Soil Carbon Pools Research Articles

Mixed cattle and sheep grazing reduces the root lifespan of the community in a desert steppe

• Mixed cattle and sheep grazing can significantly shorten root longevity and may accelerate carbon sequestration. • Grazing inhibits fine root longevity of plant community in the temperate desert steppe. • Sheep grazing alone has a greater inhibitory effect on root longevity than cattle grazing alone. • Adjusting the combination of herbivores is an effective strategy to shorten the root lifespan of the community. • The factors affecting root longevity were analyzed by the COX proportional-hazards model. The soil is the primary carbon pool in grassland ecosystems, and the turnover of plant roots is an essential way of organic carbon input. Grazing intensity under a single animal species is usually used to explore the effects of herbivores on grassland, but multi-species grazing is common in grassland utilization. However, few studies have examined the impact of different livestock species and herbivore combinations on the root growth of the grassland community. We used the minirhizotron method to explore the response of root growth in a temperate desert steppe community to cattle and sheep grazing over two years. Among root characteristics and environmental factors, grazing method(cattle grazing; sheep grazing; cattle and sheep grazing; no grazing) is the most significant inhibiting factor affecting root longevity. We found that mixed cattle and sheep grazing significantly reduced the root lifespan of the community, with a median survival time of 120 d, and a survival rate of only 30 % at the end of the observation period. Compared with other treatments, mixed cattle and sheep grazing significantly reduced the number of live roots (0.3724 ± 0.0453 piece/cm 2 ). The change in fine root length of mixed grazing (-0.012 ± 0.0013 mm/cm 2 ) was considerably greater than other treatments. The root lifespan of the community was significantly negatively correlated with the ratio of belowground to aboveground net primary productivity (BNPP/ANPP). The mixed cattle and sheep grazing changed in the patterns of plant carbon contribution, and increased the organic carbon content of the soil. Therefore, under moderate grazing intensity, adjusting the combination of herbivores is an effective strategy to accelerate root turnover rate of the community, accelerate the input of carbon from plant photosynthesis into the soil carbon pool, and may increase soil carbon storage.

Responses of microbial necromass carbon and microbial community structure to straw- and straw-derived biochar in brown earth soil of Northeast China.

Soil microbial organisms are conducive to SOC sequestration. However, little attention has been given to the contributions of living MBC and microbial necromass carbon to the SOC pool under biochar and straw amendments. The aims of the study were to explore (1) the effects of maize straw and biochar on MBC, POC, MAOC, DOC and microbial necromass carbon; (2) the contribution of MBC and microbial necromass carbon to the SOC pool; and (3) the relationships among the soil microbial community structure, microbial necromass carbon and other SOC fractions under maize straw and biochar application for nine consecutive years. Three treatments were studied: CK (applied chemical fertilizer only), BC (biochar applied annually at a rate of 2.625 t ha−1 combined with chemical fertilizer), and SR (straw applied annually at a rate of 7.5 t ha−1). Both biochar and straw increased the SOC contents after nine successive maize plant seasons; the DOC and MAOC contents were also increased by biochar and straw amendments. Biochar had advantages in increasing POC contents compared to straw. Biochar and straw increased MBC contents by 48.54% and 60.83% compared to CK, respectively. Straw significantly increased the Galn, GluN, MurA, ManN and total amino contents (P < 0.05); however, biochar significantly increased the Galn and GluN contents (P < 0.05) but had no impact on the MurA contents and decreased the ManN contents. Biochar mainly increased the fungal-derived necromass carbon contents but had no effect on the bacterial-derived necromass carbon, and straw increased both the bacterial- and fungal-derived necromass carbon contents. Straw had no influence on the ratios of microbial necromass carbon accounting for SOC and MAOC, but biochar decreased the ratios in the current study. Similarly, biochar mainly increased the fungal PLFA and total PLFA contents compared to CK, but straw increased bacterial PLFAs, fungal PLFAs and Actinomycetes PLFAs. Maize yield were increased by 7.44 and 9.16% by biochar and straw application, respectively. These results indicate that biochar stimulates fungal activities and turnover to contribute to the stable soil carbon pool and that biochar also improves POC contents to improve the soil organic carbon sink.

Soil quality under different land uses in eastern India: Evaluation by using soil indicators and quality index.

