Soil Organic Carbon Mineralization Rate Research Articles

Microbial-mediated conversion of soil organic carbon co-regulates the evolution of antibiotic resistance

The influence of organic carbon on the proliferation of antibiotic resistance genes (ARGs) in the soil has been widely documented. However, it is unclear how soil organic carbon (SOC) interacts with the evolution of antibiotic resistance in bacteria. Here, we examined the variations in ARGs abundance during SOC mineralization and explored the microbiological mechanisms and key metabolic pathways involved in their coevolution. The results showed that the SOC mineralization rate was closely correlated with ARGs abundance (p < 0.05). High organic carbon (OC) mineralization was conducive to the occurrence of multidrug resistance genes. For example, multidrug_transporter and mexB increased 2.26 and 7.83 times from the initial level. The competitor (stress) evolutionary strategy model revealed that higher OC inputs drive environmental microorganisms to evolve from stress tolerant to high resistance and strong adaptation. Meta-genomic and transcriptomic analyses revealed that the conversion process of pyruvate to acetyl-CoA to acetate was the critical metabolic pathway for the co-regulation of antibiotic resistance. Gene deletion validation trials have demonstrated that the key functional genes (ackA and pta) involved in this process can modulate the development of vancomycin and multidrug resistance. This outcome provides a preliminary framework for microbial mechanisms that target the co-regulation of microbial OC conversion and the evolution of antibiotic resistance.

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p &lt; 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

Preparation of Mn modified waste dander biochar and its effect on soil carbon sequestration

In order to reduce the mineralization of soil organic carbon (SOC) and enhance the ability of soil carbon sequestration. Mn-modified waste dander biochar (Mn-BC) was successfully prepared via impregnation and pyrolysis, and MnSO4 was formed on its surface. Mn-BC increases the carbon retention and reduces the emissions of CO2 and SO2 in way of forming CO, Mn–O–C bond and MnSO4. At the same time, the stability of the original biochar was reserved due to forming a conjugated structure (CC and pyridine-N bond), and the carbon sequestration content was increased to 25.63%. Importantly, the application of Mn-BC can directly regulate the transformation of microbial bacterial community and lead to create stable carbon dominant bacteria (Firmicutes). And the mineralization rate of SOC is reduced to 0.48 mg CO2/(g·d), together with an increased content of TOC (48.16%), thus the purpose of efficient carbon sequestration is achieved in soil.

Disentangle the drivers of soil organic carbon mineralization and their temperature sensitivity in both topsoil and subsoil: Implication of thermal stability and chemical composition

Information about the temperature dependence of soil organic carbon (SOC) mineralization is important to predict the possible carbon (C) release from the terrestrial ecosystem facing global warming. However, the way in which SOC quality and mineral protection of SOC affects mineralization rates and their response to increasing temperature remains poorly understood. Here, we focused on investigating thermal stability and chemical composition of soils which differed greatly with the type and extent of organo-mineral associations, and revealing their implications for SOC mineralization. Chemical composition and thermal stability of SOC were analyzed with 13C nuclear magnetic resonance spectroscopy (13C NMR) and simultaneous thermogravimeteric analysis and differential scanning calorimetry (TG-DSC), respectively. Soil mineralization and its temperature sensitivity (Q10) were assessed by incubating soils at 15 and 25 °C for 90 days.Our results showed that SOC of subsoil was more biologically stable, but exhibited higher temperature sensitivity than those of topsoil. Significant differences in chemical composition and thermal stability of SOC were detected across soils developed from four parent materials but not between two soil layers, and indicators obtained from the two techniques showed apparent associations with depth-specific SOC mineralization rates. Increase in SOC mineralization rates at two incubation temperatures and two soil layers were observed when the soils were characterized by higher percentage of labile SOC fractions (i.e., O-alkyl C and organic carbon oxidized during exothermic reactions). The Q10 values of topsoil were positively and mostly related to the percentage of Alkyl C. In addition to notable relationships with chemical composition, the Q10 values of subsoil were positively correlated with Exo1/Exo2 ratios and Energy density values, and negatively correlated with TG-50. It was interesting to note that thermal stability was possibly as a function of soil texture and total oxides. Results from VPA analysis further revealed that SOC mineralization rates at two soil layers and Q10 of topsoil were mainly driven by SOC quality, while it was related to both SOC quality and chemical protection for subsoil, implying that factors controlling the temperature sensitivity of SOC mineralization were depth-specific. Altogether, substrate accessibility as a function of chemical composition and chemical protection would play vital role in determining the feedbacks of the subsoil SOC pool to the future climate warming.

