Labile Carbon Pools Research Articles

How Do Mixed Cover Crops (White Mustard + Oats) Contribute to Labile Carbon Pools in an Organic Cropping System in Serbia?

Sustainable farming is one of the priority goals of the "4 per 1000" concept with regard to the preservation of soil fertility and carbon sequestration. This paper presents a study on the use of a mixture of cover crops of self-grown oats (Avena sativa L.) and sown white mustard (Sinapis alba L.) in organic farming under the agroecological conditions of Serbia. The main objective was to identify sensitive carbon pools (microbial carbon and nitrogen, basal respiration and a number of specific groups of soil microorganisms) in organic farming with and without cover crops. The inclusion of a mixture of white mustard and self-grown oats as a cover crop led to a significantly increased biogenity of the soil compared to a control after only a few years of investigation. The number of microorganisms, soil respiration and microbial biomass carbon were significantly higher in the cover crop treatment compared to the control soil on an organic farm in Serbia. This is the first study in Serbia to investigate the effect of self-grown oats as a cover crop. Further research will incorporate a wider range of variables and factors in order to develop a sustainable and effective site-specific system for organic crop production in Serbia.

Effects of Understory Vegetation Conversion on Soil Greenhouse Gas Emissions and Soil C and N Pools in Chinese Hickory Plantation Forests

Forest management, especially understory vegetation conversion, significantly affects soil greenhouse gas (GHG) emissions and soil C and N pools. However, it remains unclear what effect renovating understory vegetation has on GHG emissions and soil C and N pools in plantations. This study investigates the impact of renovating understory vegetation on these factors in Chinese hickory (Carya cathayensis Sarg) plantation forests. Different understory renovation modes were used in a 12-month field experiment: a safflower camellia (SC) (Camellia chekiangoleosa Hu) planting density of 600 plants ha−1 and wild rape (WR) (Brassica napus L.) strip sowing (UM1); SC 600 plants ha−1 and WR scatter sowing (UM2); SC 1200 plants ha−1 and WR strip sowing (UM3); SC 1200 plants ha−1 and WR scatter sowing (UM4); and removal of the understory vegetation layer (CK). The results showed that understory vegetation modification significantly increased soil CO2 and emission fluxes and decreased soil CH4 uptake fluxes (p < 0.01). The understory vegetation transformation significantly improved soil labile carbon and labile nitrogen pools (p < 0.01). This study proposes that understory vegetation conversion can bolster soil carbon sinks, preserve soil fertility, and advance sustainable development of Chinese hickory plantation forests.

Three years of cover crops management increased soil organic matter and labile carbon pools in a subtropical vegetable agroecosystem

AbstractCover crops have been widely adopted to improve soil functions in agroecosystems, including providing carbon (C) inputs that can contribute to soil C sequestration. However, soil C changes may be slow after introducing cover crops in unfavorable environments for soil organic matter (SOM) accumulation, like the Southeast United States subtropical region characterized by a warm humid climate, and coarse‐textured soils. We examined labile C pools as potential early indicators of SOM changes after cover crop introduction in a sandy subtropical vegetable production system. We compared the effects of four cover crop monocultures namely two grasses [sorghum sudangrass, Sorghum bicolor × S bicolor var. Sudanese and pearl millet, Pennisetum glaucum (L.) R. Br.], two legumes (sunn hemp, Crotalaria juncea L., and cowpea, Vigna unguiculata Walp.), and one four‐species mixture on soil organic carbon pools for 3 years. Soil samples were collected at a 15‐cm depth before cover crop planting and post cover crop incorporation to assess changes in SOM, permanganate‐oxidizable carbon (POX‐C), mineralizable carbon (Cmin), and water extractable organic carbon (WEOC). The incorporation of cover crops increased concentrations of SOM, POX‐C, and Cmin in year 3 relative to their baseline values in year 1. Concentration of SOM increased by 0.24 ± 0.05% (mean ± standard error) after 3 years of cover crop management. However, concentrations of WEOC significantly decreased in years 2 and 3 relative to the baseline. Monocultures and the mixture had similar effects on measured C pools, likely due to comparable aboveground biomass production. Our findings highlight the potential of POX‐C and Cmin as early indicators of SOM accumulation driven by cover crops use, as well as the capacity of cover crops to build SOM in similar subtropical systems and coarser textured soils.