Indian soils are inherently poor in quality due to the warm climate and erosion. Conversion of land uses like forests to croplands and faulty management practices in croplands further cause soil degradation. This study aimed to understand the extent of these impacts in a small representative part of eastern India, covering Himalayan terai and nearing alluvial plains. Soils were collected from (i) forests, (ii) croplands (under agricultural practices for more than 50–60 years) and (iii) converted lands (converted from forests to croplands or tea gardens over the past 15–20 years). Different soil quality indicators were assessed and soil quality index (SQI) was generated to integrate, scale and allot a single value per soil. Results indicated that continuous organic matter deposition and no disturbances consequence the highest presence of soil carbon pools, greater aggregation and maximum microbial dynamics in forest soils whereas high application of straight fertilizers caused the highest available nitrogen and phosphorus in cropland soils. The SQI scorebook indicated the best soil quality under forests ( 0.532), followed by soils of converted land ( 0.432) and cropland ( 0.301). Comparison of the SQI spatial distribution with land use and land cover confirmed the outcome. Possibly practices like excessive tillage, high cropping intensity, no legume in crop rotations, cultivation of heavy feeder crops caused degraded soil quality in croplands. This study presented an example of soil quality degradation in India due to land use change and faulty management practices. Such soil degradation on a larger scale may affect future food security.

Increased forest coverage will induce more carbon fixation in vegetation than in soil during 2015–2060 in China based on CMIP6

As components of terrestrial carbon sinks, vegetation and soil carbon pools are important for offsetting CO2 emissions. However, differences in their carbon sequestration capacities and their responses to global change in the future are poorly understood. This study assessed the changes in vegetation and soil carbon and their ratios and drivers under the SSP126 scenario from 2015 to 2060, using Coupled Model Intercomparison Project phase 6 simulations in China, a major carbon sink region in global terrestrial ecosystems. The content of vegetation carbon (29 ± 1 PgC) was observed to be lower than that of soil carbon (113 ± 23 PgC), and the ratio of vegetation to soil carbon was the highest in the subtropical-tropical monsoon climatic region (0.55 ± 0.12). Moreover, the total stock of vegetation and soil carbon increased by 10 ± 1 PgC during the study period, and the increase in vegetation carbon was 4.31 times that of soil carbon, because the responses of vegetation carbon stocks to increased forest coverage and atmospheric CO2 were greater than that of soil carbon stocks, especially in the subtropical-tropical and temperate monsoonal climatic regions. However, bare land encroachment on grasslands reduced their increments in the temperate monsoonal and high-cold Tibetan Plateau climatic regions. Furthermore, compared with SSP245 and SSP585 scenarios, vegetation and soil carbon sinks can offset a greater amount of carbon emissions in 2060 under the SSP126 scenario, accounting for 53% of all carbon emissions, offsetting 60%–79% of carbon emissions from China under its policy of increasing forest coverage. The study revealed the important role of afforestation in increasing ecosystem carbon stocks, additionally, grassland conservation and deep reductions in carbon emissions cannot be ignored in the future. This study provides a basis for determining the response of vegetation and soil carbon to environmental factors and the realization of net-zero emissions globally.

Application of soil amendments to enhance soil carbon and biological properties in a paddy field under elevated CO2 conditions

ABSTRACT A field experiment was carried out to elucidate the effect of elevated carbon dioxide (eCO2 – 550 ± 30 ppm) on soil enzymes (dehydrogenase, β-glucosidase, fluorescein diacetate, urease, acid and alkaline phosphatase), soil carbon pool (Soil Organic Carbon (SOC), Microbial Biomass Carbon (MBC), oxidizable carbon, humic acid (HA), fulvic acid (FA) fractions), microbial population dynamics (heterotrophs, fungi, actinobacteria, diazotrophs, methanotrophs, and total anaerobes), carbon sequestration and yield in a flooded paddy soil in open top chambers (OTCs) in relation to rhizospheric and bulk soil. Responses of most of the observed parameters to eCO2 with biochar application in rhizosphere soil were significantly higher. The carbon (C) sequestration potential was found higher in the biochar applied plot under eCO2 with 0.59 Mg C sequestered ha−1. The same recorded the highest biomass yield and grain yield which is 12.8 and 30.8% higher than the control. Principal Component Analysis (PCA) recognized soil dehydrogenase, β – glucosidase, SOC, FA, Substrate Induced Respiration (SIR), metabolic quotient (qCO2) and counts of heterotrophs as key drivers of variability. The current study thus provides some dependable biological indicators to assess the paddy ecosystems, vis-à-vis anticipatory climate change.

