Active Soil Organic Carbon Research Articles

Distribution characteristics of soil active organic carbon at different elevations and its effects on microbial communities in southeast Tibet.

Global mountain ecosystems have garnered significant attention due to their rich biodiversity and crucial ecological functions; however, there is a dearth of research on the variations in soil active organic carbon across altitudinal gradients and their impacts on microbial communities. In this study, soil samples at an altitude of 3,800 m to 4,400 m were collected from Sejira Mountain in the southeast Tibet, and soil active organic carbon components, soil microbial community diversity, composition and structure distribution and their relationships were systematically analyzed. The results revealed a non-linear relationship between the elevation and the contents of soil organic carbon (SOC) and easily oxidized organic carbon (ROC), with an initial increase followed by a subsequent decrease, reaching their peak at an altitude of 4,200 m. The Shannon diversity of bacteria exhibited a significant decrease with increasing altitude, whereas no significant change was observed in the diversity of fungi. The bacterial community primarily comprised Acidobacteria, Proteobacteria, Chloroflexi, and Actinobacteriota. Among them, the relative abundance of Proteobacteria exhibited a negative correlation with increasing altitude, whereas Actinobacteriota demonstrated a positive correlation with elevation. The fungal communities primarily consisted of Basidiomycota, Ascomycota, and Mortierellomycota, with Ascomycota prevailing at lower altitudes and Basidiomycota dominating at higher altitudes. The diversity and composition of bacterial communities were primarily influenced by altitude, SOC, ROC, and POC (particulate organic carbon). Soil carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC), and available phosphorus (AP) emerged as key factors influencing fungal community diversity, while POC played a pivotal role in shaping the composition and structure of the fungal community. In conclusion, we believe that soil active organic carbon components had a greater impact on the bacterial community in the primary forest ecosystem in southeast Tibet with the elevation gradient increasing, which provided a theoretical basis for further understanding of the relationship between the microbial community and soil carbon cycle in the plateau mountain ecosystem under the background of climate change.

Simulated warming reduced greenhouse gas emissions by lowering soil moisture in a Pinus tabulaeformis forest of the temperate zone

The forest soil carbon represents the largest carbon pool in the terrestrial ecosystem. To clarify the effect of climate warming on the soil carbon pool of a Pinus tabulaeformis plantation in the northern temperate zone, an Open-Top Chamber was used to study the effects of warming on soil temperature and moisture, soil enzyme activity, soil active organic carbon, and greenhouse gas emissions in different soil layers. The results showed that (1) warming increased the temperature and decreased the moisture content of the atmosphere and soil. Atmospheric temperature increased by 0.9°C on average, and atmospheric moisture decreased by 0.05%. (2) Warming had no significant effect on soil active organic carbon or enzyme activity, but had a significant effect on the active organic carbon content and enzyme activity in individual soil layers in individual months. (3) Warming reduced soil CO2 emissions from the control treatment, from 996.35 to 781.57 g·m−2. The soil of the P. tabulaeformis forest in Daqing Mountain is a sink of atmospheric CH4. Therefore, after the short-term warming treatment, the soil moisture was reduced; greenhouse gas emissions were significantly reduced, and the warming formed a negative feedback with soil greenhouse gas flux.

Spatial variations of annual net ecosystem productivity and its trend over Chinese terrestrial ecosystems based on spatial downscaling.

Annual net ecosystem productivity (NEP), the amount of net carbon sequestration during a year, serves as the basis of terrestrial carbon sink. Quantifying the spatial variations of NEP and its trend would enhance our understandings on the response and adaption of ecosystems to environmental change, which also serves for the regional carbon management targeting at carbon neutrality. Based on process-based model and data-driven model simulating NEP, we selected the optimal simulating NEP mostly representing NEP spatial variations with multiple site eddy covariance measurements to develop the spatial downscaling method and generate high resolution NEP data of China, which was used to examine the spatial variations of NEP and its trend and driving factors during 2000-2017. Compared with process-based model results, data-driven model simulating NEP could mostly represent the spatial variation of site measurements. The random forest regression based on climate, soil, and biological data combining with the simple scaling could successfully downscale NEP to a high spatial resolution. From 2000 to 2017, the total amount of NEP in China was (1.30±0.03) Pg C·a-1, showing a decreasing-increasing pattern with the inflection point in 2009. Chinese NEP decreased from southeast to northwest, showing a descending latitudinal distribution and an ascending longitudinal distribution, with the combined effects of climate and biotic factors. NEP trend decreased from east towards west, which was only accompanied with a slightly ascending longitudinal distribution, while photosynthetically active radiation and soil organic carbon content dominated the spatial variations of NEP trend. Therefore, the spatial patterns of generated NEP obviously differed from those of NEP trend, suggesting the obvious difference between the responses and adaptions of ecosystems to environmental changes.