Can Plant Nutrient Dynamics and Indian Mustard Yield Be Influenced by Addition of Organic Amendments Under Saline Sodic Soils?

ABSTRACT Arid and semi-arid regions are having huge potential for agricultural production but also have limitations of salinity and alkalinity. By mediating rhizospheric environment with the application of organic and inorganic nutrient sources, Indian mustard yield could be enhanced in these areas. For this, a field experiment was conducted to study the effect of organic (FarmYard Manure and vermicompost) and inorganic (urea) amendments with irrigation water of different sodium absorption ratios (SAR; 6, 10, 20 and 30). The experiment was laid out in a split-plot design (SPD) with 24 treatment combinations keeping different SAR in main plots and organic and inorganic nitrogen sources in sub plots. Experiment results revealed that increasing SAR levels reduced the availability of major plant nutrients, i.e. nitrogen, phosphorus and potassium. The soil organic carbon mineralization rate and Indian mustard seed yield were also deceased with increasing levels of SAR. Application of nitrogen through farm yard manure (FYM) and vermicompost decreased the electrical conductivity (EC), pH, and enhanced the cation exchange capacity (CEC) of soil solution. Application of 50% recommended dose of nitrogen (RDN) through urea and 75% through vermicompost produced maximum seed and stover yield of Indian mustard. Thus, supply of recommended dose of nitrogen as inorganic (50%) and organic (75%) sources improved the soil health and Indian mustard yield of arid lands with sodic irrigation water. The use of organic sources in place of sole application of N fertilizer may be a potential management option in sodic groundwater irrigated areas for enhancing mustard crop yield.

Fe‐modified biochar improved the stability of soil aggregates and organic carbon: Evidence from enzymatic activity and microbial composition

AbstractBiochar modifications are used to improve soil organic carbon (SOC) content, while its effects on soil structure stability and carbon (C) mineralization are less known especially in saline–alkaline soils. A 5 years field experiment was arranged with organic amendments addition in the Yellow River Delta, including (i) NPK, only 255, 56, and 190 kg ha−1 N, P, and K each year, (ii) RS, NPK + rice straw, (iii) BC, NPK + straw‐derived biochar, and (iv) FeBC, NPK + biochar modified with ferric chloride. Relative to NPK treatment, the mean weight diameter was significantly increased with organic amendments addition, which was the highest in FeBC treatment. Meanwhile, SOC content in the soil added with organic amendment was increased by 2%–18%. Compared with the RS and BC, FeBC addition increased the content of stable humin (HU), crystalline Fe oxides (Fed), and amorphous Fe oxides (Feo). There was a positive correlation between HU and Feo/Fed, indicating HU and Fe oxides might form organic mineral complexes to limit SOC biodegradation. While the mineralization rate of SOC in FeBC treatment was decreased by more than 30.4% than that in BC treatment. This might be due to the decrease of soil β‐glucosidase and cellobiohydrolase activities, as well as the abundance of Gammaproteobacteria and Actinobacteria. These results were the mechanism of soil enzyme activity and bacterial community regulating C stability. Therefore, Fe‐modified biochar is a better organic amendment to improve the stability of aggregates structure and SOC in saline–alkaline paddy soil.

Crop diversification effects on soil organic carbon and nitrogen storage and stabilization is mediated by soil management practices in semiarid woody crops