Estimation of carbon pool at mangrove forest of Kudat, Sabah, Malaysia

Abstract. Hatta SM, Salleh E, Suhaili NS, Besar NA. 2022. Estimation of carbon pool at mangrove forest of Kudat, Sabah, Malaysia. Biodiversitas 23: 4601-4608. Mangroves play a significant role in reducing tropical carbon emissions and preventing climate change. This study was carried out in Kudat's Tun Mustapha Park mangrove forest. This research aims to quantify the aboveground, belowground, and soil carbon pools. Nine 125-meter-long transect lines were set up, and every 25 meters, a 7-meter-diameter circle was placed. A forest inventory was conducted to determine the diameter at the breast height of standing trees. For soil analysis and bulk density, soil samples were collected at four different depths (0-15 cm, 15-30 cm, 30-50 cm, and 50-100 cm). An ICP-OES analyzer was used to determine the value of soil nutrients, and a CHNS analyzer was used to determine the soil carbon concentration. The aboveground and belowground biomass was calculated using the allometric equation, and the carbon stock was estimated at 50% of the total biomass. The outcome showed a 455.87 MgCha-1 total carbon pool. The soil carbon has the highest value with 273.76 MgCha-1, followed by aboveground carbon (living trees) with 136.58 MgCha-1 and belowground carbon (roots) with 45.53 MgCha-1. This study found that soil carbon stock made up almost 60% of the total carbon stock in the mangrove forest.

Effects of micronutrient fertilization on soil carbon pools and microbial community functioning

Fertilization with macronutrients, e.g., nitrogen (N) and phosphorus (P), has wide-ranging and well-characterized effects on terrestrial ecosystem functions. In contrast, influences of other elements, e.g., sodium (Na), calcium (Ca), and potassium (K), hereafter, ‘micronutrients’, are poorly understood. To determine effects of macronutrients, micronutrients, and their interactions on soil carbon (C) cycling, we conducted a full factorial experiment where treatments consisted of fertilizing experimental plots with Na, Ca, and K (each manipulated individually) and macronutrients (N + P added together). Each year of the experiment we measured aboveground plant biomass and sampled soils to quantify mineralizable C pools and active microbial biomass. To further explore micronutrient effects on microbial-mediated soil C cycling, in the final year of the experiment we assessed microbial C cycle functions using a catabolic profiling technique and quantified multiple additional soil C pools: particulate (POM-C), mineral-associated (MAOM-C), and total (TC). Macronutrients (N + P) affected nearly all measured variables – when N + P was added, active microbial biomass increased, catabolic profiles were altered, and mineralizable C, POM-C, and TC pools all increased. Micronutrients also had effects on soil C cycling that were generally smaller than effects of macronutrients – Ca addition reduced mineralizable C pools relative to the other treatments and K addition increased POM-C and TC pools. Further, Ca + K addition altered microbial catabolic profiles, but only when N + P was also added. Our study reveals several influences of micronutrients on soil C cycling – specifically, that Ca and K may influence the size of soil C pools by influencing the C cycle functions of soil microbial communities.

Change of tillage system affects the soil carbon pools characters, reduces carbon emissions and improves maize yield in the Loess Plateau