Effects of Replacing Chemical Nitrogen Fertilizer with Organic Fertilizer on Active Organic Carbon Fractions, Enzyme Activities, and Crop Yield in Yellow Soil

Taking the typical yellow soil in Guizhou as the research object, four treatments were set up： no fertilization （CK）, single application of chemical fertilizer （NP）, 50% organic fertilizer instead of chemical nitrogen fertilizer [1/2（NPM）], and 100% organic fertilizer instead of chemical nitrogen fertilizer （M）. The effects of organic fertilizer instead of chemical nitrogen fertilizer on organic carbon and its active components, soil carbon pool management index, soil enzyme activity, and maize and soybean yield in yellow soil were studied in order to provide theoretical basis for scientific fertilization and soil quality improvement in this area. The results showed that the replacement of chemical nitrogen fertilizer by organic fertilizer significantly increased soil pH, organic carbon （SOC）, total nitrogen （TN） content, and C/N ratio. Compared with those in the CK and NP treatments, the content and distribution ratio of soil active organic carbon components and soil carbon pool management index （CPMI） were improved by replacing chemical nitrogen fertilizer with organic fertilizer, and the effect of replacing chemical nitrogen fertilizer with 50% organic fertilizer was the best. Compared with those in the NP treatment, the 1/2 （NPM） treatment significantly increased the contents of soil readily oxidizable organic carbon （ROC333, ROC167）, dissolved organic carbon （DOC）, and microbial biomass carbon （MBC） by 22.90%, 8.10%, 29.32%, and 23.22%, respectively. Compared with those under the CK and NP treatments, organic fertilizer instead of chemical nitrogen fertilizer increased soil enzyme activities. The activities of catalase, urease, sucrase, and phosphatase in the 1/2 （NPM） treatment were significantly increased by 21.89%, 8.24%, 34.91%, and 18.78%, respectively, compared with those in the NP treatment. Compared with that of the NP treatment, the maize yield of the 1/2 （NPM） and M treatments was significantly increased by 44.15% and 17.39%, respectively. There was no significant difference in soybean yield among different fertilization treatments. Correlation analysis showed that soil SOC was significantly positively correlated with ROC333, ROC167, ROC33, DOC, MBC, and soil active organic carbon components, and CPMI was significantly positively correlated with soil organic carbon and its active components （P<0.01）. Corn yield was significantly positively correlated with soil enzyme activity, CPMI, total organic carbon, and its active components （P<0.05）. Therefore, from the perspective of yield increase and soil fertility, 50% organic fertilizer instead of chemical nitrogen fertilizer was conducive to improving soil quality and soil fertility, which is the key fertilization technology to achieve a high yield of crops in the yellow soil area of Anshun, Guizhou.

Assessing flood-depth effects on water quality, nutrient uptake, carbon sequestration, and rice yield cultivated on Histosols

In the Everglades Agricultural Area (EAA), Florida, cultivating rice in flooded paddies is becoming increasingly popular to conserve water and soil health. Flood depth is a critical factor affecting the discharged water quality, soil carbon, and yield production. However, few studies have comprehensively investigated the optimal flood depth in EAA, considering multi-functional indices. To address this gap, we investigated drainage water quality, water quantity, nutrient uptake, soil carbon, and rice yield in rice paddies in histosol soils over a two-year period at four flood depths (5, 10, 15, and 20 ​cm). For each flood depth, averaged over two years, total outflow loadings of suspended solids, nitrogen, phosphorus, and potassium were significantly reduced by 40 ​%, 38 ​%, 36 ​%, and 32 ​%, respectively, compared to inflow water loadings (p ​< ​0.001). Soil organic carbon (SOC) in 5, 10, 15, and 20 ​cm flood treatments increased annually at a rate of 3.85 ​%, 5.64 ​%, 6.86 ​%, and 6.86 ​%, respectively; for these same treatments, soil active organic carbon (AOC) decreased annually at rates of 11.75 ​%, 8.63 ​%, 20.07 ​%, and 8.48 ​%, and rice grain yield was 4488, 5103, 5450, and 5386 ​kg ​ha−1, respectively. Overall, considering the water quality, SOC, AOC, and rice yield production, irrigating rice paddies at a flood depth of 15 ​cm most effectively improves water quality, increases carbon sequestration, reduces active carbon, and yields more rice than other flood depths. By evaluating the effects of flood depth on the soil–water–plant nexus in a holistic manner, we propose a more sustainable and environmentally friendly mode of rice cultivation within the EAA.