Regulation of Precipitation on Soil Dissolved Organic Matter in Perturbed Mangrove Ecosystems

Carbon sinks in mangrove soils play a critical role in climate change mitigation globally. Soil dissolved organic matter (DOM) is a major form of labile organic matter and influences carbon cycling in wetland ecosystems. However, the factors regulating DOM pools in mangrove soils on a regional scale are not well understood. Here, we used a novel approach to assess soil DOM dynamics and its environmental drivers in mangrove wetlands on a national scale in China. Soil samples were collected from 43 sampling sites and distributed in mangroves across the coastline of China. DOM extracted from mangrove soils was characterized by fluorescence spectroscopy. We estimated that dissolved organic carbon (DOC) content ranged from 0.20 ± 0.02 g/kg to 3.85 ± 0.09 g/kg and nationally averaged 0.73 ± 0.07 g/kg in mangrove soils. Soil DOM was composed of humic-like substances, including humic acid-like (53.46 ± 8.74%) and fulvic acid-like (46.54 ± 8.74%). DOM pools in mangrove soils were identified to be perturbed by terrestrial inputs. Besides, the coupling interactions of environmental controls on the soil DOM pool were validated by establishing the structural equation modeling (SEM). We found that precipitation is the most important driver, which controlled directly the inputs and outputs of DOM pools. It also indirectly influenced DOM pools by regulating soil parameters through the cascade reactions. Cu, salinity, and clay are key mediators among soil parameters for precipitation affecting DOM pools. Precipitation influences soil DOC negatively and CDOM and FDOM positively markedly. The results provide novel insights into the labile carbon pool in mangrove soils and are beneficial for improving the assessment frameworks in the blue carbon ecosystems.

Sensitivity of Labile Carbon Pools and Soil Organic Carbon Stocks to Organic and Mineral Fertilization Across Foothill Himalayas

ABSTRACTWhile soil organic carbon (SOC) is instrumental in soil fertility and soil productivity, thus offers an extremely imperative part in sandy soils of foothill Himalayas, scarce documentation has been surfaced regarding the short-term SOC changes and carbon stocks. The current study was conducted over two consecutive years (2016 and 2017) to assess the soil organic carbon changes under varied fertilization practices in black gram monoculture. A total of 13 treatments were replicated thrice in randomized block design in sandy loam soil. The results revealed that application of farmyard manure @ 2 t ha−1 (FYM) and inorganic fertilization under T13 recorded the highest labile carbon (LC), particulate organic carbon (POC), microbial biomass carbon (MBC), and soil organic carbon. Further, it has recorded lowest bulk density, while the treatment T2 marked the highest value for bulk density. A significant and positive relationship was observed among different carbon fractions. The sensitivity index (SI) of MBC, POC, KOC and SOC varied from 3.14 to 15.37%, 2.42 to 5.06%, 1.87 to 17.40% and −0.40 to 4.45%, respectively and differences were greatest in FYM treatments. The results inferred that application of FYM holds a prime prominence and should be preferred in the nutrient management to boost soil fertility and properties of soils, for maintenance of soil quality and crop production.

The Labile and Resistant Soil Organic Carbon Pools in the North America Great Plains

Among the three major global carbon cycle components, the terrestrial one has been the most uncertain because of the complexity of the soil organic carbon (SOC) dynamics. Previous tracer studies, however, have shown that SOC consists of labile and resistant pools. Labile pools turn over in decades, and resistant pools turn over in hundreds or thousands of years. Labile pools are active in carbon and nutrient cycles and responsive to land-use management changes, whereas resistant pools are less so. Very few studies have actually quantified labile and resistant SOC pools because the isotopic tracer methods, such as the paired-plot bulk-carbon (PPBC) method, can only be applied to a few special cases. I found a study of SOC in the North America Great Plains, in which some of the data are suitable for the PPBC method. The results revealed that the turnover times of the labile SOC pools ranged from 17 years to 93 years, and the sizes ranged from 1.2 g kg−1 to 17.6 g kg−1. The turnover times of the resistant pools ranged from 899 years to 5138 years, and the sizes ranged from 5.0 g kg−1 to 12.4 g kg−1. Land management practices changed the sizes of the labile pools but not their turnover times. This study also pointed out a possibility that allows the application of the PPBC method to a set of much broader cases.