Understanding the response of soil aggregates and soil carbon pools to different tillage practices is an important way to illustrate the role of conservation tillage in climate change mitigation. Therefore, a long-term tillage experiment was conducted from 2007 to 2020 with four tillage practices: 1) The rotational tillage practice consisting of no-tillage in the first year, conventional tillage in the second year, subsoiling in the third year and a cycle of three years (NCS); 2) no-tillage (NT); 3) subsoiling (ST); and 4) conventional tillage (CT) to explore the relationship among soil aggregates, soil carbon pools, soil carbon sequestration and emissions. After long-term experiment, NCS and NT improved the soil total organic carbon (TOC) stock by 14.4% and 9.0% compared with CT in the 0–40 cm soil depth. Meanwhile, NCS, NT, ST decreased carbon emissions by 18.6∼36.6% during the observation period, when compared with CT. Partial least squares path model revealed that soil aggregates structures and soil carbon pools stability were the main causes of soil carbon sequestration and emissions affected by conservation tillage. NCS, NT and ST increased soil aggregates proportion, mean weight diameter, geometric mean diameter and aggregates associated carbon compared with CT. Meanwhile, NCS and NT improved the carbon pools management index (CPMI) by 11.1% and 16.5%, respectively. The increased stability of soil aggregates and the improvement of soil carbon pools reduced soil carbon emissions and increased soil carbon sequestration. However, NT and ST significantly increased the TOC stratification ratios (SR) by 38.8% and 30.1% in the 0–10 and 10–20 cm soil depth compared with NCS, which was not conducive to the vertical distribution of TOC. In additional, NCS, NT and ST increased yield by 16.7∼22.6% compared with CT. Collectively, based on the combined effects of environmental protection, production, and soil physicochemical property improvement, we recommend NCS (with highest comprehensive index: 6.76) as a sustainable tillage practice that can improve yield with ecological effects.

Seasonal changes in soil carbon storage capacity and glomalin-related soil protein under different agricultural activities, abandonment, and wildfire occurrence in Mediterranean region

Agricultural practices can directly affect soil environmental conditions and consequently soil ecosystems and fertility. Soils under different agricultural practices like tillage and grazing were studied and compared to other soils affected by wildfire and different ages of abandonment. Atmospheric CO 2 , soil C-CO 2 loss, soil temperature, soil moisture, bulk density, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), Redfield ratios of C:N:P, easily exactable and total glomalin-related soil protein (GRSP EE and GRSP T ), and morphology, quantity, and stability of soil aggregates (WSA) were seasonally analyzed. Statistical significance checked using the two-factor ANOVA. Intense tillage and wildfire occurrence revealed a deficiency in soil nutrients and fertility more than grazing practices. Steady soil fertility conditions occurred in soils preserved by fire and ancient abandonment. The GRSP seasonal means varied significantly among all soils because of land-use effects. GRSP T , SOC, TN, and TP increased from winter to spring and reached the highest values in summer then decreased again in autumn. GRSP was positively correlated (P < 0.01) with atmospheric CO 2 , SOC, TN, and TP with high peaks in summer indicating the dependent GRSP production on plant nutrients acquisition as well as soil carbon pools. Moreover, the correlation between GRSP and emitted C-CO 2 may indicate the contribution of GRSP fractions to the labile as well as the stable SOC fractions. The GRSP EE showed rapidly transformed into stable forms in more fertile and better-structured soils than in less fertile soils with vulnerable soil structures. In conclusion, the stoichiometric balance of soil nutrients, aggregate stability, and stabilized GRSP pools improved relatively across the seasonal rhythms from winter to summer. Moreover, environmental soil conditions developed to preserve organic carbon in soils with long abandonment than in mid abandonment, while the worst conditions were in the vulnerable soils intensively mismanaged and devastated by fire.

Ecological homogenization of soil properties in the American residential macrosystem

AbstractThe conversion of native ecosystems to residential ecosystems dominated by lawns has been a prevailing land‐use change in the United States over the past 70 years. Similar development patterns and management of residential ecosystems cause many characteristics of residential ecosystems to be more similar to each other across broad continental gradients than that of former native ecosystems. For instance, similar lawn management by irrigation and fertilizer applications has the potential to influence soil carbon (C) and nitrogen (N) pools and processes. We evaluated the mean and variability of total soil C and N stocks, potential net N mineralization and nitrification, soil nitrite (NO2−)/nitrate (NO3−) and ammonium (NH4+) pools, microbial biomass C and N content, microbial respiration, bulk density, soil pH, and moisture content in residential lawns and native ecosystems in six metropolitan areas across a broad climatic gradient in the United States: Baltimore, MD (BAL); Boston, MA (BOS); Los Angeles, CA (LAX); Miami, FL (MIA); Minneapolis–St. Paul, MN (MSP); and Phoenix, AZ (PHX). We observed evidence of higher N cycling in lawn soils, including significant increases in soil NO2−/NO3−, microbial N pools, and potential net nitrification, and significant decreases in NH4+pools. Self‐reported yard fertilizer application in the previous year was linked with increased NO2−/ NO3−content and decreases in total soil N and C content. Self‐reported irrigation in the previous year was associated with decreases in potential net mineralization and potential net nitrification and with increases in bulk density and pH. Residential topsoil had higher total soil C than native topsoil, and microbial biomass C was markedly higher in residential topsoil in the two driest cities (LAX and PHX). Coefficients of variation for most biogeochemical metrics were higher in native soils than in residential soils across all cities, suggesting that residential development homogenizes soil properties and processes at the continental scale.