Short-term effects of irrigation and nitrogen management on paddy soil carbon pools under deep placement of basal fertilizer nitrogen

Active soil organic carbon (SOC) fractions are major driving factors of soil fertility. Understanding the effects of water and fertilizer management on changes in active SOC fractions helps improve soil quality and maintain high agricultural productivity. We conducted a 3-year field experiment in Northeast China. In this experiment, natural soil (CKT) was used as a blank, and two irrigation regimes were established: conventional flooded irrigation (FI) and controlled irrigation (CI). Four nitrogen application levels were set for both irrigation regimes under deep placement of basal fertilizer N: Nd0 (0 kg ha–1), Nd (110 kg ha–1), Nd1 (99 kg ha–1), and Nd2 (88 kg ha–1). After 3 years, at similar N fertilizer application rate, the rice yield, total organic carbon (TOC), and active SOC fraction content of CI were higher under CI than FI. The growth rate of rice yield was 3.8% − 8.63% under CI than FI. Under CI, the rice yield, active SOC fractions contents and carbon pool management index (CPMI) did not decrease with decreasing N application rate but instead reached the highest level in the CNd1 treatment. Overall, CI with Nd1 treatment appears to be the best practice for improving soil fertility and crop productivity in Northeast China.

Microbial transformation mechanisms of particulate organic carbon to mineral-associated organic carbon at the chemical molecular level: Highlighting the effects of ambient temperature and soil moisture

Soil dissolved organic matter (DOM), an important component of active soil organic carbon (C), plays a crucial role in controlling C transformation. However, the role of DOM in mediating the conversion of particulate organic C (POC) into mineral-associated organic C (MAOC) at the molecular level remains unclear. In this study, the microbial conversion of POC to MAOC at the molecular level was investigated at different ambient temperatures and soil moisture levels. An increase in ambient temperature led to the conversion of POC to labile C, whereas MAOC increased with soil moisture. CHO, CHNO, and CHOS increased with soil moisture and temperature. The highest temperature (35 °C) promoted conversion of lignin/cram (carboxyl-rich alicyclic molecules)-like molecules into aromatic components with the highest intragroup transformation of DOM (74%). The highest soil moisture (60%) favoured the conversion of refractory substances into aliphatic/peptide and lipid components with the highest intergroup transformation (28%). Compared to fungi, bacteria were the main driving force for DOM transformation. Therefore, changes in ambient temperature and soil moisture control the microbial formation and transformation of different C fractions (i.e. POC and MAOC) via DOM differently at the molecular level.

Active Soil Organic Carbon Pools Decrease with Increased Time since Land-Use Transition from Rice Paddy Cultivation to Areca Nut Plantations under the Long-Term Application of Inorganic Fertilizer

Many croplands in the tropics of China have been converted over the last decades into areca nut plantations due to their high economic returns. This land-use transition was accompanied by changes in agricultural practices such as soil moisture regimes and fertilizer inputs, which may affect soil organic carbon (SOC) and its fractions, especially in tropical soils with low fertility and high nitrogen loss. Yet, how the time since land-use transition from rice paddy cultivation to areca nut plantations affects soil carbon dynamics and their underlying mechanisms in the tropics of China remains elusive. Here, areca nut plantation soils with different ages (2, 5, 10, 14, and 17 years) and paddy fields in the tropical region of China were investigated. The study result indicates that the contents of dissolved organic carbon (DOC), particulate organic carbon (POC), easily oxidized organic carbon (EOC), light organic carbon (LFOC), and microbial biomass carbon (MBC) decreased significantly with increased time since land-use transition from rice paddy cultivation to areca nut plantations. Similarly, the ratios of DOC/SOC, MBC/SOC, POC/SOC, LFOC/SOC, and EOC/SOC decreased significantly with increased time since land-use transition. Compared with the paddy soil, the carbon pool management index decreased by 36.6–76.7% under the areca nut plantations, concluding that increasing the time since land-use transition from rice paddy cultivation to areca nut plantations with high application rates of chemical fertilizers resulted in reduced soil active carbon fractions and SOC supply capacity. Therefore, agricultural practices such as the use of organic fertilizers should be applied to improve the soil’s ability to supply organic carbon in managed plantation ecosystems in the tropics of China.