Conservation agriculture's impact on total and labile organic carbon pools in calcareous and non-calcareous floodplain soils under a sub-tropical rice-based system.

To evaluate the effects of conservation agriculture (CA) on SOC pools and their lability, field experiments (2015-2020) were conducted on contrasting soils under subtropical climates. The experiment on non-calcareous soils, was comprised of tillage (minimum [MT] vs. conventional [CT]) in main plots, cropping systems (Wheat [Triticum aestivum]-Aus and Aman rice [Oryza sativa L.], WRR; Lentil [Lens culinaris]-Aus and Aman rice, LRR; and Mustard [Brassica nigra]- Boro and Aman rice, MRR) in the sub-plots, and crop residue (with or without 20% residue) in the sub-sub plots. The experiment on calcareous soils, was comprised of tillage (strip-till, ST; no-till, NT; and CT) and crop residue (high residue, HR at 50% by height vs. low residue, LR at 15%). Results showed that the MT had higher SOC contents by 18.8% than the CT in non-calcareous soils. Likewise, SOC was 12.5% and 6.7% higher in the NT and ST, respectively, than in the CT in calcareous soils. Significantly higher particulate organic (POC), permanganate oxidizable (POXC), and microbial biomass carbon (MBC) were observed in the MT, NT, and ST than in the CT at both locations. Reduced tillage with residue retention under LRR had a higher SOC, including labile C pools compared to WRR and MRR systems. Similarly, carbon management index (1.2-1.5 and 1.0-1.2) in both soils had significant positive correlations with SOC lability via POXC, POC, and MBC pools, indicating a SOC sequestration potential. In conclusion, our results showed positive effects of CA on SOC and its lability across soils.

The effects of straw returning and nitrogen fertilizer application on soil labile organic carbon fractions and carbon pool management index in a rice–wheat rotation system

Straw returning and nitrogen (N) fertilizer application are important agricultural measures to improve soil carbon pool. However, the combined effect of various straw-returning amounts and N-fertilizer application rates on soil carbon pool is still unclear. Therefore, a field experiment with three straw-returning amounts and three N-fertilizer application rates was conducted for 4 years in central China. The results revealed that the addition of N fertilizer clearly enhanced the contents of soil organic carbon (SOC) by 2.2%− 2.7%, dissolved organic carbon (DOC) by 20.1%− 39.2%, microbial biomass carbon (MBC) by 37.9%− 44.2%, and easily oxidizable carbon (EOC) by 18.4%− 23.6%. Moreover, it also enhanced the activities of invertin by 33.4%− 46.4%, cellulase by 23.5%− 32.4%, and polyphenol oxidase by 20.5%− 27.1%, as well as the carbon pool management index (CPMI) by 21.3%− 27.6%. The CPMI increased gradually as the N-fertilizer application rate increased. However, straw returning did not significantly change the contents of SOC, EOC, and MBC; invertin activity, or CPMI. Based on the structural equation model, it was observed that N fertilizer application enhances MBC and subsequently improves CPMI by increasing EOC. This highlights the vital role of soil microorganisms in the soil carbon cycle and the significance of supplementing N to improve and sustain agricultural soil carbon reservoirs. Additionally, this study indicates that the combined application of N fertilizer and straw returning has a more positive effect on improving the soil carbon pool.

Spatial Heterogeneity of Total and Labile Soil Organic Carbon Pools in Poplar Agroforestry Systems

Agroforestry systems are considered effective methods of carbon sequestration. In these systems, most of the carbon is stored in the soil, and the pattern of tree planting can influence the spatial distribution of organic matter input into the soil. However, limited information is available about the extent of this influence. In this study, the horizontal and vertical distributions of soil organic carbon (SOC) and labile fractions were investigated in four planting systems: a pure poplar (Populus deltoides cv. “35”) planting system, a wide-row (14 m spacing) poplar and wheat (Triticum aestivum L.) agroforestry system, a narrow-row (7 m spacing) poplar and wheat agroforestry system, and a pure wheat field. The results showed that although the poplar system had the highest vegetation biomass (147.50 t ha−1), the agroforestry systems overall had higher SOC contents than the pure poplar system and wheat fields. Especially in the wide-row agroforestry system, the SOC, readily oxidizable carbon, and dissolved organic carbon contents were, respectively, 25.3%, 42.4%, and 99.3% higher than those of the pure poplar system and 60.3%, 148.7%, and 6.3% higher than those of the wheat field in a 1 m soil profile, and it also had the highest fine root biomass. However, the microbial biomass carbon content was highest in the pure poplar system. The SOC of the three poplar planting systems was spatially heterogeneous, with the highest values occurring at 1.5 m in the narrow-row systems and within the tree rows in the wide-row system, similar to the distribution of fine root biomass. Additionally, we found that the larger the diameter at the breast height of the trees, the greater their positive effect on SOC at greater distances.