Crop diversification is a promising strategy to mitigate climate change through soil carbon sequestration while ensuring soil fertility maintenance and food security. Here, we assess the impact of different inter-cropping practices on soil organic carbon (SOC) and nitrogen (N) storage and stabilization under rainfed and irrigated semiarid conditions. Under rainfed conditions, an almond (Prunus dulcis Mill.) monocrop was compared with an almond inter-cropped with caper (Capparis spinosa) or with winter thyme (Thymus hyemalis). Under irrigated conditions, a mandarin (Citrus reticulata Blanco) monocrop was compared with a mandarin inter-cropped with an annual crop rotation (including Hordeum vulgare, Vicia sativa and Vicia faba) or with a triennial crop rotation (including Vicia faba, Portulaca oleracea and Vigna unguiculata L.). The SOC and N stocks, SOC mineralization rates, water-stable aggregates and associated OC and N contents were estimated at 0–10 and 10–30 cm depth in each monocrop and inter-cropping system after three years. Contrasting effects of inter-cropping on SOC and N stabilization were found in the rainfed and irrigated systems. The combination of inter-cropping and no tillage did not affect the SOC stocks or mineralization rates at any soil depth in the rainfed system, while it significantly increased the OC and N contents within the large macro-aggregates in the subsoil. Compared to the irrigated mandarin monocrop, the mandarins inter-cropped with the annual crop rotation showed a significant increase of 10% and 18% in the topsoil and subsoil N stocks, respectively, while the SOC mineralization rates were reduced by 30% at both soil depths. On the contrary, the topsoil SOC stock in the mandarins inter-cropped with the triennial crop rotation were reduced by 38% compared to the monocrop. Significant reductions ranging between 24% and 66% were also observed in the OC and N contents associated to the macro- and micro-aggregates in the topsoil and subsoil of both crop diversifications compared to the monocrop system. Our results highlight the potential of inter-cropping rainfed woody crops with perennials for boosting SOC and N storage and stabilization. In irrigated woody monocrops, inter-cropping with annual crop rotation schemes that include two or more leguminous and reducing tillage frequency operations seems to be more appropriate in terms of SOC and N stabilization.

Anthropogenic N input increases global warming potential by awakening the “sleeping” ancient C in deep critical zones

Even a small net increase in soil organic carbon (SOC) mineralization will cause a substantial increase in the atmospheric CO2 concentration. It is widely recognized that the SOC mineralization within deep critical zones (2 to 12m depth) is slower and much less influenced by anthropogenic disturbance when compared to that of surface soil. Here, we showed that 20 years of nitrogen (N) fertilization enriched a deep critical zone with nitrate, almost doubling the SOC mineralization rate. This result was supported by corresponding increases in the expressions of functional genes typical of recalcitrant SOC degradation and enzyme activities. The CO2 released and the SOC had a similar 14C age (6000 to 10,000years before the present). Our results indicate that N fertilization of crops may enhance CO2 emissions from deep critical zones to the atmosphere through a previously disregarded mechanism. This provides another reason for markedly improving N management in fertilized agricultural soils.

Moisture-dependent response of soil carbon mineralization to temperature increases in a karst wetland on the Yunnan-Guizhou Plateau.

Wetlands are facing gradual drying, leading to large carbon loss due to the transformation from anaerobic to aerobic conditions, but the temperature and drought effects from the temperature and moisture fluctuation on soil organic carbon (SOC) mineralization remain uncertain. An incubation study with three moisture levels (100%, 60%, and 40% WHC, marked as W100, W60, and W40, respectively) and four temperature levels (5, 10, 15, 20°C, marked as T5, T10, T15, and T20, respectively) was conducted to determine the effect of temperature and moisture interactions on SOC mineralization in the karst wetland of the Yunnan-Guizhou Plateau. Compared with T5, the cumulative mineralization CO2 in T20 increased by 83.18% (W40), 154.63% (W60), and 148.16% (W100), respectively. The mineralized CO2 at W60 and W40 significantly decreased compared to that at W100 at the four temperature levels. Temperature, moisture and their interactions had significant positive effects on SOC mineralization rates and cumulative mineralized CO2. The temperature sensitivity of SOC mineralization rates (Q10) under W40 and W60 increased by 22.03% and 24.52%, respectively, compared to that under W100. The cumulative mineralized CO2 was positively related to soil urease activity and negatively related to soil pH, N-NH4+, SOM, and catalase activity. Temperature and moisture fluctuation and soil properties explained 85.40% of the variation in SOC mineralization, among which temperature and moisture fluctuation, soil properties, and their interactions explained 19.71%, 4.81%, and 60.88%, respectively. Our results indicated that SOC mineralization is influenced by the joint effect of temperature and drought, as well as their induced changes in soil properties, in which higher temperatures can increase soil CO2 emissions by enhancing the SOC mineralization rate, but the positive effect may be weakened from the drying wetland.