Effects of nitrogen addition on soil active organic carbon in a temperate grassland of Nei Mongol, China

Effects of nitrogen addition on soil active organic carbon in a temperate grassland of Nei Mongol, China

Soil active organic carbon and carbon management index in different land use types

Permanganate oxidized organic carbon (POXC) is used as a standardized methodology for the determination of labile carbon due to its correlation with other soil labile fractions, high accuracy, and practical application. The main goals of this study were to assess labile carbon in the soil across different types of land use and establish the Carbon Management Index (CMI), which is a numerical index that evaluates the carbon status of soil in a given area and is derived from the outcomes of POXC analysis. The study was carried out in the Bukhmurun soum of Uvs province. Soil samples were collected from riverbeds, pastures, and forests at a depth of 0-20 and 20-40 cm, and analyzed for the physical and chemical properties of the soil following the standard methods, and labile carbon was determined using international methods in the Soil Laboratory of the Institute of Geography and Geoecology. According to the results, soil organic carbon (SOC) was detected in all samples and ranged between 9.4 and 73.2 g kg-1, with the highest value in forest soil and the lowest value in grassland soil. It was found that the POXC had a strong correlation (R2=0.62) with SOC. POXC exhibited a similar pattern as the SOC, it was highest in the forest soil, followed by alluvial and grassland soils. The percentage of the POXC ranged from 1.7% to 20% of the SOC. The CMI value varied with the depth. At the depth of 0-20 cm, it was 216 in forest soil, 192 in alluvial soil, and 83 in pasture soil, whereas, at the depth of 20-40 cm, it was 156 in forest soil, 129 in alluvial soil, and 73 in pasture soil. The CMI provides an assessment of how effectively soils are sequestered and storing carbon, as well as how susceptible they are to carbon loss. POXC is a relatively new and inexpensive method for determining labile organic carbon that is less harmful and can be executed without the need for special equipment such as centrifuges. This method of POXC determination is of practical importance in predicting soil quality or determining soil quality by the color change of the permanganate solution after soil-solution interaction. It is deemed prudent to employ this method further for the comprehensive assessment of soil quality. Газар ашиглалтын янз бүрийн хэлбэрүүд дэх хөрсний идэвхтэй органик нүүрстөрөгч ба нүүрстөрөгчийн менежментийн индекс Перманганатаар исэлдүүлсэн органик нүүрстөрөгчийг (POXC) хөрсний бусад хөдөлгөөнт фракцтай харилцан хамааралтай, нарийвчлал сайтай, практикт ашиглаж болохуйц учир хөдөлгөөнт нүүрстөрөгчийг тодорхойлох стандарт арга болгон ашигладаг. Энэхүү судалгааны ажлын зорилго нь хөрсний хөдөлгөөнт нүүрстөрөгчийг газар ашиглалтын өөр хэлбэрүүдэд тодорхойлоход оршино. Судалгааны зорилгын хүрээнд нүүрстөрөгчийн менежментийн индекс (CMI) бодох зорилт тавьсан. CMI нь тухайн газар нутгийн хөрсний нүүрстөрөгчийн төлөв байдлыг үнэлдэг тоон үзүүлэлт бөгөөд POXC шинжилгээний дүнгээс бодож гаргадаг. Судалгааны талбайгаар Увс аймгийн Бөхмөрөн сумыг сонгон авлаа. Хөрсний дээжийг голын татам, бэлчээр, ойгоос 0-20, 20-40 см гүнээс авч Газарзүй, геоэкологийн хүрээлэнгийн хөрсний лабораторид хөрсний физик, химийн шинж чанарыг стандарт аргуудаар, хөдөлгөөнт нүүрстөрөгчийг олон улсын аргаар тодорхойлсон. Хөрсний органик нүүрстөрөгч (SOC) нь нийт хөрсөнд 9.4-73.2 г кг-1 хооронд агуулагдаж, ойн хөрсөнд хамгийн их, бэлчээрийн хөрсөнд хамгийн бага байна. Бидний судалгаагаар POXC нь хөрсний SOC хэмжээтэй хүчтэй хамааралтай (R2=0.62) байсан. Иймээс POXC нь SOC –ийн адил ойн хөрсөнд хамгийн их, дараа нь голын татам, бэлчээрийн хөрсөнд хамгийн бага байна. POXC нь нийт органик нүүрстөрөгчийн 1.7-20%-ийг эзэлж байна. CMI нь 0-20 см гүнд ойн хөрсөнд 216, голын татмын хөрсөнд 192, бэлчээрийн хөрсөнд 83 , харин 20-40 см гүнд ойн хөрсөнд 156, голын татмын хөрсөнд 129, бэлчээрийн хөрсөнд 73 тус тус байна. Нүүрстөрөгчийн менежментийн индекс нь хөрс нүүрстөрөгчийг хэр үр дүнтэй шингээж, хадгалж байгааг, мөн нүүрстөрөгчийн алдагдалд хэр өртөмтгий болохыг үнэлэх боломжийг өгдөг. POXC нь хөдөлгөөнт органик нүүрстөрөгчийг тодорхойлдог хор хөнөөл багатай, центрифуг зэрэг тусгай багаж хэрэглэхгүйгээр хийж болдог харьцангуй шинэ хямд арга юм. POXC тодорхойлох энэ арга нь хөрсний чанарыг урьдчилан таамаглах буюу хөрс уусмал харилцан урвалд орсны дараа перманганатын өнгөөр хөрсний чанарыг тодорхойлох бололцоо олгодог практик ач холбогдолтой. Хөрсний чанарыг тодорхойлоход цаашид ашиглах нь зүйтэй юм гэж үзэж байна. Түлхүүр үгс: Хөрсний органик нүүрстөрөгч, Перманганатаар исэлдүүлсэн органик нүүрстөрөгч, нүүрстөрөгчийн менежментийн индекс