Biological soil health with conventional and qPCR based indicators under conservation agriculture based rice-wheat cropping system in Indo-Gangetic Plain

Conservation agriculture (CA) entails resource sustainability, crop productivity and climate benefits. We assessed biological soil health index (BSHI) using both conventional and state-of-the-art indicators for a long-term rice-wheat system under a regime of CA-practices in Indo-Gangetic Plains (IGP). The practices include zero till direct seeded rice (ZTDSR)–zero till wheat (ZTW), ZTDSR + wheat residue (WR)-ZTW + rice residue (RR), ZTDSR + WR + sesbania brown manuring (SBM)–ZTW + RR, ZTDSR–ZTW–zero till mungbean (ZTMB), ZTDSR + mungbean residue (MR)–ZTW + RR-ZTMB + WR, transplanted rice (TPR)-conventional till wheat (CTW)–conventional till mungbean (CTMB). Collected soil samples (0–5 cm depth) were analysed for 8 labile organic carbon pools, 8 soil enzyme activities, population of 7 microbes viz., bacteria, fungi and actinomycetes, and two microbial functions. Further, abundance of different phylogenetic groups and nutrient cycling genes was quantified by molecular based qPCR technique. In general, triple/double ZT + crop residues caused an increase in most of the pools of carbon, enzymes, and microbial population including qPCR-led genes in soils. Specifically, inclusion of mungbean residues in triple ZT and sesbania brown manuring in double ZT improved nifH gene abundance over other double and triple ZT treatments. Of the analysed parameters, β-glucosidase, Bacterial amoA, Archaeal 16S rRNA, Bacteroidetes 16S rRNA, Bacterial 16S rRNA, and mineralizable C were screened out as the key indicators of BSHI; its value was maximised under triple ZT with residues (ZTDSR + MR–ZTW + RR–ZTMB + WR) treatment. Attempt may be made to use the screened indicators for assessment of BSHI and upscale the identified practice for rice-wheat system in IGP.

Short-term changes in soil labile carbon and nitrogen pools with biochar application in a suburban native forest in subtropical Australia

Short-term changes in soil labile carbon and nitrogen pools with biochar application in a suburban native forest in subtropical Australia

Biochar Aged for Five Years Altered Carbon Fractions and Enzyme Activities of Sandy Soil

Biochar applied to soil has been considered as an effective tool for mitigation of atmospheric carbon dioxide emission and enhancement of carbon storage in soil, which may also enhance soil quality. However, the effect of biochar aged for 5 years on the different carbon fractions and enzyme activities as well as its changes, is not well understood in the cropland sandy soil of northern China. Therefore, a field trial was carried out in 2014 with biochar applied once at 0, 5.25, 10.50, 21.00 and 42.00 g·kg−1 (BC0, BC1, BC2, BC3, and BC4, respectively). We evaluated the influence of biochar addition to the changes in soil organic carbon (SOC), labile carbon pools (readily oxidized carbon, dissolved organic carbon, and microbial biomass carbon) and enzyme activities (invertase, urease, and catalase). Biochar significantly increased SOC (122.00%) and altered the content of labile carbon (increased ROC, DOC and MBC by 71.29%, 10.35%, and 900.00%, respectively). Soil urease and invertase activities increased by 55.81% and 46.76%, respectively, with an increase in biochar application rate, but catalase activity significantly decreased by 31.79%. The values of the geometric means of labile carbon (0.88) and enzyme activities (2.39) for the BC3 treatment were higher than others, which indicated that the biochar application rate of 21.00 g·kg−1 is suggested for the sandy soil. Our results suggest that the application of biochar in sandy soil for five years increased soil carbon sequestration, changed enzyme activities and ameliorated soil quality.