Probing the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice (Oryza sativa) - wheat (Triticum aestivum) cropping system

Biochar incorporation as a soil amendment has been shown to improve soil quality by sequestering carbon in soil for longer period of time. The two years field experiment was done at Agronomy research fields of Lovely Professional University, Phagwara, Punjab, India during 2018-19 and 2019-20 to probe the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice-wheat cropping system. The experiment was comprised with nine treatments viz., 100% Recommended Dose of Fertilizer (RDF), 50% RDF + Biochar, 50% RDF +25% FYM + Biochar, 50% RDF + 50% FYM + Biochar, 50% RDF +25% VC + Biochar, 50% RDF + 50% VC + Biochar, 50% RDF + 25% PM + Biochar, 50% RDF + 50% PM + Biochar, control (no fertilizer) and imposed in RBD design with three replications for each treatment. Pusa basmati 1121 and PBW550 varieties of rice and wheat was taken as a test crops. The results revealed that application of 50 % RDF + 50% PM + Biochar in rice and 50% RDF + 50% FYM + Biochar in wheat crop to soil significantly improved the soil carbon fractions i.e., Permanganate oxidizable carbon, Particulate organic carbon and Microbial biomass carbon at harvest of the crops during both years. This study has demonstrated that C pools in the soil can be enhanced by the biochar through stimulating soil microorganisms. Carbon storage in the soil is improved after biochar addition. By adding biochar with fertilizer and manures C sequestration can be enhanced. Based on the findings in this study, conventional fertilizer and manure application to soils could be associated with biochar through which multi-benefits (e.g., soil amendment, environment protection, and C sequestration) could be obtained simultaneously. Thus, converting rice straw to biochar for its application as soil amendment and C sequester decrease straw burning in open field in Northern India.

Probing the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice (Oryza sativa) - wheat (Triticum aestivum) cropping system

Biochar incorporation as a soil amendment has been shown to improve soil quality by sequestering carbon in soil for longer period of time. The two years field experiment was done at Agronomy research fields of Lovely Professional University, Phagwara, Punjab, India during 2018-19 and 2019-20 to probe the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice-wheat cropping system. The experiment was comprised with nine treatments viz., 100% Recommended Dose of Fertilizer (RDF), 50% RDF + Biochar, 50% RDF +25% FYM + Biochar, 50% RDF + 50% FYM + Biochar, 50% RDF +25% VC + Biochar, 50% RDF + 50% VC + Biochar, 50% RDF + 25% PM + Biochar, 50% RDF + 50% PM + Biochar, control (no fertilizer) and imposed in RBD design with three replications for each treatment. Pusa basmati 1121 and PBW550 varieties of rice and wheat was taken as a test crops. The results revealed that application of 50 % RDF + 50% PM + Biochar in rice and 50% RDF + 50% FYM + Biochar in wheat crop to soil significantly improved the soil carbon fractions i.e., Permanganate oxidizable carbon, Particulate organic carbon and Microbial biomass carbon at harvest of the crops during both years. This study has demonstrated that C pools in the soil can be enhanced by the biochar through stimulating soil microorganisms. Carbon storage in the soil is improved after biochar addition. By adding biochar with fertilizer and manures C sequestration can be enhanced. Based on the findings in this study, conventional fertilizer and manure application to soils could be associated with biochar through which multi-benefits (e.g., soil amendment, environment protection, and C sequestration) could be obtained simultaneously. Thus, converting rice straw to biochar for its application as soil amendment and C sequester decrease straw burning in open field in Northern India.

Increasing the Contents of Paddy Soil Available Nutrients and Crop Yield via Optimization of Nitrogen Management in a Wheat-Rice Rotation System.