Variations in organic carbon mineralization of the biological soil crusts following revegetation in the Tengger Desert, North China

Revegetation is an effective measure to combat desertification worldwide, which parallelly facilitates the colonization and development of biological soil crusts (BSCs), and thereby affecting C cycles of BSCs in desert regions. However, knowledge about soil organic carbon (SOC) mineralization of BSCs and the involved mechanisms during long-term revegetation process in desert is rather limited. In this study, SOC mineralization rates of the mobile sand dune (MSD) and the BSCs in revegetated sites along chronosequence in the Tengger Desert were investigated, and the relationships between the SOC mineralization and the characteristics of vegetation and BSCs, soil properties and incubation temperature (T) and soil water content (SWC) were analyzed. The results showed that SOC mineralization rate of the BSCs and the corresponding subsoils was significantly greater than those of the MSD, and it increased considerably with increasing site age, regardless of the T, SWC, soil layer and sampling time (p < 0.001). The maximum instantaneous mineralization rates (MIR), cumulative CO2-C release (CCR) and the potentially mineralizable SOC (C0) of BSCs and subsoils were 1.29–12.63, 3.67–23.16 and 3.78–23.41 times, and 0.16–2.26, 0.12–1.84 and 0.17–1.26 times greater than those of the MSD, respectively; while the proportion of C0 to total SOC (C0/SOC) decreased by 31–88 % and 24–72 % in comparison with MSD, respectively. The mineralization rate increased with T and SWC, and the temperature sensitivity of BSCs increased with site age, indicating that the loss of SOC would be accelerated with the succession of BSCs upon the future global change. The variation magnitude of SOC mineralization was largely dependent on revegetation-induced changes in the properties of BSCs and the incubation T and SWC, and their interactions. The C:N, pH, and the activities of POD and PPO and DOC, and the coverage of moss-dominated crusts, SOC, C:N, the content of clay and silt and AYL activity were the main factors affecting SOC mineralization of BSCs and the subsoils, respectively. These results indicated that multiple factors that co-varied with the succession of BSCs led to variable SOC mineralization. Our findings suggested that planting xerophytic shrubs in desert drives the development and the SOC mineralization of BSCs, but decreased SOC loss due to mineralization, leading to SOC sequestration.

Landscape Change Affects Soil Organic Carbon Mineralization and Greenhouse Gas Production in Coastal Wetlands

AbstractPlant invasion and aquaculture activities have drastically modified the landscape of coastal wetlands in many countries, but their impacts on soil organic carbon (SOC) mineralization and greenhouse gas production remain poorly understood. We measured SOC mineralization rate and soil CO2 and CH4 production rates in three habitat types from 21 coastal sites across the tropical and subtropical zones in China: native mudflats (MFs), Spartina alterniflora marshes (SAs), and aquaculture ponds (APs). Landscape change from MFs to SAs or APs increased total and labile fraction of SOC, as well as carbon mineralization rate and greenhouse gas production, but there were no discernible differences in SOC source‐sink dynamics between SAs and APs. SOC mineralization rate was highest in SAs (20.4 μg g−1 d−1), followed by APs (16.9 μg g−1 d−1) and MFs (11.9 μg g−1 d−1), with CO2 as the dominant by‐product. Bioavailable SOC was less than 2% and was turned over within 60 days in all three habitat types. Proliferation of S. alterniflora marshes and expansion of AP construction had resulted in a net increase in soil CO2‐eq production of 0.4–4.3 Tg yr−1 in the last three decades. Future studies will benefit from better census and monitoring of coastal habitats in China, complementary in situ measurements of greenhouse gas emissions, and more sampling in the southern provinces to improve spatial resolution.