Plant invasion strengthens the linkages between dissolved organic matter composition and the microbial community in coastal wetland soils

Exotic plant invasion dramatically alters soil carbon transformation and shapes the structure and diversity of the microbial community in coastal wetlands. However, it remains unclear how the dissolved organic matter (DOM) optical components and chemical composition and their linkages with soil microorganisms change with increasing time since invasion. Here, we explored the impacts of Spartina alterniflora (S. alterniflora) invasion on DOM compositions and relationships with microbial communities along a short-term chronosequence (i.e., 3-, 5-,10-, and 15-year) in the Yellow River Delta. The results showed an increase in the soil water content, soil organic carbon, dissolved organic carbon, and C/N ratio along the invasion chronosequence, whereas bulk density showed the opposite trend. Moreover, invaded wetland soils had a higher abundance of total phospholipid fatty acids, gram-positive bacteria (G + ), gram-negative bacteria (G-), and fungi than tidal flat soils. The DOM in invaded wetland soils was mainly composed of endogenous protein-like components, and the proportion of autochthonous DOM increased over invasion time. The DOM was characterized by low molecular weight, low aromatic content, and low hydrophobic compounds in S. alterniflora wetland soils, whereas in tidal flat soils, the humification degree and DOM molecular weight were higher. The soil microbial communities exhibited stronger linkages with various environmental variables and DOM fluorescence components in invaded wetlands based on redundancy analysis (RDA) and correlation analysis using Mantel tests. Structural Equation Model (SEM) revealed that the soil microbial abundance and community structure induced by increasing S. alterniflora invasion time were the most important drivers of DOM content and chemical composition. The findings of this work provide a better understanding of labile carbon pool turnover in coastal wetlands invaded by S. alterniflora.

The role of blue carbon stocks becomes more labile with mangrove development

Soil labile organic carbon (LOC) is a crucial component in carbon cycling in coastal wetlands and serves as an important indicator of SOC. Despite this, little is known about the stabilization of SOC and its LOC during mangrove development. The objective of our study was to quantify SOC and LOC in the soil at depths ranging from 0 to 100 cm across four sites, including a mudflat and three mangrove sites of varying ages (15-, 45-, and 80-yr old) were selected in Yingluo Bay, China. The concentration of SOC, POC (particulate organic carbon), DOC (dissolved organic carbon), MBC (microbial biomass carbon), and KMnO4-C (potassium permanganate-oxidizable carbon) were measured. The CMI (soil carbon management index) was also calculated to precisely and directly reflect the dynamic changes of soil carbon pools. Mangrove natural expansion showed a significant positive effect on both SOC and LOC. The concentration of KMnO4-C in the top 50 cm of soil layer showed a significant increase in three different mangrove forest sites. The POC, DOC and MBC were also significantly increased in response to mangrove development. The 80-yr old mangrove site had the highest SOC concentrations, LOC concentrations, soil carbon lability Index (LI) and CMI among all sites. These findings suggested that the development of mangroves increases soil organic carbon fractions through vegetation production and enhances long-term carbon sequestration rates by expanding soil labile carbon pools. As a management option, promoting the natural expansion of mangroves can maximize the sequestration potential of soil organic carbon.

Nitrogen and phosphorus addition did not affect neutral sugars in plant but decreased them in soil in an alpine grassland on the Tibetan Plateau

As crucial carbon (C) and energy sources for soil microorganisms, neutral sugars are essential component of the labile soil organic carbon (SOC) pool derived from plants and microorganisms and can directly affect the accumulation of SOC. However, the changes in labile SOC components with elevated soil nitrogen (N) and phosphorus (P) inputs remain unclear. Taking advantage of a 10-year field N and P addition experiment in an alpine grassland on the Tibetan Plateau, we analyzed the compositions and concentrations of neutral sugar in plant versus soil, coupled with soil nutrient properties and plant biomass, we assessed factors affecting the preservation of neutral sugars in soil. We found that the concentrations of neutral sugar were lower in plant shoots than those in roots. The concentrations of neutral sugar and the GM/AX ratio (GM: galactose and mannose; AX: arabinose and xylose) in shoots and roots were insensitive to nutrient addition. The concentrations of neutral sugar in the topsoil were significantly lower than those in the subsoil, and both significantly decreased with N alone and P alone addition. The GM/AX ratio was significantly higher in the topsoil than that in the subsoil and both increased with nutrient addition (except for NP addition in the topsoil). Additionally, SOC was negatively correlated with soil neutral sugar concentrations but positively correlated with the GM/AX ratio. This result emphasizes the important role of microbial transformation of neutral sugars in regulating the relative magnitude of the labile SOC pool versus the stable SOC pool, which is consistent with the concept of “microbial carbon pump” (MCP). This study demonstrates differential compositions and concentrations, as well as responses of neutral sugars to N and P addition in plant versus soil, providing new information to understand the effect of nutrient addition on the SOC pool in the plant-soil system.