Variations in Soil Organic Carbon Fractions and Microbial Community in Rice Fields under an Integrated Cropping System

Combining rice cultivation and aquaculture into an integrated cropping system is a management approach that enhances the sustainability of rice fields. However, how soil characteristics influence soil microbial community characteristics following implementation of such an integrated system, particularly in the waterlogged paddies of the Pearl River Delta, is poorly understood. An integrated cropping system (rice–fish–duck integrated cropping system, RFD) and a rice–pepper rotation system (RPS) were compared using a conventional rice cropping system (CRS) as a reference. We used phospholipid-derived fatty acid (PLFA) analysis to assess soil microbial community structure and function and measured soil nutrient content and organic carbon fractions. Our results indicated that the soil nutrient content, organic carbon fractions, and C-hydrolyzing activities differed among the cropping systems. The RFD resulted in higher microbial PLFA concentrations and a lower ratio of Gram-positive to Gram-negative bacteria than CRS. Additionally, the integrated system reduced microbial nutrient stress by increasing soil pH. Further analysis revealed that active soil organic carbon significantly affected the soil microbial community. Thus, the RFD integrated cropping systems that alter the combined actions of pH and active organic carbon fractions can be used to improve soil microbial communities.

Reproducibility of Rock-Eval® thermal analysis for soil organic matter characterization

Rock-Eval® (RE) is a thermal analysis technique increasingly used to characterise soil organic matter. To interpret the results, particularly when investigating differences between samples, it is necessary to know the expected ranges of analytical error associated with the RE measurements. Moreover, the RE analyzer is now at its seventh version (RE7) while most literature results were produced using the previous version (RE6). Thus, a characterization of the reproducibility of RE measurements is necessary. We measured the reproducibility of RE measurements using fifteen samples from French croplands and forests that were analysed on five different RE instruments, located in different laboratories and belonging to both generations RE6 and RE7. From each RE analysis, we extracted RE parameters commonly used for soil organic matter characterization and we performed the prediction of the active and stable soil organic carbon fractions using a machine learning model (PartySOC) that uses RE parameters. We obtained a measure of the expected relative errors in RE parameters and PartySOC predictions per instrument, across instruments of the same generation and across generations. We found that the parameters total organic carbon (TOC), mineral carbon (MinC) and R-index are well reproducible, even across the RE6 and RE7 generations. Instead, the hydrogen index (HI) and oxygen index (OI) are more sensitive to signal variations, even within the same generation, especially when TOC is low. The PartySOC predictions were well reproducible across RE6 instruments but not across RE generations. In the future, the results of this study will help discriminate relevant differences between soil samples characterised using RE thermal analysis.