To explore the impact of nitrogen (N) rate during the wheat season and N fertilizer management during the rice season on carbon and soil nutrient pools in paddy soil, a wheat–rice rotation system for 2 successive years was implemented. In the rotation system, a conventional N rate (Nc; 150 kg/ha) and a reduced N rate (Nr; 120 kg/ha) were applied in the wheat season. Based on an application rate of 150 kg/hm2 N in the rice season, three N management models were applied, in which the application ratio of base:tiller:panicle fertilizer was 20%:20%:60% in treatment M1, 30%:30%:40% in treatment M2, and 40%:40%:20% in treatment M3. Zero N was used as the control (M0). Experimental results indicate that, under Nc, the M2 management model during the rice season, improvements were seen in paddy soil urease, organic carbon, and annual yield relative to other conditions. The average organic matter and total N associated with the M2 rice management model and conventional N application during the wheat season were 5.13% and 4.95% higher, respectively, relative to the use of a reduced N application rate during the wheat season. Similarly, the average total carbon content and annual yields were 6.61% and 5.56% higher under the model M2 with conventional N application during the wheat season, respectively, relative to reduced N application after the two-year study period. These findings indicate that production and carbon fixation in paddy fields can be optimized through a conventional N application rate during the wheat season, and an M2 N management model during the rice season in southern China under a wheat–rice rotation system.

Responses of Soil Carbon Pools and Carbon Management Index to Nitrogen Substitution Treatments in a Sweet Maize Farmland in South China.

In China, excessive nitrogen fertilizer application in sweet maize fields contributes to greenhouse gas emissions. This study used maize straw (MS), cow dung (CD), biogas residue (BR), and straw-based biochar (CB) to substitute the mineral nitrogen fertilizer at 20% and 50% ratios in the Pearl River Delta in China. In comparison with a conventional amount of mineral nitrogen fertilizer (CK), the soil organic carbon (SOC) storages of the different treatments increased by 6.5–183.0%. The CB treatment significantly improved the inert organic carbon pool in the soil, while other types of organic materials promoted the formation of activated carbon pools. The treatments increased the soil carbon pool management index by 21.1–111.0% compared to the CK. Moreover, the CB treatments increased the soil carbon sequestration index by 78.3% and 155.8% compared to the CK. In general, substituting the mineral N fertilizer with BR, CB, and CD could improve the SOC accumulation in sweet maize farmland in South China. The CB at the high substitution level was the best measure for stabilizing carbon sequestration in the sweet maize cropping system. This experiment provides valuable information for ensuring the clean production of sweet maize in a typical subtropical area in East Asia.

Enhanced suppression of saprotrophs by ectomycorrhizal fungi under high level of nitrogen fertilization

Ectomycorrhizal fungi (EMF) are widespread in northern conifer forests. By competing with the free-living saprotrophic fungal and bacterial communities for limited soil nitrogen, EMF are expected to suppress litter decomposition and thus drive soil carbon accumulation. The EMF may also stimulate rhizosphere microbial growth through inputs of labile plant carbon, and subsequently contribute to the soil carbon pool via microbial necromass. Here we examined the relative strength of these two potential EMF effects in a northern conifer plantation of the Saihanba Forest, the largest plantation in China. The soil fungal and bacterial biomass, as well as their respiration, were quantified within the two types of soil cores that either allow or exclude the ingrowth of EMF. We also set up a nitrogen fertilization gradient (0, 5, 10, 15 g N m–2 y–1) in this plantation to quantify the influence of external inorganic nitrogen on the EMF effects. We found evidence that EMF inhibit the overall fungal and bacteria biomass, confirming the suppression of saprotrophs by EMF. In addition, high levels of external nitrogen fertilization (15 g N m–2 y–1) might further enhance the suppression by EMF. In contrast, the presence of EMF consistently increased soil microbial respiration across all nitrogen fertilization levels, indicating that the carbon allocated to EMF could have been largely consumed by microbial respiration and contributed minimally to the accumulation of microbial biomass. Our results also indicated that the suppression of saprotrophs by EMF may play a critical role in driving continuous soil carbon accumulation in this northern pine plantation under atmospheric nitrogen deposition.

Estimation of Soil Organic Carbon Using Vis-NIR Spectral Data and Spectral Feature Bands Selection in Southern Xinjiang, China.

