enzyme activity or soil microbial activity. Our results showed that co-exposure of earthworms to MPs and heavy metals had no impact on soil nitrogen and phosphorus but caused a decrease in total soil carbon content, with a possible associated risk of increased CO2 emissions.

Annual burying of straw after pelletizing: A novel and feasible way to improve soil fertility and productivity in Northeast China

Increasing the amount of straw returning has the potential to improve soil fertility, but is not widely accepted due to yield reductions in regions with low temperatures and precipitation. Thus, annual straw burying with large amounts after pelletizing was established considering soil fertility, crop yield and economic income. A three-year field trial with a large amount (75 Mg ha−1 year−1) of pelletized straw (PS75) and chopped straw (CS75), normal amount (15 Mg ha−1 year−1) of chopped straw (CS15), and no straw returning (CK) was conducted for spring maize. PS75 increased the soil total carbon content by 8–17 % and 29–51 % as compared to the other treatments between 0–20 and 20–40 cm respectively. PS75 also had a higher total nitrogen content, moderate soil C/N ratio, lower bulk density, and comparable soil pH in the third year. Specifically, PS75 increased grain yield by 5–7 % relative to CK, and 6–21 % relative to CS15 in the second and third years. PS75 also increased grain yield by 5–28 % than CS75 in the three years with higher kernel number and 100-kernel weight. This was partly attributed to a longer grain filling period due to higher soil carbon and nitrogen contents for PS75 than others. Notably, PS75 exhibited increased trends in grain yield and economic income with experimental year compared to CK. Overall, annual pelletized straw burying with a large amount is a feasible pathway for improving the soil fertility and crop yield in Northeast China.

Soil nitrification and denitrification in Cunninghamia lanceolata plantations with different stand ages.

The variations in soil nitrification and denitrification processes, together with the abundances of functional microbes were investigated in Cunninghamia lanceolata plantations with different stand ages of 5, 8, 21, 27, and 40 years old. The results showed that the net nitrification rate fluctuated with increasing forest ages, with that of 8-year- and 27-year-old C. lanceolata plantations being significantly lower than other stand ages. The abundance of ammonia-oxidizing archaea (AOA) amoA in the 27-year-old plantation was significantly lower than that of the 40-year-old plantation, while there was no significant difference among the other stand ages. There was no significant difference in the abundance of AOB amoA gene, denitrifying functional genes or soil denitrification potential among different stand ages. The results of stepwise regression analysis showed that the abundance of AOA amoA gene was not significantly affected by soil physical and chemical properties. In addition, the abundance of AOB was positively associated with soil total carbon content and soil pH. The abundance of denitrifying functional genes including narG, nirK and nosZ increased with increasing soil pH. The abundance of nirK and nirS was influenced by soil total carbon. Stand age influenced soil net nitrification rate through the AOA amoA abundance. Moreover, soil denitrification potential was directly affected by stand age, or indirectly affected by stand age through soil microbial biomass carbon, soil pH and denitrifying gene abundance of narG and nirK. Compared with the denitrification process, soil nitrification and associated AOA amoA gene abundance were more sensitive to the development of C. lanceolata plantations. The rotation period sould be appropriately extended to reduce the risk of nitrogen losses resulting from soil nitrification.

Reapplication of biochar, sewage waste water, and NPK fertilizers affects soil fertility, aggregate stability, and carbon and nitrogen in dry-stable aggregates of semi-arid soil

Biochar has been applied to increased soil nutrients, especially C. In RCBD, control fresh water (CFW), sewage wastewater (SWW), NPK fertilizer, rice husk biochar (RHB), and NPK + RHB treatments were arranged with four replications. Soil chemical properties, dry-stable aggregate fractions [4.75–2.00 (Lma), 1.00–2.00 (Mma), 0.25–1.00 (Sma), and < 0.25 mm (Mia)], and aggregate total carbon (TC) and total nitrogen (TN) concentrations were evaluated over a 4-year period with repeated treatment additions in a vegetable-based rotation system. Soils amended with RHB, NPK and NPK + RHB showed slight acidification but no significant change in exchangeable cation content. The concentration of TC increased with NPK + RHB, NPK and RHB, while TN and available P increased with NPK and NPK + RHB treatments. The SWW increased soil pH and Na+ but decreased K+ concentration. Reapplication of SWW and NPK + RHB resulted in an increase in Lma formation by 28 % and 29 %, and MWD by 19 % and 21 %, respectively. The NPK and NPK + RHB treatments increased TC and TN in all aggregate fractions, while RHB only increased TC in macro-aggregates (4.75–0.25 mm) and TN in Sma. The increase in aggregate TC concentration was approximately 1.50–2.00 folds greater with NPK + RHB than with NPK and RHB treatments. Although the TC concentration was highest in both Mma and Sma fractions with the NPK + RHB treatment, the greater association of Lma (44 %) and Mma (31 %) with soil TC content may significantly affect the soil sustainability. The TC in Mma fraction was reflected in MWD (r = 0.53*, P = 0.05). Reapplication of RHB had limited potential for C and N sequestration in soil aggregates, but its combination with NPK produced a superior response in soil nutrients retention, soil structural stability, and TC and TN sequestration potential in micro- and macro- aggregate fractions. Therefore, NPK + RHB treatment is best suited for the sustainable management of the study and similar soils.

Dispersal limitation and host selection drive geo-specific and plant-specific differentiation of soil bacterial communities in the Tibetan alpine ecosystem

Soil bacteria, which are active in shrub encroachment, play key roles in regulating ecosystem structure and function. However, the differentiation characteristics and assembly process of bacterial communities in scrubbed grasslands remain unknown. Taking the Qinghai-Tibet Plateau, a hotspot of shrub encroachment, as the study area, we collected 192 soils near nine natural typical shrubs' roots on a trans-longitude transect (about 1800 km) and investigated the bacterial communities using 16S rRNA amplicon sequencing. We found that the bacterial communities exhibited plant-specific and geographic-specific differentiation. On the one hand, bacterial communities differed significantly across plant species, with widely distributed shrubs harboring high diversity communities but few plant-specific taxa, and narrowly distributed shrubs possessing low diversity communities but more plant-specific taxa. Besides, there was a significant negative correlation between bacterial community similarity and plant phylogenetic distance. On the other hand, bacterial communities differed across geographic sites, with a significant decay in bacterial community similarity with geographic distance. The bacterial alpha diversity varied in an inverted V-shape from west to east, peaking at 91°E, which could be largely driven by mean annual temperature, soil pH and soil total carbon content. Community differentiation increased with the heterogeneity degree of assembly processes, and the dominant assembly process in these two specific differentiations differed. Dominated by stochastic and deterministic forces, respectively, geography diverged bacterial communities primarily through increased dispersal limitation, whereas plants diverged bacterial communities primarily through increased variable selection. Our study provides new insight into the characteristics and mechanisms of root-surrounding soil bacteria differentiation in scrubbed grasslands, contributing to the scientific management of degraded grasslands and the prediction of bacterial community structure and ecosystem function in response to global change.