Frozen carbon is gradually thawing: Assessing interannual dynamics of thawed soil organic carbon stocks in the Tibetan Plateau permafrost area from 1901−2020

Large amounts of frozen carbon stored in the permafrost of the Tibetan Plateau (TP) are gradually thawing due to climate warming. The thaw of frozen carbon allows more active soil organic carbon (SOC) on the TP to participate in the global carbon cycle, which has usually been neglected in previous studies of permafrost carbon. This paper assesses the thawed SOC stock and its historical dynamics in TP permafrost areas based on a data-driven scheme. The results show that the current permafrost area of the TP is 1.14 × 106 km2, and the SOC stock in the top 10 m of permafrost areas is 47.36 Pg. The active layer of the TP permafrost has a regional average thickness of 2.37 m during the baseline period (2000−2020), storing 18.19 Pg of SOC, accounting for about 38.4 % of the total SOC stock in the top 10 m, with the remaining more than 60 % perennially frozen in permafrost. The dynamics of thawed SOC are calculated based on baseline period SOC pools. Despite significant fluctuations, there is a general trend of 0.074 Pg SOC thaw per decade over 1901−2020 as the active layer has deepened. Significantly, the thaw trend of frozen SOC after 1976 is more prominent, reaching 0.420 Pg decade−1. Moreover, this paper reconstructs the SOC pool at the beginning of the last century by incorporating historical deep carbon emissions (1 − 10 m) in the current SOC pool. It recalculates the thaw trend of frozen carbon based on this and finds that the general thaw trend of SOC from 1901−2020 is more significant, with a rate of 0.092 Pg decade−1. Additionally, the dynamics of SOC pools in surface soils (0 − 1 m) of TP permafrost areas are also discussed. Our study highlights the importance of permafrost carbon thaw and provides valuable information for TP carbon studies.

Effects of Long-term Combined Application of Organic and Inorganic Fertilizers on Soil Carbon Pool and Greenhouse Gas Emissions in Orchards

Applying organic fertilizer can increase the contents of soil organic carbon (SOC) and active organic carbon, which are crucial for strengthening soil quality and fertility. Four treatments were established:no fertilization (CK), single application of organic fertilizer (M), single application of chemical fertilizer (NPK), and combined application of organic and inorganic fertilizers (MNPK). The changes in SOC and active components under long-term combined application of organic and inorganic fertilizers were investigated, as were the effects of various fertilization measures on greenhouse gas emissions. Moreover, we evaluated the variation in the soil carbon pool management index (CPMI). Total organic carbon (TOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), easily oxidized organic carbon (EOC), and particulate organic carbon (POC) increased by 82.84%, 66.30%, 21.12%, 93.28%, and 145.80%, respectively, when compared to those in the CK treatment. The NPK treatment had no discernible effect on SOC and organic carbon components. The combined application of organic and inorganic materials could enhance LI, CPI, and the soil carbon pool management index, with the increase in LI and CPI being the primary reason for the increase in CPMI. Correlation analyses revealed that soil organic carbon components and CPMI were significantly positively correlated with greenhouse gas emissions. The combined application of organic and inorganic materials enhanced cumulative CO2 emissions and warming potential (GWP) but decreased GHGI and yielded a maximum of 56365 kg·hm-2. Compared with that in the CK treatment (29073 kg·hm-2), apple yield in MNPK increased by 93.87%. Therefore, applying organic and inorganic fertilizers in dryland apple orchards can improve the accumulation of organic carbon and stabilize the soil carbon pool, which is more beneficial to the sustainable development of orchards.