Soil organic carbon (SOC) plays an important role in the global carbon cycle and soil fertility supply. Rapid and accurate estimation of SOC content could provide critical information for crop production, soil management and soil carbon pool regulation. Many researchers have confirmed the feasibility and great potential of visible and near-infrared (Vis-NIR) spectroscopy in evaluating SOC content rapidly and accurately. Here, to evaluate the feasibility of different spectral bands variable selection methods for SOC prediction, we collected a total of 330 surface soil samples from the cotton field in the Alar Reclamation area in the southern part of Xinjiang, which is located in the arid region of northwest China. Then, we estimated the SOC content using laboratory Vis-NIR spectral. The Particle Swarm optimization (PSO), Competitive adaptive reweighted sampling (CARS) and Ant colony optimization (ACO) were adopted to select SOC feature bands. The partial least squares regression (PLSR), random forest (RF) and convolutional neural network (CNN) inversion models were constructed by using full-bands (400–2400 nm) spectra (R) and feature bands, respectively. And we also analyzed the effects of spectral feature band selection methods and modeling methods on the prediction accuracy of SOC. The results indicated that: (1) There are significant differences in the feature bands selected using different methods. The feature bands selected methods substantially reduced the spectral variable dimensionality and model complexity. The models built by the feature bands selected by CARS, PSO and ACO methods showed the different potential of improvement in model accuracy compared with the full-band models. (2) The CNN model had the best performance for predicting SOC. The R2 of the optimal CNN model is 0.90 in the validation, which was improved by 0.05 and 0.04 in comparison with the PLSR and RF model, respectively. (3) The highest prediction accuracy was archived by the CNN model using the feature bands selected by CARS (validation set R2 = 0.90, RMSE = 0.97 g kg−1, RPD = 3.18, RPIQ = 3.11). This study indicated that using the CARS method to select spectral feature bands, combined with the CNN modeling method can well predict SOC content with higher accuracy.

Impact of deforestation and temporal land-use change on soil organic carbon storage, quality, and lability.

Soil organic carbon (SOC) plays a key role in regulating soil quality functions and ecosystem services. The objective of our study was to evaluate the impact of deforestation and subsequent land-use change on the SOC and total nitrogen (TN) concentration, quality, and lability under otherwise similar soil and environmental conditions. Geo-referenced composite soils (0 to 30 cm depth at 7.5 cm interval) sampled from agriculture, bioenergy plantations (Miscanthus x giganteus), Conservation Reserve Program (CRP), and wetland were analyzed for SOC, TN, active C (AC), humic- and fulvic acid (HA and FA), non-humic C (NH), E4: E6 ratio, humification indices (HI, HR, and DH), and carbon and nitrogen management indices (CPI, NPI, and CMI), compared to soils under protected forest as a control. Results showed that the CRP had the highest depth distribution and profile-wise stocks of SOC, TN, AC, and FA with respect to the lowest in agriculture upon conversion of forest. Moreover, the SOC and TN contents were significantly stratified in the CRP when compared to agriculture. While agriculture had the wider HA: FA ratios with highest HI and HR but lowest DH values, the CRP, in contrast, had the narrow HA: FA ratios with lowest HI but highest DH values, when compared to the forest. Spectral analyses have shown lower E4: E6 ratios under the forest when compared to both agriculture and the CRP; however, the later had significantly higher E4: E6 ratios than that of agriculture. The CPI, as measures of SOC accumulation or depletion, significantly decreased by 16% under agriculture but increased by 12% under the CRP. While the CMI, as measures of SOC accumulation or depletion and lability, with higher values under the CRP suggested a proportionally more labile SOC accumulation, in contrast, the smaller values under agriculture indicated a greater depletion of labile SOC over time. Moreover, the CRP may have favored a more labile SOC accumulation with higher proportions of aliphatic C compounds, whereas agriculture may have a SOC with high proportions of non-labile aromatic C compounds. Principal components analysis clearly separated and/or discriminated the land-use impacts on soil carbon pools and TN. Likewise, redundancy analysis of the relationship between measured soil parameters and land-use validated that the TOC, TN, FA, humin, and CPI were significantly impacted due to synergism among soil properties as positively influenced by the CRP upon conversion of agriculture.