Limited Potential for Mineralization of Permafrost Peatland Soil Carbon Following Thermokarst: Evidence From Anoxic Incubation and Priming Experiments

AbstractPermafrost thaw in peatlands risks emitting vast stores of soil organic carbon (SOC) as greenhouse gases to the atmosphere, yet anoxic conditions and low peat quality may prevent rapid SOC loss. To assess differences in anaerobic SOC mineralization following thaw and vulnerability of previously‐frozen peat, we incubated peat (5° and 14°C) from 15 depths of ⁓6 m cores from different thaw sites including an intact permafrost peat plateau and thermokarst bogs that thawed ∼30 and ∼200 years ago. Furthermore, a glucose‐addition experiment after &gt;700 days assessed whether labile C inputs occurring following thermokarst could accelerate SOC mineralization (priming). We found a common pattern of SOC mineralization rate decreasing with depth and peat age. However, we found no differences in peat mineralization rates among sites for samples of similar age and of corresponding peatland developmental stage. Priming effects were minor and short‐term, and did not vary among sites or with peat developmental stage. We also found mineralization rates from anoxic incubations more than an order of magnitude higher than rates implied from field observations, suggesting mineralization rates from anaerobic incubations should be used mainly to interpret relative differences. Peat humification and peat nitrogen and phosphorous content explained more than 85% of the variability in mineralization rates. Peat quality did not influence the temperature sensitivity of peat mineralization. Overall, the absence of substantial priming effects and the lack of differences in mineralization rates between permafrost peat and peat thawed 200 years ago suggests that rapid peatland SOC loss following thaw is unlikely.

Linking soil organic carbon mineralization with soil variables and bacterial communities in a permafrost-affected tussock wetland during laboratory incubation

Microtopography can cause great soil heterogeneity in both abiotic and biotic factors, which leads to different soil organic matter decomposition rates. However, the quantitative effects of soil variables and microbial properties on soil organic carbon (SOC) mineralization in microfeatures in permafrost wetlands largely remain unknown. Here, soil samples of 0–10 cm from hummocks and hollows in a permafrost-affected tussock wetland were collected for laboratory incubation. The results showed that the temperature sensitivities (Q10 value) of SOC mineralization were 3.14 and 2.44 for hummocks and hollows, respectively. After an 80-day laboratory incubation, the microfeatures had no significant effects on the relative abundance of bacteria, but significantly affected bacterial α-diversity (Shannon indices) of soil. The incubation temperature also separated the bacterial community structure of the two microfeatures. Laboratory warming and the microfeatures influenced the SOC mineralization rate by regulating bacterial communities and labile substrates, with a joint contribution of 72 % of the total variances in SOC mineralization. Our study quantified the differences in soil variables, bacterial community indices, and their contribution to SOC mineralization between the two microfeatures in a permafrost-affected wetland, and thus improved our understanding of the microbial processes driving soil carbon cycling in permafrost regions.

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.

The variation in organic carbon mineralization and its temperature sensitivity in soils after long-term planting of different tea varieties

Evaluating soil organic carbon (SOC) mineralization and its temperature sensitivity (Q10) is essential to understand SOC sequestration capacity. However, little is known about the changes in the SOC mineralization process in soils when planting different tea varieties. In the current study, we collected soil samples from a tea plantation planted with four tea varieties (Chuancha No. 3 (CC3), Chuanmu No. 217 (CM217), Chuannong Huangyazao (CN), and C. Sinensis ‘Fuding Dabaicha’ (FD)). SOC mineralization and Q10 were investigated through a 90-day laboratory incubation experiment. The results demonstrated that both SOC mineralization and Q10 were variable among the soils after planting different tea varieties. Overall, CM217 soil had the highest cumulative mineralization amount (Cm), mineralization rate of SOC (Cr), potentially mineralizable carbon (C0), and the proportion of C0 in SOC (C0/SOC) at each incubation temperature, and FD soil had the lowest C0 and C0/SOC. These results indicated that CM217 and FD soil had the lowest and highest SOC sequestration capacity, respectively. This difference was explained by varied SOC stability (SI), which was further dominated by the SOC composition and aggregate distribution. FD soil showed the highest aggregate stabilization index (mean weight diameter, MWD) in both soil layers, accumulated the greatest recalcitrant organic carbon (ROC) and further contributed the highest sequestration capacity. In contrast, the lowest SI of CM217 soil reflected a low SOC sequestration capacity, which would be detrimental to long-term SOC storage and ultimately explained the lowest SOC stock. In addition, the variations in Q10 among the soils planted with different tea varieties were explained by the different mechanisms in the topsoil and subsoil. The varied Q10 in topsoil and subsoil was predominantly explained by semi-labile organic carbon (LOCII) and ROC, respectively, and the contribution of aggregate protection to explain the varied Q10 in subsoil was greater than that in topsoil.