Effects of Short-term Nitrogen Addition on Soil Organic Carbon Components in Robinia pseudoacacia L. Plantation

Nitrogen (N) deposition in the context of human activities continuously affects the carbon cycle of ecosystems. The effect of N deposition on soil organic carbon is related to the differential responses of different carbon fractions. To investigate the changes in soil organic carbon fraction and its influencing factors in the context of short-term N deposition, four N addition gradients:0 (CK), 1.5 (N1), 3 (N2), and 6 (N3) g·(m2·a)-1 were set up in acacia plantations based on field N addition experiments, and the soil physicochemical properties, microbial biomass, and enzyme activities were measured in June and September. The results showed that:① exogenous N input reduced soil pH, promoted the increase in soluble organic carbon content, and increased soil nitrogen effectiveness. ② Short-term N addition significantly reduced soil organic carbon content, and the response of each component of organic carbon to N addition was different. Among them, the content of easily oxidized organic carbon was significantly reduced and reached the lowest value under the N2 treatment, with 54.4% and 48.2% reduction compared with that of the control, respectively, and the content of inert organic carbon increased, although the increase was not significant. Nitrogen addition reduced the soil carbon pool activity and improved the stability of the soil carbon pool. Soil carbon pool activity reached its lowest under the N3 and N2 treatments, with a decrease of 53.3% and 52.80%, respectively, compared to that of the control. ③Random forest modeling indicated that the soil microbial biomass stoichiometry ratio, microbial biomass carbon, and AP were the key factors driving the changes in soil organic carbon activity under short-term N addition, explaining 65.96% and 66.68% of the changes in oxidizable organic carbon and inert organic carbon, respectively. Structural equation modeling validated the results of the random forest modeling, and soil microbial biomass stoichiometric ratios significantly influenced carbon pool activity. Short-term nitrogen addition changed soil microbial biomass and its stoichiometric ratio in the acacia plantation forest mainly through two pathways, i.e., increasing soil nitrogen effectiveness and promoting soil acidification and inhibiting extracellular carbon hydrolase activity, thus changing the soil carbon fraction ratio and participating in the soil organic carbon cycling process.

围栏禁牧对滇西北高寒湿地土壤活性有机碳的影响

围栏禁牧对滇西北高寒湿地土壤活性有机碳的影响

Effects of long-term vegetation restoration on soil active organic carbon fractions content and enzyme activities in karst rocky desertification ecosystem of southwest China

Effects of long-term vegetation restoration on soil active organic carbon fractions content and enzyme activities in karst rocky desertification ecosystem of southwest China

Effects of Understory Vegetation Heterogeneity on Soil Organic Carbon Components in Cunninghamia lanceolata Plantation

As one of the important factors affecting forest soil organic carbon stocks, the effect of understory vegetation types on soil organic carbon and its components was explored to provide a theoretical basis for understory vegetation management and sustainable management in plantation forests. In order to determine the characteristics of soil organic carbon and its components under different understory vegetation types in Subtropical Cunninghamia lanceolata plantation, Indocalamus tessellatus, Diplazium donianum and Oreocnide frutescenssp were taken as research objects. The mass fractions of total organic carbon, recalcitrant organic carbon, readily oxidizable organic carbon, microbial biomass carbon and dissolved organic carbon in each soil layer at 0–10, 10–20, 20–40 and 40–60 cm were measured, and the change characteristics of soil organic carbon components were also studied and compared. The results showed that: (1) The mass fractions of total organic carbon, recalcitrant organic carbon, readily oxidizable organic carbon and microbial biomass carbon in the soils of the three understory vegetation types showed significant decreasing trends along the profile, while the mass fraction of dissolved organic carbon in 0–40 cm soil layer was significantly higher than those in 40–60 cm soil layer. (2) The mass fraction of total organic carbon (5.98–20.66 g·kg−1) had no significant difference among understory vegetation types. The mass fraction and proportion of microbial biomass carbon were higher in the 0–60 cm soil layer under cover of Indocalamus tessellatus, and the mass fractions of recalcitrant organic carbon in the 20–40 cm soil layer under Indocalamus tessellatus cover (8.57 g·kg−1) was significantly higher than that of Oreocnide frutescenssp (5.73 g·kg−1). The soil layer of 0–20 cm under the Diplazium donianum community has a higher mass fraction and proportion of readily oxidizable organic carbon. (3) Correlation analysis showed that soil organic carbon and its components were positively correlated with total nitrogen, dissolved total nitrogen, dissolved organic nitrogen and microbial biomass nitrogen. There is a significant positive correlation among the components of soil organic carbon. (4) Redundancy analysis showed that soil bulk density (41.6%), microbial biomass nitrogen (41.2%), dissolved total nitrogen (43.7%), total nitrogen (9.9%), dissolved organic nitrogen (43.6%) and pH (6.6%) were the most significant environmental factors affecting organic carbon components in four soil layers. Understory vegetation type can influence the distribution characteristics of soil organic carbon components in Cunninghamia lanceolata plantation, and soil active organic carbon components are more susceptible to the influence of understory vegetation type than total organic carbon and recalcitrant organic carbon.