High intensity fire accelerates accumulation of a stable carbon pool in permafrost peatlands under climate warming

Peatland carbon pools store one-third of global soil carbon, but are increasingly threatened by wildfires, particularly high intensity wildfires, as a consequence of climate warming. However, with only a limited understanding of fire history reconstruction available, the long-term impacts of fire intensity on the stability of the peatland carbon pool remains poorly understood. Here, based on Fourier transform infrared spectroscopy and chemical analysis of PyC and organic matter in Hongtu (HT) peat core in the northern Great Khingan Mountains (China), historical fire intensity and fuel sources during the last 700 years were reconstructed and their effects on carbon stability evaluated. Our results showed that the major stable carbon pool (i.e. aromatics) and the retained labile carbon pool (i.e. iron-bound organic carbon, Fe-OC) in HT peatland are 278.1 ± 6.2 mg·g−1 and 6.78 ± 3.85 mg·g−1, respectively. High-intensity herb fires in peatlands occurred more easily under wet conditions and caused more PyC accumulation than shrub fires. Both climate warming and high-intensity fire promoted more aromatics and Fe-OC accumulation, increasing the overall stability of peatland carbon pool. High-intensity fire under warm climate conditions resulted in Fe-OC accumulation rates threefold higher (ca. 0.02 mg·cm−2 yr−1 to ca. 0.06 mg·cm−2 yr−1) but had no marked effects on the aromatic and PyC accumulation rates. Overall, our results suggest that high-intensity fires can accelerate stable carbon pool accumulation in peatlands during climate warming.

Comparative accounting of methane and nitrous oxide fluxes with related soil parameters of degraded mangrove wetlands and adjacent rice fields in Sundarban, India

In Sundarban, around 10.5% of mangroves are primarily converted to rice-based system by anthropogenic activities during last 80 years. Both mangrove wetlands and rice fields, typically providing a passage for transporting the greenhouse gases (methane and nitrous oxide) from soil systems to atmosphere. In this article, we attempted to quantify the seasonal methane (CH4) and nitrous oxide (N2O) fluxes from six different degraded mangroves and adjacent rice fields to know how the land use change affects the fluxes. In mangroves, the average CH4 fluxes were higher in monsoon compared to pre-monsoon, winter, and summer season. Methane emissions were also higher in monsoon and summer in rice than winter and pre-monsoon. Overall, the mean CH4 fluxes were more in rice (2665 μg m−2 h−1) than mangrove (159 μg m−2 h−1). However, the average N2O fluxes were higher in summer followed by monsoon in mangroves, while, in rice, it was higher in monsoon. Like CH4 the higher mean N2O flux was observed in rice (72 μg m−2 h−1) over mangrove (69 μg m−2 h−1). The soil labile carbon pools were higher in mangroves than rice, but the enzymatic activities were more in rice. The fluxes were positively correlated with the soil enzymatic activities, whereas those were negatively correlated with soil pH, EC, and salinity. So, we found shifting of mangrove to rice resulting in higher CH4 and N2O fluxes from surface soils. Therefore, regeneration and protection of mangroves should be given priority in upper Sundarban where anthropogenic activities are prevailed to mitigate climate change.

Warming Stimulated Soil Respiration in a Subalpine Meadow in North China

In order to explore the response of soil respiration in grassland to global warming, we carried out a warming experiment with open top chambers (OTCs) in the subalpine meadow, Mount Wutai in north China. Our results showed in the subalpine meadow across 2 500-2 700 m above the sea level (ASL), with OTCs, soil respiration increased by 2.00 μmol·m-2·s-1 as soil temperature increased by 1.25 ℃ on average. Warming decreased soil moisture over the experiment periods except in October 2019 when snow melted in OTCs. Warming effect on soil respiration peaked at 178.31% in October 2019. In control and warming treatment, based on exponential regression equations, soil temperature alone accounted for 85.3% and 61.2% of soil respiration variation, respectively. In control treatment soil moisture alone explained 23.2% of soil respiration variation based on the power regression equation while in warming treatment they were not significantly correlated with each other. The response of soil respiration to warming relied on altitudes as well as the time of the year, but was not inhibited by soil moisture, labile carbon pool, and available nitrogen. We concluded soil temperature was the main factor influencing soil respiration, and global warming would stimulate soil respiration in the subalpine meadows of Mount Wutai in the future. Our analysis provided new data on characteristics and mechanisms of the response of soil respiration to warming, and helped to further understand the relationship between carbon cycle and climate change.