In situ formed CaSO4 on waste dander biochar to inhibit the mineralization of soil organic carbon

In order to reduce CO2 emissions, as well as realize the resource utilization of waste dander (WD) and the goal of international “peak carbon dioxide emissions” and “carbon neutrality”, Biochar was prepared with WD via pyrolysis technology, achieving CaSO4 in situ generated on its surface, which could be used to inhibit soil organic carbon (SOC) from mineralizing and enhance soil carbon sequestration ability. The characterization results showed that the unstable carbon (C) structures as well as more conjugated structures were generated on Ca-BC, obtaining an increased C sequestration of Ca-BC to 21.70 %. With the application of Ca-BC, the mineralization rate of SOC was reduced to 0.451 mg CO2/(g·d), and the soil moisture content, pH and TOC content were increased to 45.48 %, 7.96 and 47.19 %. In addition, the bioinformatics analysis and redundancy analysis revealed that the application of Ca-BC promoted bacteria to convert into the stable C-dominant phyla (Firmicutes).

Revegetation enhances soil organic carbon mineralization and its temperature sensitivity in the Tengger Desert, North China

Revegetation plays a critical role in the soil organic carbon (SOC) cycle, especially in desert regions. However, the effects of this restoration practice on SOC mineralization are poorly understood, which inhibit the accurate estimation of SOC sequestration. In this study, SOC mineralization rates in revegetated sites along a chronosequence in the Tengger Desert were investigated by the incubation method, and the relationships between SOC mineralization rate and the temperature (T) and soil moisture (SM) of incubation, soil properties and vegetation characteristics were analyzed. The results showed that SOC mineralization rates and its temperature sensitivity (Q10) significantly increased after revegetation. The maximum CO2-C emission rates (MR), cumulative CO2-C emissions (CCE), potentially mineralizable SOC (C0) and Q10 increased by 0.04–5.62, 0.78–4.88, 0.94–4.04 and 0.37–0.47 times in 64 years following revegetation, respectively, while the proportion of C0 to total SOC (C0/SOC) decreased by 2.12–7.22 times. T and SM and their interaction had significant influences on MR, CCE, C0 and C0/SOC, while SM had no significant effect on Q10. The stepwise multiple linear regression analysis showed that the SOC mineralization rate had greater R2 with stand age and smaller R2 with SM, indicating that the SOC mineralization was mainly regulated by the stand age. The SEMs indicated that the soil properties were the main direct factors affecting SOC mineralization. The RDA indicated that soil AP, C:N ratio and T were the key factors controlling SOC mineralization during the revegetation process. Our findings indicated that long-term revegetation in desert regions enhanced SOC transformation and its temperature sensitivity, but decreased the percentage of CO2-C loss from soil, thus leading to SOC accumulation.

Tree species mixing enhances rhizosphere soil organic carbon mineralization of conifers in subtropical plantations

Tree species mixing is a prevalent practice to improve soil quality in monoculture plantations and the rhizosphere soil organic carbon (SOC) dynamics of conifers will be affected by mixing the species with broad-leaved trees; however, the influence characteristics and underlying mechanism of mixing on rhizosphere SOC mineralization remain elusive. Herein, the rhizosphere soils of two conifers (Pinus massoniana and Pinus elliottii) from pure and mixed plantations were incubated for 50 days. Bacterial communities were investigated by high-throughput sequencing and qPCR of the 16S rRNA gene. The SOC quality represented by carbon functional groups was analyzed using a Fourier transform infrared spectrometer. A higher rhizosphere SOC quality of conifers, particularly the lower ratios of aromatic/aliphatic compounds and (aromatic + aliphatic compounds)/polysaccharide, was found in the mixed plantation compared to the pure plantation. Mixing increased the relative abundance of the conifer rhizosphere copiotrophic bacteria (Proteobacteria and Bacteroidetes) and led to an increase in the bacterial copiotroph:oligotroph ratio. The redundancy analysis showed that the aromatic/aliphatic compound ratio was the predominant factor that significantly affected the soil bacterial communities. The rhizosphere SOC mineralization rate increased after mixing and had a positive relationship with copiotrophic bacteria and the bacterial copiotroph:oligotroph ratio. Our analyses indicate that planting broad-leaved trees in coniferous plantations increases organic carbon mineralization from the rhizosphere soil of conifers and provide potential driving patterns of SOC mineralization related to SOC quality and bacterial life strategy.