Effects of Applying Different Organic Materials on Grain Yield and Soil Fertility in a Double-Season Rice Cropping System

Double-cropping rice cultivation reduces soil fertility, and the extensive use of chemical fertilizers has harmful effects on both the environment and grain yield. The application of organic materials could be used as a practical strategy to maintain soil fertility and improve grain yield in a double-season rice cropping system. For this purpose, field experiments with six growing seasons over three years, from 2016 to 2018, were conducted to assess the effects of five organic materials (biochar, Chinese milk vetch, rice straw, rapeseed cake fertilizer, and manure) on the grain yield and soil fertility, aiming to save about 25% of the chemical nitrogen (N) fertilizer required for all rice growing stages. The result showed that, compared with CK (the most common dose of fertilizer in this study region; 100% chemical fertilizer without organic fertilizer), the grain yield and soil fertility of double-cropped rice were increased after applying organic fertilizers for three consecutive years. Specifically, the CRC treatment (Chinese milk vetch (10.77 t ha−1 in fresh)/rice straw (26.51 t ha−1 in fresh) + 75% chemical fertilizer) showed significantly higher rates of effective panicles (4.65–10.92%) and annual grain yield (8.00–8.82%). The total N, total phosphorus (P), total potassium (K), alkaline N, and available P content in the CRC soil were significantly increased by 11.85%, 12.22%, 15.08%, 23.32%, and 41.04%, respectively, relative to CK. The decomposition of the applied Chinese milk vetch and rice straw combined with 75% chemical fertilizer resulted in more soil humus (9.50 g kg−1), humic acid (3.19 g kg−1), fulvic acid (3.26 g kg−1), and active organic carbon (5.78 g kg−1) and a significantly higher carbon pool management index (13.5%), as well as significantly higher soil urease activity (18.10%) and acid phosphatase activity (17.64%). Therefore, in this study, Chinese milk vetch (10.77 t ha−1 in fresh) in the early rice season/rice straw (26.51 t ha−1 fresh) in the late rice season + 75% chemical fertilizer treatment was the optimal dose for the double-season rice cropping system. It resulted in higher rice yields and has the potential to be used for more sustainable soil fertility.

Effects on soil organic carbon accumulation and mineralization of long-term vegetation restoration in Southwest China karst

Vegetation restoration significantly changes soil organic carbon (SOC) accumulation and mineralization, obviously affects soil carbon pool. To clarifying effects of vegetation restoration on SOC accumulation and mineralization is of great significance in reducing carbon emission and increasing carbon sequestration. In the present study, the effects on SOC accumulation and mineralization of four types of vegetation restoration engineering including seven species planting measures, all carried out for 28–31 years, were studied. Results showed the long-term vegetation restorations had significant effects on SOC accumulation and mineralization. Tree and vine forest construction measures significantly increased total SOC content and reserves, recalcitrant organic carbon content and proportion, and also obviously raised SOC mineralization rate and cumulative mineralization amount. Grassland construction measures significantly reduced total SOC content and reserves, obviously increased the proportion of soil active organic carbon, and also remarkably raised SOC cumulative mineralization proportion. In addition, the long-term vegetation restoration measures significantly changed the temperature sensitivity of SOC mineralization. The long-term vegetation restoration has remarkable effects on SOC mineralization and accumulation in Southwest China karst area. In the restoration, tree and vine forest construction measures should be preferred, and grassland construction measures should not be implemented. The present study results provide theoretical bases for scientific vegetation restoration of degraded karst ecosystems in Southwest China Karst and are of great significances in reducing soil carbon emission and increasing soil carbon sequestration.