Soil warming decreases carbon availability and reduces metabolic functions of bacteria

Plastic film mulch (PFM) is effective to save soil water and increase temperature and consequently, to increase crop yield. Therefore, PFM has become one of the most widely used on-farm management practices for maize cultivation in semi-arid regions. The effects of PFM-induced warming on the labile carbon (C) pools and microorganisms remain unclear. We used high-throughput genomic sequencing to assess bacterial community structure and metabolic functions in soils after short- (2 years) and long-term (10 years) cover with PFM in a dryland agriculture system. Strong decrease of dissolved organic C (DOC) pool (14–18 % less than in Control soil) by warming (2.4 °C) raised bacterial ⍺-diversity. The short-term mulch reduced the absolute abundance of bacteria by 36–43 % due to the temperature rise and labile C reduction. Bacteria developed with lower abundance (e.g., smaller colonies) but with higher diversity in soils with less available resources. During the long-term mulching and microbial acclimation to increased temperature and the reduced labile C, the bacterial community strongly changed towards an oligotrophic life history. The PFM increased the abundance of bacterial species with high nutrient uptake (e.g. Patescibacteria increased by 83 %), while chemotrophs that prefer eutrophic conditions were reduced in the PFM soil (e.g. Actinobacteriota by 11 %). The PFM increased the complexity of co-occurring networks of bacterial communities and decreased their stability. Almost all bacterial marker taxa screened by random forest algorithm differed between Control and Mulch soils. Long-term mulching reduced the rate of bacterial metabolism associated with organic matter degradation, such as metabolism of carbohydrates, esters (propanoate and butanoate decreased strongly), lipids (the greatest reduction was for fatty acids), and amino acids (lysine, valine, leucine, and isoleucine degradation pathways dropped the most). Structural equation modeling indicated that bacterial metabolism was mainly influenced by bacterial community structure. Consequently, the metabolic functions of bacteria were reduced after the decrease of C availability induced by warming under PFM, and this reduction was dependent on the duration of PFM application.

Biochar-Based Fertilizer Decreased Soil N2O Emission and Increased Soil CH4 Uptake in a Subtropical Typical Bamboo Plantation

Soil is a crucial contributor to greenhouse gas (GHG) emissions from terrestrial ecosystems to the atmosphere. The reduction of GHG emissions in plantation management is crucial to combating and mitigating global climate change. A 12-month field trial was conducted to explore the effects of different fertilization treatments (control, without fertilizer (CK); biochar-based fertilizer treatment (BFT); chemical fertilizer treatment (CFT); and mixture of 50% BFT and 50% CFT (MFT)) on the soil GHG emissions of a typical bamboo (Pleioblastus amarus (Keng) Keng f.) plantation. The results demonstrated that compared with the CK, BFT reduced the annual cumulative soil N2O emission by 16.3% (p < 0.01), while CFT and MFT significantly increased it by 31.0% and 23.3% (p < 0.01), respectively. Meanwhile, BFT and MFT increased the annual cumulative soil CH4 uptake by 5.8% (p < 0.01) and 7.5% (p < 0.01), respectively, while there was no statistically significant difference between CFT and the control. In addition, BFT, CFT, and MFT significantly increased the annual cumulative soil CO2 emission by 9.4% (p < 0.05), 13.0% (p < 0.01), and 26.5% (p < 0.01). The global warming potential (GWP) of BFT did not change significantly, while CFT and MFT increased the GWP by 13.7% (p < 0.05) and 28.6% (p < 0.05), respectively, compared with the control. Structural equation modeling revealed different treatments affected soil N2O and CH4 emission by changing soil labile carbon and labile nitrogen pools. This study suggests utilizing BFT new ideas and strategies for mitigating GHG emissions from soils in subtropical Pleioblastus amarus plantations.