Effects of Organic Fertilizer Replacing Chemical Fertilizer on Organic Carbon Mineralization and Active Organic Carbon in Dryland Yellow Soil

At present, the effect characteristics and mechanism of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil remain unclear. In order to explore the effect of organic fertilizer replacing chemical fertilizer on organic carbon mineralization and active organic carbon in dryland yellow soil, we used soil with no fertilization (CK), only chemical fertilizer (NP), 50% organic fertilizer replacing chemical fertilizer (1/2(NPM)), and 100% organic fertilizer replacing chemical fertilizer (M). We examined the indoor mineralization culture of organic carbon and explored the characteristics of soil organic carbon and the change in active organic carbon under the condition of organic fertilizer replacing chemical fertilizer. The results showed that organic fertilizer replacing chemical fertilizer increased soil pH, organic carbon (SOC), total nitrogen (TN), and C/N. During the culture period, the soil organic carbon mineralization rate of all treatments decreased sharply in the initial stage (2-4 days), decreased slightly in the middle stage (4-20 days), and tended to be stable in the last stage (20-60 days). After fertilization, the cumulative mineralization of soil organic carbon significantly increased by 7.9%-27.7%. Compared with that in the NP treatment, the cumulative mineralization of soil organic carbon decreased by 5.2% in the 1/2(NPM) treatment and increased by 12.2% in the 1/2(NPM) treatment. Before mineralization culture, the substitution of organic fertilizer for chemical fertilizer had no significant effect on soil recalcitrant organic carbon (ROC) but significantly increased the content of microbial biomass carbon (MBC). The content of dissolved organic carbon (DOC) was significantly increased in the 1/2(NPM) treatment and decreased in the M treatment. After 60 days of culture, the content of soil active organic carbon in all treatments decreased compared with the initial content, of which MBC decreased the most (30.6%-41.2%). The accumulated mineralization of organic carbon was significantly positively correlated with soil pH and SOC and significantly positively correlated with the initial value of MBC and the change value before and after culture. To summarize, 100% organic fertilizer replacing chemical fertilizer significantly promoted soil organic carbon mineralization and reduced soil organic carbon stability; 50% organic fertilizer replacing chemical fertilizer inhibited soil organic carbon mineralization, which was beneficial to soil sequestration and fertilization; and 50% organic fertilizer replacing chemical fertilizer significantly increased soil active organic carbon content, and MBC was used as the main carbon source in the process of soil organic carbon mineralization.

Biochar addition stabilized soil carbon sequestration by reducing temperature sensitivity of mineralization and altering the microbial community in a greenhouse vegetable field

Biochar is widely used for soil carbon sequestration and fertility improvement. However, the effects of biochar interacted with nitrogen (N) on the mineralization of soil organic carbon (SOC) and microbial community have not been thoroughly understood, particularly no reports have been published on the long term effects of biochar in vegetable field. Here, we examined soil properties, SOC mineralization and microbial community affecting by biochar (0, 20 and 40 t ha−1; C0, C1 and C2, respectively), N (0 or 240 t ha−1; N0 or N1, respectively) and their interaction in a greenhouse vegetable field. Results indicated that biochar addition increased soil pH, SOC, recalcitrant C pool, especially for the 40 t ha−1 treatment. Biochar addition generally decreased soil C-cycling enzyme activity while increasing N and P-cycling enzyme and oxidase activities. Biochar combined with N addition reduced SOC mineralization rate and metabolic quotient (qCO2) by 10.2–22.0% and 6.85–30.4%, respectively, across 15–35 °C and the temperature sensitivity (Q10) by 0.96–4.70%, except for the N1C2 at 25–35 °C. Apparent changes in bacterial alpha diversity and community structures were observed among treatments. Besides, biochar mixed with N application significantly enhanced the relative abundance of Proteobacteria and decreased Acidobacteria, while did not result in significant differences in fungal diversity and community composition. Redundancy analysis indicated that the microbial community composition shifts induced by the interaction between N and biochar were attributed to the changes in soil chemical properties, such as pH and SOC. Overall, the combination of biochar and N fertilizer is recommended to improve SOC sequestration potential and regulate bacterial community diversity and composition in vegetable field for sustainable intensification.