The Soil Aggregates and Associated Organic Carbon across the Greater Khingan Mountains: Spatial Patterns and Impacting Factors

(1) Background: The preservation of soil organic carbon (SOC) by soil aggregates (SA) is a key mechanism for the stability of the soil carbon (C) pool. (2) Methods: Soil samples were collected at a 0–20 cm depth from 75 sites across the forest regions of the Greater Khingan Mountains, China, and were fractionated as SA of 0.25–2 mm, 0.053–0.25 mm, and &lt;0.053 mm by a wet-sieving method. The spatial patterns of SA and associated organic C (OC) were investigated, as well as their associations with environmental factors. (3) Results: The predominant SA was the SA fraction (SAF) of 0.25–2 mm. The spatial pattern of SA, with moderate spatial autocorrelation, was found to be associated with aggregate size. SOC was mainly accumulated in the 0.25–2 mm SAF, accounting for 50.39% of the total content of aggregate SOC; the total SOC content in all SAF showed strong spatial autocorrelations without significant differences. No significant correlations were found between temperature and SA variables. Precipitation presented significantly positive and negative correlations with the SAF of &lt;0.053 mm and 0.053–0.25 mm, respectively. SOC was favorably associated with macroaggregate, geometric mean diameter (GMD), and mean weight diameter (MWD); however, the correlation between SOC and aggregate SOC lessened as particle size decreased. The aggregate SOC contents were significantly linked with NH4+-N, AK, and TP, while 0.25–2 mm SA content was negatively related with pH. (4) Conclusions: Precipitation was helpful for the development of clay aggregates (&lt;0.053 mm), i.e., increasing rainfall-induced aggregate disruption. SOC encourages small SA cementing to large SA, which improves SA stability. OC associated with the SAF of 0.25–2 mm and 0.053–0.25 mm was positively correlated with soil nutrients such as nitrogen, phosphorus, and potassium, suggesting that the formation of aggregates was conducive to the preservation of soil nutrients.

Carbon dynamics in tree plantings: How changes in woody biomass impact litter and soil carbon

Understanding carbon sequestration from tree planting and management activities is important for contributing to the mitigation of climate change. Although rates of growth and resulting sequestration of carbon in live above-ground biomass are relatively well understood in various woody plantings and commercial plantations in Australia, less is known about associated changes in live below-ground biomass, and the turnover and decomposition of biomass, and hence, resulting changes in carbon stocks of litter and soil. Our objective was to develop a modelling approach for predicting these processes and the resulting changes in litter and soil carbon following the establishment and/or management of tree plantings (EMTP) to facilitate their inclusion in carbon abatement projects. We reviewed and collated data on allocation of biomass, litterfall, litter decomposition, litter/harvest residue mass and soil organic carbon (N = 5,655 estimates). Data were sourced from existing field studies of woody plantings (mixed-species environmental and mallee eucalypt), commercial plantations (hardwood and softwood) and in some cases, eucalypt-dominant native forests. After constraining a carbon accounting model to observed measures of growth, allocation of biomass, and rates of litterfall and litter decomposition, the model was calibrated to maximise the efficiency of prediction of litter and soil pools. Although large uncertainties in ‘observed’ results meant that precision of prediction in any given data source was relatively poor, model predictions had negligible overall bias. The size and diversity of datasets applied in the process of calibration improved overall confidence in model predictions of litter and soil carbon pools. The calibrated model will therefore be a useful tool for informing land managers and policy makers seeking to understand on-site dynamics of all carbon pools, and hence, the total contribution to carbon abatement of different EMTP projects in Australia.

The effect of dissolved char on microbial activity in an extract from the forest floor

Abstract Climate change is associated with an increased risk in the occurrence of wildfires. Forests store large amounts of carbon (C), which are threatened by these wildfires. Pyrogenic material produced after a wildfire constitutes an important part of the soil organic carbon pool in forest soils. Microorganisms play an important role in the cycling of C. This study investigated microbial activity in dissolved char from burned wood from two tree species in different stages of decay. The char from branches of beech and Norway spruce was produced under laboratory fire conditions and extracted in water after which microbial activity was measured for a 4-week period. Further stages of decay resulted in increased flammability with higher peak temperatures and combustion completeness. For the beech samples, further decay also resulted in a decrease of extractable C but a higher proportion of stable C. Further decay resulted in less respiration for beech and more for Norway spruce. With less C being respired, this points towards an increased C sequestration potential in the form of microbial C and microbial derived products for beech compared to Norway spruce. This study provided a workflow to assess the effects of dissolved char on microbial activity by mimicking natural fire conditions. It also indicated the need for future research to further elucidate the underlying mechanisms explaining why fire-originated dissolved char of wood in different decay stages influences microbial respiration with diverging effects per species.